How to calculate increase of home wireless router range?

Beverly Erlebacher

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Jul 4, 2006, 1:57:12 AM7/4/06

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Can you help me roughly CALCULATE how to increase the range of my home
Internet wireless WiFi setup to a shed 300 feet away from my house?

Presently, I can walk about half the way through the wooded area to the
shed with my laptop in hand before I lose the connection to the PCMCIA
802.11b,g Linksys card. Basically I need to gain 150 feet in "range".

But how?

At the store, I immediately become confused as I try to compare $30 USD
omnidirectional antennas (D-Link ANT24-070) that boost "power" by a claimed
7 db; $50 USD directional corner antennas (Hawking HAI15SC) that claim 15
dbi (whatever a dBi is); and $150 USD 802.11N routers that claim to boost
omnidirectional "range" by 4x (Linksys WRT300N).

How does an omnidirectional 7 db or directional 15 dBi boost in "power"
equate to range?

Approximately how many decibels of (omnidirectional or directional) power
do I really need to boost my WiFi range from about 150 feet to the 300 feet
I need?

Looking up what a decibel is
(http://en.wikipedia.org/wiki/Decibel#Definition), I
calculate the D-Link ANT24-070 omnidirectional antenna gives me about 5
times the power (assuming 7 db = 10^7/10 ~= 5); but does this get me the
additional 150 feet of range to my shed?

Spending almost twice as much money on the Hawking HAI15SC directional
antenna gets me roughly 30 times the power (assuming 15 db = 10^15/10 ~=
32); but is that enough power to get me the range to my shed?

Indeed, is there some way to add a Hawking 15db antenna on the receiving
end to get 1,000 times the power (15 db + 15 db = 30 db = 10^30/10 ~=
1,000); but what would I hook the wire output from this receiving antenna
to in the shed (I can't hook it to the pcmcia card, can I)?

Given those db calculations, how do I compare the antenna options with
replacing my home 802.11b,g router with the 4X range $150 USD Linksys
802.11n WRT300N router and the required $120 USD Linksys WPC300N PCMCIA
card (assuming 6 db = 10^6/10)?Will this three-antenna 802.11n router be
forced to drop down to 1X speeds because inside my house my kid's laptops
will all be using 802.11b or 802.11g? Or can the router work on both
802.11g to one computer and on 802.11n to the other computer at the same
time?

I'm so confused!

All I want is to make a well-informed buying decision to increase my WiFi
range reliably to 300 feet to a known point.

Can you help me sort out all these very confusing variable (to me anyway)?
I have no training in electrical engineering; but I can google.

Thank you,
Beverly

Dave Platt

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Jul 4, 2006, 2:28:16 AM7/4/06

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In article <2hqacpnj1nwj$.1683sqqzgbbo2$.d...@40tude.net>,
Beverly Erlebacher <b...@cs.toronto.edu> wrote:

>Can you help me roughly CALCULATE how to increase the range of my home
>Internet wireless WiFi setup to a shed 300 feet away from my house?
>
>Presently, I can walk about half the way through the wooded area to the
>shed with my laptop in hand before I lose the connection to the PCMCIA
>802.11b,g Linksys card. Basically I need to gain 150 feet in "range".

Doubling the range requires 6 dB of additional gain from the antennas
at one end or the other. You'd probably want more additional gain
than that, so that your connection is solid and reliable rather than
hanging right on the edge of failure.

>But how?
>
>At the store, I immediately become confused as I try to compare $30 USD
>omnidirectional antennas (D-Link ANT24-070) that boost "power" by a claimed
>7 db; $50 USD directional corner antennas (Hawking HAI15SC) that claim 15
>dbi (whatever a dBi is);

dB numbers are a ratio. When you see a figure given in dB, you have
to ask "dB relative to *what*, precisely?".

There are two common standards in use. dBi refers to gain relative to
an "isotropic" antenna - an imaginary antenna which radiates power
equally in all directions. dBd refers to gain relative to a half-wave
dipole - a common and well-studied type of antenna.

dBi numbers are approximately 2 dB higher than dBd numbers, for the
same actual amount of gain.

> and $150 USD 802.11N routers that claim to boost
>omnidirectional "range" by 4x (Linksys WRT300N).
>
>How does an omnidirectional 7 db or directional 15 dBi boost in "power"
>equate to range?

3 dB of additional gain equates to twice the delivered power at a
specific range. Because power falls off in proportion to the square
of the distance, twice the power yields sqrt(2) or about 1.4 times the
range, all else being equal (which it often isn't).

6 dB of additional gain is four times the delivered power at a given
distance, or twice the range for the same amount of power.

>Approximately how many decibels of (omnidirectional or directional) power
>do I really need to boost my WiFi range from about 150 feet to the 300 feet
>I need?

The _minimum_ you appear to need is 6 dB of additional gain. I'd
recommend trying for 10 dB or more in order to ensure a reliable
connection.

>Looking up what a decibel is
>(http://en.wikipedia.org/wiki/Decibel#Definition), I
>calculate the D-Link ANT24-070 omnidirectional antenna gives me about 5
>times the power (assuming 7 db = 10^7/10 ~= 5); but does this get me the
>additional 150 feet of range to my shed?

I think that it might, but without a lot of safety margin.

>Spending almost twice as much money on the Hawking HAI15SC directional
>antenna gets me roughly 30 times the power (assuming 15 db = 10^15/10 ~=
>32); but is that enough power to get me the range to my shed?

Yes, probably so. That's well over the 10 dB I guesstimate you would
need.

>Indeed, is there some way to add a Hawking 15db antenna on the receiving
>end to get 1,000 times the power (15 db + 15 db = 30 db = 10^30/10 ~=
>1,000); but what would I hook the wire output from this receiving antenna
>to in the shed (I can't hook it to the pcmcia card, can I)?

That depends on the PCMCIA card. Some have antenna jacks, many do not.

There may be a cheaper way for you to get the gain you need, from your
existing equipment, without spending any money at all. It's possible
to fabricate a corner reflector, or (even better) a parabolic
reflector, out of material as inexpensive as cardboard (or posterboard
or something like that) lined with aluminum foil. Simply make one,
and then set it behind your existing router's vertical antenna... aim
the parabola in the direction of your shed and place the router's
antenna at the focal point of the parabola. Aim carefully, and it
wouldn't be surprising for you to get 8 - 10 dB of additional gain.

For even more gain you could buy one of the D-Link omnidirectional
gain antennas, and then use the same trick of putting a parabolic or
corner reflector behind it.

See http://www.freeantennas.com/projects/template/
and http://www.freeantennas.com/projects/template2/index.html

The latter states an achievable gain of around 11 dB just from the
homemade reflector.

--
Dave Platt <dpl...@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Beverly Erlebacher

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Jul 4, 2006, 2:49:19 AM7/4/06

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On Tue, 04 Jul 2006 06:28:16 -0000, Dave Platt wrote:
>>Can you help me roughly CALCULATE how to increase the range of my home

>>Internet wireless WiFi setup from 150 feet to a shed 300 feet away?

> Doubling the range requires 6 dB of additional gain from the antennas
> at one end or the other.

Hi Dave,

First thank you for taking the time to help me and anyone who read this.
Second, I'm going to have to go slowly with you so I'll respond one by one.

Third, does your statement that 6 dB of gain equates to 2 times the range
mean that the "square root" of the power difference is my key to
calculating the range?

That is, is this range calculation from dB power roughly true (based on
what you said)?

6 dB = 10^(6/10) ~= 4X the power, where the square root of 4X equals a
doubling the range (assuming an omnidirectional antenna)?

Beverly

Beverly Erlebacher

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Jul 4, 2006, 3:22:44 AM7/4/06

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> 6 dB = 10^(6/10) ~= 4X the power, where the square root of 4X equals a
> doubling the range (assuming an omnidirectional antenna)?

I'm hoping I can extrapolate from the above statement to calculate the dB
gain for the $150 Linksys WRT300N router which claims a 4X range
improvement (so I can compare the $50 antenna's effect with that of the
802.11n router).

Following your lead, the power improvement necessary for a 4X range
improvement is 4^2 = 16X power gain.

This 16X power gain then equates to about 12 dB (since 12 dB = 10^[12/10]
~= 16X power).

So, is it safe to calculate that the claimed 4X range improvement of the
Linksys WRT300N wireless broadband router can be compared to that of a 12
dB gain omnidirectional antenna?

Beverly

Beverly Erlebacher

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Jul 4, 2006, 3:36:53 AM7/4/06

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On Tue, 04 Jul 2006 06:28:16 -0000, Dave Platt wrote:
>>Can you help me roughly CALCULATE how to increase the range of my home
>>Internet wireless WiFi setup to a shed 300 feet away from my house?
>

> dBi refers to gain relative to an "isotropic" antenna

> dBd refers to gain relative to a half-wave dipole

> dBi numbers are approximately 2 dB higher than dBd numbers,
> for the same actual amount of gain.

Hi Dave,

Oh my. I guess the Hawking marketing folks were trying to trick me by
quoting a decibel number that was higher those I compared with.
15 dBi ~= 15 -2 ~= 13 dBd

That makes the $50 USD 15 dBi Hawking HAI15SC Hi_Gain Antenna drop down
from a gain of 32X power to only 20X power which gives me about a 4X range.

13 dBd = 10^(13/10) power ~= 20x power

Assuming the square of the power is the range, I get 4X range.
20^(1/2) ~= 4X range

Assuming my reliable range is 100 feet, that equates to 400 feet of range.
100 feet * 4 = 400 feet range

Interestingly, for comparison purposes, that is the SAME RANGE that the
much more expensive Linksys (Cisco) WRT300N router claims.

Do these calculations make sense?
Beverly

Beverly Erlebacher

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Jul 4, 2006, 3:48:38 AM7/4/06

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On Tue, 04 Jul 2006 06:28:16 -0000, Dave Platt wrote:
>>Can you help me roughly CALCULATE how to increase the range of my home
>>Internet wireless WiFi setup to a shed 300 feet away from my house?

> 3 dB of additional gain equates to twice the delivered power at a

> specific range. Because power falls off in proportion to the square
> of the distance, twice the power yields sqrt(2) or about 1.4 times the
> range, all else being equal (which it often isn't).
>
> 6 dB of additional gain is four times the delivered power at a given
> distance, or twice the range for the same amount of power.

So that I may compare the different options available at the store to me
for increasing my range, are these simplified calculations below correct?

a. 3 dBd additional gain = 10^(3/10) ~= 2x the delivered power
b. 2x power = 2^(1/2) effective range ~= 1.4X the range

b. 6 dBd additional gain = 10^(6/10) ~= 4x the delivered power
b. 4x power = 4^(1/2) effective range ~= 2X the range

Can someone let me know if these calculations are correct because that
helps me equate the different antennas and routers to the one measure I
desire, which is effective range in the area of 400 feet.

Beverly

Beverly Erlebacher

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Jul 4, 2006, 3:53:30 AM7/4/06

to

On Tue, 04 Jul 2006 06:28:16 -0000, Dave Platt wrote:

>> Approximately how many decibels of (omnidirectional or directional)
>> power do I really need to boost my WiFi range from about 150 feet
>> to the 300 feet I need?
>
> The _minimum_ you appear to need is 6 dB of additional gain. I'd
> recommend trying for 10 dB or more in order to ensure a reliable
> connection.

May I ask WHERE that 6 dBd of gain is coming from?

Is it ONLY from the "better" antenna?

If that additional 6 dBd is coming from a "better" antenna, then why didn't
they put that better antenna on my router in the first place?

Since the antenna isn't "powerered", there is no external amplifier .... so
I am a bit confused as to WHERE that power is coming from?

Can you unconfusify me here?
Beverly

Beverly Erlebacher

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Jul 4, 2006, 4:06:53 AM7/4/06

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On Tue, 04 Jul 2006 06:28:16 -0000, Dave Platt wrote:

> There may be a cheaper way for you to get the gain you need, from your
> existing equipment, without spending any money at all. It's possible
> to fabricate a corner reflector, or (even better) a parabolic
> reflector, out of material as inexpensive as cardboard (or posterboard
> or something like that) lined with aluminum foil. Simply make one,
> and then set it behind your existing router's vertical antenna... aim
> the parabola in the direction of your shed and place the router's
> antenna at the focal point of the parabola. Aim carefully, and it
> wouldn't be surprising for you to get 8 - 10 dB of additional gain.

Hmm. I wonder. This is too good to be true. So, I will be a bit critical
with you (i.e., the scientific method) just to "test" the assumption so
that I can be sure I understand your position.

Assuming a 9 dBd increase in the directional gain from putting a pie tin
behind one of my existing router antennas, that equates to either 280 or
380 feet of range based on the calculations below.

a) 9 dBd = 10^(9/10) power gain ~= 8x power gain
b) 8x power gain = sqrt(8) range gain ~= 2.8X range gain
c) 100 foot range * 2.8 ~= 280 foot range

I'm a bit confused about the "range gain". May I ask if thta 280 foot range
is the total range or the range improvement?

That is, is my range with a pie tin behind the antenna 280 feet in toto; or
is the range now the 100 original feet + 280 additional feet which equals
380 feet in toto?

Beverly

Beverly Erlebacher

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Jul 4, 2006, 4:19:17 AM7/4/06

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On Tue, 04 Jul 2006 06:28:16 -0000, Dave Platt wrote:
>>Can you help me roughly CALCULATE how to increase the range of my home
>>Internet wireless WiFi setup to a shed 300 feet away from my house?

> See http://www.freeantennas.com/projects/template/

> and http://www.freeantennas.com/projects/template2/index.html
> The latter states an achievable gain of around 11 dB just from the
> homemade reflector.

The skeptic in me wonders "if it's this easy to get 3.5X the 802.11b,g WiFi
range, then why don't the router manufacturers add this cheap parabola as
standard equipment on all their antennas?"

a) 11 dBd = 10^(11/10) power gain ~= 12.5 power gain
b) 12.5 power gain ~= sqrt(12.5) range gain ~= 3.5X range gain
c) 100 feet range * 3.5X range gain = 350 feet range

Being a firm believer in "you don't get nothin' for nothin'", I must ask:

What am I losing by putting a parabola behind one of the two antennas on my
home router so that it increases the directional range from approximately
100 feet to about 300 feet?

Beverly

Beverly Erlebacher

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Jul 4, 2006, 4:48:09 AM7/4/06

to

On Tue, 04 Jul 2006 06:28:16 -0000, Dave Platt wrote:

> It's possible to fabricate a corner reflector, or (even better) a
> parabolic reflector, out of material as inexpensive as cardboard
> (or posterboard or something like that) lined with aluminum foil.

Hmm. At first, I thought you were pulling my leg; but a simple google for
more details gave me more homemade WiFi antenna reading than I can handle
in a month. Whew. Here, for others to share, are the Yagi pringles can
antennas (aka cantenna) which purport to "refocus" the WiFi signal from my
router in my house to my shed 300 feet away.

http://en.wikipedia.org/wiki/Cantenna
http://www.oreillynet.com/cs/weblog/view/wlg/448
http://www.seattlewireless.net/index.cgi/PringlesCantenna
http://www.wi-fiplanet.com/reviews/article.php/3401501
http://www.turnpoint.net/wireless/has.html
http://www.binarywolf.com/249/pringles_cantenna.htm
http://verma.sfsu.edu/users/wireless/pringles.php
http://www.seattlewireless.net/index.cgi/CookieCantenna
http://webserver.computoredge.com/editorial/2339/cover.htm
http://www.signonsandiego.com/news/computing/personaltech/20050613-9999-lz1b13canned.html
http://www.overclock.net/faqs/17669-how-make-pringles-can-signal-booster.html
http://www.g4tv.com/screensavers/features/40546/Pringles_Can_WiFi_Antenna.html
http://www.netscum.com/~clapp/wireless.html
http://www.flickr.com/photos/binarywolf/sets/837698/
http://linuxathome.com/files_images/cantenna.pdf

Given that there are two fundamental design styles:
a) Parabola
b) Tube

Do folks here recommend the pringles cantenna or the pie tin antenna for my
2-antenna router 802.11b,g directional application where I need to also
feed the computers within the house in addition to the shed 300 feet away?

Beverly

Rod Speed

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Jul 4, 2006, 5:44:36 AM7/4/06

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Beverly Erlebacher <b...@cs.toronto.edu> wrote
> Dave Platt wrote

>>> Can you help me roughly CALCULATE how to increase the range of my
>>> home Internet wireless WiFi setup to a shed 300 feet away from my house?

>> See http://www.freeantennas.com/projects/template/
>> and http://www.freeantennas.com/projects/template2/index.html

>> The latter states an achievable gain of around 11 dB just from the
>> homemade reflector.

> The skeptic in me wonders "if it's this easy to get 3.5X the
> 802.11b,g WiFi range, then why don't the router manufacturers add
> this cheap parabola as standard equipment on all their antennas?"

Because most dont want something that directional.

> a) 11 dBd = 10^(11/10) power gain ~= 12.5 power gain
> b) 12.5 power gain ~= sqrt(12.5) range gain ~= 3.5X range gain
> c) 100 feet range * 3.5X range gain = 350 feet range

Both I'd guess, for "diversity antenna gain."

Nick

Dan Richardson <k6mhek6mhe<dot>com>

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Jul 4, 2006, 9:11:27 AM7/4/06

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On Tue, 04 Jul 2006 05:57:12 GMT, Beverly Erlebacher
<b...@cs.toronto.edu> wrote:
[snip]

>How does an omnidirectional 7 db or directional 15 dBi boost in "power"
>equate to range?

[snip a whole bunch of stuff]

AN antenna passive divice. It does not increase power. Gain is
achieved by focusing more radial tion in one direction by reducing it
in another direction.

Now more to the point (extending the range of your wireless LAN) . If
you goal is to increase your range then add an extender (hams would
prefer to call them repeaters).

You mentioned using D-Link. They make a good extender for around $70
USD. I have one installed up on the second floor (I have a two story
home) and am able to have good connections at distances over 500 FT.

Check it out.

73,
Danny, K6MHE

bear...@cruller.invalid

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Jul 4, 2006, 10:07:39 AM7/4/06

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In article <1sr34qtndtz8m.8y1znh8b5w9o$.d...@40tude.net>,
Beverly Erlebacher <b...@cs.toronto.edu> wrote:

> Do folks here recommend the pringles cantenna or the pie tin antenna for my
> 2-antenna router 802.11b,g directional application where I need to also
> feed the computers within the house in addition to the shed 300 feet away?

The pringles antenna works great for me and some low-income neighbors I
know in Seattle.

Also, here is an easy way to hack your $60 wireless router into a $600
router (they use Linksys as the example):

<http://image.lifehacker.com/software/router/hack-attack-turn-your-60-rou
ter-into-a-600-router-178132.php?server=63&id=161208410&secret=b727c3e5d7
>

or if that link breaks:

<http://makeashorterlink.com/?C21413D5D>

son...@moog.netaxs.com

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Jul 4, 2006, 10:38:14 AM7/4/06

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In article <1ofdyrcyyqhff$.qzkvubda...@40tude.net>, Beverly Erlebacher
wrote:

Omnidirectionality! 'Scuse the weird word, but the important thing to
remember is that antenna gain is always specified with respect to an
"isotropic" antenna, which is a theortical antenna with the ability to
radiate(or receive) energy equally well in _all_ directions. This is as
omnidirectional as you can get. If a real antenna has the ability to focus or
selectively transmit energy in some directions better than others, the focused
energy gives the antenna a "gain" in those preferred directions over what
would be transmitted from an isotropic antenna. So, what you get from an
antenna with gain is directivity; as long as your receiving antenna is lined
up with along the preferred axis of the transmitting antenna, you'll receive
more of the energy put out by the transmitter. The trade-off is that the
higher the gain, usually the smaller the allowable line-up error can be
between the antennas.

SJO

>
> Beverly

Peter Pan

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Jul 4, 2006, 11:03:49 AM7/4/06

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> On Tue, 04 Jul 2006 06:28:16 -0000, Dave Platt wrote:
>>> Can you help me roughly CALCULATE how to increase the range of my
>>> home Internet wireless WiFi setup to a shed 300 feet away from my
>>> house?

You may want to consider doing it the way cheaper way (using any of the N
((actually pre-n cuz there are no N standards yet)) is IMO the hard and
expensive way)... I Had a linksys WRT54G in the house attached to my sat,
and used one of the 4 router outputs to daisy chain one to the wan input of
another WRT54G (same ssid) and a semi-directional antenna pointed towards
the garage about 500ft away, (and another to the guest house (about 800 FT
away) out back on my 5 acres).. The Linksys WRT54G (not the GS) are
available at wal-mart for under $50 each... Cat 5 cables a few bucks, and
the semi-directional antennas (not highly directional, just semi) where a
few bucks each for the 2nd and 3rd wap/routers.. Am even thinking about
adding a 4th wap/router so I can use my PDA (with wifi) out by the horse
corral.

Think increased range by using multiple wap/routers and multiple antennas,
rather than trying to get one that is more powerful and does it all..

David

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Jul 4, 2006, 11:10:26 AM7/4/06

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>
> I also see, as Rod Speed so kindly noted, that the give and take is that we
> lose range in some directions in favor of range in the desired direction.
> Fair enough.
>
> My one question is a practical one.
>
> Why are there two antennas on my router anyway?

Antenna diversity

Is one transmit and the
> other receive?

NO

Or are they both transmit and receive?

Yes

>
> Given I have TWO omnidirectional antennas on my wireless router, if I put
> the parabolic dish antenna on one to direct it to my shed, does that allow
> the OTHER antenna to radiate around the house to handle the other computers
> roving around the house?
>

Not really. Most routers are set to use the antenna with the most
signal strength. Therefore if you are using a directional antenna on on
and a omni antenna for the other. The directional will win out, since it
will have more available signal. This is part of that antenna diversity
thing.

The reason for the two antennas was so one could change the antenna to
different planes to receive a better signal due to phase shifting of the
signal that occurs when a given signal hit an object and bounces off
that said object. The signal is no longer in phase, with that which was
originally transmitted.

David

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Jul 4, 2006, 11:17:19 AM7/4/06

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Dan Richardson <k6mhe<at>k6mhe wrote:
> On Tue, 04 Jul 2006 05:57:12 GMT, Beverly Erlebacher
> <b...@cs.toronto.edu> wrote:
> [snip]
>> How does an omnidirectional 7 db or directional 15 dBi boost in "power"
>> equate to range?
> [snip a whole bunch of stuff]
>
> AN antenna passive divice. It does not increase power. Gain is
> achieved by focusing more radial tion in one direction by reducing it
> in another direction.
>
> Now more to the point (extending the range of your wireless LAN) . If
> you goal is to increase your range then add an extender (hams would
> prefer to call them repeaters).

A hi gain dish or flat panel here would actually be better. A "range
extender" or as it is commonly known as a"repeater" will actually cut
the given speed of the signal in half. Since these items are "half duplex".

Since she also mentioned that there were some trees between the house
and the shed. She most likely will need to have a directional antenna on
both ends.

Dave Platt

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Jul 4, 2006, 12:58:48 PM7/4/06

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In article <ak3am11qrjdw$.12snkojoszmz0$.d...@40tude.net>,
Beverly Erlebacher <b...@cs.toronto.edu> wrote:

>Third, does your statement that 6 dB of gain equates to 2 times the range
>mean that the "square root" of the power difference is my key to
>calculating the range?

Yes. You need four times the power (radiated in the direction of
interest) to double the range, nine times the ERP (effective radiated
power) to triple the range, etc., all else being equal.

>6 dB = 10^(6/10) ~= 4X the power, where the square root of 4X equals a
>doubling the range (assuming an omnidirectional antenna)?

Yes, assuming the correct interpretation of "omnidirectional".

The only _truly_ omnidirectional antenna is an isotropic antenna...
and these don't actually exist. All other antennas have stronger
radiation in some directions than in others. The more power they
radiate in some directions (that is, the higher the gain in those
directions) the less power they radiate in other directions.

The usual meaning of "omnidirectional antenna", in the context of
wireless networking, is a vertical antenna which emits a pattern of RF
which resembles a donut. It's "omnidirectional" in the sense that it
emits the same amount of power in each horizontal direction. At
angles above and below the horizontal, the antenna radiates less
power. Directly above and below the antenna, there's a deep "null" in
the radiation - in fact a theoretically-perfect vertical dipole would
radiate no power at all in those directions.

An "omnidirectional antenna with gain" achieves its gain by
"squashing" the donut shape of the radiation pattern, in effect
"squeezing" the pattern vertically. It radiates more power out
towards the horizon, at the expense of radiating less pattern at
angles above and below the horizon.

It's not hard to get a few dB of gain by this sort of squeezing of the
vertical pattern. It's usually difficult and expensive and tricky to
get a _lot_ of gain this way - it requires a relatively tall antenna
(roughly doubling the length for each additional 3 dB of gain) and the
antenna's positioning and design becomes fairly critical.

To get higher amounts of gain, it's usually necessary to use a
directional antenna, with some form of reflector... in effect, taking
power away from some "slices" of the "donut" and redistributing it in
the slice towards which you really want to send the power.

As you can see, any antenna which gives you a positive gain in some
direction, is going to have other directions in which the gain is
negative - in which the signal is weaker than if you used an
omnidirectional (or isotropic) antenna. It can't be otherwise, due to
the principle of conservation of energy. Antennas don't create energy
or power - they simply convey it.

Beverly Erlebacher

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Jul 4, 2006, 12:58:50 PM7/4/06

to

On Tue, 4 Jul 2006 11:03:49 -0400, Peter Pan wrote:
>> Can you help me roughly CALCULATE how to increase the range of my
>> home Internet wireless WiFi setup to a shed 300 feet away

...

> I Had a linksys WRT54G in the house attached to my sat,
> and used one of the 4 router outputs to daisy chain one to the wan input of
> another WRT54G (same ssid) and a semi-directional antenna pointed towards
> the garage about 500ft away,

Hi Peter Pan,

Oh my! Is "wireless" daisy chaining workable? Is it that easy?

I did not think I could just daisy chain multiple routers! Are you sure?
(My shed has no power but I think I could run an extension cord into it if
that would make things workable.)

Would I just set the second Linksys router (which, amazingly, has it's own
wikipedia entry at http://en.wikipedia.org/wiki/WRT54G) in the shed on the
same channel (SSID=12, name = default) as the first router in the house?

That is, could I put one linksys WRT54G in the house (perhaps with one
antenna replaced with a 7 dBd higher-gain directional antenna); and then
put the other Linksys WRT54G in the shed 300 feet away (perhaps with one of
it's antennas replaced with a similar 7 dBd directional antenna)?

Or, is it best to hardwire with cat5 the first router downstairs in the
house to the second router, say upstairs in the attic window pointing the
antenna toward the shed? I didn't even know that two routers could be daisy
chained. That might solve my dilemma.

Can someone confirm that two routers could be daisy chained either by wire
cat5 cable or by wireless signals as long as they use the same SSID channel
and network name? That solution seems to easy to be true ...

Beverly

Dave Platt

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Jul 4, 2006, 1:02:44 PM7/4/06

to

In article <c12amw79hacg$.c2e0aki9...@40tude.net>,
Beverly Erlebacher <b...@cs.toronto.edu> wrote:

>So, is it safe to calculate that the claimed 4X range improvement of the
>Linksys WRT300N wireless broadband router can be compared to that of a 12
>dB gain omnidirectional antenna?

Possibly, _if_ the claimed range improvement is meaningful.

_If_ the WRT300N can actually sustain a connection over 4x the
distance of your current router, then this could come from higher
transmit power or receiver sensitivity (which would be independent of
the antenna's pattern), or a higher-gain antenna, or the use of an RF
modulation scheme which is less vulnerable to interference. The 4x
figure could also be optimistic marketing puffery. The only way to be
sure would be to try it in your environment, and see if it helps.

Dave Platt

unread,

Jul 4, 2006, 1:12:37 PM7/4/06

to

In article <1aea0pztwz017$.67s063yt...@40tude.net>,
Beverly Erlebacher <b...@cs.toronto.edu> wrote:

>> dBi refers to gain relative to an "isotropic" antenna
>> dBd refers to gain relative to a half-wave dipole
>> dBi numbers are approximately 2 dB higher than dBd numbers,
>> for the same actual amount of gain.
>
>Hi Dave,
>
>Oh my. I guess the Hawking marketing folks were trying to trick me by
>quoting a decibel number that was higher those I compared with.
> 15 dBi ~= 15 -2 ~= 13 dBd

Quoting dBi rather than dBd is a very common marketing practice...
many vendors do it, because it gives their antennas an apparent
competitive advantage. Sorta like quoting EPA gas mileage on a car
rather than real-world mileage. The buyer just has to be aware of
what's being done.

>Interestingly, for comparison purposes, that is the SAME RANGE that the
>much more expensive Linksys (Cisco) WRT300N router claims.
>
>Do these calculations make sense?

I think you've got the idea!

Remember that antenna gain isn't the whole story. The other factors
are the router/AP's actual transmitter power output (which is usually
measured in dBm - that is, decibels referred to 1 millwatt of power)
and receiver sensitivity. Different manufacturers' transmitters may
vary by several dB of power - typical models seem to run between 15
dBm and 20 dBm. Higher transmitter power, and a more sensitive
receiver in one model of router might give you more advantage than a
high-gain antenna on another router which has a wimpier transmitter
and a less-sensitive receiver.

In practice, the best way to figure out what's going to work well in
your situation is to actually buy/borrow the equipment in question and
test it. You can get some idea of what's likely to work by doing
calculations, but there's enough variation in actual performance that
you'll have to test the equipment to see what truly works and what
doesn't.

Dave Platt

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Jul 4, 2006, 1:15:49 PM7/4/06

to

In article <8gaum8k8ji29$.1iy8idw9...@40tude.net>,
Beverly Erlebacher <b...@cs.toronto.edu> wrote:

>So that I may compare the different options available at the store to me
>for increasing my range, are these simplified calculations below correct?
>
>a. 3 dBd additional gain = 10^(3/10) ~= 2x the delivered power
>b. 2x power = 2^(1/2) effective range ~= 1.4X the range
>
>b. 6 dBd additional gain = 10^(6/10) ~= 4x the delivered power
>b. 4x power = 4^(1/2) effective range ~= 2X the range

Well, that's close. Saying "6 dBd of additional gain" isn't quite
right, though... you'd need 6 dB of additional gain compared to
whatever your antenna's current gain is. If your current antenna is a
0 dBd antenna (that is, it's a dipole), then your new antenna would be
6 dB above that, or 6 dBb.

On the other hand, if your existing antenna already has some amount of
gain... if it's a 3 dBd stacked dipole for example, then you'd need 6
dB more than that to double the range - you'd need 9 dBd in your new
antenna.

Beverly Erlebacher

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Jul 4, 2006, 1:15:39 PM7/4/06

to

On Tue, 04 Jul 2006 09:07:39 -0500, bear...@cruller.invalid wrote:
> Here is an easy way to hack your $60 wireless router into a $600

> router (they use Linksys as the example):

Wow. I've never "modified" a router before but that is interesting that one
can increase the $75 Linksys WRT54G router
(http://en.wikipedia.org/wiki/WRT54G) RF output from 28 millwatts up to 251
milliwatts (http://tinyurl.com/lpk7w).

Being true to the original intent of this thread, how do I CALCULATE what
that does to my range?

Is this 9 dBd calculation of the modification roughly correct?
a) Power gain = Power2/Power1 = 251/28 milliwatts = 9x power gain
b) Range gain = sqrt(Power gain) = sqrt(9) = 3X range gain
c) Range = original range * range gain = 100 feet * 3 = 300 feet

Beverly

Beverly Erlebacher

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Jul 4, 2006, 1:18:49 PM7/4/06

to

Hi Highland Ham,

I see there are multiple solutions. Probably on the end of my list is
adding a wire to the laptop because then it wouldn't be wireless. Still,
it's an intriguing idea (I never knew laptops could have fixed antenna's
connected to them by wire).

If I do use two antennas, does that "add" the gain?

a) Antenna 1 transmits with a directional gain of, say 7 dBd
b) Antenna 2 receives with a directional gain of, say 7 dBd
c) Does that get me a 14 dBd overall gain?

Beverly

John Weiss

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Jul 4, 2006, 1:16:49 PM7/4/06

to

"Beverly Erlebacher" <b...@cs.toronto.edu> wrote...

>
> Why are there two antennas on my router anyway? Is one transmit and the
> other receive? Or are they both transmit and receive?

AFAIK, the 2 antennae both Xmit and receive. The exception is the new "pre-N"
system that uses some kind of multipath scheme with 3 antennae.

The 2 antennae are installed so you can adjust the coverage somewhat for your
setup, e.g., one horizontal and one vertical for a multi-story house.

> Given I have TWO omnidirectional antennas on my wireless router, if I put
> the parabolic dish antenna on one to direct it to my shed, does that allow
> the OTHER antenna to radiate around the house to handle the other computers
> roving around the house?

It might...

John Weiss

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Jul 4, 2006, 1:10:51 PM7/4/06

to

"Beverly Erlebacher" <b...@cs.toronto.edu> wrote...

>
> May I ask WHERE that 6 dBd of gain is coming from?
>
> Is it ONLY from the "better" antenna?
>
> If that additional 6 dBd is coming from a "better" antenna, then why didn't
> they put that better antenna on my router in the first place?

High-gain antennae are more directional than lower-gain antennae. You may get 6
dB gain horizontally, but less coverage vertically, causing problems in a
multi-story home.

John Weiss

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Jul 4, 2006, 1:12:50 PM7/4/06

to

"Beverly Erlebacher" <b...@cs.toronto.edu> wrote...

>
> The skeptic in me wonders "if it's this easy to get 3.5X the 802.11b,g WiFi
> range, then why don't the router manufacturers add this cheap parabola as
> standard equipment on all their antennas?"

Because the average user wants omni-directional coverage in a multi-story house.

> What am I losing by putting a parabola behind one of the two antennas on my
> home router so that it increases the directional range from approximately
> 100 feet to about 300 feet?

Try it and find out.

Dave Platt

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Jul 4, 2006, 1:31:30 PM7/4/06

to

In article <1dynvcz1px2i3.p...@40tude.net>,
Beverly Erlebacher <b...@cs.toronto.edu> wrote:

>
>Hmm. I wonder. This is too good to be true. So, I will be a bit critical
>with you (i.e., the scientific method) just to "test" the assumption so
>that I can be sure I understand your position.
>
>Assuming a 9 dBd increase in the directional gain from putting a pie tin
>behind one of my existing router antennas,

Say "9 dB of additional gain", not "9 dBd of additional gain".

> that equates to either 280 or
>380 feet of range based on the calculations below.
>
>a) 9 dBd = 10^(9/10) power gain ~= 8x power gain
>b) 8x power gain = sqrt(8) range gain ~= 2.8X range gain
>c) 100 foot range * 2.8 ~= 280 foot range
>
>I'm a bit confused about the "range gain". May I ask if thta 280 foot range
>is the total range or the range improvement?

Total range.

>That is, is my range with a pie tin behind the antenna 280 feet in toto; or
>is the range now the 100 original feet + 280 additional feet which equals
>380 feet in toto?

It's 280 feet. Try redoing the above calculations with 0 dB of
additional gain:

a) 0 dB = 10^(0/10) = 1x power gain
b) 1x power gain -> sqrt(1) = 1X range gain
c) 100 foot range * 1 = 100 foot range

As you can see, the final figure is the total, not an amount which is
added to the original. Otherwise, you'd be able to double the range
of the system by adding no gain at all (0 dB) and that clearly doesn't
work.

With respect to reflectors and so forth... there are a lot of ways to
boost the range of WiFi systems using simple, easy-to-make antenna
systems. Corner reflectors, parabolics, Pringles-can waveguides, and
so forth. What I've read (and heard) is that "the first 8 to 10 dB of
gain is easy. Beyond that is hard." Getting more than about 10 dB of
additional gain from a signel antenna generally requires the use of a
commercially-made antenna - usually a parabolic wire dish or something
like that.

Oh... there's another possibility you might want to consider. So far
we've talked about improving the directional gain of your router /
access point, because it isn't all that easy to improve your laptop's
antenna system (PCMCIA card with no antenna jack).

Another option is to use a different sort of wireless network
interface to hook up to the laptop. If you're going to be using the
laptop in only one location (e.g. your shed), then you could buy an
outboard wireless network interface and hook it to your PC, and then
use some sort of improved antenna at the laptop interface.

Two possibilities for the laptop: an Ethernet-to-802.11 bridge (often
called a "game adapter" - e.g. a Netgear WGE111), or a USB-to-802.11
dongle.

If you were to stick a parabolic cardboard-and-aluminum-foil reflector
behind the antenna of your router in your house, and were to use a
game adapter or USB dongle in your shed with a second parabolic
reflector behind it, and aim the two parabolas towards one another
through a couple of clear windows, you'd end up with somewhere between
15 dB and 20 dB of total antenna gain. This would certainly give you
a solid connection, and would probably be a lot less trouble and
expense than trying to get extremely high gain from just one end of
the connection (the router).

I've heard of people getting ranges of a mile or more, over clear
terrain, with setups no more complex than this.

Jeff Liebermann

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Jul 4, 2006, 12:12:44 PM7/4/06

to

Beverly Erlebacher <b...@cs.toronto.edu> hath wroth:

>Can you help me roughly CALCULATE how to increase the range of my home
>Internet wireless WiFi setup to a shed 300 feet away from my house?

Yes. See the alt.internet.wireless FAQ section on link calcs at:
http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations

>Presently, I can walk about half the way through the wooded area to the
>shed with my laptop in hand before I lose the connection to the PCMCIA
>802.11b,g Linksys card. Basically I need to gain 150 feet in "range".

The trees are going to be a problem. The water in the leaves
attenuate the signal and they impinge on the Fresnel zone. Calculating
foliage attenuation is difficult as it varies with season, weather,
type of foliage, etc.

The Fresnel Zone may also be a problem. You need at least 0.8 times
the zone radius of clearance at midpoint to avoid edge diffraction and
other nasty effects. At 300 ft, the Fresnel zone radius at midpoint
is about 5.5ft. You'll need to be at least 4.4ft clear of any objects
at midpoint including the ground. The problem is usually that the
antennas on each end are at desk level which is not high enough to
clear the ground.
http://www.terabeam.com/support/calculations/fresnel-zone.php

>But how?

Start with something simple:
http://www.freeantennas.com
You can get substantial directional gain with a simple reflector at
little cost.

>At the store, I immediately become confused as I try to compare $30 USD
>omnidirectional antennas (D-Link ANT24-070) that boost "power" by a claimed
>7 db; $50 USD directional corner antennas (Hawking HAI15SC) that claim 15
>dbi (whatever a dBi is); and $150 USD 802.11N routers that claim to boost
>omnidirectional "range" by 4x (Linksys WRT300N).

Muddle. Antennas do not boost the "power". That's what an amplifier
does. Antennas only redirect the available RF power. That means that
for an increase in signal in one direction, the signal must decrease
in another. This is also known as the Free Lunch axiom.

Be VERY careful of specifications from antenna vendors that supply
pigtails with their antennas. The published specifications never seem
to mention the coax cable and connector losses. Figure on 0.5dB per
connector pair.

dBi is the gain over a theoretical isotropic radiator. This is
commonly used as a reference point for antenna calculations.

When comparing different types of routers, it's common to claim that
some have better range. For example, the range difference between
MIMO routers and beam switching routers was tested in:
| http://groups.google.com/group/alt.internet.wireless/msg/11a8efd2638d674b
MIMO has much better range than beam switching. The problem is that
neither technology is useful for point to point which is apparently
what you're doing. That's because it's impossible to attach external
antennas.

>How does an omnidirectional 7 db or directional 15 dBi boost in "power"
>equate to range?

That depends on what you're comparing them to. Let's say we start
with the stock rubber ducky antenna supplied with most access points.
It has a gain of about 2dBi. The 7dBi antenna has 5dB more gain. The
15dBi antenna has 13dB more gain. The relative range improvement is:
range improvement = 10^(dB/20)
or 1.8 times for the 7dBi antenna
and 4.5 times for the 15dBi antenna.

The range improvement is the same for a given gain no matter what type
of antenna. However, there is a big difference in the radiation
angles. An 8dBi omni antenna will have a -3dB vertical radiation
angle of perhaps 13 degrees. Tilt this antenna 7 degrees in any
direction and the signal is gone. An 8dBi panel or biquad will have a
radiation angle of about 60 degrees. It can be tilted 30 degrees
vertically or horizontally before the signal is lost.

>Approximately how many decibels of (omnidirectional or directional) power
>do I really need to boost my WiFi range from about 150 feet to the 300 feet
>I need?

Want me to do the calculations? I need to know what you are going to
use for hardware and how long are the coax cable runs. It's quite
easy once you have the numbers. See:
http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations
for the procedure.

>Looking up what a decibel is
>(http://en.wikipedia.org/wiki/Decibel#Definition), I
>calculate the D-Link ANT24-070 omnidirectional antenna gives me about 5
>times the power (assuming 7 db = 10^7/10 ~= 5); but does this get me the
>additional 150 feet of range to my shed?

Range and power are related by the inverse square law, which roughly
states that you need 4 times the power to double your range. An
increase of 5 times in power will only yield a 2.2 times increase in
range.

>Spending almost twice as much money on the Hawking HAI15SC directional
>antenna gets me roughly 30 times the power (assuming 15 db = 10^15/10 ~=
>32); but is that enough power to get me the range to my shed?

One of the fun calculations is to work out the cost per decibel gain
for each type of antenna. Using prices from:
http://www.fab-corp.com

Type Gain Cost Cost/dB
dBi
dish 15 $35 $2.3
yagi 15 $65 $4.3
panel 19 $68 $3.8
omni 12 $70 $5.8

So, from my random assortment of typical antennas, it seems that the
dish is the cheapest way to get lots of gain, while the omni is the
most expensive. Obviously, the cost/dB is going to vary depending on
vendor, discounts, shipping, taxes, selection, and such. However, the
numbers should be considered before buying.

>Indeed, is there some way to add a Hawking 15db antenna on the receiving
>end to get 1,000 times the power (15 db + 15 db = 30 db = 10^30/10 ~=
>1,000); but what would I hook the wire output from this receiving antenna
>to in the shed (I can't hook it to the pcmcia card, can I)?

No, you can't connect it to your PCMCIA card. You can butcher you
card to add an external antenna pigtail. Other options are to
purchase a PCMCIA wireless card with an antenna connector, or use an
ethernet client bridge radio such as a WAP54G. Also a "game adapter".

>Given those db calculations, how do I compare the antenna options with
>replacing my home 802.11b,g router with the 4X range $150 USD Linksys
>802.11n WRT300N router and the required $120 USD Linksys WPC300N PCMCIA
>card (assuming 6 db = 10^6/10)?Will this three-antenna 802.11n router be
>forced to drop down to 1X speeds because inside my house my kid's laptops
>will all be using 802.11b or 802.11g? Or can the router work on both
>802.11g to one computer and on 802.11n to the other computer at the same
>time?

No clue. There's not enough info to make a proper comparison. You
can't attach an external antenna to a MIMO router anyway so that's
out.

What's missing is:
1. What equipment do you currently have to work with?
2. What are the exact distances involved?
3. How long a coax cable run? Can the radio be mounted next to the
antenna?
4. What obstructions are in the line of sight? Is the Fresnel zone
clear? Are you going through any walls or windows? Trees and bushes?
5. Any limitations to antenna selection and placement (i.e. CC&R)?
6. Any performance expectations? What's the minimum thruput speed
you're willing to tolerate? Thruput is about 50% of wireless
connection speed.
7. Any local sources of interference? Any other wireless networks
including municipal networks?
8. Any budget limit?

--
Jeff Liebermann je...@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Beverly Erlebacher

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Jul 4, 2006, 1:40:18 PM7/4/06

to

On Tue, 04 Jul 2006 06:11:27 -0700, Dan Richardsonk6mhe wrote:
> If your goal is to increase your range then add an extender

> (hams would prefer to call them repeaters).

Oh my. The seemingly perfect option.

I had come across the concept of wireless "repeaters" in my initial
googling before I went to the store, e.g., in this Microsoft "how to
increase range" article
http://www.microsoft.com/athome/moredone/wirelesstips.mspx and in this
"Extending WLAN Range" article
http://www.wi-fiplanet.com/tutorials/article.php/1571601

The repeater most often recommended was the "Linksys Wireless-G Range
Expander WRE54G".

However, I can't find that 802.11b,g WiFi repeater (aka range expander or
extender) anywhere in the local stores. The salesperson who sold me the
$300 USD 802.11n router and PCMCIA card combination said they didn't work
so they dropped it.

This solution seems to be the most elegant of all (but someone else
suggested just using a second router).

Can someone unconfusify the situation?

Is placing a repeater (on the same SSID) in the shed really the same as
adding a second router instead?

Beverly

Beverly Erlebacher

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Jul 4, 2006, 1:47:27 PM7/4/06

to

On Tue, 04 Jul 2006 08:17:19 -0700, David wrote:
> A "range extender" or "repeater" will cut the speed in half.

Hi David,

Interesting this speed difference. I'm worried about RANGE and all of a
sudden other factors come into play! Thank you for enlightening me. I know
more now than I ever did from you wonderful guys!

As I noted to someone else just now, I DID try to find the "Linksys
Wireless-G Range Expander WRE54G" WiFi repeater in the local stores but
they did not exist in any of the three stores I checked.

Also, some of the articles talk about an "access point"
(http://www.wi-fiplanet.com/tutorials/article.php/1571601).

Can someone tell me what part of my setup I would call the "access point"?

Beverly

stephen

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Jul 4, 2006, 1:57:22 PM7/4/06

to

"Beverly Erlebacher" <b...@cs.toronto.edu> wrote in message
news:2hqacpnj1nwj$.1683sqqzgbbo2$.dlg@40tude.net...

> Can you help me roughly CALCULATE how to increase the range of my home
> Internet wireless WiFi setup to a shed 300 feet away from my house?
>

//SNIP//

Beverly - i will leave the radio complications to the experts.

but - you mentioned you could run power out to your shed. Why not plumb it
in for power and networking?

then you can add a separate access point there and avoid antennae, gain,
loss through leaves and the rest.

If you run a power line, then there are homeplug devices which can provide
network links through the mains feed - or you could just run some Cat 5
cable with the mains link (not forgetting earthing, safety and all those
other details) - 300 ft is within the standard 100 m run for 100 Base-T.

> Thank you,
> Beverly
--
Regards

stephe...@xyzworld.com - replace xyz with ntl

Dave Platt

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Jul 4, 2006, 2:03:29 PM7/4/06

to

In article <ly6pp2c8zwp.1e...@40tude.net>,
Beverly Erlebacher <b...@cs.toronto.edu> wrote:

>This solution seems to be the most elegant of all (but someone else
>suggested just using a second router).
>
>Can someone unconfusify the situation?
>
>Is placing a repeater (on the same SSID) in the shed really the same as
>adding a second router instead?

Repeaters normally need to be placed somewhere around halfway between
the existing router / access point and the location of use. In your
case, that'd probably put the repeater smack-dab in the middle of the
woods - probably not the best location for it?

Beverly Erlebacher

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Jul 4, 2006, 2:06:56 PM7/4/06

to

On Tue, 04 Jul 2006 17:57:22 GMT, stephen wrote:
> but - you mentioned you could run power out to your shed. Why not plumb it
> in for power and networking?
> then you can add a separate access point there and avoid antennae, gain,
> loss through leaves and the rest.

Hi Stephen,
I'm confused about this "access point" thing.

Is that the same as a "router"?

Is it as simple as buying a second router (routers are familiar to me) and
just hooking that second router to the first router by cable and that would
extend my range by the distance of the cable connecting the two routers?

This is a key confusion point for me!
Beverly

Don K

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Jul 4, 2006, 2:11:06 PM7/4/06

to

"Beverly Erlebacher" <b...@cs.toronto.edu> wrote in message

news:1i8d1tcl66zdn$.7knr5ebizk69.dlg@40tude.net...
>
> After reading all the articles posted, I now understand that:
>
> b) The coffee cantenna is more effective than the pringles cantenna
> http://www.oreillynet.com/cs/user/view/wlg/1124
>
> c) The dish antenna is the simplest of all and almost as good
> http://www.freeantennas.com/projects/template
> http://www.freeantennas.com/projects/template2/index.html

Actually, the coffee can is the simplest antenna to build since
there's nothing too critical about its construction:

Drill a hole in the can a quarter-wavelength from the end.
Solder a coaxial connector there.
Solder a quarter wavelength of solid wire as the radiator.
And you're done.

I built some 30 years ago at 2155 MHz for picking up MDS TV channels
and they were as effective as a 22 element loop yagi, and almost as
good as a "real" 24 inch dish. I used 16 oz coffee cans.

Don

Rod Speed

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Jul 4, 2006, 2:11:35 PM7/4/06

to

The wireless part.

Rod Speed

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Jul 4, 2006, 2:11:43 PM7/4/06

to

Beverly Erlebacher <b...@cs.toronto.edu> wrote:

> On Tue, 04 Jul 2006 05:50:02 -0400, Rôgęr wrote:
>>> Do folks here recommend the pringles cantenna or the pie tin
>>> antenna for my 2-antenna router 802.11b,g directional application
>>> where I need to also feed the computers within the house in
>>> addition to the shed 300 feet away?
>>

>> I use panel antennas almost exclusively, exceptions being some 24dbi
>> mesh antennas for backhaul.
>
> Hi Rôgęr,

>
> After reading all the articles posted, I now understand that:
>

> a) The pringles can is hip; but it's the worst performer
> http://www.oreillynet.com/cs/weblog/view/wlg/448
> (it's not even metal foil lined and it's too small in diameter)

>
> b) The coffee cantenna is more effective than the pringles cantenna
> http://www.oreillynet.com/cs/user/view/wlg/1124
>
> c) The dish antenna is the simplest of all and almost as good
> http://www.freeantennas.com/projects/template
> http://www.freeantennas.com/projects/template2/index.html
>

> I also see, as Rod Speed so kindly noted, that the give and take is
> that we lose range in some directions in favor of range in the
> desired direction. Fair enough.
>
> My one question is a practical one.
>

> Why are there two antennas on my router anyway?

That gives a more reliable coverage than with one.

> Is one transmit and the other receive?
> Or are they both transmit and receive?

They're normally both transmit and receive.

> Given I have TWO omnidirectional antennas on my wireless router,
> if I put the parabolic dish antenna on one to direct it to my shed,
> does that allow the OTHER antenna to radiate around the house
> to handle the other computers roving around the house?

Yes.

Beverly Erlebacher

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Jul 4, 2006, 2:26:27 PM7/4/06

to

On Tue, 04 Jul 2006 18:03:29 -0000, Dave Platt wrote:
>>Is placing a repeater (on the same SSID) in the shed really the same as
>>adding a second router instead?
>
> Repeaters normally need to be placed somewhere around halfway between
> the existing router / access point and the location of use. In your
> case, that'd probably put the repeater smack-dab in the middle of the
> woods - probably not the best location for it?

Hi Dave Platt,

You made me laugh when I read this just now. Yes, it would be "up a tree"
somewhere. Maybe I could put it next to the Hummingbird feeders so they can
nest on it!

I have to run to a holiday BBQ right now so I'll try to respond later.

Thank you all for the help, I'm still confused if I can just use a second
wired router ... but with your help, I'm working on that.
Beverly

Peter Pan

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Jul 4, 2006, 3:19:26 PM7/4/06

to

Yes.. Daisy chaining the wrt54g ('s ((plural)), NOT to be confused with the
GS) is that easy.. I have the main one for the house (in the house), and the
second (third and maybe soon a fourth) up a ways (a metal snow roof on the
house, so the 2nd/3rd etc are actually in an upstairs closet with power, and
the semidirectional antennas are outside (other side of the steel roof/up
higher((about 13ft, on the antenna pole for my cell/sat/etc)).. No need to
run an extension cord, idea is to have them both in the house, one with an
omnidirectional antenna for inside the house, and the second cabled to the
first and a semi-directioanl antenna aimed at the outbuilding..

Make sure the router output goes to the WAN input of the second (wap/router)
device..

The jury is out on whether you want the same ssid/same channel, for me, I
just wanted one big area covered so I could walk around and be connected, so
just made it the same, some people want to know which router they are on and
use different channels.. (I figger hey if I am connected, I don't really
care to which, I just want it to work automatically)

In your case, the main floor and attic/upstairs windows, with the one
upstairs having a semi-directional antenna sounds like a reasonable idea...

As an aside, when I travel, I use a device called a WiFlyer
(www.alwaysonwireless.com) basically a travel router and dial-up modem
combo... I use it at home as a backup so if the sat is out, I can daisy
chain THAT to the local wap/router to give me dial-up as a
backup/alternative, from any wifi-enabled computer..

I'm at my sisters right now connected to her system (basically cable
internet and a wap/router upstairs cabled to a second wap/router downstairs,
that covers the downstairs and backyard.. I was writing from outside, but
it's too hot, so I came in to finish this post.. never lost connection when
I moved from the backyard to my study on the top floor ((two different
wap/routers))..

As for hardwire or wireless bridge, if` the units are near each other, then
a hardwire for 10-20 bucks is a whole lot less than two more wap's and
extension cords... In your case, I'd suggest hardwire..

John Navas

unread,

Jul 4, 2006, 3:26:55 PM7/4/06

to

On Tue, 04 Jul 2006 09:12:44 -0700, Jeff Liebermann
<je...@comix.santa-cruz.ca.us> wrote in
<vc0la29vg94njlict...@4ax.com>:

>>Indeed, is there some way to add a Hawking 15db antenna on the receiving
>>end to get 1,000 times the power (15 db + 15 db = 30 db = 10^30/10 ~=
>>1,000); but what would I hook the wire output from this receiving antenna
>>to in the shed (I can't hook it to the pcmcia card, can I)?
>
>No, you can't connect it to your PCMCIA card. You can butcher you
>card to add an external antenna pigtail. Other options are to
>purchase a PCMCIA wireless card with an antenna connector, or use an
>ethernet client bridge radio such as a WAP54G. Also a "game adapter".

Also the Hawking HWU8DD
<http://www.hawkingtech.com/products/productlist.php?CatID=32&FamID=60&ProdID=280>

--
Best regards, FAQ for Wireless Internet: <http://Wireless.wikia.com>
John Navas FAQ for Wi-Fi: <http://wireless.wikia.com/wiki/Wi-Fi>
Wi-Fi How To: <http://wireless.wikia.com/wiki/Wi-Fi_How_To>
Fixes to Wi-Fi Problems: <http://wireless.wikia.com/wiki/Wi-Fi_Fixes>

John Navas

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Jul 4, 2006, 3:27:56 PM7/4/06

to

On Tue, 04 Jul 2006 17:57:22 GMT, "stephen" <stephe...@xyzworld.com>
wrote in <6_xqg.86010$uP.6...@newsfe2-gui.ntli.net>:

>If you run a power line, then there are homeplug devices which can provide
>network links through the mains feed - or you could just run some Cat 5
>cable with the mains link (not forgetting earthing, safety and all those
>other details) - 300 ft is within the standard 100 m run for 100 Base-T.

unread,

Jul 4, 2006, 4:29:05 PM7/4/06

to

"Peter Pan" <PeterPa...@NOSPAMAkamail.com> hath wroth:

>There is one point that the salepeople NEVER mention.. Range extenders have
>to be plugged in for power.. Doubt you have a plug in your yard 1/2 way to
>the shed, nor power in the shed for a 2nd ap, so consider multiples at the
>house, same bat time, same bat channel (sorry, watching TVland on cable, old
>batman shows.. meant ssid and channel :)

Solar powered wi-fi repeater?
| http://www.popsci.com/popsci/how20/5781cbd2b791b010vgnvcm1000004eecbccdrcrd.html (2 pages)

For 300ft through the trees, I would run outdoor (gel filled) CAT5
cable. About $150/1000ft. If power at the shed is a problem, use PoE
to run whatever's at the end.

Geoffrey S. Mendelson

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Jul 4, 2006, 5:31:06 PM7/4/06

to

Beverly Erlebacher wrote:
> I'm confused about this "access point" thing.

An access point is a device with an ethernet port on one side and a wifi
port on the other. In technical terms it would be called a "bridge". It
"bridges" two seperate network segments, although in this case they use
different topologies (100Base-T and WiFi).

> Is that the same as a "router"?

The usual WiFi router consists of a four port ethernet hub (LAN ports),
a seperate single ethernet port (WAN port) and a WiFi access point.
It is set up to "route" between the single (aka WAN) port and the other
two ports, the LAN and WiFi. Most of what it does for routing is NAT (network
address translation) and some sort of IP tunneling.

If you ignore the WAN port and just use the LAN ports, you have a four port
hub and an access point.

> Is it as simple as buying a second router (routers are familiar to me) and
> just hooking that second router to the first router by cable and that would
> extend my range by the distance of the cable connecting the two routers?

Yes. Just make sure to use the LAN ports. It would be best to use different
channels. Most WiFi clients are smart enough to use the channel that is the
strongest if they have access points on more than one with the same SSID.

Make sure to use encryption. Encryption is NOT to keep your data safe,
nothing can do that. If someone is intent on accessing your network, WEP
encryption will not keep them out.

What it is for is to convince the guy driving down the street looking for an
open network to send out SPAM, or "share" kiddie porn, to drive on.
Unfortunately, most users don't even change the SSID of their network, let
alone set an encryption key.

Having tuned in late, if you want to have an open network, look up PublicIP.
It's a "live cd" that runs on a PII or better (x86) computer and provides
all the functions you need to offer a secure and safe open network.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel g...@mendelson.com N3OWJ/4X1GM
IL Voice: (07)-7424-1667 IL Fax: 972-2-648-1443 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/

Geoffrey S. Mendelson

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Jul 4, 2006, 5:31:07 PM7/4/06

to

Rod Speed wrote:
>> Is one transmit and the other receive?
>> Or are they both transmit and receive?
>
> They're normally both transmit and receive.

That's a shame. Here in Israel we are limited to 100mw EIRP, which
severly limits the transmit antenna. There is NO limitation on the
receive antenna.

Wolfgang S. Rupprecht

unread,

Jul 4, 2006, 5:43:00 PM7/4/06

to

Jeff Liebermann <je...@comix.santa-cruz.ca.us> writes:
> Type Gain Cost Cost/dB
> dBi
> dish 15 $35 $2.3
> yagi 15 $65 $4.3
> panel 19 $68 $3.8
> omni 12 $70 $5.8

A while ago I posted about an open (non-radome enclosed) yagi that
claimed 15dbi for ~$30
(http://www.mfjenterprises.com/products.php?prodid=MFJ-1800). Well as
you mentioned elsewhere "most manufacturers lie, but thats ok, nobody
calculates", I'm coming to the conclusion that they related the gain
of this yagi to a reference bag of male bovine excrement. Comparing
it to a 15dbi bbq-type dish, it is 5dbi lower in signal strength.
Call it a 10dbi IFF the bbq is rated well.

(Is there a department of the government thats the slightest bit
interested in chasing fraud like this? If the gas pumps were
calibrated 5dbi short you can bet that the establishment would be shut
down pretty damn fast.)

-wolfgang
--
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/

David

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Jul 4, 2006, 5:46:10 PM7/4/06

to

The router

David

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Jul 4, 2006, 5:48:38 PM7/4/06

to

Beverly Erlebacher wrote:
> On Tue, 04 Jul 2006 06:11:27 -0700, Dan Richardsonk6mhe wrote:
>> If your goal is to increase your range then add an extender
>> (hams would prefer to call them repeaters).
>
> Oh my. The seemingly perfect option.
>
> I had come across the concept of wireless "repeaters" in my initial
> googling before I went to the store, e.g., in this Microsoft "how to
> increase range" article
> http://www.microsoft.com/athome/moredone/wirelesstips.mspx and in this
> "Extending WLAN Range" article
> http://www.wi-fiplanet.com/tutorials/article.php/1571601
>
> The repeater most often recommended was the "Linksys Wireless-G Range
> Expander WRE54G".
>
> However, I can't find that 802.11b,g WiFi repeater (aka range expander or
> extender) anywhere in the local stores. The salesperson who sold me the
> $300 USD 802.11n router and PCMCIA card combination said they didn't work
> so they dropped it.
>
> This solution seems to be the most elegant of all (but someone else
> suggested just using a second router).

as a repeater

>
> Can someone unconfusify the situation?
>
> Is placing a repeater (on the same SSID) in the shed really the same as
> adding a second router instead?
>
> Beverly

I was at the local Radio Shack yesterday and they had repeaters (range
extenders) on the shelf (Linksys)

Wolfgang S. Rupprecht

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Jul 4, 2006, 5:54:46 PM7/4/06

to

Beverly Erlebacher <b...@cs.toronto.edu> writes:
> (My shed has no power but I think I could run an extension cord into it if
> that would make things workable.)

Why not run cat-5 to it then??? A 1000-ft spool of cat-5 is under
$50. Wireless is wonderful for laptops that move around, but if you
have a fixed point that is hard to get to because of RF blockage, then
a real wire seems like the way to go.

David

unread,

Jul 4, 2006, 6:06:06 PM7/4/06

to

Jeff Liebermann wrote:
> "Peter Pan" <PeterPa...@NOSPAMAkamail.com> hath wroth:
>
>> There is one point that the salepeople NEVER mention.. Range extenders have
>> to be plugged in for power.. Doubt you have a plug in your yard 1/2 way to
>> the shed, nor power in the shed for a 2nd ap, so consider multiples at the
>> house, same bat time, same bat channel (sorry, watching TVland on cable, old
>> batman shows.. meant ssid and channel :)
>
> Solar powered wi-fi repeater?
> | http://www.popsci.com/popsci/how20/5781cbd2b791b010vgnvcm1000004eecbccdrcrd.html (2 pages)
>
> For 300ft through the trees, I would run outdoor (gel filled) CAT5
> cable. About $150/1000ft. If power at the shed is a problem, use PoE
> to run whatever's at the end.
>
>

Perhaps a D5 cat would get the job of clearing a path through the trees?

Rod Speed

unread,

Jul 4, 2006, 6:27:05 PM7/4/06

to

Geoffrey S. Mendelson <g...@mendelson.com> wrote
> Rod Speed wrote

>>> Is one transmit and the other receive?
>>> Or are they both transmit and receive?

>> They're normally both transmit and receive.

> That's a shame. Here in Israel we are limited to 100mw EIRP, which severly
> limits the transmit antenna. There is NO limitation on the receive antenna.

A receive antenna has no EIRP, it doesnt radiate any real power.

Jeff Liebermann

unread,

Jul 4, 2006, 9:18:16 PM7/4/06

to

"Wolfgang S. Rupprecht"
<wolfgang+gnus2...@dailyplanet.dontspam.wsrcc.com> hath
wroth:

>Why not run cat-5 to it then??? A 1000-ft spool of cat-5 is under
>$50. Wireless is wonderful for laptops that move around, but if you
>have a fixed point that is hard to get to because of RF blockage, then
>a real wire seems like the way to go.
>-wolfgang

Ummm.... not just ordinary CAT5. She's in Toronto where is gets
rather cold in the winter. Ordinary PVC jacketed CAT5 will become
rather hard stiff and crack. It's also not UV stable and will develop
a rather rough surface after a few years.

What's needed is gel filled, outdoor, and possibly shielded CAT5. The
stuff is often also suitable for direct burial. For example:
http://www.cat5ecableguy.com/outdoor_bulk_cable
I have a few runs of generic CAT5 running through the redwoods. The
run in the sun is slowly crumbling after about 7 years. Same with the
runs on my roof. If I touch, the jacket cracks.

However, the real problem is not freezing or UV. It's the critters.
Squirrels in the trees and gophers in the ground. They seem to enjoy
eating cables around here. I once tracked it down to the sweat from
my hands during the install. Also the food that I was eating was
transferred to the cable. I now wear latex gloves when doing
installs. However, that was years ago. The squirrels like to bite
into literally anything to see how it tastes, even if they know they
won't like it. I have squirrel bites in my tree fruit, coax cables,
and data cables. Even the fiber runs got chewed. If the critters
weren't so cute, I would make myself a new squirrel hat or coat.
Anyway, the shielded CAT5 seems to discourage them somewhat. I get
bites into the jacket, but not past the foil.

If you have power at both ends of the link, do NOT ground one end of
the drain wire or shield as it will create a ground loop.

Terminating the gel filled cable is no fun. The cable is stiff,
doesn't bend well, and the gel is like sticky goo. It's not
impossible, but it can be a mess. Plan on doing some trial and error,
plus the requisite cursing.

Incidentally, one can go much farther then just 300ft with CAT5. The
catch is that it has to be 10baseT-HDX (half-duplex). 100baseTX will
not work. Full duplex is a crap shoot. I often take a 1000ft roll of
CAT5, terminate the ends, and run it through a data error test (SNMP
on a Cisco 1900 switch) or a borrowed certifier. No problems at
1000ft but things started to get weird at about 1300ft. Probably
timing.

meme

unread,

Jul 4, 2006, 9:38:09 PM7/4/06

to

The first thing I would do before calling the yagi wrong would be to
compare it against a known standard. IE: a dipole at the same
frequency. the 15dbi means that it has 15db gain over an 'isotropic
dipole' (standards dipole mounted in 'freespace')

maybe your dish is not what it's supposed to be??

Then, after seeing the difference when comparing the dipole to the
yagi you would have a difinitive answer as to the yagi gain,

Bob Smith
Robert Smith Consulting
NA6T

Jeff Liebermann

unread,

Jul 4, 2006, 10:30:49 PM7/4/06

to

"Wolfgang S. Rupprecht"
<wolfgang+gnus2...@dailyplanet.dontspam.wsrcc.com> hath
wroth:

>

>Jeff Liebermann <je...@comix.santa-cruz.ca.us> writes:
>> Type Gain Cost Cost/dB
>> dBi
>> dish 15 $35 $2.3
>> yagi 15 $65 $4.3
>> panel 19 $68 $3.8
>> omni 12 $70 $5.8
>
>A while ago I posted about an open (non-radome enclosed) yagi that
>claimed 15dbi for ~$30
>(http://www.mfjenterprises.com/products.php?prodid=MFJ-1800).

In ham radio circles, MFJ is not known for quality products. That
antenna might be suitable for temporary installation, but the exposed
copper driven element and unprotected connector is just asking for
problems outdoors. Also, I made no attempt to price shop or optimize
the cost/dB ratio. Interestingly, at one time, the yagi was the most
expensive, while the omni was the cheapest. I can do it again using
approximately the same gain antennas, which should produce more useful
results, but I was just hoping that the OP would do her own
calculations based on prospective antennas.

>Well as
>you mentioned elsewhere "most manufacturers lie, but thats ok, nobody
>calculates", I'm coming to the conclusion that they related the gain
>of this yagi to a reference bag of male bovine excrement. Comparing
>it to a 15dbi bbq-type dish, it is 5dbi lower in signal strength.
>Call it a 10dbi IFF the bbq is rated well.

Well, the maximum gain of a dish is very easy to calculate.
http://en.wikipedia.org/wiki/Microwave_antenna
Gain(dBi) = Pi^2 * Dia^2 / wavelength^2 * feed-efficiency
where Dia and wavelength are in the same units and efficiency is a
function of feed illumination accuracy and is no more than 50% at best
for typical small dish antennas.

Climbing onto my roof and trying the numbers on a PacWireless 24dBi
dish:
Gain = 9.87 * 68cm^2 / 12.5cm^2 * 0.50
Gain = 9.87 * 4624 / 156.25 * 0.5 = 146 = 21.6dBi
Close enough to 24dBi.

The gain of a yagi is approximately the gain of a dipole, 1.66 scalar
(or 2.2 dBi) times the number of elements (including the driven
element). So, the MFJ yagi should have a gain of:
1.66 * 16 = 14.2dBi
Close enough to 15dBi.

Basically, if the antennas were built perfectly, they would be
sufficiently close to theory to make the advertising correct. However,
this is rarely the case. Manufacturing tolerances, surface coating
inefficiency, connector losses, sloppy construction, VSWR losses,
boresight errors, effects of the mounting hardware, local reflections,
and sloppy installations all conspire to reduce the gain below the
maximum. Your mileage and gain may vary.

>(Is there a department of the government thats the slightest bit
>interested in chasing fraud like this?

It's not fraud. You might try the better biz burro or Federal Trade
Commish. I doubt that they care.

>If the gas pumps were
>calibrated 5dbi short you can bet that the establishment would be shut
>down pretty damn fast.)

It's not 5dB short. There are plenty of other abominations in the
antenna business. I've often considered going into the commercial
antenna business because few people can understand how they work, make
valid comparisons, and have the necessary test equipment. Perfect for
an evil exploiter like me. Anyway, I can do without hand drawn
antenna patterns, unrealistic free space antenna patterns,
non-standard scales on antenna patterns, claims of range improvement
(compared to what?), forgetting about coax cable and pigtail losses,
ignoring bandwidth issues, failing to measure up-tilt on omnis, crappy
mounts, use of easily corroded materials for unsealed outdoor
antennas, etc. It's not really distorting the numbers as much as
conveniently forgetting to mention some important items.

Wolfgang S. Rupprecht

unread,

Jul 4, 2006, 11:16:38 PM7/4/06

to

Jeff Liebermann <je...@comix.santa-cruz.ca.us> writes:
> Ummm.... not just ordinary CAT5. She's in Toronto where is gets
> rather cold in the winter. Ordinary PVC jacketed CAT5 will become
> rather hard stiff and crack. It's also not UV stable and will develop
> a rather rough surface after a few years.

I like to prototype things first with disposable parts. For all I
know something else might pop up that would prevent the whole idea
from working well. If I spent too much time trenching and buying
special outdoor cable I'd feel really stupid. Indoor cat-5 is so
cheap I wouldn't even think twice about running a 150ft run knowing
that it would have to be redone with higher quality parts once all the
other details had been worked out.

One trick I learned from the cable guys when they installed my athome
connection many years ago is to use the soft black fountain hose as
poor-man's conduit. That method did have its problems as water tended
to pool in the low parts of the conduit. I wonder if small bleed
holes in the conduit would have helped. Thoughts? Or just go for
direct burial/gel and forgo the conduit?

> However, the real problem is not freezing or UV. It's the critters.
> Squirrels in the trees and gophers in the ground. They seem to enjoy
> eating cables around here.

Thanks for that tip! I'm sure I'd have fallen for that.

> If you have power at both ends of the link, do NOT ground one end of
> the drain wire or shield as it will create a ground loop.

Yup.

> Terminating the gel filled cable is no fun. The cable is stiff,
> doesn't bend well, and the gel is like sticky goo. It's not
> impossible, but it can be a mess. Plan on doing some trial and error,
> plus the requisite cursing.

Sounds like the goop ma-bell used to put into the phone electronics.
You could wash your hands 10x and the crap would still be stuck to
your fingers.

Wolfgang S. Rupprecht

unread,

Jul 4, 2006, 11:32:50 PM7/4/06

to

Jeff Liebermann <je...@comix.santa-cruz.ca.us> writes:
> "Wolfgang S. Rupprecht"
> <wolfgang+gnus2...@dailyplanet.dontspam.wsrcc.com> hath
> wroth:

>>Well as
>>you mentioned elsewhere "most manufacturers lie, but thats ok, nobody
>>calculates", I'm coming to the conclusion that they related the gain
>>of this yagi to a reference bag of male bovine excrement. Comparing
>>it to a 15dbi bbq-type dish, it is 5dbi lower in signal strength.
>>Call it a 10dbi IFF the bbq is rated well.
>
> Well, the maximum gain of a dish is very easy to calculate.
> http://en.wikipedia.org/wiki/Microwave_antenna
> Gain(dBi) = Pi^2 * Dia^2 / wavelength^2 * feed-efficiency
> where Dia and wavelength are in the same units and efficiency is a
> function of feed illumination accuracy and is no more than 50% at best
> for typical small dish antennas.
>
> Climbing onto my roof and trying the numbers on a PacWireless 24dBi
> dish:
> Gain = 9.87 * 68cm^2 / 12.5cm^2 * 0.50
> Gain = 9.87 * 4624 / 156.25 * 0.5 = 146 = 21.6dBi
> Close enough to 24dBi.
>
> The gain of a yagi is approximately the gain of a dipole, 1.66 scalar
> (or 2.2 dBi) times the number of elements (including the driven
> element). So, the MFJ yagi should have a gain of:
> 1.66 * 16 = 14.2dBi
> Close enough to 15dBi.

The 15dbi bbq dish I have is only the small 12"x16" 15dbi one from
Sharper-Concepts.

http://sharperconcepts.zoovy.com/product/YSC-HG2415G-NF

It has a N-female just like the MFJ antenna so I can move the pigtail
from one antenna to the other. The difference between the two
antennas was 5db in signal strength. The test source was the mystery
"Mt Allison" wifi source which came in with 2db above the noise floor
with the yagi and 7db with the dish. Both claimed to be 15dbi
antennas. I supposed the dish could be vastly better than it is
rated, but what is the chance of that?

Jeff Liebermann

unread,

Jul 4, 2006, 11:55:26 PM7/4/06

to

"Wolfgang S. Rupprecht"
<wolfgang+gnus2...@dailyplanet.dontspam.wsrcc.com> hath
wroth:

>I like to prototype things first with disposable parts.

I can't afford to do that for my customers. They don't want to pay me
to do things twice. I have to get it right the first time. However,
at home, I can experiment.

>One trick I learned from the cable guys when they installed my athome
>connection many years ago is to use the soft black fountain hose as
>poor-man's conduit.

Yep. I have several runs of black poly something flex water pipe
running under the road and buried along the shoulder. However, I
spent quite a bit of effort to keep it waterproof. I originally had
it pressurized but the later decided that it was a waste of effort. No
water inside that I can find.

>That method did have its problems as water tended
>to pool in the low parts of the conduit. I wonder if small bleed
>holes in the conduit would have helped. Thoughts? Or just go for
>direct burial/gel and forgo the conduit?

No, a drain hole won't work because there's not enough pressure inside
the pipe to eject the water through the small hole. Small holes
require pressure to get past the surface tension of the water drops.
The obvious question is why is there water inside? Condensation?
Capillary action? Siphon action? Keep the water out and you won't
need to worry about drainage.

>> Terminating the gel filled cable is no fun. The cable is stiff,
>> doesn't bend well, and the gel is like sticky goo. It's not
>> impossible, but it can be a mess. Plan on doing some trial and error,
>> plus the requisite cursing.
>
>Sounds like the goop ma-bell used to put into the phone electronics.
>You could wash your hands 10x and the crap would still be stuck to
>your fingers.

Yep, that's the goo. Some type of silicon greasy gel. The state of
the art waterproof cable now uses "Poly-Gel" which is a white powder.
I've never played with the stuff and know nothing about it.

Jeff Liebermann

unread,

Jul 5, 2006, 12:20:08 AM7/5/06

to

"Wolfgang S. Rupprecht"
<wolfgang+gnus2...@dailyplanet.dontspam.wsrcc.com> hath
wroth:

>The 15dbi bbq dish I have is only the small 12"x16" 15dbi one from
>Sharper-Concepts.
> http://sharperconcepts.zoovy.com/product/YSC-HG2415G-NF

That's a 15dBi dish antenna. I have several similar ones from
PacWireless. They work well enough.

>It has a N-female just like the MFJ antenna so I can move the pigtail
>from one antenna to the other. The difference between the two
>antennas was 5db in signal strength. The test source was the mystery
>"Mt Allison" wifi source which came in with 2db above the noise floor
>with the yagi and 7db with the dish. Both claimed to be 15dbi
>antennas.

That's the same general method that I use except that I have a
convenient line-o-sight signal from Loma Prieta. It's a good way to
do it. A stronger test signal might be a bit better.

>I supposed the dish could be vastly better than it is
>rated, but what is the chance of that?

There's a big difference between a high gain yagi and a dish. The
dish feed is a relatively broadband device when compared to the yagi.
If the yagi were mistuned even slightly, the gain will drop like a
rock. That's another reason why I like dish and panel antennas.
They're not overly frequency sensitive. Also, all of these antennas
will have some variation in gain with frequency withing the 2400 to
2483.5MHz band. 1 - 3 dB gain variations are typical.

If you want, I can crank out some 4NEC2 simulations for the two
antennas. However, I'm lazy and don't wanna do anything tonite.

John Navas

unread,

Jul 5, 2006, 2:12:40 PM7/5/06

to

On Tue, 4 Jul 2006 11:03:49 -0400, "Peter Pan"
<PeterPa...@NOSPAMAkamail.com> wrote in
<4gveasF...@individual.net>:

>> On Tue, 04 Jul 2006 06:28:16 -0000, Dave Platt wrote:
>>>> Can you help me roughly CALCULATE how to increase the range of my

>>>> home Internet wireless WiFi setup to a shed 300 feet away from my
>>>> house?
>
>You may want to consider doing it the way cheaper way (using any of the N
>((actually pre-n cuz there are no N standards yet)) is IMO the hard and
>expensive way)... I Had a linksys WRT54G in the house attached to my sat,

>and used one of the 4 router outputs to daisy chain one to the wan input of
>another WRT54G (same ssid) and a semi-directional antenna pointed towards

>the garage about 500ft away, (and another to the guest house (about 800 FT
>away) out back on my 5 acres).. The Linksys WRT54G (not the GS) are
>available at wal-mart for under $50 each... Cat 5 cables a few bucks, and
>the semi-directional antennas (not highly directional, just semi) where a
>few bucks each for the 2nd and 3rd wap/routers.. Am even thinking about
>adding a 4th wap/router so I can use my PDA (with wifi) out by the horse
>corral.
>
>Think increased range by using multiple wap/routers and multiple antennas,
>rather than trying to get one that is more powerful and does it all..

Increase coverage by adding access points (network bridges), not
routers. You want only one router on the typical small network.
Otherwise you'll likely run into problems of multiple NAT and DHCP
conflict. You use additional routers to increase coverage if you
configure them as access points rather than routers, as described in the
How To wiki below. That means connecting LAN port on the router to LAN
(not WAN) port on additional routers configured as access ports.

John Navas

unread,

Jul 5, 2006, 2:23:53 PM7/5/06

to

On Tue, 4 Jul 2006 15:19:26 -0400, "Peter Pan"
<PeterPa...@NOSPAMAkamail.com> wrote in
<4gvta4F...@individual.net>:

>Make sure the router output goes to the WAN input of the second (wap/router)
>device..

You want only one router on the typical small network. Otherwise you'll

likely run into problems of multiple NAT and DHCP conflict. You use
additional routers to increase coverage if you configure them as access
points rather than routers, as described in the How To wiki below. That
means connecting LAN port on the router to LAN (not WAN) port on
additional routers configured as access ports.

>The jury is out on whether you want the same ssid/same channel, for me, I

>just wanted one big area covered so I could walk around and be connected, so
>just made it the same, some people want to know which router they are on and
>use different channels.. (I figger hey if I am connected, I don't really
>care to which, I just want it to work automatically)

Using the same SSID is the best way to have wireless clients connect
automatically to the best access point, but using the same channel is a
bad idea, because of possible interference. It's best to use different

channels with minimum overlap (1, 6, 11).

>As for hardwire or wireless bridge, if` the units are near each other, then

>a hardwire for 10-20 bucks is a whole lot less than two more wap's and
>extension cords... In your case, I'd suggest hardwire..

Other options to consider for wiring additional access points:
* Power line networking
* Phone line networking
* Coax (CATV) networking

Mark McIntyre

unread,

Jul 5, 2006, 6:25:56 PM7/5/06

to

On Tue, 04 Jul 2006 18:18:16 -0700, in alt.internet.wireless , Jeff
Liebermann <je...@comix.santa-cruz.ca.us> wrote:

>"Wolfgang S. Rupprecht"
><wolfgang+gnus2...@dailyplanet.dontspam.wsrcc.com> hath
>wroth:
>
>>Why not run cat-5 to it then??? A 1000-ft spool of cat-5 is under
>>$50. Wireless is wonderful for laptops that move around, but if you
>>have a fixed point that is hard to get to because of RF blockage, then
>>a real wire seems like the way to go.
>>-wolfgang
>
>Ummm.... not just ordinary CAT5. She's in Toronto where is gets
>rather cold in the winter. Ordinary PVC jacketed CAT5 will become
>rather hard stiff and crack.

Only if it flexes.

> It's also not UV stable and will develop
>a rather rough surface after a few years.

She's not in africa... :-)

Anyway ducting is also dirt cheap. I just ran 240v power to my garden
shed in 100ft of ducting as per uk building regs, and it cost me about
ten pounds.
--
Mark McIntyre

Mark McIntyre

unread,

Jul 5, 2006, 6:30:55 PM7/5/06

to

On Tue, 04 Jul 2006 20:55:26 -0700, in alt.internet.wireless , Jeff
Liebermann <je...@comix.santa-cruz.ca.us> wrote:

>Yep, that's the goo. Some type of silicon greasy gel. The state of
>the art waterproof cable now uses "Poly-Gel" which is a white powder.
>I've never played with the stuff and know nothing about it.

I've used a similar product for mains-voltage cabling and its quite
annoying to work with, though about as flexible as 10mm soft-annealed
copper central heating pipe, if you're familiar with that (you can tie
knots in it). Special glands required at the ends of course, and
special units at any junctions / connectors etc.

A heck of a lot cheaper to run cat5 and replace it every few years,
I've had a length of cat5 bought from Maplin running round the outside
of my house (south and west elevations) for about three years now,
with no discernible signal degradation. I'll tell you in about another
three years whether the 40m running to my garden shed causes
problems... :-)
--
Mark McIntyre

Gary Heston

unread,

Jul 5, 2006, 9:28:56 PM7/5/06

to

In article <1ofdyrcyyqhff$.qzkvubda...@40tude.net>,

Beverly Erlebacher <b...@cs.toronto.edu> wrote:
>On Tue, 04 Jul 2006 06:28:16 -0000, Dave Platt wrote:
>>>Can you help me roughly CALCULATE how to increase the range of my home
>>>Internet wireless WiFi setup to a shed 300 feet away from my house?

>> See http://www.freeantennas.com/projects/template/
>> and http://www.freeantennas.com/projects/template2/index.html
>> The latter states an achievable gain of around 11 dB just from the
>> homemade reflector.

>The skeptic in me wonders "if it's this easy to get 3.5X the 802.11b,g WiFi
>range, then why don't the router manufacturers add this cheap parabola as
>standard equipment on all their antennas?"
[ ... ]

FCC and similar agency regulations prohibit it.

>Being a firm believer in "you don't get nothin' for nothin'", I must ask:

>What am I losing by putting a parabola behind one of the two antennas on my
>home router so that it increases the directional range from approximately
>100 feet to about 300 feet?

Some of the signal strength normally radiated through the rest of the
coverage area.

An omnidirectional antenna is like a hose with a spray nozzle pointed
straight up--water will go in all directions, but not very far.

A directional antenna is like a hose with a nozzle creating a tight
stream--the water will go a lot farther, but only in one fairly narrow
path.

Gary

--
Gary Heston ghe...@hiwaay.net What do you call two SUVs colliding?
Poetic justice.
A worthwhile endeavour:
http://www.thebreastcancersite.com/cgi-bin/WebObjects/CTDSites

Gary Heston

unread,

Jul 5, 2006, 9:35:09 PM7/5/06

to

In article <410kzzswtlgd$.1jcc2o88kv83h$.d...@40tude.net>,
Beverly Erlebacher <b...@cs.toronto.edu> wrote:
>On Tue, 04 Jul 2006 11:48:12 +0100, Highland Ham wrote:

>> Beverly Erlebacher wrote:
[ ... ]
>>> Presently, I can walk about half the way through the wooded area to the
>>> shed with my laptop in hand before I lose the connection to the PCMCIA
>>> 802.11b,g Linksys card. Basically I need to gain 150 feet in "range".

>>> But how?
>> ====================================================
>> Having followed today's postings on this topic , I see that there is a
>> wooded area between your house and shed, hence there seems to be no free
>> line of sight between the house and the shed.
>> That's why it is difficult to calculate/predict the Gain you need to
>> penetrate the wooded area with a 2.4 GHz signal.

>> If you wish to use the laptop inside the shed at a fixed location it
>> MIGHT be good enough if you install a corner reflector yagi (High
>> Gain)antenna at both the house AND the shed. However then your laptop
>> needs a plug-in PCMCIA WiFi tansceiver with a connection for an external
>> antenna.
[ ... ]

>I see there are multiple solutions. Probably on the end of my list is
>adding a wire to the laptop because then it wouldn't be wireless. Still,
>it's an intriguing idea (I never knew laptops could have fixed antenna's
>connected to them by wire).
[ ... ]

Install a compatible WAP (wireless access point) in your shed with another
directional antenna pointing toward the one at your house. The WAPs will
connect to each other, and the one in the shed will then relay to your
laptop. (Your wireless router is a WAP.) No wires needed.

John Navas

unread,

Jul 6, 2006, 2:09:24 AM7/6/06

to

On Thu, 06 Jul 2006 01:35:09 -0000, ghe...@hiwaay.net (Gary Heston)
wrote in <12aoq6d...@corp.supernews.com>:

>Install a compatible WAP (wireless access point) in your shed with another
>directional antenna pointing toward the one at your house. The WAPs will
>connect to each other, and the one in the shed will then relay to your
>laptop. (Your wireless router is a WAP.) No wires needed.

Unfortunately, it's not that simple. You either need (a) a wireless
client bridge connected to an access point, which works fine with a
directional antenna, or (b) a repeater (e.g., WDS), which generally has
to be the same make and model as the host, and which won't work terribly
well with a directional antenna.

John - KD5YI

unread,

Jul 8, 2006, 12:08:23 PM7/8/06

to

Actually, when properly matched, it radiates half the received power.

Don K

unread,

Jul 8, 2006, 1:37:45 PM7/8/06

to

"John - KD5YI" <groups...@verizon.net> wrote in message news:XLQrg.2896$bd4.372@trnddc01...

> Rod Speed wrote:
>>
>> A receive antenna has no EIRP, it doesnt radiate any real power.
>
> Actually, when properly matched, it radiates half the received power.

How do you get that?
If the receiver input impedance is matched to the antenna, all the
received power is absorbed. There is no reflection. There is no radiation.

If the receiver matching is for optimal noise figure, there may be
some reflection and reradiation, but there's nothing pinning it to
be half the received power.

Don

Roy Lewallen

unread,

Jul 8, 2006, 3:26:18 PM7/8/06

to

John is correct. A receiving antenna, when matched, reradiates half the
power it receives. An impinging field induces current in the antenna.
This causes radiation, just like the current in a transmitting antenna.
As it turns out, when the antenna is matched, the amount of power
radiated equals the amount of power delivered to the load, and that's
the best you can do. If you'd like a more in-depth and mathematical
explanation, you can find it in any antenna text, often discussed as
"scattering".

If a receiving antenna did absorb all the impinging power, it would be a
lot easier to make a shield or a stealth aircraft.

Roy Lewallen, W7EL

Rod Speed

unread,

Jul 8, 2006, 3:35:39 PM7/8/06

to

Wrong.

Rod Speed

unread,

Jul 8, 2006, 3:39:30 PM7/8/06

to

Roy Lewallen <w7...@eznec.com> wrote

> Don K wrote
>> John - KD5YI <groups...@verizon.net> wrote

>>> Rod Speed wrote

>>>> A receive antenna has no EIRP, it doesnt radiate any real power.

>>> Actually, when properly matched, it radiates half the received power.

>> How do you get that?
>> If the receiver input impedance is matched to the antenna, all the
>> received power is absorbed. There is no reflection. There is no
>> radiation.

>> If the receiver matching is for optimal noise figure, there may be
>> some reflection and reradiation, but there's nothing pinning it to
>> be half the received power.

> John is correct.

Nope.

> A receiving antenna, when matched, reradiates half the power it receives.

Yes but that ISNT ANY REAL POWER in the EIRP restriction sense.

> An impinging field induces current in the antenna. This causes radiation, just like the
> current in a transmitting antenna. As it turns out, when the antenna is matched, the
> amount of power radiated equals the amount of power delivered to the load, and that's
> the best you can do.

Yes but that ISNT ANY REAL POWER in the EIRP restriction sense.

> If you'd like a more in-depth and mathematical explanation, you can find it in any
> antenna text, often discussed as "scattering".

Not relevant to the original point, any effect on the EIRP restriction.

> If a receiving antenna did absorb all the impinging power, it would be a lot easier to
> make a shield or a stealth aircraft.

Not relevant to the original point, any effect on the EIRP restriction.

John L. Sielke

unread,

Jul 8, 2006, 4:42:59 PM7/8/06

to Rod Speed

Always amazinmg how when some people are proven wrong, the revert to the "Is
NOT, IS NOT," type of argument used by small children, then when that doesn't
work, the argument becomes irrelevant.

Rod, I suggest you LEARN something from your intellectual and technical betters
BEFORE you show the world your ignorance.

John

John L. Sielke

unread,

Jul 8, 2006, 4:45:20 PM7/8/06

to

Roy Lewallen

unread,

Jul 8, 2006, 5:00:56 PM7/8/06

to

Rod Speed wrote:
> Roy Lewallen <w7...@eznec.com> wrote

> . . .

>> A receiving antenna, when matched, reradiates half the power it receives.
>
> Yes but that ISNT ANY REAL POWER in the EIRP restriction sense.

> . . .

It's real power, but that power all comes from the impinging field; it's
not contributing any new power. So you're right that the EIRP
restriction doesn't apply. The receive antenna reduces the amount of
power in the field by the amount delivered to the antenna's termination,
plus any losses along the way. The intent of the EIRP restriction is to
limit the amount of field strength added by a transmitter.

Roy Lewallen, W7EL

Rod Speed

unread,

Jul 8, 2006, 5:12:11 PM7/8/06

to

Never ever could bullshit its way out of a wet paper bag.

> Rod, I suggest you LEARN something from your intellectual and
> technical betters BEFORE you show the world your ignorance.

Never ever could bullshit its way out of a wet paper bag.

While your original was technically correct, its completely
irrelevant to what was actually being discussed, WHETHER
THE RECEIVE ANTENNA EVER RADIATES ENOUGH TO
BE RELEVANT TO THE EIRP RESTRICTION.

Rod Speed

unread,

Jul 8, 2006, 5:15:05 PM7/8/06

to

Roy Lewallen <w7...@eznec.com> wrote:
> Rod Speed wrote:
>> Roy Lewallen <w7...@eznec.com> wrote
>> . . .
>>> A receiving antenna, when matched, reradiates half the power it
>>> receives.
>>
>> Yes but that ISNT ANY REAL POWER in the EIRP restriction sense.

> It's real power,

Yes, BUT NOT IN THE EIRP RESTRICTION SENSE.

> but that power all comes from the impinging field; it's not contributing any new power.
> So you're right that the EIRP restriction doesn't apply.

And that is what was being discussed when John made such a
spectacular fool of himself mindlessly rabbiting on about what
is no news to anyone with a clue about receiving antennas.

> The receive antenna reduces the amount of power in the field by the amount delivered to
> the antenna's termination, plus any losses along the way. The intent of the EIRP
> restriction is to limit the amount of field strength added by a
> transmitter.

Duh. So John was mindlessly rabbiting on about a complete
irrelevancy WHEN THE EIRP RESTRICTION WAS BEING DISCUSSED.

Mark McIntyre

unread,

Jul 8, 2006, 6:08:34 PM7/8/06

to

I've not been following this thread, but I can tell you straight off,
I am significantly more inclined to believe the guys who are not
shouting and hurling abuse.

Make of that what you will, but my suggestion is to counter with
rational argument backed up by references and facts, rather than
insults and obscenities.

--
Mark McIntyre

Rod Speed

unread,

Jul 8, 2006, 7:30:46 PM7/8/06

to

Mark McIntyre <markmc...@spamcop.net> wrote

> Rod Speed <rod.sp...@gmail.com> wrote
>> John L. Sielke <w2agn...@w2agn.net> wrote

>>> Always amazinmg how when some people are proven wrong, the
>>> revert to the "Is NOT, IS NOT," type of argument used by small
>>> children, then when that doesn't work, the argument becomes irrelevant.

>> Never ever could bullshit its way out of a wet paper bag.

>>> Rod, I suggest you LEARN something from your intellectual and
>>> technical betters BEFORE you show the world your ignorance.

>> Never ever could bullshit its way out of a wet paper bag.

>> While your original was technically correct, its completely
>> irrelevant to what was actually being discussed, WHETHER
>> THE RECEIVE ANTENNA EVER RADIATES ENOUGH TO
>> BE RELEVANT TO THE EIRP RESTRICTION.

> I've not been following this thread, but I can tell you
> straight off, I am significantly more inclined to believe
> the guys who are not shouting and hurling abuse.

You have always been, and always will be, completely and utterly irrelevant.

What you may or may not be inclined to believe in spades.

Anyone with a clue considers the facts, not the style stuff, fuckwit.

> Make of that what you will,

I flush it where it belongs.

> but my suggestion is to counter with rational
> argument backed up by references and facts,

Dont need 'references' on that basic fact that even
when the receiving antenna does reradiate about
half of what it receives, THAT IS COMPLETELY
IRRELEVANT TO THE LEGISLATED ERIP LEVEL.

> rather than insults and obscenities.

I suggest you take your stupid suggestion
and shove it up your arse, where it belongs.

Don K

unread,

Jul 8, 2006, 8:50:07 PM7/8/06

to

"Roy Lewallen" <w7...@eznec.com> wrote in message news:12b01mu...@corp.supernews.com...

Maybe to some extent, it's a matter of nit-picking over what
"received power" means. You can think of an antenna as having an
effective aperture size over which it captures all the energy
crossing that cross-sectional area. To me it's logical to think
of "received power" as the power that actually gets scooped
up and delivered.

unread,

Jul 9, 2006, 2:11:48 PM7/9/06

to

Some terminal fuckwit claiming to be
Mark McIntyre <markmc...@spamcop.net>
wrote just the puerile shit thats all it can ever manage.

Rex

unread,

Jul 9, 2006, 4:12:30 PM7/9/06

to

Look at this part of the thread...

[John said:]

If the receiver matching is for optimal noise figure, there may be
some reflection and reradiation, but there's nothing pinning it to
be half the received power.

[Roy said:]
John is correct.

[Rod said:]
Nope.

[Roy said:]

A receiving antenna, when matched, reradiates half the power it
receives.

[Rod said:]

Yes but that ISNT ANY REAL POWER in the EIRP restriction sense.

---
So John made a factual statment. Roy agreed. Your opinion was to
disagree with the simple factual statment.

Roy added a clarifying statment. You started to go off the hook and
SHOUT because you were fixated on EIRP. When I read it I never saw any
direct implication about EIRP or legalities in the explanation; it was a
simple explanation about antennas.

Your *opinion* was involved in deciding you knew the exact intent of the
posting and that it had implications in the EIRP thing, just because
that is the interpretation that passed through your mind.

Ok, I'm done here. Not sure why I took the time for this one last post.

Rod Speed

unread,

Jul 9, 2006, 4:25:14 PM7/9/06

to

Rex <m...@hutmail.invalid> wrote

> Rod Speed <rod.sp...@gmail.com> wrote
>> xray <notr...@hotmail.invalid> wrote
>>> Rod Speed <rod.sp...@gmail.com> wrote

>>> Most of what you have been posting here

>>> recently seems to be opinion rather than fact.

>> Best get your seems machinery seen to then.

>> Its a fact that even when a receiving antenna does radiate back
>> half of what it recieves, THAT IS NOT RELEVANT TO WHAT WAS
>> BEING DISCUSSED, THE LEGISLATED EIRP LEVEL ALLOWED.

>> Not a shred of opinion involved what so ever.

> Look at this part of the thread...

> [John said:]
> If the receiver matching is for optimal noise figure, there may be
> some reflection and reradiation, but there's nothing pinning it to
> be half the received power.
>
> [Roy said:]
> John is correct.
>
> [Rod said:]
> Nope.

Not about that particular para of John's. I was saying that John was
not correct on the original point about whatever the receiving anntenna
radiates BEING RELEVANT TO THE LEGISLATED EIRP LEVEL.

No opinion there, just fact.

> [Roy said:]
> A receiving antenna, when matched, reradiates half the power it
> receives.

> [Rod said:]
> Yes but that ISNT ANY REAL POWER in the EIRP restriction sense.

> ---
> So John made a factual statment. Roy agreed.

It wasnt relevant to what was actually being discussed,
WHETHER WHATEVER THE RECEIVING ANTENNA
RADIATES HAS ANYTHING TO DO WITH THE LEGISLATED
EIRP WAS ACTUALLY BEING DISCUSSED.

> Your opinion was to disagree with the simple factual statment.

It wasnt an opinion, it was a statement of fact that that
comment John made WAS NOT RELEVANT TO THE
LEGISLATED EIRP LEVEL THAT WAS BEING DISCUSSED.

> Roy added a clarifying statment. You started to go off the
> hook and SHOUT because you were fixated on EIRP.

The legislated EIRP level WAS WHAT WAS BEING DISCUSSED
WHEN JOHN MADE SUCH A SPECTACULAR FOOL OF HIMSELF
RABBITING ON ABOUT WHAT THE RECIEVING ANTENNA RADIATES.

> When I read it I never saw any direct implication about EIRP or legalities
> in the explanation; it was a simple explanation about antennas.

Pity it was a comment made WHEN THE LEGISLATED EIRP LEVEL WAS
BEING DISCUSSED WITH REFERENCE TO THE RECEIVING ANTENNA.

> Your *opinion* was involved in deciding you knew the exact intent of the posting

Wrong again. It is a FACT that John's comment had no
relevance what so ever to what was being discussed,
whether the receiving antenna has any relevance what
so ever to the legislated EIRP level. It doesnt.

> and that it had implications in the EIRP thing, just because
> that is the interpretation that passed through your mind.

Nothing to do with my mind, it was what was being discussed.

> Ok, I'm done here. Not sure why I took the time for this one last post.

Yeah, you just made a VERY spectacular fool of yourself, yet again.

Jeff Liebermann

unread,

Jul 9, 2006, 4:33:43 PM7/9/06

to

[misc.consumers.frugal-living dropped from distribution list.]

Roy Lewallen <w7...@eznec.com> hath wroth:

I'm not so sure. I couldn't find any specific references to this
effect in several books I skimmed. Same with internet searches. If
true, then the concept of converting solar power in an orbital
satellite, converting it to microwaves, beaming it down to an antenna
array in the middle of the desert, and converting it back to
electricity, isn't going to work if the array re-radiates half the
power. That's going to ruin quite a few nifty science fiction stories
and innovative business plans.

I also note that the common microwave path analysis calculations don't
take re-radiation into account. For example, if I start with an EIRP
of perhaps XX dBm from a transmit antenna, -YY dB of path loss, and ZZ
dB receive antenna gain, the power delivered to the receiver (ignoring
coax losses) is calculated at (XX - YY + ZZ) dBm without any mention
of the -3dB that would need to be subtracted if half the receive power
is re-radiated from the rx antenna. It would seem that the common
formula and web forms for link calculations are -3dB off.

I trust your judgement in such matters and you have far more expience
than me, but something seems wrong or I'm missing something. Can you
point me to any books or refernences? I just skimmed Chapter 2
(Fundamentals of Antennas) in "Antenna Engineering Handbook" by Jasik
(1961) and found no obvious mention of this effect.

--
Jeff Liebermann je...@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

John - KD5YI

unread,

Jul 9, 2006, 5:40:28 PM7/9/06

to

Antennas For All Applications by John D. Kraus and Ronald J. Marhefka
Third Edition
Page 746, Paragraph 21-15

"Prec=(Rr/(Ra+Rr))Pa

where

Rr=receiver impedance, ohms
Ra=antenna radiation resistance, ohms

For a perfect match, Rr=Ra, so that

Prec=(Rr/(Rr+Rr))Pa=0.5Pa (W)

and the receiver gets 1/2 the power collected by the antenna. The other half
is reradiated."

Also see "TV and Other Receiving Antennas" by Arnold B. Bailey published in
1950 by Rider Publishing. Beginning on page 235 near the bottom:

"In radio receiving antennas the predominant resistance is, strangely
enough, largely due to the fact that no electrons can move on the antenna
surface *without also sending radio energy back out into space*. So here we
have the paradox of a receiving antenna, having the prime function of
collecting or extracting energy from space, but unable to do so *without
itself returning radio energy of like kind* into space. The amount which it
returns is one-half of the total that it extracts under properly matched
conditions. In a good installation, with the antenna properly connected to
its receiver load, the receiving antenna will be able to *deliver to its
load one-half of the energy* it extracts from the oncoming radio wave but,
by necessity, *must return the other half to free space*. A receiving
antenna, then, is itself a *new source* of radiation. This is not so
surprising, since *any* reflecting surface, as we have seen, establishes a
new source of radiation"

(Note: The emphasis in the book was italics)

Cheers,
John

John - KD5YI

unread,

Jul 9, 2006, 5:40:41 PM7/9/06

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Message has been deleted

Mark McIntyre

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Jul 9, 2006, 5:49:02 PM7/9/06

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On Sun, 09 Jul 2006 13:33:43 -0700, in alt.internet.wireless , Jeff
Liebermann <je...@comix.santa-cruz.ca.us> wrote:

>[misc.consumers.frugal-living dropped from distribution list.]
>
>Roy Lewallen <w7...@eznec.com> hath wroth:
>

>>John is correct. A receiving antenna, when matched, reradiates half the
>>power it receives.

>>If a receiving antenna did absorb all the impinging power, it would be a

>>lot easier to make a shield or a stealth aircraft.
>>
>

>I'm not so sure. I couldn't find any specific references to this
>effect in several books I skimmed.
>

>I trust your judgement in such matters and you have far more expience
>than me, but something seems wrong or I'm missing something. Can you
>point me to any books or refernences? I just skimmed Chapter 2
>(Fundamentals of Antennas) in "Antenna Engineering Handbook" by Jasik
>(1961) and found no obvious mention of this effect.

Scroggie's "Foundations of Wireless", the book I cut my teeth on (and
my father before me...) mentions this in the chapter on Radiation and
Aerials where he describes the reratiation as a fact of great
importance in recieving aerial design.

I think however Rod's final remark is perhaps the most telling - if an
antenna really did absorb all the energy landing on it, there would be
highly curious side effects.
--
Mark McIntyre

Jeff Liebermann

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Jul 9, 2006, 10:02:09 PM7/9/06

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John - KD5YI <groups...@verizon.net> hath wroth:

>Antennas For All Applications by John D. Kraus and Ronald J. Marhefka
>Third Edition
>Page 746, Paragraph 21-15
>
>"Prec=(Rr/(Ra+Rr))Pa
>
>where
>
>Rr=receiver impedance, ohms
>Ra=antenna radiation resistance, ohms
>
>For a perfect match, Rr=Ra, so that
>
>Prec=(Rr/(Rr+Rr))Pa=0.5Pa (W)
>
>and the receiver gets 1/2 the power collected by the antenna. The other half
>is reradiated."

OK, that make sense. Thanks much.

So, why is NASA and other disreputable organizations still pushing
beaming solar power down to earth via microwaves?
| http://en.wikipedia.org/wiki/Solar_power_satellite
| http://en.wikipedia.org/wiki/Microwave_power_transmission
| http://science.nasa.gov/headlines/y2001/ast23mar_1.htm
| http://www.spacefuture.com/archive/conceptual_study_of_a_solar_power_satellite_sps_2000.shtml
| http://www.msfc.nasa.gov/news/news/releases/1999/99-096.html
| http://www.ieee-virtual-museum.org/exhibit/exhibit.php?id=159265&lid=1&seq=13
No mention in any of these that half the delivered power gets
re-radiated. If the receive array were anywhere as directional as the
xmit array, then it would cook the satellite. The re-radiated power
has to go somewhere. Oh, maybe because it's a government project the
number don't need to be correct?

I'll spare you the usual anal joke about rectenna.

Also, why is there no -3dB added loss on the receive end of wireless
path calculation? From what I can deduce from the path calcs, the
receive antenna delivers all the power to the coax cable and then to
the receiver. Where's the half power (-3dB) loss?

I'm still (half way) mystified.

>Also see "TV and Other Receiving Antennas" by Arnold B. Bailey published in
>1950 by Rider Publishing. Beginning on page 235 near the bottom:

Argh. That was published 2 years after I was born.

>"In radio receiving antennas the predominant resistance is, strangely
>enough, largely due to the fact that no electrons can move on the antenna
>surface *without also sending radio energy back out into space*.

Resistance? Unless he's thinking of ohmic resistance, most antennas
don't have any resistance. (Well, a rhombic has a 300-400 ohm load,
but that's not what we're discussing). If the signal gets
re-radiated, without any loss, there can't be any dissipative elements
in the system. What resistance?

Roy Lewallen

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Jul 10, 2006, 1:15:00 AM7/10/06

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Jeff Liebermann wrote:
>
> I'm not so sure. I couldn't find any specific references to this
> effect in several books I skimmed. Same with internet searches. If
> true, then the concept of converting solar power in an orbital
> satellite, converting it to microwaves, beaming it down to an antenna
> array in the middle of the desert, and converting it back to
> electricity, isn't going to work if the array re-radiates half the
> power. That's going to ruin quite a few nifty science fiction stories
> and innovative business plans.
>
> I also note that the common microwave path analysis calculations don't
> take re-radiation into account. For example, if I start with an EIRP
> of perhaps XX dBm from a transmit antenna, -YY dB of path loss, and ZZ
> dB receive antenna gain, the power delivered to the receiver (ignoring
> coax losses) is calculated at (XX - YY + ZZ) dBm without any mention
> of the -3dB that would need to be subtracted if half the receive power
> is re-radiated from the rx antenna. It would seem that the common
> formula and web forms for link calculations are -3dB off.
>
> I trust your judgement in such matters and you have far more expience
> than me, but something seems wrong or I'm missing something. Can you
> point me to any books or refernences? I just skimmed Chapter 2
> (Fundamentals of Antennas) in "Antenna Engineering Handbook" by Jasik
> (1961) and found no obvious mention of this effect.

I could add more references to the ones already mentioned, but you
should be able to find it in most antenna texts. Look in the index under
aperture and scattering cross section. When dealing with path loss
calculations, the effective aperture is used, and this has the
reradiation already accounted for. In fact, the reradiated power has its
own descriptive unit, the scattering aperture. A good and brief
description of these can be found in Kraus' _Antennas_, p. 29ff, and
many other texts.

You're right that the antennas used to receive beamed power will catch
only half of it at best. But many, many business plans have been
developed and billions in stock sold for schemes which are much less
plausible. For starters, how about the current idea of hydrogen "fuel",
"made from water"? (For those not acquainted with the harsh reality of
thermodynamics, it takes more energy to extract hydrogen from water than
you'll get back when you burn it. Charlatans notwithstanding, there's
just flat no way around this little fact.) Then there's SDI. . .

Roy Lewallen, W7EL