How do I find the antenna gain (dBi) of a Lenovo X61t laptop?

[Chuck Banshee]

Does anyone know where I can find the dBi specification for the Lenovo
X61t laptop built-in antenna?

I'm sure it's around 1 to 3 dBi (probably 2dBi - but I'm just guessing).

I want to run realistic calculations of what signal strengths I can pick
up theoretically.

I found all the calculations that I'll run I need in these two files:
http://wndw.net/pdf/wndw2-en/wndw2-ebook.pdf
http://www.cs.uml.edu/~xinwenfu/paper/ICDCS09_Marauder_Fu.pdf

And, I found all the Lenovo X61t internal WiFi card (Intel 4965AGN)
specifications needed in this HP document:
http://tinyurl.com/76pz46a

The one thing I just can't find (which should be easy to find!) is simply
the directional & power specification (dBi) of the built-in Lenovo X61t
laptop antenna!

[Chuck Banshee]

On Wed, 01 Feb 2012 11:09:26 +0000, Chuck Banshee wrote:

> The one thing I just can't find (which should be easy to find!) is
> simply the directional & power specification (dBi) of the built-in
> Lenovo X61t laptop antenna!

I found a picture of the antenna in situ over here:
http://www.portatronics.com/guide/PC-Laptop-Repair/lenovo-x61-repair-
guide.html

But I still can't find the antenna specifications (part number "FRU
93P4554") from this site:
http://support.lenovo.com/en_US/detail.page?LegacyDocID=MIGR-67024

[Jeff Liebermann]

On Wed, 1 Feb 2012 11:25:40 +0000 (UTC), Chuck Banshee
<chuckb...@private.com> wrote:

>On Wed, 01 Feb 2012 11:09:26 +0000, Chuck Banshee wrote:
>
>> The one thing I just can't find (which should be easy to find!) is
>> simply the directional & power specification (dBi) of the built-in
>> Lenovo X61t laptop antenna!
>
>I found a picture of the antenna in situ over here:
><http://www.portatronics.com/guide/PC-Laptop-Repair/lenovo-x61-repair-guide.html>

What are you trying to accomplish?

The blurry and distorted photo you referenced above:
<http://www.portatronics.com/guide/images/laptops/lenovox61/019.jpg>
<http://www.portatronics.com/guide/images/laptops/lenovox61/018.jpg>
appears to be some manner of PIFA antenna. Very difficult to tell
from the photos.

These are very common in laptops as that's about all that will fit
inside the case. If it's a PIFA, it's a 1/4 wave bent monopole above
a ground plane.
<http://www.antenna-theory.com/antennas/patches/pifa.php>
There are many forms of the PIFA antenna. I can't tell from the
blurry photo which one is inside the x61t. Optimistically, it has an
average gain of about -2dBi gain at 2.4GHz. Realistically, it's
somewhat less.

If PIFA, it's probably a dual band antenna, which is considerably more
complex:
<http://www.google.com/patents?id=w34VAAAAEBAJ>
From the polar graphs, it looks like an average gain of about -5dBi
for both 2.4 and 5.7GHz.

If you're doing calculations, don't forget about the rather high coax
cable losses.

Incidentally, the location of the antenna under the palm rest is not a
good place to hide the antenna as the signal is blocked by the nearby
metal components and shields.

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

[Chuck Banshee]

On Wed, 01 Feb 2012 07:55:33 -0800, Jeff Liebermann wrote:
> What are you trying to accomplish?

Hi Jeff,

You're going to be sorry you asked. :)

What I'm trying to understand is much more than just the Lenovo X61t
native antenna dBi so that's why I was hoping to just ask about that
small missing piece of the puzzle in this post.

STOP READING NOW ... BELOW IS ONLY MORE DETAIL ON THAT STATEMENT!

The bigger picture is I'm trying to figure out what real-world equipment
I need to communicate with various access points that my outdoor radio
+antenna sees (but it can't connect to them all) - and that my laptop
radio+antenna does not see (but I hope to see with a USB WiFi extender).

In addition, I'd like to add a TV antenna to the top of my WISP antenna,
so, AFTER I fully figure out the (more interesting to me) WiFi
calculations, I'll adapt them for TV signal calculations (but I don't
have ANY existing TV equipment yet to do any real-world tests).

For a WiFi example, just one (of many) interesting SSIDs found in my site
survey shows a signal strength of -89dBm with a noise of -96dBm but I
can't connect to it even though it's open. I want to calculate whether my
current equipment has the capability to connect to it, and, if not, I
want to understand how to calculate what I need to purchase
(specification wise) that will connect to it successfully.

This then leads on to the 'second step' which is to take the FCC coverage
information for TV signal to calculate what equipment I would need to
pick up certain TV stations.

For example, tvfool.com indicates PBS is on station KVIE-DT, real channel
9, virtual channel 6.1, NM=-15.4DB, Pwr=-106.9dBm, path=2edge, and
distance=82.3 miles away.

After I figure out what WiFi equipment I'd need to connect to every SSID
that is of interest to me, I'd like to then use that knowledge to figure
out what TV equipment I need to calculate what I'd need to receive NBC,
PBS, CBS, etc. at my home.

All these calculations are not something that can be easily done in a
USENET post - so - that's why I JUST asked about the laptop antenna spec.
I was just fleshing out this starting-point chart of the capabilities of
my existing equipment:

Lenovo X61t (Intel 4964AGN)
- TX=15dBm (30mW)
- RX=-90dBm@6Mbps
- Omni=2dBi ? (FRU 93P4365)

Ubiquiti Bullet M2
- TX=28dBm (630mW)
- RX=-83dBm
- Directional=19dBi

Linksys WRT54G v5 (CDFB)
- TX=18dBm (63mW)
- RX=-65dBm for 11g@54Mbps, -80db for 11b 11Mbps
- Omni=2dBi

And, I was investigating what this will be able to pick up if added to
the Lenovo X61t Linux Laptop:

Alfa Networks AWUS036H ($28)
- TX = 20dBm (100mW)
- RX = -91dBm@11Mbps 802.11b CCK
- Omni = 2dBi

Once I understand the equipment specifications I need, THEN I will
proceed to the calculations of what signals they can pick up. I am not
doing this theoretically - I'm only interested in real live signals that
I know are available to me such as what shows up in a site survey on my
outdoor WiFi equipment above or what the FCC coverage maps tell me for TV
(since I have no TV equipment as yet).

But, I figured I'd start simply with understanding what the capabilities
were of the equipment that I had on hand. For that, I simply needed to
figure out the specs.

I'm amazed that the dBi spec for the antenna on the Lenovo X61t is so
hard to find!

[Char Jackson]

On Thu, 2 Feb 2012 00:43:42 +0000 (UTC), Chuck Banshee
<chuckb...@private.com> wrote:

>In addition, I'd like to add a TV antenna to the top of my WISP antenna,

If it's not already getting tossed around in the wind, that should do
it.

[gregz]

The only thing I know is I found the antenna in my laptops on one side of
the display. On my new hp, the card has two antenna coax connections. I
wonder if that's for diversity or band change. I'm have not really
pinpointed antenna location.

Greg

[Chuck Banshee]

On Wed, 01 Feb 2012 20:47:32 -0600, Char Jackson wrote:

> If it's not already getting tossed around in the wind, that should do
> it.

I'll put up another antenna 'just' for the TV if I have to. It would best
be in different place anyway, based on the tvfools web site maps.

But, so far, the 16-foot 2" pipe stuck in a 3.5" hole is holding up
remarkably well. Time will tell ...

[miso]

> I'm amazed that the dBi spec for the antenna on the Lenovo X61t is so
> hard to find!

The built in antenna is for coffee shop use. For a complete system like
a notebook, you won't find the antenna spec but rather a system spec.

You should really go USB. Note the Alfa Tube/U has slightly better specs
than the plain 036. It has less power, but high power on one end isn't
all that useful. Both are good devices. The RPSMA to N adapter is $5, so
add that to the price of the AWUS036H.

If you want to mess with HDTV, I'd suggest getting a HD Homerun. I have
the old version. It is hard to get test specs on consumer gear. The
numbers exist since QA parameters need to be established, but on
consumer gear, the numbers don't leave the factory.

The old HD Homerun works OK with XMBC. No idea about the current
version. Installing MythTV is a kick in the groin. You can run the HD
Homerun with VLC. If you know what you are doing, you can demod
satellite streams with VLC. VLC has far more capabilities than most
people realize.

Obviously the advantage to the HD Homerun is you can put it on that
network you just set up.

[Char Jackson]

On Wed, 01 Feb 2012 19:22:42 -0800, miso <mi...@sushi.com> wrote:

>If you want to mess with HDTV, I'd suggest getting a HD Homerun.

...

>Obviously the advantage to the HD Homerun is you can put it on that
>network you just set up.

I second that suggestion. I love my HD Homerun units. They just work,
and that's more than I can say for the tuners I tried before the HR's.
I'm using them with SageTV (bought by Google awhile back) and Win 7
Media Center.

[Chuck Banshee]

On Wed, 01 Feb 2012 19:22:42 -0800, miso wrote:

>> I'm amazed that the dBi spec for the antenna on the Lenovo X61t is so
>> hard to find!
>

> you won't find the antenna spec but rather a system spec.

It's interesting that it's hard to find the antenna spec but it's easy to
find the same specs for the wifi card.

For example, I ran all of these Ubuntu commands:
"lspci -nnk | grep -iA2 net"
"sudo lshw -C network"
"dmesg | grep 4965"

All these commands showed my Lenovo X61t internal WiFi card to be an
"Intel 4965AGN" WiFi card.

The "iwconfig wlan0" & "iw list" commands even show the Intel 4965AGN
radio transmit power at 14dBm (about 25mW) at 54Mbps.

Independently, this HP PDF lists the Intel 4964AGN transmit power as 15dBm
(30mW).
http://service1.pcconnection.com/PDF/WLAN_Solutions_for_HP_Notebooks.pdf

That same PDF lists the Intel 4964AGN receiver sensitivity as -68dBm@300
Mbps, -74dBm@54Mbps & -90dBm@6Mbps.

Yet I can't find the stinkin' spec for a simple antenna!

For now, I'm going to move forward in my calculations and assume
something less than 2dBi.

How does 1.5 dBi sound as a guess (in lieu of specs)?

[Jeff Liebermann]

On Thu, 2 Feb 2012 00:43:42 +0000 (UTC), Chuck Banshee
<chuckb...@private.com> wrote:

>On Wed, 01 Feb 2012 07:55:33 -0800, Jeff Liebermann wrote:
>
>You're going to be sorry you asked. :)

Nope. I'm already sorry that I asked. No need to wait.

>What I'm trying to understand is much more than just the Lenovo X61t
>native antenna dBi so that's why I was hoping to just ask about that
>small missing piece of the puzzle in this post.

It's still backwards. Questions like yours (and answers like mine)
make little sense without the proper context.

>The bigger picture is I'm trying to figure out what real-world equipment
>I need to communicate with various access points that my outdoor radio
>+antenna sees (but it can't connect to them all) - and that my laptop
>radio+antenna does not see (but I hope to see with a USB WiFi extender).

Ok, but first a short lecture. If you understand how things work, you
can usually work out the details of how to make things work for your
specific application. I like to supply theory and rules-of-thumb,
rather than suggest you go out and buy some specific device.

In this case, the reason you can see more AP's than you can connect to
is because it takes exactly one packet for the computah to announce
that it can hear an AP. It takes far more packets, going in both
directions, to associate with an AP, negotiate an encryption key,
obtain a DHCP assigned IP address, and setup a route to the internet.
Hearing one packet requires just luck. Making a connection, requires
a good signal.

For Wi-Fi, the signal has two specifications. Signal level and signal
quality, also known as SNR (signal to noise ratio). You could have a
situation, where the signal level is adequate, but because of
interference from other stations on the same channel, the signal
quality sucks. This might be why you can't connect to the distant
stations. You may be experiencing interference at either or both
ends. A clue is to sniff the management packets going in both
directions. The connection speed does *NOT* need to be the same in
both directions. If there's a large difference in connection speed,
in both directions, the end receiving the slow speed, probably has an
interference problem.

So, now that you understand what it takes to get a decent connection,
how is it calculated. Welcome to link calculations:
<http://wireless.navas.us/index.php?title=Wi-Fi#Link_Calculations>
Plug in the numbers for the remote AP with which you want to
communicate, assume a 20dB minimum fade margin, and see how close you
get. If you have problems, post the numbers, and I'll use them as an
example.

The basic idea is to have a sufficiently good SNR to insure reliable
communications. So, what's reliable? See the SOM to % reliability to
downtime table in the above URL. For a 20dB SOM (same as fade
margin), you'll get 99% reliability, which will produce about 88 hrs
per year of outage. If you can live with 15 minutes per day outage,
you're done. If not, you'll need to add more gain somewhere in the
system. Usually, the antennas are the easiest.

Enough on Wi-Fi calculations for now.

>In addition, I'd like to add a TV antenna to the top of my WISP antenna,

Bad idea. If they're too close, they'll affect each others antenna
pattern. Keep them apart. I don't want to get into TV antennas in a
wireless newsgroup.

>I'm amazed that the dBi spec for the antenna on the Lenovo X61t is so
>hard to find!

That's because there is no single number that clearly describes the
antennas. You could specify maximum gain, average gain, gain range,
directivity, bandwidth for VSWR<2:1, and other important info. None
of these are particularly useful because the mounting method and
location has a HUGE effect on the gain and pattern. The antenna may
look reasonable in free space, but crammed into a laptop, the pattern
is probably an embarrassment.

[Chuck Banshee]

On Wed, 01 Feb 2012 19:22:42 -0800, miso wrote:

> You should really go USB.

> The Alfa Tube/U has slightly better specs

Wow. Nice suggestion!

I had never heard of the Alfa Network Tube/U which looks suspiciously
almost exctly like the Ubiquiti Bullet M2 that I already have on my WISP
antenna (only the 600mW Bullet M2 is powered by its RJ45 jack while the
1Watt Tube/U appears to be powered by a standard USB "B" cable).

Here's a link to the Alfa Network Tube-U(N):
http://tinyurl.com/7zb7sqb

I am only considering USB WiFi extenders for my Ubuntu laptop if their
datasheet expressly says it supports Linux 2.6 (because I've been burned
before).

Luckily, both the $28 Alfa Network AWUS036H and this previously-unknown-
to-me $35 Tube-U(N) datasheets state they support Linux.

Alfa Networks AWUS036H ($28)
- TX = 20dBm (100mW)
- RX = -91dBm@11Mbps 802.11b CCK

- Antenna = Omni 2dBi
- Power = USB
- Linux = yes

Alfa Network Tube-U (N)
- TX = 30dBm (1 Watt)
- RX = -95dBm @ 11Mbps (802.11b)
- Antenna = N-Type Male connector <--- add antenna that mounts on a table
- Power = USB
- Linux = yes

This Tube-U(N) looks good. I'll need to look for a desk-mount antenna to
attach to it - but the good news is it has 1Watt of power and -95dBm
sensitivity which is great for a laptop USB-port device!

[Chuck Banshee]

On Wed, 01 Feb 2012 22:40:43 -0600, Char Jackson wrote:

> I second that suggestion. I love my HD Homerun units.

I had never heard of HD Homerun so I had to google it.
http://en.wikipedia.org/wiki/HDHomeRun
http://www.hdhomerun.com

I like its premise that all the laptops in the house instantly become TV
displays because the HDHomeRun apparently attaches to the home broadband
router. Even the kid's iPhone (apparently) becomes a TV display.

But the "HD Home Run Dual" still needs a digital TV antenna (there is no
cable where I live), so the reception calculations will still need to be
made when I install the TV antenna.

Interestingly this $130 HDHR3-US requires a 100BaseTX high-speed network.
I wonder what the star network is that I just put in a month ago? I
seriously doubt its all that fast.

[Chuck Banshee]

On Wed, 01 Feb 2012 23:01:12 -0500, Anthony R. Gold wrote:

>> Does anyone know where I can find the dBi specification for the Lenovo
>> X61t laptop built-in antenna?
>

> In general it's negative (i.e. it's less that 0dBi).

Wow. I had never considered (or seen) an antenna with less than a dBi or
two of gain!

I understood your point. The gain is minuscule. I'm surprised it works at
all given how bad it must be. No wonder I couldn't find a spec for the
Lenovo X61t laptop anywhere on the net!

[Char Jackson]

If you did it right, the Ethernet cables are capable of Gigabit and
will only be limited by the speed of the connected devices. You can
use tools like JPerf to test the actual throughput between two
endpoints.

[miso]

> I like its premise that all the laptops in the house instantly become TV
> displays because the HDHomeRun apparently attaches to the home broadband
> router. Even the kid's iPhone (apparently) becomes a TV display.
>
> But the "HD Home Run Dual" still needs a digital TV antenna (there is no
> cable where I live), so the reception calculations will still need to be
> made when I install the TV antenna.

Yes, you still need an antenna. But my point is the HD Home run device
works well. None of these receivers really have what I would call specs
these days. Rather they have check marks. That is, it will do QAM and
8VSB. How well in terms of say the noise figure of the receiver is unknown.

Possible you could get a NEMA box and place it near the antenna, but
that is another topic.

[miso]

I didn't have any issues with the RL8187 chipset under linux. The other
chipset (RALINK) they use in the high speed device has linux issues out
of the box (i.e. whatever drive was in the last rev of opensuse), but I
got it to work with the linux driver they supplied. The driver install
was well documented, but certainly not trivial.

Again, you probably want to get a right angle N adapter to reduce the
size of the "lever" arm that the Tube/U creates.

[Chuck Banshee]

On Thu, 02 Feb 2012 09:35:21 -0500, Anthony R. Gold wrote:
> That implies having a negative value is inferior and an embarrassment,
> which misses the point. It is neither - it is just the simple maths of
> the physics involved.

Ah, I see. I was thinking small numbers were bad.

For some reason, I was fixated on antenna gain. I'd still like to know
what the gain is (even if it's so small that it's negative compared to
the 0dbi isotropic standard).

Anyway, for now, so that I have a calculation to compare to the real-
world results, I'll simply use 1dBi for starters - and if that doesn't
come up with the real-world experience - I'll lower the dBi numbers in
the calculations accordingly.

Now I'm going to move on to the rest of the calculations of range.

Thanks.

[Jeff Liebermann]

On Fri, 3 Feb 2012 16:18:53 +0000 (UTC), Chuck Banshee
<chuckb...@private.com> wrote:

>I'd still like to know
>what the gain is (even if it's so small that it's negative compared to
>the 0dbi isotropic standard).

You may have missed my rant on the topic. See:
<http://groups.google.com/group/alt.internet.wireless/msg/4ef752425ef72165>
for a copy.

>Anyway, for now, so that I have a calculation to compare to the real-
>world results, I'll simply use 1dBi for starters - and if that doesn't
>come up with the real-world experience - I'll lower the dBi numbers in
>the calculations accordingly.

Try starting with about -6dBi gain due to the combination of the coax
losses, miserable antenna location, directivity issues, and internal
reflections. 0dBi for a monopole (PIFA) antenna is under ideal
conditions only. The link calculation numbers never get better, only
worse.

>Now I'm going to move on to the rest of the calculations of range.

Please note that speed and range are inversely related. Slower speeds
go farther. High speeds, don't go very far.

[Jeff Liebermann]

On Fri, 03 Feb 2012 12:52:01 -0500, "Anthony R. Gold"
<not-fo...@ahjg.co.uk> wrote:

>Starting with a value that is 1dB greater than perfection is optimistic.

Reality sucks when it gets in the way of progress.

>if some direction from that antenna really does show that gain of 1dBi there
>must be other directions with gains correspondingly less than -6dBi.

Yep. Here's some typical PIFA antenna patterns:
<http://www.edaboard.com/thread92362.html>
They're anything but spherical.

<http://www.unictron.com/Antennas_unique_chip_antennas.php>
(note the gain figures at the bottom of the page).

MIMO 2x2 antenna:
<http://www.unex.com.tw/product/ee2-2x2>
Click on "antenna pattern".
Shows an average gain (whatever that means) of -4.5dBi.

Note that the gains specified do NOT include coax losses and losses
due to crappy antenna location in the middle of the X61T laptop.

[Chuck Banshee]

On Fri, 03 Feb 2012 12:52:01 -0500, Anthony R. Gold wrote:

> your real world antenna may have an average gain of -6dBi

In all (i.e., both) my previous WiFi antenna experiences (setting up WISP
reception for two different antennas and two different providers), I was
used to antenna gains in the teens and twenties.

Since both you and Jeff (whom I admire and trust for reality figures) say
I'd be lucky to get -6dBi out of that laptop antenna, that's the number
I'll go with in my calculations.

I re-read Jeff's (prior) note and realize I have a lot more studying to
do before posting more about the effective range at the slowest speeds
(802.11b/g at <6Mbps) I'm likely to find usable.

For now, I'll assume (in lieu of any published specifications) that the
Lenovo antenna in the X61t is -6dBi (IBM part number FRU 93P4365).

[Chuck Banshee]

On Fri, 03 Feb 2012 08:32:31 -0800, Jeff Liebermann wrote:
> You may have missed my rant on the topic.

There is a lot of technical details I have missed.

That's why I just wanted to know the antenna gain in this thread.

While I'm shocked that it's -6dBi, I will certainly use that number in my
calculations.

No wonder I can "see" a dozen or more access points with my 28dBm 630mW
Bullet M2 with a 19dBi antenna while I can't see a single access point
(other than my home broadband router) with my puny Lenovo X61t laptop
15dBm (30mW) Intel 4964AGN radio card & -6dBi internal antenna.

> Try starting with about -6dBi gain due to the combination of the coax
> losses, miserable antenna location, directivity issues, and internal
> reflections.

I'm surprised that I can't find the spec for the IBM FRU 93P4365 antenna
on the net but, in lieu of a spec, -6dBi is what I'll use in my
calculations!

> Please note that speed and range are inversely related.

I'm only interested in real-world speeds that I'm likely to get. In
practice, that's the slowest spec (1Mbps to 6Mpbs 802.11b).

So, that's the spec I'm going to concentrate on.

[alexd]

Chuck Banshee (for it is he) wrote:

> In all (i.e., both) my previous WiFi antenna experiences (setting up WISP
> reception for two different antennas and two different providers), I was
> used to antenna gains in the teens and twenties.

Note that -6dBi [relative to isotropic radiator] != -6dBd [relative to a
dipole].

--
<http://ale.cx/> (AIM:troffasky) (UnSoEs...@ale.cx)
18:36:11 up 23 days, 22:05, 3 users, load average: 0.09, 0.15, 0.15
"People believe any quote they read on the internet
if it fits their preconceived notions." - Martin Luther King

[miso]

On 2/4/2012 10:37 AM, alexd wrote:
> Chuck Banshee (for it is he) wrote:
>
>> In all (i.e., both) my previous WiFi antenna experiences (setting up WISP
>> reception for two different antennas and two different providers), I was
>> used to antenna gains in the teens and twenties.
>
> Note that -6dBi [relative to isotropic radiator] != -6dBd [relative to a
> dipole].
>

Did you mean -9DBI?

[alexd]

miso (for it is he) wrote:

>> Note that -6dBi [relative to isotropic radiator] != -6dBd [relative to a
>> dipole].
>>
> Did you mean -9DBI?

No, but then -9dBi != -9dBd either.

However, a) dBi seems to be the standard for performance claims for
antennae [so it's unlikely the OP was confusing the two], and b) the
difference between dBd and dBi isn't as great as I'd expected anyway, so the
point I was making is moot.

--
<http://ale.cx/> (AIM:troffasky) (UnSoEs...@ale.cx)

17:02:37 up 24 days, 20:32, 3 users, load average: 0.08, 0.21, 0.22

[Jeff Liebermann]

On Fri, 3 Feb 2012 21:10:44 +0000 (UTC), Chuck Banshee
<chuckb...@private.com> wrote:

>I re-read Jeff's (prior) note and realize I have a lot more studying to
>do before posting more about the effective range at the slowest speeds
>(802.11b/g at <6Mbps) I'm likely to find usable.

ICTP Radio Laboratory Handbook:
<http://wireless.ictp.trieste.it/handbook/index.html>
<http://wireless.ictp.trieste.it/handbook/Handbook.pdf> 68MBytes

Wireless Networking in the Developing World
<http://wndw.net>
<http://wndw.net/download.html> (110MBytes or 5MBytes for e-book)

[Jeff Liebermann]

On Sun, 05 Feb 2012 17:20:22 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

>On Fri, 3 Feb 2012 21:10:44 +0000 (UTC), Chuck Banshee
><chuckb...@private.com> wrote:
>
>>I re-read Jeff's (prior) note and realize I have a lot more studying to
>>do before posting more about the effective range at the slowest speeds
>>(802.11b/g at <6Mbps) I'm likely to find usable.
>
>ICTP Radio Laboratory Handbook:
><http://wireless.ictp.trieste.it/handbook/index.html>
><http://wireless.ictp.trieste.it/handbook/Handbook.pdf> 68MBytes
>
>Wireless Networking in the Developing World
><http://wndw.net>
><http://wndw.net/download.html> (110MBytes or 5MBytes for e-book)

Intel Hotspot Guide Sept 2005
<http://802.11junk.com/jeffl/crud/Intel%20HotSpot%20Guide.pdf>

802.11 Wireless Networks, 2nd Edition (2005)
<http://www.amazon.com/802-11-Wireless-Networks-Definitive-Second/dp/0596100523/>
$8 to $30.

[miso]

On 2/5/2012 6:23 AM, Anthony R. Gold wrote:

> http://msdn.microsoft.com/en-us/library/ms190296.aspx

I didn't notice the bang before the equals. ;-)

Generally dipole versus the mythical perfect isotropic radiator is 3dB.

[Jeff Liebermann]

On Tue, 07 Feb 2012 00:11:43 -0500, "Anthony R. Gold"
<not-fo...@ahjg.co.uk> wrote:

>On Mon, 06 Feb 2012 19:56:35 -0800, miso <mi...@sushi.com> wrote:
>
>> Generally dipole versus the mythical perfect isotropic radiator is 3dB.
>

>FCC rules use 0dBd = 2.15dbi.

The ITU uses dBd (gain referenced to a dipole) for field strength
calcs, and dBi (gain referenced to an isotropic radiator), for most
everything else. The FCC does much the same thing, adding dBd to
exposure and SAR calcs. Some details (if anyone is interested):
<https://apps.fcc.gov/eas/comments/GetPublishedDocument.html?id=204&tn=255011>
<http://vk1od.net/antenna/concepts/erp.htm>
(See first section).

I use dBi for everything, and pretend that dBd does not exist. I
prefer the myth to the physical reality.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com je...@cruzio.com
# http://www.LearnByDestroying.com AE6KS

[Chuck Banshee]

On Sat, 04 Feb 2012 18:37:58 +0000, alexd wrote:

> Note that -6dBi [relative to isotropic radiator] != -6dBd [relative to a
> dipole].

Thanks for the fair warning.

I looked it up just now.

Apparently: GdBi = GdBd + 2.15

Given that, am I right to asssume that -6dBi antenna would be -8.15dBd if
it were listed relative to an ideal half-wave dipole (i.e., two perfect
circles just touching by the edges at the antenna location) as opposed to
an ideal isotropic radiator (i.e., one perfect circle with the antenna
centered)?

[Chuck Banshee]

On Sun, 05 Feb 2012 17:07:23 +0000, alexd wrote:

> However, a) dBi seems to be the standard for performance claims for
> antennae [so it's unlikely the OP was confusing the two]

I'm sorry if I wrote dBd instead of dBi by mistake.

For my WiFi-antenna gain calculations, I'm going to use dBi throughout as
that appears to be microwave convention.

When I finally get to my TV-antenna gain calculations, I may be forced to
use dBd simply because VHF/UHF manufacturers compare their antennas to a
dipole, in practice (or so I've read).

[Chuck Banshee]

On Sun, 05 Feb 2012 17:20:22 -0800, Jeff Liebermann wrote:
> Wireless Networking in the Developing World <http://wndw.net>
> <http://wndw.net/download.html> (110MBytes or 5MBytes for e-book)

Yup. I'm reading chapter 6 as we speak:
wndw.net/pdf/wndw2-en/wndw2-ebook.pdf

> http://wireless.ictp.trieste.it/handbook/Handbook.pdf

Thanks. That 65MB handbook is downloading as I type!

BTW, this was interesting:
www.cs.uml.edu/~xinwenfu/paper/ICDCS09_Marauder_Fu.pdf

[miso]

> I use dBi for everything, and pretend that dBd does not exist. I
> prefer the myth to the physical reality.
>

dBi always makes the numbers look better. ;-)

How fast can your car go? Well 200mph compared to a car doing 80mph in
reverse.