Minimum gauge wire for connection to ground rod
KJ4NTS
that is acceptable for this connection?
Richard Clark
>What's the minimum gauge wire that is acceptable for this connection?
Code.
KJ4NTS
On 2-Aug-2009, Richard Clark <kb7...@comcast.net> wrote:
> >What's the minimum gauge wire that is acceptable for this connection?
>
> Code.
I'm not aware of any electrical code that covers the wire gauge required to ground an amateur radio
and antenna.
Brad
Is this intended as an RF ground or lightning protection?
KJ4NTS
On 3-Aug-2009, Brad <goo...@vk2qq.com> wrote:
> Is this intended as an RF ground or lightning protection?
Primarily an RF ground since the antennas will be in my attic. However, I would appreciate the
information for both cases.
Richard Clark
>> >What's the minimum gauge wire that is acceptable for this connection?
>> Code.
>I'm not aware of any electrical code that covers the wire gauge required to ground an amateur radio
>and antenna.
Get acquainted. It is a very simple matter of a non-trivial issue.
kb9...@yahoooo.com
wrote:
I know my local electircal say nothing about radio in any form or
fashion
"one useless man is disgrace 2 become a law firm 3 or more become a congress"
adams
woger you are a Congress all in your own head
"http://www.3ix.org/sys/aff.php?aff=7439" target="_blank"
altopia is never used by KB9RQZ
http://kb9rqz.cc.cc
http://kd8ctl.com
nor is Kons...@hotmail.com ever
btw i can be found at
17366 N River Rd
Chassel Mi
but the cowards asking lack the gut to act
JB
"KJ4NTS" <KJ4...@dontask.com> wrote in message
news:O9ydnTjsW8hXJuvX...@giganews.com...
I think code calls for #6 solid Copper or Aluminum for lightning protection.
Consider the 50 ft as part of the antenna though. Rather than even trying
to have an RF "ground" try to make a counterpoise instead. Read up on the
difference between RF ground, lightning ground, and electrical ground. You
don't say what kind of antenna.
Art Unwin
> "KJ4NTS" <KJ4...@dontask.com> wrote in message
>
> news:O9ydnTjsW8hXJuvX...@giganews.com...
>
>
> > > Is this intended as an RF ground or lightning protection?
>
> > Primarily an RF ground since the antennas will be in my attic. However, I
>
> would appreciate the
>
> > information for both cases.
>
> I think code calls for #6 solid Copper or Aluminum for lightning protection.
> Consider the 50 ft as part of the antenna though. Rather than even trying
> to have an RF "ground" try to make a counterpoise instead. Read up on the
> difference between RF ground, lightning ground, and electrical ground. You
> don't say what kind of antenna.
Interesting question.
The poster is in an attic which suggests he will need a very long wire
to get to a "ground." Presumably the chassis of his radio is
connected to a "ground" at a service pole via the power plug.
The antenna I assume is floating above "ground" via a inter connecting
capacitor of a low breakdown voltage to the chassis. So one has to ask
what an added "ground" wire is going to do for you and what
disadvantages with respect to protections it is it putting in place?
KJ4NTS
On 3-Aug-2009, "JB" <nos...@goofball.net> wrote:
> > Primarily an RF ground since the antennas will be in my attic. However, I
> would appreciate the
> > information for both cases.
>
> I think code calls for #6 solid Copper or Aluminum for lightning protection.
> Consider the 50 ft as part of the antenna though. Rather than even trying
> to have an RF "ground" try to make a counterpoise instead. Read up on the
> difference between RF ground, lightning ground, and electrical ground. You
> don't say what kind of antenna.
I could put a surface wire counterpoise in the crawl space under my office where the radio is
located. If I did that, there would be only about a 5 or 6 foot run to the center point of the
counterpoise.
Assuming the counterpoise wires are laying on the dirt floor of the crawl space, how many wires
would I need, and how long do they need to be. I want to be able to work 6 through 40 meters.
If I install a wire counterpoise like this, is there any problem also connecting the earth ground
connection to the central ground bar in my office?
The attic antenna is an Alpha Delta DX-EE.
Michael Coslo
Is a nice station grounding pdf from Polyphasor. Sorry for the tinyurl,
the original url is a mile long.
Everyone should have a copy, and the writer should get an award for his
or her clarity.
Richard is correct. It is simple, and it is not trivial.
- 73 de Mike N3LI -
John Ferrell
>I have about a 50 foot run from my radio to the outside ground rod. What's the minimum gauge wire
>that is acceptable for this connection?
The last time I checked the minimum wire size for a ground intended to
protect from lightning is #6.
50 feet of any wire will not work as an RF ground for anything other
than a quarter wave at 50 feet!
Your next question is about driving another ground rod: If you do, the
second ground must be tied to the first with a minimum of #6 wire or
you set up a dangerous ground loop.
KJ4NTS
On 3-Aug-2009, Michael Coslo <mj...@psu.edu> wrote:
> http://tinyurl.com/ns7jjd
>
> Is a nice station grounding pdf from Polyphasor. Sorry for the tinyurl,
> the original url is a mile long.
>
> Everyone should have a copy, and the writer should get an award for his
> or her clarity.
That's a good article, but it is focused on grounding for lightning protection. I am interested in
that, but I am also interested in having an effective RF ground.
I've been able to get a total of 16 feet of ground rod down in the form of 4 four-foot rods, but I
have a 50 foot run from my office to the ground rods, and I'm concerned about RF impedance in that
connection.
KJ4NTS
On 3-Aug-2009, John Ferrell <jferr...@triad.rr.com> wrote:
> >I have about a 50 foot run from my radio to the outside ground rod. What's the minimum gauge
> >wire
> >that is acceptable for this connection?
> The last time I checked the minimum wire size for a ground intended to
> protect from lightning is #6.
>
> 50 feet of any wire will not work as an RF ground for anything other
> than a quarter wave at 50 feet!
OK. Would it work to construct a radial counterpoise in the crawl space under my office? It would
only be about a 5 foot run to the center of the counterpoise.
If I lay wires on the dirt floor of the crawl space, how many radials would be required and what
would the length be to handle 6-40 meters?
Richard Clark
> I'm concerned about RF impedance in that connection.
Add a capacitor.
Bruce in alaska
"KJ4NTS" <KJ4...@dontask.com> wrote:
The two are pretty much Mutually Exclusive. What makes for Good
Lightning Protection, really doesn't have ANYTHING to do with RF
Grounding, especially if your using an End Feed Vertical, for an
Antenna. Lightning Protection is a Ground Rod that meets NEC.
Low Impedance RF Grounding System design is a Science and Art all in
itself.
--
Bruce in alaska
add <path> after <fast> to reply
Art Unwin
> In article <UZOdnZWJsoFGvurXnZ2dnUVZ_jKdn...@giganews.com>,
>
>
>
> "KJ4NTS" <KJ4...@dontask.com> wrote:
Atta boy Bruce!
A ground plane or counterpoise is part and parcel of a antenna all of
which does not necessarily radiate and it is not of the same potential
of the true ground that should be at the lowest potential of them all.
It is for this reason the transmitter chassis is grounded and
separated from the radiator system which has it's own closed circuit
and where the potential is above that of true ground. In this way your
transmitting circuit does not have a ground loop which is the last
thing that you want.
Lightning tries to get to the true ground by the shortest route and
the requirement is for you to not be part of it's route, even if your
radio has to be the sacrificial lamb if you haven't pulled the plug.
Dave
"Art Unwin" <Arthu...@gmail.com> wrote in message
news:7bf6b00d-74d4-41ed...@a13g2000yqc.googlegroups.com...
On Aug 3, 3:09 pm, Bruce in alaska <f...@btpost.net> wrote:
> In article <UZOdnZWJsoFGvurXnZ2dnUVZ_jKdn...@giganews.com>,
>separated from the radiator system which has it's own closed circuit
>and where the potential is above that of true ground. In this way your
>transmitting circuit does not have a ground loop which is the last
>thing that you want.
i don't know where you get your radios, but in all of them here the coax
connector is connected to the transmitter chassis which also has a lug for
going to the safety ground.
>Lightning tries to get to the true ground by the shortest route and
>the requirement is for you to not be part of it's route, even if your
>radio has to be the sacrificial lamb if you haven't pulled the plug.
there ain't no such thing as 'true ground', tis all relative.
Rollie
suppliers that furnish it. I use whatever I have that is high current
carrying. #4 or #6 or bigger. Grounding is an art of it's own so you
should study it as any other aspect of electronics. The experts run all the
ground absorbers to a common buss bar and and the ground collectors to that
bar. Make a study of this as there is no easy answer.......Rollie
Art Unwin
> "Art Unwin" <ArthurUn...@gmail.com> wrote in message
>
> news:7bf6b00d-74d4-41ed...@a13g2000yqc.googlegroups.com...
> On Aug 3, 3:09 pm, Bruce in alaska <f...@btpost.net> wrote:
>
> > In article <UZOdnZWJsoFGvurXnZ2dnUVZ_jKdn...@giganews.com>,
> >It is for this reason the transmitter chassis is grounded and
> >separated from the radiator system which has it's own closed circuit
> >and where the potential is above that of true ground. In this way your
> >transmitting circuit does not have a ground loop which is the last
> >thing that you want.
> i don't know where you get your radios, but in all of them here the coax
> connector is connected to the transmitter chassis which also has a lug for
> going to the safety ground.
By golly, I believe you are correct! I thought that was a bad
practice! Are all electronics at the same potential in the U.S. as
its container? So with a ground connection at the electrical supply
point and a provided connection for another generated "ground", is
that not an invitation for ground loops?
>
> >Lightning tries to get to the true ground by the shortest route and
> >the requirement is for you to not be part of it's route, even if your
> >radio has to be the sacrificial lamb if you haven't pulled the plug.
>
> there ain't no such thing as 'true ground', tis all relative.
H'mm, the ground point with the lowest potential relative to other
ground potentials in the same system is the "true" ground of the
system. Now can you tell me which "ground" is protected and from
what? And RF ground; is that protected from lightning? Lightning is
multi frequency oriented so it would appear to me it would gyrate
towards a radiator.
What about just one wire to the antenna and let the earth be the
return line to close the circuit! Seems like the definitions have gone
awry without involvement of a chassis ground
but then it is you that is electrically educated and the better judge.
Brad
. I am interested in
> that, but I am also interested in having an effective RF ground.
>
> I've been able to get a total of 16 feet of ground rod down in the form of 4 four-foot rods, but I
> have a 50 foot run from my office to the ground rods, and I'm concerned about RF impedance in that
> connection.
That's about a quarter wave at 5MHz. It sure isn't an effective
ground.You'd need a tuner on the ground wire as well.
Michael Coslo
Gathering from your other posts, you are in a difficult situation. RF
grounding from a non ground floor or basement location is an issue. The
problem is proportional to the frequency and wavelength, which is to say
that at 10 meters, your RF ground won't.
Is there any possibility of putting in a balanced antenna? Or one of the
so called no-ground verticals? All antenna setups are a compromise of
one sort or another. Your setup will be a little bit more of a compromise.
This isn't to say there is no solution. There is always a solution of
some sort.
295
I ran attic mounted antennas for a period time and here is my
experience. First, don't bother running any ground to the antenna,
especially at 50 feet long. It will act more like a radiating element
than a ground, then you will get to meet Mr. RFI as you will discover
all types items your RF can affect. Since your antennas are in the
attic, static and lightning should not be an issue, unless you or a
close neighbor takes a direct hit.
I keep everything disconnected unless I am operating, it is the only
way I know of to keep lightning from destroying your station. If you
or your neighbor takes a direct hit, there is not much you can do to
prevent damage, unless you have everything disconnected, AC/Ground/
Antennas/Control lines/etc.
Second, your four foot ground rods are about useless for both RF and
DC ground. Minimal is eight feet. My current station has 7 eight foot
ground rods, spaced no more than eight feet apart, and all grounds are
tied together, including the panel box ground. This is done to make
sure all grounds are at the same potential.
You did not describe your station so the information someone can
provide is limited. In my case, my station was on the second floor,
so instead of having a ground, I used a tunable counterpoise system as
my RF ground. MFJ makes the tune boxes, and Ten-Tec may still sell
them in kit from too. I used the one from Ten-Tec, it worked well at
my location, but it still was a compromise, when compared to having a
true ground system and outside antennas.
73
Dave
On Aug 3, 4:51 pm, "Dave" <no...@nowhere.com> wrote:
> "Art Unwin" <ArthurUn...@gmail.com> wrote in message
>> connector is connected to the transmitter chassis which also has a lug
>> for
>> going to the safety ground.
>
>
>By golly, I believe you are correct! I thought that was a bad
>practice! Are all electronics at the same potential in the U.S. as
>its container? So with a ground connection at the electrical supply
>point and a provided connection for another generated "ground", is
>that not an invitation for ground loops?
yes, it is. that is why your 'shack' ground has to be connected to the
service entrance ground.
>
>> >Lightning tries to get to the true ground by the shortest route and
>> >the requirement is for you to not be part of it's route, even if your
>> >radio has to be the sacrificial lamb if you haven't pulled the plug.
>>
>> there ain't no such thing as 'true ground', tis all relative.
>
>H'mm, the ground point with the lowest potential relative to other
>ground potentials in the same system is the "true" ground of the
>system.
you have to define the 'system'. but there is always the possibility that
someone outside the 'system' can reach in and measure your 'ground '
connection relative to something else and measure a potential. potential is
what is relative, hook a 12v battery to a meter and set it on a table,
connect another 12v battery between a ground rod and one terminal of the
first battery... does the meter reading change? what is the potential of
the positive terminal of the battery? if you were sitting on the table and
couldn't reach the ground rod or 2nd battery terminals could you tell what
the voltage of the 2nd battery was?
>Now can you tell me which "ground" is protected and from
>what?
'ground' is not protected from anything. 'ground' is a convenient point to
connect everything and to make measurements from.
> And RF ground; is that protected from lightning?
there is no such thing as an 'rf ground'. there is at best a low impedance
path for return currents to get back to the feedpoint... if that happens to
be through the earth (note for you, earth means dirt, not earth as in
electrical ground that we call it in the states) then we may want to call it
'ground' but it really isn't.
now, why do i say there is no such thing as an rf ground? consider what
happens around a 10m 1/4 wave vertical mounted on the ground connected to
the center conductor of the coax, with a single ground rod as the
connection for the shield of the coax. The current going into the 1/4 wave
vertical and the current coming out of the ground rod have to be equal at
the coax connection... so, current flows up the vertical, back through the
ground, up the ground rod and back to the coax... very simple... until you
take your rf voltmeter and connect it to the ground rod and stick the other
probe in the ground some distance from the rod, lets say about 1/4 wave away
(more or less, propagation velocity through the ground is slower so it would
be physically less than 1/4 wave in free space, etc, etc). what voltage do
you read on your meter?? it is difficult to calculate because of all the
interfaces and bulk conductivities, the sizes of the ground rod and probe,
etc... but suffice it to say, it ain't zero. why not, aren't both probes
connected to 'ground'?? well, yes, and no. because there is current
flowing through the earth trying to get back to that coax connection there
has to be a voltage difference. current in earth * resistivity of earth =
voltage between points on the earth, give or take a few units. now lets say
we add a radial wire to connect the ground rod at the feed point of the
vertical to the probe where you measure the voltage of the earth... does the
voltage go away? after all you just shorted out your voltmeter didn't you??
but no! there is still voltage! why you ask?? well, even though you have
made a lower impedance path there is still current on the wire, and since
the wire has inductance and capacitance the propagation time is not zero, so
there is still a voltage difference causing that current to flow along the
radial wire... why is it necessary to insulate the ends of raised radials if
they are a 'ground' plane under a vertical antenna?
lightning 'ground' is even worse because the currents are bigger... consider
a 100ka bolt with a rise time of 1usec hitting the ground and spreading out
at about .3c (approximately what i measured in one experiment for a buried
radial wire)... the potential difference between points just a few feet
apart can be huge, that is a common cause of lightning deaths, current hits
tree, goes through ground, up one leg, down the other, or up one leg and out
an arm that is closer to something conductive away from the tree... like a
golf club. the key with designing lightning 'ground' systems is to realize
that this potential exists and make sure you can handle it. the 'single
point ground' is the classic way because it makes the distance zero which
takes the rise time and propagation speed out of the equation.
unfortunately that is not always possible, so that is where other methods
are needed to keep voltages across protected equipment equalized.
>Lightning is multi frequency oriented so it would appear to me it would
>gyrate
>towards a radiator.
i have never known lightning to gyrate. it takes all sorts of convoluted
paths, but none that i would call gyrating.
>What about just one wire to the antenna and let the earth be the
>return line to close the circuit!
certainly, and many have done that, and some have gotten burned. consider
this case... sit on your table with the 12v battery again, but instead of
the meter hook up a transmitter to it. assume there is one so-239 output
jack mounted on the radio's metal case and no other connections, just 12v
in, rf out. run a wire straight out from the so-239 center conductor then
touch the radio's metal case... what happens? if the power is high enough
you get burned... why? you are touching the radio case, isn't that
'ground'? you aren't touching the earth? so what is happening??? well,
you are now part of the return path for current that has to find a way back
to the chassis side of the so-239, and since you are likely much larger than
the case of the radio you make a more efficient collector.
change the setup, now run a wire from the case of the radio to the ground
rod where the 2nd battery used to be connected... now you have another path
for current to get back to the chassis side of the connector, from the
'earth' through the ground rod up the wire and to the radio... now touch the
case and what happens? well, if the earth to radio circuit is lower
impedance than your body to radio, more current flows on that side and you
don't get burned... not good enough? still getting burned??? get one of
those counterpoise resonator thingies... they are really just a small match
box for a long wire... run the wire around the floor and tune it up. why
does it work better? it provides a lower impedance path for collecting up
that return current and getting it back to the radio. no magic, it is just
providing the return current instead of letting your body collect it.
> Seems like the definitions have gone awry without involvement of a chassis
> ground
ah, chassis ground, yet another type of ground.
>but then it is you that is electrically educated and the better judge.
one of the few things you have said that i agree with
JB
This is a balanced antenna and if the antenna is stretched out in an area
where there is no metal it should do it's best. You probably won't benefit
from a counterpoise at all. In fact, any RFI you might encounter will have
to be specifically addressed because of the antenna is within the living
quarters. Your antenna will be too close to the ground and partly shielded
by roofing materials as it is for optimal performance, but we do what we can
just to get on the air when there is no good solution. Having said that, You
should be able to load up with an outboard tuner and make some contacts.
JB
"Dave" <no...@nowhere.com> wrote in message
news:UX2em.642$Jg....@nwrddc01.gnilink.net...
The electrical ground is Neutral at the entrance so that any wires shorting
to the boxes or metal cabinets will pull the breaker and so that none of the
cabinets can have AC potential on them. The lightning ground should be
there at the entrance because that is the common tie point of all grounds,
and any lightning currents flowing on the ground wires throughout the house
will induce massive voltages into the house wiring. If you have multiple
ground rods, they should tie together with heavy cable to the panel before
all else. There is a problem with a good RF ground at the antenna, because
lightning strikes to the power pole or house will want to flow through your
station to the good ground in addition to the panel ground. So it is a good
Idea to at least bring the coax and all wires to the electrical entrance for
protection before entering the house and preferable to site the tower
outside the electrical box and bond all grounds with heavy gauge conductors.
The man is putting a dipole in the attic, so this talk about ground is a
moot point.
Richard Clark
>The man is putting a dipole in the attic, so this talk about ground is a
>moot point.
The "balanced" antenna is connected to an "unbalanced" system if the
rig has AC power through any device or has a powered mike connection,
or has a computer control line, or has a powered speaker, or has a ...
and so on. It takes supreme effort to maintain "balance" but most
are happy to ignore analysis and put a rubber stamp to it.
That an antenna is in a attic space is, no doubt, a cry that it is
insulated from the sky. If that were all that was needed, every
plastic covered wire in the air would be lightning proof. That is a
superstition. If it were as effective as supposed, no one could use
the antenna for its purpose.
The only bright point of there being so few reports of lightning
strikes to attic antennas is that they present so little individual
risk that low within a neighborhood of equally available targets - you
could as easily use a closeline. Every home in a community over 30
years old has a vertical radiator penetrating the roof line, the
plumbing system vent that dives solidly straight into ground. How
often is a house struck there?
73's
Richard Clark, KB7QHC
KJ4NTS
On 5-Aug-2009, "JB" <nos...@goofball.net> wrote:
> This is a balanced antenna and if the antenna is stretched out in an area
> where there is no metal it should do it's best. You probably won't benefit
> from a counterpoise at all.
The idea behind the counterpoise was to provide an RF ground for the radio, not as a part of the
antenna.
> Your antenna will be too close to the ground and partly shielded
> by roofing materials as it is for optimal performance, but we do what we can
> just to get on the air when there is no good solution. Having said that, You
> should be able to load up with an outboard tuner and make some contacts.
I have a friend with an Alpha Delta DX-EE in his attic, and he has achieved DX CC -- contacts with
100 countries. I don't know if it is a one or two story house. I'm going over to look at his
installation his weekend.
KJ4NTS
On 5-Aug-2009, Richard Clark <kb7...@comcast.net> wrote:
> The only bright point of there being so few reports of lightning
> strikes to attic antennas is that they present so little individual
> risk that low within a neighborhood of equally available targets - you
> could as easily use a closeline. Every home in a community over 30
> years old has a vertical radiator penetrating the roof line, the
> plumbing system vent that dives solidly straight into ground. How
> often is a house struck there?
As far as I know, we've never had a lightning strike. From a lightning perspective, we are fortune
to have a hill at least 4 times as high as the house immediately behind us. Pity the house on the
top of that hill.
Michael Coslo
> On 5-Aug-2009, "JB" <nos...@goofball.net> wrote:
>
>> This is a balanced antenna and if the antenna is stretched out in an area
>> where there is no metal it should do it's best. You probably won't benefit
>> from a counterpoise at all.
>
> The idea behind the counterpoise was to provide an RF ground for the radio, not as a part of the
> antenna.
Ah, I'd never mind the counterpoise if you are using the balanced
antenna. Just put up the antenna, run the coax or ladder line, get
yourself a good station ground and some lightning protection. You are
not likely to get struck directly, but could be the victim of a large
static buildup. Polyphaser makes very good ones, and there is a simpler
one that uses a spark gap, which also provides protection. Don't know
the brand of that one. Disconnect the antenna and ground it when not in use.
I'd say with this setup, you could do DXCC. DXCC and other awards have
been achieved on more modest setups than what you are looking at
building. You won't be the loudest signal on the band, but there can
only be one of those anyhow.
Now get to work! 8^)
JB
news:h5eu08$dk1a$1...@tr22n12.aset.psu.edu...
> KJ4NTS wrote:
> > On 5-Aug-2009, "JB" <nos...@goofball.net> wrote:
> >
> >> This is a balanced antenna and if the antenna is stretched out in an
area
> >> where there is no metal it should do it's best. You probably won't
benefit
> >> from a counterpoise at all.
> >
> > The idea behind the counterpoise was to provide an RF ground for the
radio, not as a part of the
> > antenna.
>
If you are feeding the radio with 50 ohm coax that is matched in a 50 ohm
non-reactive load (ie tuner or dummy load) the RF will stay where it
belongs. The only concern for the balanced antenna, is lightning protection
and shock hazard from the power supply.
The best lightning protection depends on your specific situation so I will
leave you to read up on that.
>
> Ah, I'd never mind the counterpoise if you are using the balanced
> antenna. Just put up the antenna, run the coax or ladder line, get
> yourself a good station ground and some lightning protection. You are
> not likely to get struck directly, but could be the victim of a large
> static buildup. Polyphaser makes very good ones, and there is a simpler
> one that uses a spark gap, which also provides protection. Don't know
> the brand of that one. Disconnect the antenna and ground it when not in
use.
>
> I'd say with this setup, you could do DXCC. DXCC and other awards have
> been achieved on more modest setups than what you are looking at
> building. You won't be the loudest signal on the band, but there can
> only be one of those anyhow.
I don't have DXCC but I do have a wall of cards from around the world. Many
of them were logged when I was mobile to and from work or school. It will
sharpen your skills to steal them from the big guns. I had a regular daily
lunch break sked with an Aussie from my truck in the parking lot.when the
sunspots were working. Conditions can even favor the well placed weak
station over the big guns. That is the sport of it all.
Michael Coslo
> I don't have DXCC but I do have a wall of cards from around the world. Many
> of them were logged when I was mobile to and from work or school. It will
> sharpen your skills to steal them from the big guns. I had a regular daily
> lunch break sked with an Aussie from my truck in the parking lot.when the
> sunspots were working. Conditions can even favor the well placed weak
> station over the big guns. That is the sport of it all.
Concur 100 percent, JB. I know that new guys love the high power and
high gain antenna setups, but NTS will learn a lot on how to be a better
operator with a modest setup such as he proposes.
KJ4NTS
On 6-Aug-2009, Michael Coslo <mj...@psu.edu> wrote:
> I'd say with this setup, you could do DXCC. DXCC and other awards have
> been achieved on more modest setups than what you are looking at
> building. You won't be the loudest signal on the band, but there can
> only be one of those anyhow.
How much attenuation is a wood roof with asphalt shingles going to introduce? All of the duct work
in my house is in the crawl space, and the phone and cable TV lines are also in the crawl space. So
there is no metal other than the roofing nails, and there's nothing between the antenna and the sky
other than the roof decking and shingles. I don't expect them to add a lot of attenuation, but I
could be wrong.
Mike Coslo
There will be a slight effect of the other wires. Nails? probably not
measurable. The roof itself at HF is not attenuating much, it increases
as the frequency goes up. The biggest issue of this sort of antenna is
the height above ground, and the possibility of RF interference with
things in the house.
JB
> other than the roof decking and shingles. I don't expect them to add a
lot of attenuation, but I
> could be wrong.
Maybe 3' makes a big difference. I have always seen a difference between
antennas in the attic or stretched out on the roof, and antennas even a few
feed above the roof. I don't know if it was shingles or what. It would
really be interesting to see what kind of shingles are transparent. I have
seen antenna farms hidden behind fake gables.
Myron A. Calhoun
I've never "played" with it at HF, but I do know that the dielectric
constant of nearby materials affects antennas at VHF.
--
--Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
NRA Life Member & Certified Instructor for Rifle, Pistol, & Home Firearm Safety
Also Certified Instructor for the Kansas Concealed-Carry Handgun (CCH) license
Michael Coslo
Well, there's nothing like ground truth, JB, so I'll defer to your
experience vs my conjecture. Possibilities for further RF attenuation
might be the materials in use. Those little rocks used for color and
grip. Fiberglass is used a lot for the base, but there may be other
fabrics too. It's a composite material, who knows, there might be carbon
in it as well.
Jim Lux
Attenuation isn't a real concern, except when it's raining or the roof
is wet.
What should be a concern is the following:
1) weird interactions between antenna and conductive stuff in the attic.
Don't expect the same feedpoint impedance vs frequency you get with
the antenna out in the open.
2) Fire: The voltage gets pretty high at the ends of a dipole when
you're radiating even 100W. Or, more to the point, the voltage gets
high in nearby wires that happen to be the "wrong" length. A small
ember smoldering in your attic is a huge problem. This is something you
need to figure out how to check.. keeping the active ends of the dipole
clear of flammable stuff is straightforward, but the accidental
excitation of something else, isn't. (wiring isn't a problem.. it's
usually connected to something else that shunts the current.. it's
isolated conductors, like plumbing, HVAC ducts, etc. In your situation,
yours is in the crawl space, so you're in good shape.)
3) RF exposure. Do your calculations and make sure you're not cooking
things you shouldn't be.