Home » Public Forums » GMCnet » CB Antenna With Best Ground Plane
| CB Antenna With Best Ground Plane [message #95210] |
Tue, 10 August 2010 10:08  |
philipswanson
Messages: 282
Registered: January 2004
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I am looking for the best CB antenna for our coaches with a good ground plane. With all the aluminum and fiberglass on the roof, getting a good ground plane is a real challenge. My CB radio is powerful but the limiting factor is definitly the antenna.
Thanks, Phil Swanson
[Updated on: Tue, 10 August 2010 10:08] Report message to a moderator |
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| Re: [GMCnet] CB Antenna With Best Ground Plane [message #95223 is a reply to message #95213] |
Tue, 10 August 2010 12:04  |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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The limiting factor will almost always be the lack of a good ground plane. Where do you intend to mount the antenna? And, how long is your intended antenna? Another factor to consider is the type and length of the coax cable connecting the antenna to the radio.
The al roof is a good medal ground plane, but putting a large enough antenna above the roof is a feat all by itself.
A 1/2 wave antenna at legal CB frequencies is about 18 1/4 feet in length. 1/4 wave vertical, using the vehicle body as a ground plane, will be about half that length, or 9 ft long. Anything shorter, even with fancy loading coils, is a compromise. Loading coils enable the radio to "think" that it is going into a 50 ohm antenna. They cost RF energy. The mentioned Hustler antenna is 25 inches (in addition to the height of the coach).
Go to you local library and see if they have a copy of "The ARRL Handbook for Radio Communications." It has excellent chapters on antennas, coax, and compromises.
One question that I have, do you have the OEM mirrors? Or, have you changed to Ramco's, etc? You can get a very simple antenna mount that will attach to the rod that the OEM mirrors are on. Then just a good ground jumper to the body, and the coach body is your ground plane. At the mirror location, you can install a spiral wrapped vertical that is less of a compromise. You see a lot of these around and they are tough and cheap. The body of the GMC will also provide some directional steering of your signal. And, if the radiating element is near the al body, it will also compromise your RF signal.
Most of this applies to transmitting a signal. If you are just going to receive CB signals, an exact antenna is not really needed.
Tom Phipps,
KA4CSG
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] CB Antenna With Best Ground Plane [message #95224 is a reply to message #95223] |
Tue, 10 August 2010 12:27 |
Gary Worobec
Messages: 867
Registered: May 2005
Karma: -1
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Senior Member |
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Hi,
We put in a CB for our trip to Mexico. I mounted the antenna to the right
hand OEM mirror. I pulled the inside passenger side panel and put in 3
square feet of copper sheet and tied that to the aluminum framwork of the
coach. Then put a big ground strap between the aluminum frame and the copper
sheet. In Yuma on the way down I made an appointment with the local CB shop.
The guy tuned the radio and indicated that we were getting excellent output.
In our Mexican convoy that sometimes stretched out 3 or 4 miles (about 11
coaches) we could easily talk back and forth from front to back. Seems to
work well on the highway as well. We don;t use it that much but it's there
if need be.
Thanks
Gary and Joanne Worobec
1973 GMC Glacier
Anza, CA
----- Original Message -----
From: "Thomas Phipps" <tph1pp5@yahoo.com>
To: <gmclist@temp.gmcnet.org>
Sent: Tuesday, August 10, 2010 10:04 AM
Subject: Re: [GMCnet] CB Antenna With Best Ground Plane
>
>
> The limiting factor will almost always be the lack of a good ground plane.
> Where do you intend to mount the antenna? And, how long is your intended
> antenna? Another factor to consider is the type and length of the coax
> cable connecting the antenna to the radio.
> The al roof is a good medal ground plane, but putting a large enough
> antenna above the roof is a feat all by itself.
>
> A 1/2 wave antenna at legal CB frequencies is about 18 1/4 feet in length.
> 1/4 wave vertical, using the vehicle body as a ground plane, will be about
> half that length, or 9 ft long. Anything shorter, even with fancy loading
> coils, is a compromise. Loading coils enable the radio to "think" that it
> is going into a 50 ohm antenna. They cost RF energy. The mentioned
> Hustler antenna is 25 inches (in addition to the height of the coach).
>
> Go to you local library and see if they have a copy of "The ARRL Handbook
> for Radio Communications." It has excellent chapters on antennas, coax,
> and compromises.
>
> One question that I have, do you have the OEM mirrors? Or, have you
> changed to Ramco's, etc? You can get a very simple antenna mount that
> will attach to the rod that the OEM mirrors are on. Then just a good
> ground jumper to the body, and the coach body is your ground plane. At
> the mirror location, you can install a spiral wrapped vertical that is
> less of a compromise. You see a lot of these around and they are tough
> and cheap. The body of the GMC will also provide some directional
> steering of your signal. And, if the radiating element is near the al
> body, it will also compromise your RF signal.
>
> Most of this applies to transmitting a signal. If you are just going to
> receive CB signals, an exact antenna is not really needed.
>
> Tom Phipps,
> KA4CSG
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: CB Antenna With Best Ground Plane [message #95241 is a reply to message #95210] |
Tue, 10 August 2010 16:21 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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Not sure why someone would say that aluminum would not make a good ground plane, Aluminum is a good electrical conductor. I'm in the radio communication business and I can tell you that all commercial base antennas (except fiberglass) are made of aluminum.
I'm sure your "Strong" transmitter is not exceeding the maximum power allowed for CB band....  therefore I would suggest if you want a decent antenna without the consumer gimmicks, install a commercial base loaded antenna on a NMO mount through the roof such as a Laird lowband 26-31Mhz:
http://lairdtech.thomasnet.com/item/vehicular-mobile-radio-antennas/mobile-load-coil-antennas-2/pn-4499?
BTW, this antenna will handle over 100 watts and more.
Just remember its 4ft tall! But it will work very well (better than a 1/4 wave on the bumper) and likely last as long as the coach.
I would not get too hung up on the slight effect of the pattern from the A/C unit. You might be able to measure some deviation from a perfect omni, but you will not be able to perceive any difference.
I forget my S-unit to Db conversion, but suffice it to say you would need to increase your signal power by 3db (double to Tx power) before someone receiving your signal would even perceive any difference in signal quality.
Me on the other hand, I just have a cheap glass mount antenna on the driver's side. Works good enough for what I want.
JMO
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
[Updated on: Tue, 10 August 2010 16:25] Report message to a moderator |
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| Re: [GMCnet] CB Antenna With Best Ground Plane [message #95261 is a reply to message #95223] |
Tue, 10 August 2010 20:30 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Senior Member |
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A little off topic, but when I was a kid I remember lots of cars with ground straps dragging on the road. What did they do, if anything?
Sent from my iPad
On Aug 10, 2010, at 10:04 AM, Thomas Phipps <tph1pp5@yahoo.com> wrote:
>
>
> The limiting factor will almost always be the lack of a good ground plane. Where do you intend to mount the antenna? And, how long is your intended antenna? Another factor to consider is the type and length of the coax cable connecting the antenna to the radio.
> The al roof is a good medal ground plane, but putting a large enough antenna above the roof is a feat all by itself.
>
> A 1/2 wave antenna at legal CB frequencies is about 18 1/4 feet in length. 1/4 wave vertical, using the vehicle body as a ground plane, will be about half that length, or 9 ft long. Anything shorter, even with fancy loading coils, is a compromise. Loading coils enable the radio to "think" that it is going into a 50 ohm antenna. They cost RF energy. The mentioned Hustler antenna is 25 inches (in addition to the height of the coach).
>
> Go to you local library and see if they have a copy of "The ARRL Handbook for Radio Communications." It has excellent chapters on antennas, coax, and compromises.
>
> One question that I have, do you have the OEM mirrors? Or, have you changed to Ramco's, etc? You can get a very simple antenna mount that will attach to the rod that the OEM mirrors are on. Then just a good ground jumper to the body, and the coach body is your ground plane. At the mirror location, you can install a spiral wrapped vertical that is less of a compromise. You see a lot of these around and they are tough and cheap. The body of the GMC will also provide some directional steering of your signal. And, if the radiating element is near the al body, it will also compromise your RF signal.
>
> Most of this applies to transmitting a signal. If you are just going to receive CB signals, an exact antenna is not really needed.
>
> Tom Phipps,
> KA4CSG
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: [GMCnet] CB Antenna With Best Ground Plane [message #95272 is a reply to message #95261] |
Tue, 10 August 2010 21:45 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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Senior Member |
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I believe it was to make an electrical contact from
the body/frame of the vehicle to ground to discharge
static electricity once the vehicle stopped moving.
Static electricity was apparently generated by the
rolling of the "rubber" tires over the road. There
used to be "grounding contacts" on the inside of
the bearing grease caps to reduce/eliminate the
static causing interference to radios. I don't know
if those still exist either.
~ ~ ~ ~ ~ ~ ~ ~ ~
~ Mac Macdonald ~
~ Hamcall-K2GKK ~
~ Since Nov '53 ~
~ Oklahoma City ~
~~ "Money Pit" ~~
~ '76 ex - P.B. ~
~ ~ ~ ~ ~ ~ ~ ~ ~
p.s. Aluminum makes a GREAT antenna ground plane!
> From: ljdavick@comcast.net
> To: gmclist@temp.gmcnet.org
> Date: Tue, 10 Aug 2010 18:30:17 -0700
> Subject: Re: [GMCnet] CB Antenna With Best Ground Plane
>
> A little off topic, but when I was a kid I remember lots of cars with ground straps dragging on the road. What did they do, if anything?
>
> Sent from my iPad
>
> On Aug 10, 2010, at 10:04 AM, Thomas Phipps <tph1pp5@yahoo.com> wrote:
>
> >
> >
> > The limiting factor will almost always be the lack of a good ground plane. Where do you intend to mount the antenna? And, how long is your intended antenna? Another factor to consider is the type and length of the coax cable connecting the antenna to the radio.
> > The al roof is a good medal ground plane, but putting a large enough antenna above the roof is a feat all by itself.
> >
> > A 1/2 wave antenna at legal CB frequencies is about 18 1/4 feet in length. 1/4 wave vertical, using the vehicle body as a ground plane, will be about half that length, or 9 ft long. Anything shorter, even with fancy loading coils, is a compromise. Loading coils enable the radio to "think" that it is going into a 50 ohm antenna. They cost RF energy. The mentioned Hustler antenna is 25 inches (in addition to the height of the coach).
> >
> > Go to you local library and see if they have a copy of "The ARRL Handbook for Radio Communications." It has excellent chapters on antennas, coax, and compromises.
> >
> > One question that I have, do you have the OEM mirrors? Or, have you changed to Ramco's, etc? You can get a very simple antenna mount that will attach to the rod that the OEM mirrors are on. Then just a good ground jumper to the body, and the coach body is your ground plane. At the mirror location, you can install a spiral wrapped vertical that is less of a compromise. You see a lot of these around and they are tough and cheap. The body of the GMC will also provide some directional steering of your signal. And, if the radiating element is near the al body, it will also compromise your RF signal.
> >
> > Most of this applies to transmitting a signal. If you are just going to receive CB signals, an exact antenna is not really needed.
> >
> > Tom Phipps,
> > KA4CSG
> > _______________________________________________
> > GMCnet mailing list
> > List Information and Subscription Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] CB Antenna With Best Ground Plane [message #95312 is a reply to message #95272] |
Wed, 11 August 2010 08:27 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Senior Member |
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On your comment about the "twin' antennas that you see mounted on the mirrors of lots of big rigs and want-to-be big rigs. Without a proper phasing harness connecting the antennas to the radio, they are just for show. It is very difficult to get 2 antennas in that frequency range far enough from each other on a vehicle's legal width footprint. Measuring from the base of each antenna and comparing it to the desired spacing would indicate that the vehicle's max width of 8 ft, would not met the distance requirements for proper phasing of twin verticals antennas. (1/4 wave length)(about 9'+ at 27 MHz)). If the antennas are not properly phased and the correct distance apart, they will work against each other. This is physics. Excellent article at
http://www.signalengineering.com/ultimate/co_phasing.html
However, it should be noted that two twin vertical antennas, phased properly, would direct most of the antenna's RF power to the front and rear of the vehicle (assuming mirror mounts) and add the equivalent of 3db gain for the over-all array.
My GMC has two matching vertical antennas, but they are connected to two different radios and do not interfere with each other. Sometimes 2 or more antennas indicate 2 or more radios. Now, where will I install the HF antenna? Looking at rear of the vehicle, mounted on the trailer hitch? Or, go with the Safari look and mount it on the front bumper?
Tom Phipps, KA4CSG
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] CB Antenna With Best Ground Plane [message #95331 is a reply to message #95312] |
Wed, 11 August 2010 12:41 |
gmcrv1
Messages: 839
Registered: August 2007
Location: Memphis
Karma: -1
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Senior Member |
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Tom,
Agree on the antenna mounting locations. I'm just glad I now have a vehicle
big enough that I can fit my matching vintage HF station in. If I remove
the Davo on the Glacier,I think the whole station may fit! I don't really
see myself working HF mobile from The GMC, but I have considered home
brewing some sort of vertical that could be stored in a piece of PVC pipe
attached to the frame. That would be a good 20' section - at least. Have
to get the ARRL antenna book out.
As you know there are all kinds of mounts for the hitch. Front bumper...I
think I'd leave that for the safari guys - besides a front mount antenna
would just block the cold are from getting through the grill to the
radiator! lol!
On Wed, Aug 11, 2010 at 8:27 AM, Thomas Phipps <tph1pp5@yahoo.com> wrote:
>
>
> On your comment about the "twin' antennas that you see mounted on the
> mirrors of lots of big rigs and want-to-be big rigs. Without a proper
> phasing harness connecting the antennas to the radio, they are just for
> show. It is very difficult to get 2 antennas in that frequency range far
> enough from each other on a vehicle's legal width footprint. Measuring from
> the base of each antenna and comparing it to the desired spacing would
> indicate that the vehicle's max width of 8 ft, would not met the distance
> requirements for proper phasing of twin verticals antennas. (1/4 wave
> length)(about 9'+ at 27 MHz)). If the antennas are not properly phased and
> the correct distance apart, they will work against each other. This is
> physics. Excellent article at
> http://www.signalengineering.com/ultimate/co_phasing.html
> However, it should be noted that two twin vertical antennas, phased
> properly, would direct most of the antenna's RF power to the front and rear
> of the vehicle (assuming mirror mounts) and add the equivalent of 3db gain
> for the over-all array.
> My GMC has two matching vertical antennas, but they are connected to two
> different radios and do not interfere with each other. Sometimes 2 or more
> antennas indicate 2 or more radios. Now, where will I install the HF
> antenna? Looking at rear of the vehicle, mounted on the trailer hitch?
> Or, go with the Safari look and mount it on the front bumper?
>
> Tom Phipps, KA4CSG
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: CB Antenna With Best Ground Plane [message #95377 is a reply to message #95210] |
Wed, 11 August 2010 18:29 |
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Roof mounted antennas on the rear corner of a coach will radiate most power forward and peak towards the opposite front corner. Antennas mounted on the front corner will radiate best to the rear opposite corner.
So, are you an optimist or pessimist?
(Long distance communication with a CB is best accomplished with a cellphone!)
John
| philipswanson wrote on Tue, 10 August 2010 08:08 |
I am looking for the best CB antenna for our coaches with a good ground plane. With all the aluminum and fiberglass on the roof, getting a good ground plane is a real challenge. My CB radio is powerful but the limiting factor is definitly the antenna.
Thanks, Phil Swanson
|
John Ruff
Chandler, AZ
1975 Eleganza
WA3RIG
If I use ZDDP in a new car - will the tappets go flat?
[Updated on: Wed, 11 August 2010 18:31] Report message to a moderator |
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