RadioReference on Facebook   RadioReference on Twitter   RadioReference Blog
 

Go Back   The RadioReference.com Forums > Commercial, Professional Radio and Personal Radio > CB Radio Forum


CB Radio Forum - Discussions regarding Citizens Band Radio (CB)

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1 (permalink)  
Old 10-10-2017, 8:59 PM
Newbie
   
Join Date: Oct 2017
Posts: 2
Default Antenna on my headache rack

I would like to mount a CB in my work truck. I realize that center of the roof would be the best

HOWEVER

I dont want to drill a hole AND I really dont like magnetic mounts

SO

I would like to install an Antenna on my headache rack. Looks wise one side or the other would be better, but would I gain anything by having it in the center. How much will mounting it on my headache rack affect the ground plane and reception / transmitting?

Thank you very much for your knowledge and expertise. Thanks
Reply With Quote
Sponsored links
  #2 (permalink)  
Old 10-11-2017, 9:52 AM
Member
  Amateur Radio Operator
Amateur Radio
 
Join Date: Mar 2014
Posts: 822
Default

As you're surely aware, a good RF ground is a necessity for a proper antenna installation. An RF ground is not the same a an electrical ground. As such, understand that a wire connecting your antenna ground to the auto body or chassis won't work as an RF ground.

There are ways around this but they come at a cost, usually in reduced performance. (Sometimes we don't have a choice so we make do). For your application I would suggest a 1/2 wave or "no ground plane" CB antenna. You'll probably recognize these as the CB antennas that are attached to big rig mirrors or sometimes on the sides of the cabs or sleepers. My CB days are long behind me so I don't know what is currently on the market. I believe Firestik manufactures some that are fairly popular.

If you opt to go this route, The location on your headache rack probably won't make a huge difference whether it is in the middle or off to one side. However, do your best to get it as high as possible. You want to keep the sides of the antenna free of an obstructions (e.g. other metal such as the cab) which could affect antenna performance.
Reply With Quote
  #3 (permalink)  
Old 10-11-2017, 10:29 AM
jonwienke's Avatar
Member
  Premium Subscriber
Premium Subscriber
 
Join Date: Jul 2014
Posts: 4,294
Default

Center of the rack will give the best RF performance. But mounting to the center of the cab roof will be significantly better.
__________________
Uniden scanner internal GPS installations--making mobile scanning work the way it always should have.
Reply With Quote
  #4 (permalink)  
Old 10-11-2017, 10:39 AM
mmckenna's Avatar
Member
   
Join Date: Jul 2005
Location: WTVLCA01DS0
Posts: 7,487
Default

Quote:
Originally Posted by uscarry45 View Post
I would like to install an Antenna on my headache rack. Looks wise one side or the other would be better, but would I gain anything by having it in the center. How much will mounting it on my headache rack affect the ground plane and reception / transmitting?
I had a truck with a headache rack back in the 1980's. Did an install like that, scanner antenna on one side, CB on the other. It did work, but SWR was always off and performance was mediocre at best. Good enough for a mile or two.

Don't expect this to be an outstanding performer, given the limitations you've chosen.
Reply With Quote
  #5 (permalink)  
Old 10-11-2017, 5:34 PM
Member
   
Join Date: Jun 2006
Posts: 6,019
Default

When you raise an antenna feedpoint above the ground plane the impedance goes up causing matching problems. The rack is itself is really inadequate for a ground plane leaving the vehicle roof several inches below as the ground plane = matching problems.
prcguy
Reply With Quote
Sponsored links
  #6 (permalink)  
Old 10-12-2017, 3:07 AM
Member
   
Join Date: Nov 2016
Location: Upper Mojave,CA/NV
Posts: 164
Default

I've considered doing the same thing with cophased Firestik NGP's (No Ground Plane) like the Firefly, but wasn't willing to spend the money on something that may or may not work.

Keep me posted if you do it and how it works out for you.
Reply With Quote
  #7 (permalink)  
Old 10-12-2017, 9:48 AM
mmckenna's Avatar
Member
   
Join Date: Jul 2005
Location: WTVLCA01DS0
Posts: 7,487
Default

Quote:
Originally Posted by swen_out_west View Post
I've considered doing the same thing with cophased Firestik NGP's (No Ground Plane) like the Firefly, but wasn't willing to spend the money on something that may or may not work.

Keep me posted if you do it and how it works out for you.
Unless you can get the two antennas about 108" (1/4 wavelength) apart, it will result in a really funky radiation pattern.

Usually, for those guys that want the dual antenna setups for "looks", the recommendation is to just hook up a single antenna and leave the other one disconnected. Unless you have your own Class 8 tractor, you won't get the full benefit.
Reply With Quote
  #8 (permalink)  
Old 10-12-2017, 10:18 AM
Chronic's Avatar
Member
   
Join Date: Nov 2004
Posts: 186
Default

Make a bracket that attaches to the headache rack that comes down and extends out over the roof of the cab and make the bracket so the base of the antenna is as close to the roof of the cab as possible
Reply With Quote
  #9 (permalink)  
Old 10-12-2017, 3:17 PM
Member
   
Join Date: Jun 2006
Posts: 6,019
Default

That will get you half way there and the ground side of the coax should attach to the vehicle roof near the base of the antenna, which is not practical.

What you can do instead is capacitor couple the ground which can work the same as a direct connection and I do this for mag mount HF antennas. For frequencies much lower than CB I got an 8 1/2 X 11" thin flexible magnet like you find on the back of refrigerator magnets. One side had peel and stick glue and I glued to it an 8 1/2 X 11" thin copper sheet about 5 thousands thick, then soldered a very short braid to the copper with a lug that attaches to my mag mount.

In testing my various HF antennas with just a large 4 magnet mount, they will not match very well and the match changes all over the place when you touch the coax, etc. With the large capacitor coupled ground attached the match is the same as when I use a permanent grounded mount and its very stable.

For a permanent mount antenna on a bracket above the roof you might be able to use a couple of wide strips of conductive tape, copper or aluminum, with one side attached to the ground of the antenna bracket and have a foot or so of the tape stuck to the roof heading away from the mount. A few lengths of tape running in different directions would be better. This will capacitor couple the ground some and can be removed without hurting the paint.

The key with any of my suggestions is having the feedpoint or base of the antenna as close as you can get to the roof.
prcguy

For CB frequencies you could get away with a much smaller magnet and copper sheet but I would consider about 6in square about the smallest I would try.

Quote:
Originally Posted by Chronic View Post
Make a bracket that attaches to the headache rack that comes down and extends out over the roof of the cab and make the bracket so the base of the antenna is as close to the roof of the cab as possible
Reply With Quote
  #10 (permalink)  
Old 10-12-2017, 4:12 PM
Member
  Amateur Radio Operator
Amateur Radio
 
Join Date: Mar 2014
Posts: 822
Default

Quote:
Originally Posted by prcguy View Post
That will get you half way there and the ground side of the coax should attach to the vehicle roof near the base of the antenna, which is not practical.

What you can do instead is capacitor couple the ground which can work the same as a direct connection and I do this for mag mount HF antennas. For frequencies much lower than CB I got an 8 1/2 X 11" thin flexible magnet like you find on the back of refrigerator magnets. One side had peel and stick glue and I glued to it an 8 1/2 X 11" thin copper sheet about 5 thousands thick, then soldered a very short braid to the copper with a lug that attaches to my mag mount.

In testing my various HF antennas with just a large 4 magnet mount, they will not match very well and the match changes all over the place when you touch the coax, etc. With the large capacitor coupled ground attached the match is the same as when I use a permanent grounded mount and its very stable.

For a permanent mount antenna on a bracket above the roof you might be able to use a couple of wide strips of conductive tape, copper or aluminum, with one side attached to the ground of the antenna bracket and have a foot or so of the tape stuck to the roof heading away from the mount. A few lengths of tape running in different directions would be better. This will capacitor couple the ground some and can be removed without hurting the paint.

The key with any of my suggestions is having the feedpoint or base of the antenna as close as you can get to the roof.
prcguy

For CB frequencies you could get away with a much smaller magnet and copper sheet but I would consider about 6in square about the smallest I would try.
The magnetic sheet is a clever idea. I've never seen it with an adhesive side though. I'll have to look for that. Oh, and I'm glad you pointed out about keeping the feedpoint close to the level of the roof top. When I suggested getting the antenna up high, I was thinking in terms of the keeping the antenna radiator away from the side of the cab. I didn't realize while I was typing that it could be construed as elevating it on a mobile mast.
Reply With Quote
  #11 (permalink)  
Old 10-12-2017, 4:23 PM
Member
   
Join Date: Nov 2016
Location: Upper Mojave,CA/NV
Posts: 164
Default

Quote:
Originally Posted by mmckenna View Post
Unless you can get the two antennas about 108" (1/4 wavelength) apart, it will result in a really funky radiation pattern.

Usually, for those guys that want the dual antenna setups for "looks", the recommendation is to just hook up a single antenna and leave the other one disconnected. Unless you have your own Class 8 tractor, you won't get the full benefit.
Actually that was the plan to use another piece of square tubing and extend the top piece out both sides to 8' giving the antennas approximately 93" of separation. I was always under the impression that the weird stuff happens at less than six and the general rule of thumb is 7 foot minimum separation.

Yes, the ideal world is 108" although some tests have revealed that anything after 102" is irrelevant, but even the big rigs running cophased antennas aren't normally 108". My biggest point isn't for looks, just to test the results. Thus, another reason I haven't done it yet. Why spend that time and money just to see first hand the results.

But to go back to what my real point was, if you were to run the antennas off of the headache bar it would have to be No Ground Plane, honestly the money spent on doing it for mediocre results would be far better spent on a Wilson 5000 mag mount.
Reply With Quote
  #12 (permalink)  
Old 10-12-2017, 5:01 PM
mmckenna's Avatar
Member
   
Join Date: Jul 2005
Location: WTVLCA01DS0
Posts: 7,487
Default

Quote:
Originally Posted by swen_out_west View Post
Actually that was the plan to use another piece of square tubing and extend the top piece out both sides to 8' giving the antennas approximately 93" of separation. I was always under the impression that the weird stuff happens at less than six and the general rule of thumb is 7 foot minimum separation.

Yes, the ideal world is 108" although some tests have revealed that anything after 102" is irrelevant, but even the big rigs running cophased antennas aren't normally 108". My biggest point isn't for looks, just to test the results. Thus, another reason I haven't done it yet. Why spend that time and money just to see first hand the results.
You can certainly space them closer if the skewed pattern is what you are going for. I could understand instances where that might be desirable. The point was, however, that those that don't understand assume that if one is good, two must be better. I've known people that mount co-phased antennas on a small pickup and then wonder why it doesn't work so well. There's some idea that the more money you spend, the better it's going to work. Often that completely ignores the physics of it. Generally, on a full size pickup or smaller, using one antenna is enough. If someone really wants duals, leave one disconnected.

Quote:
Originally Posted by swen_out_west View Post
But to go back to what my real point was, if you were to run the antennas off of the headache bar it would have to be No Ground Plane, honestly the money spent on doing it for mediocre results would be far better spent on a Wilson 5000 mag mount.
It does get to the point where it's easier to just do the NMO mount and get it over with. Chasing compromise mounts and trying to get them to behave well can take a lot of work. By the time the headache rack has been modified to mount the antenna, it's probably going to look like a hack job and make a lot of noise when driving at highway speed.
Reply With Quote
  #13 (permalink)  
Old 10-13-2017, 3:04 PM
cmdrwill's Avatar
Member
   
Join Date: Mar 2005
Location: So Cali
Posts: 2,573
Default

Quote:
Originally Posted by mmckenna View Post

It does get to the point where it's easier to just do the NMO mount and get it over with. .
Exactly. On the roof of your truck with NMO-27 or a Comtelco A1801AH-27 antenna.
Reply With Quote
  #14 (permalink)  
Old 10-13-2017, 10:45 PM
mmckenna's Avatar
Member
   
Join Date: Jul 2005
Location: WTVLCA01DS0
Posts: 7,487
Default

Quote:
Originally Posted by cmdrwill View Post
Exactly. On the roof of your truck with NMO-27 or a Comtelco A1801AH-27 antenna.
Yeah, hard to beat and they really work well.

I understand that some are reluctant to drill holes in a nice truck. It takes some guts the first few times. Not for everyone, but the OP could get a shop to do it for him/her.

I've got my new work truck (2017 F-350) sitting in my driveway waiting for antennas/radios to be installed tomorrow. Easier when it's work truck, that's for sure.
Reply With Quote
  #15 (permalink)  
Old 10-14-2017, 3:36 AM
Member
   
Join Date: Jan 2016
Posts: 77
Default

However, if someone else owns the work truck, a new hole in the roof may not be welcomed.
Reply With Quote
  #16 (permalink)  
Old 10-14-2017, 6:23 AM
jonwienke's Avatar
Member
  Premium Subscriber
Premium Subscriber
 
Join Date: Jul 2014
Posts: 4,294
Default

Unlikely if the radio is required for the job.
__________________
Uniden scanner internal GPS installations--making mobile scanning work the way it always should have.
Reply With Quote
  #17 (permalink)  
Old 10-14-2017, 1:42 PM
Member
   
Join Date: Feb 2009
Location: Pittsburgh, Pa.
Posts: 303
Default

you would need to use a 1\2 wave design antenna.

Only a 1\2 wavelength antenna will work on installations with less than 1\4 wavelength ground plane in all directions
Reply With Quote
  #18 (permalink)  
Old 10-15-2017, 7:22 AM
Member
   
Join Date: Dec 2007
Location: Mojave Ca
Posts: 638
Default

Hello All: I have a good friend that lives about 22 miles from me and he put a 102 inch whip antenna on his work rack on his pick up truck, and as mentioned we didn't like its poor performance. The work rack was removed and the antenna mounted on the top center of the cap of the truck. A improved performance was measured.

Again as mentioned the lack of a metal ground plane was blamed. We were going to attach a couple of pieces of sheet metal from Home Depot that are 2 feet square on to the rack with L brackets and give that a try. Say with two or three of these 2 Ft Square sheet metal pieces would give us the ground plane just like a car of small truck, that work quit well. The antenna can be mounted off to the side or in the center, it makes little insignificant difference.

Gee whiz, Motex, if that was true none of the mobile installations would work. Is that in a book some were?

Jay in the Great Mojave Desert
Reply With Quote
  #19 (permalink)  
Old 10-15-2017, 5:36 PM
Newbie
   
Join Date: Oct 2017
Posts: 2
Default

Thanks for all the information. How do semi trucks do it with mirror mounted antennas? I would think the same principles would apply to my headache rack?
Reply With Quote
  #20 (permalink)  
Old 10-15-2017, 8:45 PM
n9mxq's Avatar
Member
  Audio Feed Provider
Audio Feed Provider
Amateur Radio Operator
Amateur Radio
 
Join Date: Dec 2005
Location: Belvidere IL
Posts: 1,411
Default

The mirror mounts (tubes) usually have a ground strap to the body which in turn is grounded to everything else. I've run into a couple that the straps have corroded away causing issues with tx/rx and need to be replaced.

Sent from my SM-G950U using Tapatalk
__________________
Gene
Is there such a thing as too many radios??
Transceivers, receivers, and SDR! Oh My!
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 7:37 AM.


Powered by vBulletin® Version 3.8.2
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
All information here is Copyright 2012 by RadioReference.com LLC and Lindsay C. Blanton III.Ad Management by RedTyger
Copyright 2015 by RadioReference.com LLC Privacy Policy  |  Terms and Conditions