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SWR and Grounding CB Toolbox Installation

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freeflpatriot

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Dec 23, 2013
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Hi, this is my first post. Read the forum a lot and learned a lot from everyone, thanks.

I installed a Galaxy 959 in my F-150 to a 4 foot Roadpro antenna on the aluminum toolbox. Mounted the bracket on the drivers side back of the toolbox. Ran the coax through the access hole in the bed into the cab.

For grounding I tried two different things. First I ran a ground wire from one of the mounting brackets bolts to the underside of the bed lip where the toolbox is secured by bolts (there's a plastic liner on the bed rail). About 6 inches of wire. I tried to sand the paint where it is secured to the bolt, didn't remove much paint.

Secondly I tried running a much longer wire from the bracket through the access hole the coax went through out to the frame. I secure the ground wire to where one of the fender braces connects to the frame. So the brace bolt is holding the wire against the frame. But I've read you want the ground wire as short as possible.

Here's what I got for SWR with the internal meter. (I am going to get an external meter but for the time being want to make sure my usage won't fry the radio):

No ground wire: SWR on CH 1 in the red zone above 3, on CH 40 around 2
Ground wire to bed rail toolbox bolt: around 3:2.1
Ground wire to fender brace at frame: same as other location

I felt like the ground wires were getting me somewhere so I attempted to tune the antenna. I'm seeing now why the 4 foot wire wound antennas are CHEAP. Anyway it'll get me by for the time being. Based on the SWR and my research I decided I needed to lengthen the antenna. So I soldered about 2 inches of braided wire to the tip of the antenna wire. SWR read around 2.5:1.5.

I thought 2 inches was a bit much but I figured it would be easier to remove wire than add more. Didn't seem quite right so I added about 2-2 1/2 inches more to the wire. Now the SWR sits at 2.3:1.

I assume this is acceptable for the time being with the antenna. However I still get the SWR alert LED on the low channels 1 to 18 till the SWR drops off to about 2 or a little lower.

Again my assumption is that the setup is working safely at this point. I have been unable to make any contacts to check how it's sounding because I live in a rural area. I guess all the CB antennas on all these rednecks trucks are for looks, lol.

Yesterday with the high SWR and ground wire to the bed rail I made a clear and loud contact about 5 miles away so I know it works.

My main question is since I have this lower SWR now could the way I've grounded the antenna simply be discharging the rf without getting out through the antenna? At one point in experimenting I just wrapped bare wire around the tip of the antenna wire without solder. I got a 1.5:1 SWR. I couldn't make any contacts but no one was talking at the time anyway. But I've read about great SWR's with ground wire problems and coax problems. I'm pretty sure it's not the coax. But since I know nothing about grounding except what I've learned online either I did it all right and I just need to make a contact to confirm it or I'm loosing all the rf because I screwed something up.

I hope the info I provided can help get some feedback on this.
 

mski

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I have my antenna mounted to my front ladder rack.('07 f150) It's a dual coil Predator 10K. The coils sit above the cab to prevent reflect. I grounded from the antenna mount down to the trucks frame with 8 gauge stranded ground wire. My swr is 1.5.
Maybe run a ground wire from the antenna mount down to the truck frame and McGyver a mount to get the antenna higher above the trucks cab. (or get a longer antenna)
 

Nighthawk424

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Oct 20, 2012
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My advice is to never mount an antenna behind the cab. Always go to the front fender. The cab against the antenna will always cause problems. Just invest in an L bracket and mount it to the front left fender and see how it does there. I am willing to bet your problems will be solved.

Oh and so much easier to run the coax too. Just run it through the firewall. Most trucks even have spare holes pre drilled on the firewall (above your pedals) Usually they have little rubber plugs in em until you want to use them. Put excess coax under hood in engine compartment. Done.

Oh and while your running that coax through the firewall run 2 wires directly to your battery to power the radio. NEVER power the radio from the fuse box or cig lighter.
 
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KB0VWG

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Lyford, Texas
I have had a 3 foot firstik mounted to back side of a toolbox and a 102 inch whip mounted on top center of the toolbox with swr around 1 to 1.5 max swr.
kb0vwg
wqoi992
 

Nighthawk424

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And to add to my last comment. The optimum place for an antenna on a pickup is of course in the center of the roof on the cab. However with these fiberglass type 4 foot antennas that is not practical because of trees etc. So the the left fender is best. You can take the time to pre drill the fender and put some nice sheet metal screws in there nice and tight. Make the antenna perfectly straight and pretty. You will never see the holes when the hood is closed. I stress that it must be straight and tight. As I hate seeing crooked or sloppy antennas. Once you do all that you will never have a problem. Just leave it and forget about it.
 

Nighthawk424

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kb0vwg

kb0vwg - That is great your antenna is working good. I have just heard so many people with the same problem. Both from pickup truck people and especially jeep owners. When they mount the antenna on the back of the jeep on the spare tire bracket. Then they ask why they can't talk a mile up the trail or have bum SWR. So I always just tell everyone to stay clear of these installations. 73'
 
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Back when I had my F150 I had mounted several different antennas of the headache rack, about halfway up, and it's swr was always a 1.8. Then I moved it to the top of the headache rack...1.1. Worked great. Always had the headache rack bolted to the bed (even with the bed rail guards on).

I'm a big fan of NMO mounts now. Both my vehicles also have fender mount brackets on the hood fenders with NMO mounts on them. I prefer on the roof, but sometimes it's just not practical.

Mounting with coils behind the cab I'd just cause for issues on 11m. On higher vhf and uhf frequencies you actually shoot through the cab's glass due to smaller wavelengths.

Sent from my ME173X using Tapatalk
 
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freeflpatriot

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Dec 23, 2013
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Thanks for the replies everyone.

Yea, my truck is an 07 F-150. Ran the power straight to the battery. For me it seemed far easier to go to the battery then try to rig the wires into the fuse box.

After I posted this thread I went back out and made a contact 13 miles away if the guys location was accurate anyway. Hadn't been paying attention to the power output but realized the last owner must have peaked it because I'm putting out around 6 watts. Is this a safe range for the 959? I know SSB can run 12 watts or more with tweaking but I'd rather not fry the radio to get more power.

So I'm pretty confident I got it grounded right now. Both on the frame and under the bed rail at the toolbox gave the same SWR. I tuned the antenna a little bit more and got a 1.5:1 SWR. I was looking for you guys to tell me I didn't screw it up! Kinda hard from the info I gave!

Anyway I ended up mounting the CB under the mirror on the dash. The size of the radio and the available space in the F-150 limits mounting positions. But I kinda like it up on the dash anyway. I pulled the face of the dash off and the stock radio. I was able to run the power and coax up by the gas pedal through the center dash and out a vent to where the radio is mounted. Wasn't very easy but paid off in the end.
 

who_dat

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Back when I had my F150 I had mounted several different antennas of the headache rack, about halfway up, and it's swr was always a 1.8. Then I moved it to the top of the headache rack...1.1. Worked great. Always had the headache rack bolted to the bed (even with the bed rail guards on).
Do you have any pictures of the whip mounted on the headache rack?
 
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Do you have any pictures of the whip mounted on the headache rack?
It's right in line with the light pole but you can make the coils out.




Kinda miss that truck...actually not really. I just miss the fact it had a locker in the rear end and a 5 speed...other than that it spent more time in the shop than it did on the road.
 

prcguy

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A ground wire, especially a long one, running from an isolated antenna mount down to the vehicle chassis is not an RF ground for the antenna. It might show great on an ohmmeter but the antenna will not be happy with it. The antenna wants to see lots of flat metal heading out in different directions away from it and it wants its feedpoint very close to the metal ground plane.Another thing that can happen is the long ground wire going from the antenna base to the chassis can become more of a dipole element with its own resonant quirks.

When a whip is sitting in the middle of a good chunk of sheet metal that is an adequate size for the frequency range, there will be RF currents flowing all over the ground plane surface, but they will be somewhat equal and flowing in opposite directions away from the antenna mount and back toward it for every RF cycle.

These equal and opposite currents cancel radiation, leaving the whip as the only radiator in a properly working ground plane. If you have just one ground radial, or a really long ground wire going to an otherwise OK ground, then the single ground radial or long ground wire can become the other half of a dipole antenna and radiate as much as the whip itself.

If you raise an antenna several feet above a good ground plane and run a single wire down to the ground plane the feedpoint impedance goes up, and one of the symptoms is the antenna will tend to tune better on the upper channels or higher in frequency, but you can never get it to completely match to 50 ohm coax. Mounting an antenna on the top bedrail towards the rear of a truck is similar, there is very little if any metal heading out in different directions and the capacitance between the whip and ground plane will be reduced, raising the feedpoint impedance and you may never be able to get the match reasonable by trimming the whip

In these cases you can fool the antenna with a small capacitor across the feedpoint of the antenna but performance will still be down compared to the same antenna mounted right over lots of flat metal.

Antennas are very complex but otherwise pretty stupid. If you learn just a little bit about them you can always win and whip them into shape every time. Or avoid a situation where the antenna wins and you or your radio looses.
prcguy


I have my antenna mounted to my front ladder rack.('07 f150) It's a dual coil Predator 10K. The coils sit above the cab to prevent reflect. I grounded from the antenna mount down to the trucks frame with 8 gauge stranded ground wire. My swr is 1.5.
Maybe run a ground wire from the antenna mount down to the truck frame and McGyver a mount to get the antenna higher above the trucks cab. (or get a longer antenna)
 

MisterLongwire

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Ok...well I am in a different predicament. I have a 2015 Toyota Tacoma double and ended up buying a REP mount for the siderail of the bed.(driver side rear) The bed is all composite so I ran a 5 inch 8g wire from the mount to a bolt by the tailgate. Sure I get flat SWR all around but I cant tell which direction my signal is going out because it is directional as all can be. Sure I am against mag mounts...scratches....lousey contact. And I really dont want a hole.in my roof..so I am basically stuck!
 
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Ok...well I am in a different predicament. I have a 2015 Toyota Tacoma double and ended up buying a REP mount for the siderail of the bed.(driver side rear) The bed is all composite so I ran a 5 inch 8g wire from the mount to a bolt by the tailgate. Sure I get flat SWR all around but I cant tell which direction my signal is going out because it is directional as all can be. Sure I am against mag mounts...scratches....lousey contact. And I really dont want a hole.in my roof..so I am basically stuck!
Fender mount.
 

prcguy

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Composite bed? You mean all composite or a composite bed liner with the original bed underneath?

I have a Toyota Tundra and mounted a Tarheel 100HP antenna to the drivers side bed wall about 8 or 9 inches behind the cab. This antenna takes a special mount so the base of the antenna is a few inches above the bed and the lower part of the antenna runs parallel to the bed wall only a few inches away and also parallel to the cab about 8 or 9 inches away.

This antenna obviously tunes more than CB but on 10M the SWR is just about perfect and it seems to be fairly omni directional. On 10m this antenna is a full 1/4 wavelength and could be compared directly to a 9ft whip.

More than likely my antenna is using much of the truck bed as a ground plane and the close proximity to the side wall and cab are not causing me any problems. The same antenna on the top of the bed rail would probably have an inadequate ground plane and related problems.
prcguy


Ok...well I am in a different predicament. I have a 2015 Toyota Tacoma double and ended up buying a REP mount for the siderail of the bed.(driver side rear) The bed is all composite so I ran a 5 inch 8g wire from the mount to a bolt by the tailgate. Sure I get flat SWR all around but I cant tell which direction my signal is going out because it is directional as all can be. Sure I am against mag mounts...scratches....lousey contact. And I really dont want a hole.in my roof..so I am basically stuck!
 

MisterLongwire

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Yup...bed is all composite....side fender walls and small section of.front is steel. According to REP since I am on 11mtrs horizontal wires across.bed wouldnt be necessary. I did throw.a.5 inch 8g.wire to rear bolt from the mount....so I do have grou d but really no.groundplane. i am baffled
 

JayMojave

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Dec 13, 2007
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Mojave Ca
Hello ML: That's something that I had no knowledge about was the composite Beds being manufactured. I learned something here.

Fiberglass small boats use to install a 96 or 102 inch fiberglass whip antenna on the center of the fiberglass bow. Then for a counterpoise 3 or 4 each, 9 Feet of copper wires was installed underneath the bow's fiberglass surface, Which worked quite well. The Counterpoise wires were not installed straight out as there wasn't enough room in bow area. They were run straight out and then bent to the boats contour going aft or forward.

Suggest you perform a before and after directional test ( driving in circles monitoring local stations watching the S-Meter ) in an empty parking lot or vacant area, with the existing antenna installation. And then add say two 9 foot wires, one going forward under the bed rail, and one in the aft direction going just forward of the bed tail gate. Wires can be temporarily installed with duck tape. The wire shown in the photo looks like 14 gauge house wire, which would work just great. Cheap and easy. Please let us know how you make out there.

Jay in the Great Mojave Desert
 

jassing

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It seems ANY car is going to be somewhat directional; moving the antenna around can help.
I seem to recall reading from (more than 1) source that ground straps needed to be straps no wires to effectively ground RF. I don't thinking proper RF grounding (not same as electrical grounding) will help with directionality tho...

Try moving the antenna around to see if you get less directionality on your field meter...
 

wyShack

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a rule of thumb is that the antenna radiation pattern will favor the direction of most metal. Even a full quarter wave on the left rear will show a lobe to the passenger side and front. Any mobile installation is going to have trade offs.
 
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