More fun with SWR

[scottjk]

nwoods - would it be possible to run a ground wire instead? I had thought about doing something similar - I mean, how often do you get to you use your Dremel tool on your Jeep body? - but my buddy talked me out of it.

I just ran a 10 gauge ground wire from the antenna mount to the frame. My only initial mistake was using too small a wire (14 gauge) for the amount of power I was putting into the antenna. The factory recommended 12 gauge, I went with 10.

Anyway - don't know what your set-up looks like so perhaps a ground wire is pointless - or perhaps it can't be hidden well and aesthetics are an issue.

Just a thought...

[Old Fart]

The "coax must be 18' long" is a myth, what little effect a "resonant length" of feedline has is pretty much lost at 27 mHz (and to actually work would need to account for the Velocity Factor of the feedline - which is different for RG8, RG58, RG8X, etc) Then you'd really need to factor in loss from your connector, etc....

The "correct length" of the feedline in pretty much any application is simple to calculate - whatever it takes to get from the transmitter to the antenna.

[scottjk]

Update...

Well - due to work schedule and being required to travel a bit, this has taken me two months.

I am keeping a positive mental attitude but this has got to be the biggest pain in the ass that I have had to deal with recently.

Right now I think I am stuck with a ground plane antenna that I cannot place to take advantage of the Jeep's metal.

If I put the antenna on the front, hood channel mount - then the windshield and my Kargo Master cargo rack crush the SWR. If I put the antenna on the rack itself, then it seems that the antenna is so high it cannot make use of the vehicle's ground plane and that the rack is insufficient to act as a ground plane.

The reason I think this is because I got GREAT readings on my SWR meter when I first put the antenna on the rack and temporarily secured it with a metal C clamp. When I removed the clamp, and actually mounted the antenna with the mounting hardware - the SWR went high again. You guessed it - when I returned the clamp, the SWR went back down in the 1.0 - 1.5 range.

So - I am inclined to think that the antenna actually on the rack fails due to lack of a ground plane.

This leaves a couple of options - which I'm not sure about.

I have been avoiding the rear of the vehicle because; (a) the cargo rack base mounts there and it complicates the easy "tail light mount"; (b) having to find a good ground point on the frame.

The other potential complication is the concern that the vertical rise of the cargo rack base will result in the same problems I was having up front.

I suppose taking off the cargo rack would solve these problems - but I need the cargo rack more than I need the CB radio.

Anyway - about ready to throw in the towel and see if I can't find a professional to make the call as to whether this is ever going to work or not.

[Kodiak Spirit]

sounds like you just need to add a few ground straps, or wires to give your mount a good ground. just because the rack doesn't supply it right now doesn't mean you can't make it right. I think the rack would be a good mount, but you need to run a lil' grounding wire.

[bruce p]

I finally? resolved my similar issues with a Wilson no ground plane antenna.

[The-Hurricane]

i agree with kodiak just run some black copper wire screwed to your frame up the side of your rack mounted with black zip ties, all the way to the antenna. should fix the grounding problem.

[avjeepfreek]

Ground

sounds like you just need to add a few ground straps, or wires to give your mount a good ground. just because the rack doesn't supply it right now doesn't mean you can't make it right. I think the rack would be a good mount, but you need to run a lil' grounding wire.

Took your advise and did this! I also moved the antenna grounding wire to the frame and my CB sounds better that ever now!

My set-up: Cobra 29 LTD Classic, 18 ft Coax, Wilson 4' Flexible Antenna mounted with a quick disconnect to the Rock Hard Jerry can rack on the back of the Jeep.

What a difference, The built in SWR Meter works perfectly now and I also hooked it up to the Radio Shack Meter I have and they both match!

Thank's for the great info, Scott

[Lumpy Grits]

Hi, one other thing, when checking SWR be out in a open dirt field somewhere and make sure you have no other metal(except your jeep) with in 100' for a true reading. Also turn off c-phone and your other radio and have the engine running for any I.F. and OHMs issues.
Respectfully,
LG