I'm putting a CB in my F-150 and I've hit a snag. I installed the antenna system, a 3' glass base loaded with the correct stud mount,nylon bushing,washers,RG58U coax on a stainless flat mount on the mirror bracket.
I pre tested for shorts and open circuits with an ohmeter, the mount is well grounded, and I'm getting a full 12+ volts to the radio. I hooked up the radio to my SWR meter and I'm getting no SWR reading. So, I hooked up another radio of mine and it pegging the SWRmeter on ch. 1,19 +40. So I'm wondering if the first radio has a blown output transister, and the 2nd radio is that mismatched to the antenna (with a really high SWR). Also even with the volume turned up while checking the SWR, both radios had next to no volume.
Thanks for any advice anybody can give.

 

Are you POSITIVE that the antenna has a proper ground? The mirrors ARE metal where you have the clamps? Put radio in another vehicle that has a working system in it to see what you get. Could you adjust the SWR's down using the 2nd radio?

OHM out your antenna by ckecking for a short between truck frame and the metal clamp where it attachs to the mirror. You SHOULD get 0 ohms (short). If you don't, you don't have a good ground for antenna and you COULD blow the final in the transmitter.

 

Thanks for the reply , yes I'm sure that the antenna mount is grounded to the chassis ground. No, I didn't try to lower the SWR on the 2nd radio yet. I was leary of cutting the antenna when I wasn't sure of the cause of the high SWR,(because neither radio had hardly any volume when I turned them on.

 

So is it the 'receive' signal or the 'transmit' signal you are worried about? I haven't used CB for over a year now, but I have heard (from another poster) that the 'skip' (probagation)we're used to hearing on most all channels is gone, hence it's very quiet on the air right now. You CAN hear locals in there can't you? If you listen to someone elses CB, is it too, quiet?

What was the SWR on that 2nd radio? 3-1, 4-1 or higher? Of course, 1-1 is the best you can do (but none will ever get), anything less than 2-1 is fine for a 5watt CB. If you are using an amplifer, you want to get it as low as you can. Attempt it on or near the channel you use the most - average it out and check SWR in the middle of all the channels...say channel 20. Only cut about 1/4 inch at a time. You don't have to bottom out the stub in the mount....the mount should give you about a 1/2 to an inch of play, so if you DO cut of a 1/4 in too much, you can still make the antenna longer using that extra play....In an earlier life, I had my own CB Sales and Service....

 

Bud , On the 1st CB I didn't get any SWR reading , and on the 2nd CB the SWR reading was all the way in the red 4.1 on all channels. Thanks again for the info, I'll try trimming the antenna 1/4" at a time to see if I can get the SWR lower. Also, what would be the most likely cause for the first CB having no SWR reading ? I'm pretty sure evereything else is right- Mount grounded, coaxial good, full 12 V to radio ,etc. Thanks, Scott

 

As I understand it, the radio and the antenna must have a good ground. The ground on the antenna is to ground the wires shielding to reject bleed over/noise from the cable. The radio's ground connects to the antenna through the body and acts as the ground plain for sending and receiving. Which is why a radio receives with a high swr antenna connection, but barely transmits. So I would suspect the problem is the ground connection between your mirror and the body or the Radio and the body. Because your mirror mounted, I would suspect a higher SWR to occur. The wave will only have so many degrees of ground plane to build a good wave.

 

The first radio with the no SWR at all probably has a bad transmit circuit...is it new? If new, return for exchange. If not new, unless it's an expensive radio, junk it. You can buy new CB's cheaper than doing repair, usually.

When starting to check SWR on 2nd radio, if you cut more than once and do NOT see it getting better, STOP! Something else is still wrong. Try both radios in a friends car that has a working system. Or take both to a shop so they can test them.... a quick test to check transmit is to solder a short piece of coax to a #47 light bulb. Center conductor to the filiment, shield to case of bulb. Press the mic and lamp should glow. Talk into mic and the lamp should flicker. If it does, you know that the radio transmits and if lamp flickers when you talk, you know the mic is good. I've used this to actually converse with friends up to 1/2 mile! Depends on your height - lower you are, shorter the distance you can talk. You can receive strong signals too. Open squelch all the way, increase volume and RF if you have it. Let me know how you make out. Oh yeah, don't forget to use a PL259 on your test bulb setup...ya gotta plug that end into radio!!! LOL.

 

Hi Bud, sorry I haven't got back to you sooner, I worked on my log truck most all of Sat. and Sun. I'll try to look at my radio this afternoon. I noticed one other thing, when I was checking for continuity and shorts or open circuits I saw that I didn't have continuity between the radio's case and the trucks ground, (1st radio). I knew the radio's mount bracket wasn't grounded but I figured the ground from the power lead would be ground for the radio chassis as well. Then I remembered that years ago the radio's came with a set of large rubber washers that went bettween the radio mount and the radio on the mounting screws. So maybe the ground or lack of on the radio's case is irrelevant.

 

Not really relevant, as when you connect the antenna, the shell of the PL259 will ground it - provided the antenna is grounded! And, if the radio turns on -the lamps light - the radio is grounded!

 

Chassis (DC) ground and RF ground are two different issues. Are the antennas on METAL mirror brackets? NO GOOD if mounted on plastic.

Also...

SWR doesn't always tell the whole story. There is the antrenna efficiency to deal with.
I can obtain a 1.1:1 swr into a "dummy" load which is a 50 ohm 1kw resistor and not be able to get a signal 25ft from the source.

See www.k0bg.com for info. It's for Ham radio installs BUT CB falls into the HF section.

Bob