Cb Swr Setting Problem

[baj25]

I tried to do the SWR on my CB last night, but couldn’t get the needle to reach the set/cal position on the scale. (the calibration bit before you actually measure SWR, with switch in FWD position). I think this indicates that not enough power is coming from the CB (?) but I did have the SWR meter resting on the side of the CB- could that effect the reading? Any other ideas? It’s my first time with CB, but I’m confident that all is connected correctly and the cables are OK. TIA, Brian

[Guest peter2b2002]

i found instructions on www.offroaders.com do a search on there it tells you how do do everything.

pete2b

[Guest Guy]

Hi Brian,

 

Check that all the connections are fine and that the patch lead is okay. If the SWR (Standing Wave Ratio) is a really long way out then the forward switch pos might not go all the way over. When you put it on REF you'll get a good idea if it's too high i.e. if it goes up to nearly the same as the forward then the SWR is a long way out (does that make sense )

 

Also, check that the CB isn't on -10dB (do they still have this switch?) Try it on the top and bottom channels as well.

[Guest hypermick]

Brian,. make sure that the aerial's ground is good as well,. (assuming the aerial base is fixed and not a mag mount). Also check the quality of the copper earth shield on the patch lead,. If it looks like a Chinese Crested dogs scalp hair, chuck it away, you need decent shield on the patch lead since its carrying full signal potential into the meter from the output of the PA, any leaks will cause the problems youve got. Also meter the plugs out to ensure youve no dead shorts on any of them !

 

Mick.

[miikae]

Antenna tuning , Setting the SWR

 

All CB antennas are tunable. Antennas that have an easy, often mechanical, tuning device are referred to as a "tunable antenna". Accordingly, lots of people think the other antennas are not tunable and so they make no attempt to have the antenna tuned. This is a critical mistake.

 

Wire-wound antennas without mechanical tuners, that test electrically long (higher SWR on ch 40), can be tuned by removing wire from the top. Remove the antenna cap, remove one wrap of wire and cut it off. Recheck the SWR again. As long as the SWR is higher on channel 40 continue to cut. Do not cut more than one wrap at a time. If SWR testing indicates the antenna is electrically short (higher SWR on ch 1), the coils at the top of the antenna can be separated and spaced further apart or accessories that increase the physical length of the antennas (springs, quick disconnects) can be added.

 

Solid fiberglass antennas (straight or helical wire impregnated in fiberglass resins) that are electrically too long (higher SWR on ch 40) can be cut shorter with a hacksaw or grinder. Cut only 1/4 of on inch at the most at one time. If the SWR test on one of these antennas indicates that it is electrically short (higher SWR on ch 1), the addition of a spring or quick disconnect (or both) is the only way to correct for the short condition.

 

Base loaded antennas with wire whips have a set screw (or two) just below the area that the whip is inserted into the loading coil. By loosening up the set screw(s) you are able to slide the whip up or down as required. If the SWR is higher on ch 40 slide the whip down, If the SWR is higher on ch 1 raise the whip.

 

If you where closer i would do it for you

Hope you sort it out ok

 

Mike (G0SWW)

[Big Jim]

you also need to be aware that the "whip" that you fit, is only part of the over-all "aeriel" the body of the car is the "ground plane" and has an effect of SWR 'ing in. and final transmission power.

Location and physical length of the whip antenna that you buy will play a big part in if it will SWR at all.

 

First and foremost, a small "bottom loaded" antenna will NEVER SWR on a Robin Hood. FULL STOP! (unless maybe you put it right in front of the windscreen, or on the top of the roll-bar)

 

The best one to get is the old faithfull DV27. this is fibreglass, with top loading, and an adjustable piece in the top for SWR'ing.

 

Now mounting it........ The base of the mounting, MUST be earthed to the chassis, so it's no good putting it into fibreglass.

Ideally, it should be mounted on the top face of the vehicle, with a Robin Hood, that's difficult. So make a bracket to mount it on.

I have mine (MK3 Hood) on a bracket coming off the roll-over bar mounts. (see photo) But on a 2B, it would again be difficult as there isn't any bolts in this area. (with a bit of luck, Mitch may post a piccy of his)

 

We've found that with a bracket made to come from the bottom of the rear panel, with the DV27, works OK. this means that you've not got any holes in any places that show.

 

Remember not to have it over the fuel filler.

[baj25]

Thanks for the replies. I was away last week so didn't get them until today. Problem now sorted- it was a dicky switch in the SWR meter. Antenna is a DV27 mounted on a bracket from the spare wheel hoop, behind the number plate, which is nice and inconspicuous. Just need nice weather and a NW run out to test it out!

Thanks again, Brian