CB mobile antenna on car high SWR

[StormShadow]

I've got a mate who wants to get back into CB, he is planing on having a mobile setup in his car, its an older car with a metal body mag mount is good, good coax and the CB whip is one of those modulator types. Can not get the SWR down enough to a safe level for TX. I'm guessing undoing the grub screw and adjusting the whip length slightly might help but if not then I don't know.

I'm just wondering if a tuner is required for mobile setups?

[Antoni]

If you need a tuner on a set-up like that something is wrong. It's a simple set-up, check security of plugs and look for short circuits with a meter.

If you take the antenna off the mag mount there should be no short-circuit across the plug. If you put a short-circuit on the mag-mount - either across the SO-239 socket or from the central stud to the mag-mount metalwork you should see a short circuit at the plug.

Bear in mind that any fault might come and go with gentle wiggling (first) or more agressive wiggling (last).

For there to be any mileage in adjusting the antenna's tuning, there would have to be a better SWR on either Ch 1 or Ch 40. If there is a difference, put your hand close to the antenna while testing. If the SWR improves lengthen it. If it gets worse shorten it.

Or none of the above.

[StormShadow]

I did all that and everything test good I even test each end of the whip for continuity, I think the whip is either too short or too long. Tested with a 9ft tank whip and SWR was fine but you can't drive with one of those on the roof when putting the mobile whip back on SWR is high so clearly an issue with the mobile whip.

[scanhermit]

Is it a long modulator style twig or one of those miniature ones like the Thunderpole Atom? I hear the shorter ones are harder to SWR.

If a long one, it may not have been set up properly in the factory and may need adjusting via the grub screws or (whisper it) cutting.

I've got a PNI ML145 that is ok on EU1 but 1:3 on UK 40. Shortening via the grub screws hasn't worked so it looks like I'll have to cut the whip. I've just been too chicken to do it yet.

[StormShadow]

Is it a long modulator style twig or one of those miniature ones like the Thunderpole Atom? I hear the shorter ones are harder to SWR.

If a long one, it may not have been set up properly in the factory and may need adjusting via the grub screws or (whisper it) cutting.

I've got a PNI ML145 that is ok on EU1 but 1:3 on UK 40. Shortening via the grub screws hasn't worked so it looks like I'll have to cut the whip. I've just been too chicken to do it yet.

I would need to trim the whip or add the inside of a junction block to it if it needed slightly more length. I wouldn't attempt to trim it without an analyzer because SWR doesn't always give you accuracy.

[Mudslinger]

Is it a long modulator style twig or one of those miniature ones like the Thunderpole Atom? I hear the shorter ones are harder to SWR.

A few months back I bought the Moonraker version of the Thunderpole Atom.

It was impossible to SWR on my car, I even fitted a different whip which was lying around so that I could shorten it. I tried to send it back but they were not having any, so don't buy one of those.

Moonraker stuff was always rubbish and it seems that nothing has changed.

[scanhermit]

A few months back I bought the Moonraker version of the Thunderpole Atom.

I remember that saga! I was rooting for it to work.

Moonraker stuff was always rubbish and it seems that nothing has changed.

Duly noted!

The Thunderpole 2ft superflexi apparently tunes well even on difficult setups.

[scanhermit]

I would need to trim the whip or add the inside of a junction block to it if it needed slightly more length. I wouldn't attempt to trim it without an analyzer because SWR doesn't always give you accuracy.

I read somewhere that an analyser tells you what the antenna should do but an SWR meter tells you what it's actually doing. I don't know the truth of this so am open to being educated.

[scanhermit]

Latest Thunderpole mini allegedly pre-SWR'd:

https://www.thunderpole.co.uk/small-cb- ... uttle.html

Nice fat coil!

[StormShadow]

I would need to trim the whip or add the inside of a junction block to it if it needed slightly more length. I wouldn't attempt to trim it without an analyzer because SWR doesn't always give you accuracy.

I read somewhere that an analyser tells you what the antenna should do but an SWR meter tells you what it's actually doing. I don't know the truth of this so am open to being educated.

SWR will give you an idea by telling you its reflective power coming back, there are so many other factors involved and an antenna that gives you a low SWR doesn't always mean it performing well, or as it should perform. An analyzer will tell you so much more.

[StormShadow]

Is it a long modulator style twig or one of those miniature ones like the Thunderpole Atom? I hear the shorter ones are harder to SWR.

A few months back I bought the Moonraker version of the Thunderpole Atom.

It was impossible to SWR on my car, I even fitted a different whip which was lying around so that I could shorten it. I tried to send it back but they were not having any, so don't buy one of those.

Moonraker stuff was always rubbish and it seems that nothing has changed.

Your right Moonraker stuff isn't very good although I'm sure many will swear by it and say Moonraker is a top brand. My experience differs. A good example of this was when I bought a Moonraker antenna and the coax braid was shorted to the center which it wasn't supposed to be and the coax was also of poor quality. Easily fixed with some better coax and better solder joints.

[scanhermit]

I would need to trim the whip or add the inside of a junction block to it if it needed slightly more length. I wouldn't attempt to trim it without an analyzer because SWR doesn't always give you accuracy.

I read somewhere that an analyser tells you what the antenna should do but an SWR meter tells you what it's actually doing. I don't know the truth of this so am open to being educated.

SWR will give you an idea by telling you its reflective power coming back, there are so many other factors involved and an antenna that gives you a low SWR doesn't always mean it performing well, or as it should perform. An analyzer will tell you so much more.

Ah, thanks. An analyser must be essential for building ones own antennas but I didn't think of using one for commercially manufactured twigs.