What is wrong with my UHF & how do I fix it?

[Cuppa]

I bought the Uniden UHF a couple of years back & have rarely had need to use it. On my recent drive up to the Murray however I wanted to use it to communicate with Mudnut whom I met up with en route. This showed up two problems, one of which I hope is now fixed - noise when driving over uneven road surfaces/bumps. I think I had insufficient flex in the coax cable where it entered the base of the antenna & it was pulling tight.

However the second problem has been a problem right from when I first fitted the unit, so much so that I ended up believing that I had done something wrong in the fitting so ended up taking it to a professional fitting service to have them re-do it. I had powered the unit direct from the starter battery positive terminal, but they changed this. I’m unsure where they’ve picked up the power supply from. I can’t recall where it is earthed & have no idea if they changed this or not.

The problem is that the squelch adjustment doesn’t work, or at least doesn’t work on some channels, some it doesn’t work at all, some it requires turning almost the full amount to work, & some it works as it should.

BUT ..... the squelch adjustment problems are only present when the ignition is turned on! (Regardless of whether the engine is running or not).

With the ignition turned off the squelch adjustment works perfectly on all channels! This was the case when I first had it powered directly from the battery & is still just the same since having it professionally re-fitted.

I’m wondering if it might fix it by running a direct earth wire back to the battery, but am loathed to start pulling it all out just to experiment with no gurantee of success.

Your thoughts are welcome before I totally spit the dummy & give up on Uniden altogether.

[Agronaught]

Ideally both wires would come from the battery, im assuming it's wired to your second battery with a common earth?

The squelch issue could simply be a lot of noise on the power supply, the little cb's don't usually come with a lot of filtering.

Add some ferrite beads to the power lines as close to the radio as possible to eliminate any common mode noise.

If the coax had been stretched the sheath has potentially been damaged. I would personally replace it with a higher grade coax (llr200) or a reputable brand (benelec rg58/u).

Check the grounding on the antenna mount, if it's the bulbar ground it to the chassis with some grounding braid.

Finally had the radio been exposed to a lot of heat/sunlight over time? Could be dry solder joints. I've seen this on some older radios.

[threedogs]

I ran an extra earth from the base of my antenna to the neg on my AUX battery
FYI Mine is wired directly to the Aux battery with a fuse of course, never had an issue ever
I'd be looking at the antenna mounting and fittings after all without the antenna its useless eh

[TPC]

By squelch not working do you mean you are getting hash noise that you cannot get rid of?
If this is the case it sounds like something else in your car is turning on with ignition and causing interference to the cb.
Have you tried disconnecting the aerial while this is happening to see if it stops? This will tell you if it is coming via the aerial or the power.
What other devices do you have in the car that turn on with ignition?

[Cuppa]

It’s done it from brand new.

I’ll try an earth from antenna base to battery neg terminal, although the fact that it works just fine without ignition on doesn’t make me optimistic that’ll fix it.

My aux batteries are all in the pod. Nothng to do with the UHF.

Yes TPC, that’s what I mean. I’ll try unscrewing the aerial whilst the noise is occurring, but suspect that I will find that it’s a power issue. Off the top of my head the things that switch on with ignition are a dash cam (not that, I already checked), TPMS, & the Redarc Dc to Dc charger.

I’m still wondering about the earthing of the UHF unit itself, but you’ve all given me a few more things to check.

[Agronaught]

I know my dash cam is a noisy thing, hash across multiple bands. Cheap jaycar crap.

Ferrites can help filter the power supply in case its a fuel pump etc.

J.

[the evil twin]

Noise over bumps - as prev posted by others if the Coax was too tight a bend radius or whatever and the inner conductor has damaged the dielectric it affects the impedance and the only fix is to replace the offending bit of cable or remove and reterminate.

Squelch - if it is perfect with ign off and then turns to poo whne ign is on then, again as prev posted by others, it is noise from another source.
Dash cams are notorious offenders for that so can you disconnect the dash cam easily and try it?

If the Antenna is ground independant the base will work on a smart bar or even a tupperware container BUT if there is any type of connection to shield or shield damage you can get some weird shit happen with earth loops esp in multi battery installs.

I think your problem is most likely noise from another device.
Maybe try Ferrites as Argo suggested

[Cuppa]

Tried a few things, but none the wiser & no closer to resolution. The problem is made more difficult because it seems to be variable.

Earthing the antenna to the chassis or direct to neg terminal of battery made no difference.

Unplugging the dash cam, the dc to dc charger & the TPMS made no difference.

I thought I was getting somewhere when holding the base of the antenna tightly with my hand I could make the noise stop. Let go & it would start again. This was repeatable. I partially dismantled the antenna & cleaned up some minor corrosion on the screw threads, put it back together & can no longer make the noise stop by holding the antenna, but the noise continues. Makes me think that it might still be the antenna though???

Unscrewing the top part of the antenna made no difference.

Don’t think it could be the fuel pump the because it happens with just ignition turned on, but without motor running.


Let me try again to explain the problem in the hope that it helps someone to help me.

With ignition off but the uhf switched on & set to a channel not in use, I turn the squelch knob anti clockwise until I get noise. I then turn it a little clockwise until the noise just disappears.So far so good. But now turn on the ignition (without starting motor, dashlights lit) & I get noise similar to what you get without the squelch adjusted. The UHF say’s ‘Busy’ on it’s screen. Try to adjust the squelch now & I either have to turn the knob almost fully clockwise before the noise stops, or I turn it to it’s full extent without any change to the noise. This varies between channels. If I set the squelch so there is no noise whilst the ignition off & then turn on ignition the noise starts, & then with no further adjustments turn ignition off & the noise stops again.

Question. Is it possible that a problem with the antenna (or the cable connection within it) could cause a a problem which only shows up with the ignition turned on?
A couple more things which may or may not be related.
With wife on a handheld, volume in car unit was fine (80ch unit) but volume on handheld (40ch) was very low even on max volume setting.

The UHF is mounted under the radio in the dash. I wondered if the radio might be the cause of the noise on the UHF. (Even though the radio comes on with key in acc position, but noise only occurs once key is turned further so that dash lights light up). I pulled the radio fuse to switch the radio off & the UHF went out too. This seems odd because the radio needs the ignition key to be turned to acc to operate, but the uhf doesn’t. Nevertheless I wonder if somehow sharing the same power supply might be the cause of the problem?

I’m clutching at straws.

Do car audio places have more sophisticated means of detecting the cause of radio interference?

EDIT. ET, you posted whilst I was ttyping the above .I think you are most likely correct & I consider the radio is the prime suspect.

[Agronaught]

Check the coax for a short with a multi Meter, also check the swr if you can. I would do it for you if you were in Sydney.

Don't underestimate how much noise can come through the power line. I needed several ferrites on the radio in my Subaru to prevent similar issues, even that didn't work when I installed led blinkers.

http://m.jaycar.com.au/m_productView.asp?ID=LF1292

Temporarily route a power line through the window direct from the battery and see if the problem persists, it could simply be something the power cable is running next to.

[TPC]

The car radio has two power sources going to it, permanent power and acc power, your cb has obviously been wired to the radio permanent power line, I would change this to go straight to the battery.
It is sounding like the interference is coming in via the aerial, can you get to the back of the cb to disconnect the aerial plug?
If the interference is coming in via the antenna the only way to fix it is at the source, or possibly by moving the antenna.

You need to visit either Adelaide, Sydney or Perth to get one of us to fix it for you.