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

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.

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.

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

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?

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.

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.

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

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.

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.

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. :)

I must admit that the idea of having to pull the uhf, (& probably the radio) out of the dash is definitely not my idea of a pleasant aftenoon’s tinkering. I hate ‘in-dash’ stuff. I may have to bite the bullet & do it myself, but if I can find anyone who knows what they are doing in my area I would be sorely tempted. A guaranteed outcome would be worth letting a few moths out of my wallet. Any recommendations for local experts Apollofish or cgm?

Re ferrites, if I do do it myself ..... can you put too many ferrites on? Don’t want to be pulling out & re-fitting multiple times.

No idea what the swr is, let alone how to check it. Re checking for a short from the coax, would I just use the continuity buzzer? Which part of the coax should have continuity to the chassis, the inner wire or the foil sheath?

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Originally Posted by 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. :)

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Contradicting opinions - interference via power wire or aerial - Argghhhh. I originally had the bl**dy thing powered direct from the battery & had the same issue then. I paid to get a new radio fitted & had them re-fit the UHF at the same time. Anyone wanna holiday in Ballarat??? ;)

You could not put to many ferrites on but I believe moving the power source to the battery will make a bigger difference.

The outer conductor on the coax will have continuity to earth and with the radio disconnected from the aerial there should be no continuity between center and outer of coax.

If it would help I would be happy to talk you through things on the phone, let me know if you want my number.

Edit-I forgot it did the same thing wired direct to the battery.

Sorry Cuppa, I bet there would be someone local, but I haven't needed anyone so don't know who to recommend. I'll ask around at work tomorrow incase anyone knows who could reliably do it.

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Originally Posted by TPC

You could not put to many ferrites on but I believe moving the power source to the battery will make a bigger difference.

The outer conductor on the coax will have continuity to earth and with the radio disconnected from the aerial there should be no continuity between center and outer of coax.

If it would help I would be happy to talk you through things on the phone, let me know if you want my number.

Edit-I forgot it did the same thing wired direct to the battery.

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Thanks, I’ll let you know if I decide to diy & get stuck.

Too many variables. Eliminate the problems one at a time. Take the radio out and hook it up to another vehicle and see what happens. If that works then take the antenna off an try it on another vehicle. Sometimes, what seems to be the long way around is in the end the quickest.

And ultimately you could simply have a radio that isn't overly immune to noise.

A SWR meter was used inline on 27mg CB radio's to test signal strength, you cut the tip of your antenna
off 1/4" at a time till the reading was correct.
How far apart are you antennas , as in radio and UHF?

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Originally Posted by BillsGU

Too many variables. Eliminate the problems one at a time. Take the radio out and hook it up to another vehicle and see what happens. If that works then take the antenna off an try it on another vehicle. Sometimes, what seems to be the long way around is in the end the quickest.

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You are of course correct but your solution is easier said than done. I don’t have an alternative vehicle to use as a test bed. Whilst trying to avoid a pain in the arse job, it is becoming more apparent that I can’t avoid it.

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Originally Posted by threedogs

How far apart are you antennas , as in radio and UHF?

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UHF on the bullbar passenger side, radio just in front of windscreen pillar drivers side.

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Originally Posted by Agronaught

And ultimately you could simply have a radio that isn't overly immune to noise.

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That is what I suspect & the idea of a whole lot of trying to sort it via a process of elimination & substitution only to confirm that would really cheese me off, but I suppose I have little choice.

Has anyone else had similar problems with one of Uniden’s ‘mini’ UHF units? My one is the UNIDEN UH7740NB.

Are you going to the australia day long weekend gathering? I can take a variety of test equipment.

To diagnose...

Run temporary power via new lines from the battery and test, you will need to disconnect the existing lines.

Rationale, interference/noise on the power supply is a big cause of issues with radios. Heck, use a small 12v SLA in the car for testing isolated from your cars power system.

If the problem is still there its probably not the power supply. If goes away we can further diagnose this issue.

Unplug the antenna and see if the problem persists.

The noise is coming via one off those two links, failing that there is an issue with the radio.

You could also pop down to Cape Jaffa caravan park between 1st & 9th Jan and I could look at it there, then stick around and do a bit of sand driving.

Thanks. No I won’t be at Kris’ do but I’ll probably have a go at doing as you suggest after christmas & will come back here with my findings.

And a thought from left field... Do you have led lighting that comes on with the ignition?

Good thought but no LED lighting which comes on with ignition. Cabin light is LED, but is not the cause. I had one light in our old bus which made the radio impossible to listen to, but not so in the Patrol. If only it were that easy!

Bugger...

I had a dodgy LED in a recent build that caused noise on a number of bands from 50MHz up through 500MHz. Apparently there are some dodgy components out of China (?who knew?) which exhibit an some form of avalanche breakdown not typically associated with LED's. The LED's I've put in the front bar blinkers have a similar effect due to the ringer circuit used to manage the voltage through the light, turn on the indicator and the radio would drop squelch every time the indicator turned on.

I eventually moved the radio to the rear of the truck, much less in the way of electronics to cause issues. (remote head).

Cheers
J.

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Originally Posted by Agronaught

Bugger...

I had a dodgy LED in a recent build that caused noise on a number of bands from 50MHz up through 500MHz. Apparently there are some dodgy components out of China (?who knew?) which exhibit an some form of avalanche breakdown not typically associated with LED's. The LED's I've put in the front bar blinkers have a similar effect due to the ringer circuit used to manage the voltage through the light, turn on the indicator and the radio would drop squelch every time the indicator turned on.

I eventually moved the radio to the rear of the truck, much less in the way of electronics to cause issues. (remote head).

Cheers
J.

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Betcha don't have a Babel Fish handy to translate that for ya Cuppa?

(Sorry Agro... totally agree but couldn't resist a smartarrs comment) :p

Is the antenna coax one piece as in the only joins are at antenna and radio?

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Originally Posted by the evil twin

Betcha don't have a Babel Fish handy to translate that for ya Cuppa?

(Sorry Agro... totally agree but couldn't resist a smartarrs comment) :p

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Lol.

I feel the same way with some of the mechanical suggestions on this list... Electronics I know, mechanics not so much ;)

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Originally Posted by the evil twin

Betcha don't have a Babel Fish handy to translate that for ya Cuppa?

(Sorry Agro... totally agree but couldn't resist a smartarrs comment) :p

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Babelfish tells me ‘Avalanche breakdown’ = Everything falls in a big heap”
‘Ringer circuit’ = Either a) the automotive equivalent of a household ‘ring main’, b) a series of campanologist powered alternators or c) something rodeo entrants entertain themselves with in the off season.

Take your radio out and hook it up to a battery, an antenna and try it out. Use a knockometer on the unit and the cables. That way you can rule out an internal fault.

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Originally Posted by mudnut

Take your radio out and hook it up to a battery, an antenna and try it out. Use a knockometer on the unit and the cables. That way you can rule out an internal fault.

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make sure it's a left handed knockometer ;)

We had issues with the 4.2 diesels at work causing RFI interference In the 150 - 172 mhz freq's. Your fault sounds similar - uhf CB is at 476 Mhz.

We traced the issue to the ECU, we had some success by warping the ecu in aluminum foil, the problem disappeared with the 3ltd patrols, as they use a different ecu.

If you can get you hands on a hand held uhf cb - turn the hand held on with the squelch open - you should hear hissing. Now turn the ignition on - If there is any RFI you might hear a buzzing sound - check all the channels. This will prove if your issue is RFI.

Cuppa I'm in melton, but as I'm on-leave at the moment don't have access to a watt meter. if you still have an issue after Christmas - I can bring a watt meter home in the first week of Jan - and check your VSWR.

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Originally Posted by GQ TANK

We had issues with the 4.2 diesels at work causing RFI interference In the 150 - 172 mhz freq's. Your fault sounds similar - uhf CB is at 476 Mhz.

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I had a similar issue on l in my Subaru. Putting the radio and antenna in the back of the car with a remote head was the best fix.

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Originally Posted by GQ TANK

We had issues with the 4.2 diesels at work causing RFI interference In the 150 - 172 mhz freq's. Your fault sounds similar - uhf CB is at 476 Mhz.

We traced the issue to the ECU, we had some success by warping the ecu in aluminum foil, the problem disappeared with the 3ltd patrols, as they use a different ecu.

If you can get you hands on a hand held uhf cb - turn the hand held on with the squelch open - you should hear hissing. Now turn the ignition on - If there is any RFI you might hear a buzzing sound - check all the channels. This will prove if your issue is RFI.

Cuppa I'm in melton, but as I'm on-leave at the moment don't have access to a watt meter. if you still have an issue after Christmas - I can bring a watt meter home in the first week of Jan - and check your VSWR.

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Hi GQ TANK, I may well take you up on that as I’m in no immediate rush, thanks. Maybe a bit later in January if that would be convenient (We may be away sometime during the first couple of weeks of Jan). I have tried using a hand held in the car, but there is no squelch adjustment on the hand held, a GME TX610 (must be automatic I suppose). It seemed to work ok without ‘noise’. Only issue with the hand held was that when transmitting I could pick it up loud & clear on the car’s UHF, but when transmitting from the car the volume on the handheld whilst clear, was very low. (Possibly an issue between 80 channel & 40 channel UHF’s?)

The volume being lower from a 80 channel radio when heard on a older 40 channel radio is correct. The 80 channel radios have half the deviation 25 Hkz - to 12.5 Khz.

Its a pain on club trips when there is a mixture of 80 and 40 channel radios - you turn the volume up to hear a transmission form a 80 channel radio - and get blown away when someone transmits on a 40 channel radio

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Originally Posted by GQ TANK

The volume being lower from a 80 channel radio when heard on a older 40 channel radio is correct. The 80 channel radios have half the deviation 25 Hkz - to 12.5 Khz.

Its a pain on club trips when there is a mixture of 80 and 40 channel radios - you turn the volume up to hear a transmission form a 80 channel radio - and get blown away when someone transmits on a 40 channel radio

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You mean channel spacing has changed from 25 Khz to 12.5 Khz and deviation has changed from 5 Khz to 2.5 Khz.
I know you know that, just being pedantic. :)

hmmmmmm very

Cuppa did you ever do anything more with this?

Forgot to mention it the other day, but I noticed when I had my dash apart it had some sort of noise filter on the 12v supply. Never noticed one of these before. Anyone who knows have an opinion if something like this is worth a try for Cuppa?

Attachment 55557 Attachment 55558

Reasonably common. Usually it's just a ferrite core and several loops of wire (aka choke). Good ones include band stop filtering.

Most radio issues I've dealt with in cars are due to:

* poor quality/badly installed coax. The feed line is very important.
* bad earthing of the antenna mount. It really does need to be bonded to the vehicle body.
* electrical noise desensitising the front end.
* crap radios... Especially in cb. (Poor front end filtering, low sensitivity)

In all cases for the best results:

* run cables from the battery to the radio. This cuts out a lot of noise and ensures a stable supply to the radio.
* if dealing with emf from the engine, move the antenna to the back of the car or avoid running the coax via the engine bay. Not so much of an issue for uhf.
* ferrite cores on the power feed as it enters the radio can help with noise. Better to fix the source is relocate the radio.
* The higher the antenna, the better. Distance from the ground changes the radiation pattern.
* the best install would be in the middle of the roof... Personally ive never been gaim to drill holes in the roof.


In my case I buy radios with a remote head option and install them in the back of the car running off the auxiliary battery.

This does mean a longer coax run so don't skimp on the coax or you will lose a good chunk of the signal, I use lmr-200 in the car which is the same size as rg58 and much better coax for uhf.

Depending on the radio a band pass filter can help remove noise, I have one that is overpowered by a local radio station as the built in filters are crap.

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Originally Posted by cgm

Cuppa did you ever do anything more with this?

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No, it’s sort of been put on the back burner what with the other stuff I’ve been doing with the car & the shed building stuff. I’m hoping I might still get to meet up with GQ Tank at some point, but might have a go at the ferrite bead stuff first.