UHF problem discovered - but what to do?

[Cuppa]

I have been putting up with a CB which has a lot of ‘noise’ for some time, mainly because I don’t use it very often. However circumstances have changed & I find myself needing to use it more often.

It is a Uniden dash mounted unit. Initially installed it myself, wired directly to the crank battery. Because of the problem I thought perhaps I had wired it incorrectly & took it to professional installers who reinstalled it using a different power source (still useable when ignition off, but power not taken directly off the battery).

No problem exists whilst the ignition is turned off, but turn on the ignition & a number of channels (but not all) become unusable. Squelch does not work & their is constant noise. (Yes I do know how to use squelch). Irritatingly sometimes some channels work & sometimes they don’t which made me think about a loose connection somewhere.

BUT last weekend I was out 4wd’ing in a convoy & needed to be able to communicate with others, so I took our hand held units. Stuff me if both hand helds didn’t suffer with exactly the same problem. Ignition off - no problem. Ignition on (didn’t even need to have the motor started showing it was something which was switched on with the ignition key turned to ‘accessories’). Clearly something in the car which comes on with the ignition turned to accessory was causing interference. Possibilities included a dash cam, TPMS, & fm radio. This was a step forward, discounting other things like the dc to dc charger & other vehicle components.

Turns out the Pioneer fm radio is the culprit. Pulled it’s fuse - no more problem. The radio is a relatively new model, bought a couple of years ago at around the same time I bought the CB.

Whilst I can obviously use the CB by first removing the fuse for the radio this is not really a satisfactory solution. I am also hoping that a new radio will not be required. So my question is ...... is there anything else I can do to resolve the problem?

Although the radio & CB are next to each other in the dash I don’t believe their proximity to each other is the cause (because the hand held units were affected).

[mjr350]

Contact pioneer and see what the unit emits that could be causing interference. As far as I knew, a headunit is purely a receiver.
Does it have bluetooth or something that it could be trying to communicate via.

[Cuppa]

No bluetooth (it’s a ‘base’ model). Just an fm/am radio, disc player & MP3 player.

[mjr350]

If its a base model then bite the bullet, bin it (or give it to somone without a uhf) and buy an alpine. Problem solved.

[mjr350]

Ive noticed that the earth wire in my gu doesn't connect through the aerpro adaptor harness for some reason and my dvd headunit earths out through the headunit body.
Then again, i cant see a bad earth emitting radio waves / jaming waves

[TPC]

Earthing is important so make sure the stereo is well earthed but I doubt you will fix this.
I have investigated why different things have caused interference for work and it is time consuming and difficult.
We had ticket reading machines in buses causing interference to Two Way Radios and it took me a couple of days to find a fix for it and has to modify all the machines.
My advice would be bite the bullet and replace the stereo.

[the evil twin]

What he said ^^^^

If the hand helds are picking it up then it is the Head Unit actually radiating a signal.
Usual cause but not always is the power supply circuitry.

Give the Head Unit to a Prado owner

[lhurley]

Before you go out and buy a new head unit, at least try re earthing the current head unit to see if that makes any different. No point binning a working product if it just needs a better ground.

I have a jvc headunit and gme UHF and they are both using the same power and ground (earthed to the metal frame in the dash) and I have no issues.

[Cuppa]

Thanks folks. I’ll try earthing it,but if it fails I’m tempted to get an MP3 only head unit. I like the look of the Alpine IDA X305S except that it has no front USB. Also I guess there are no guarantees that whatever replacement I got wouldn’t have the same problem. Anyone else have a head unit with full ipod control which works ok with your CB that you’d recommend?(Prefer a MP3 only unit - never use CD’s these days). It seems that paying more gets you a heap of features which I doubt I’d use - eg bluetooth, hands free, net streaming etc. I just want a clean sound (accepting the constraints of a ute cab) & a working CB. Easy uncluttered controls & a nice crisp/clear display which tells me what’s playing are also desirable.

[Kelvinator]

Ive bashed around an alpine head unit through 3 4wds now over 10 years. Still goes strong. Benefit of rearward usb is you can run it under the carpet and have it come up near your centre console and not have cables hanging past your shifter. Got a new alpine unit in my ute as well, pretty happy with it, has usb, bluetooth car phone(damn useful, never had one of those before) and tonnes of other features which actually work really well. I got it from JB HIFI, wasnt the base model was a few up, single din and it ended up around $200 with 5 year warranty. I've had tonnes of other units (ive owned too many cars) and I just keep going back to the alpine. And here's the best bit you wanna hear, never impacted on my UHF.

Side note, Is the aerials frequency/impedance/doohickety or whatever suited the the uhf? Excuse my laymans terms but I had trouble with that once before when they were mismatched. Never knew what set it off though.

[mjr350]

I very rarely use cds/dvds anymore. All my music is on a small stick but a rear mounted one on a lead would be better because ive lost count how many times ive almost snapped the little stick when going to change gears.

[TPC]

It would be very unlikely you would buy another stereo with the same problem, it is not common for them to cause interference like this.
I have a rear usb socket with ext lead to centre console and as others have said it is a better way to have it.

[the evil twin]

Agree with TPC, very unusual problem to encounter these days and 99.9% must be an internal fault in that specific head unit.

I have only used Chinnee Head Units for 10 years or so now and they have all been quite reasonable performers.
In the name brands Alpine seem to have hit a good price point versus features but I think you could purchase whatever caught your eye without any issues

[mudnut]

Humour me,Cuppa, and wrap all of the unit and its cables in alfoil, (without shorting out anything). Turn it on for a short time and see if the problem disappears.

[4bye4]

Earth the alfoil??

[mudnut]

Yeah. And put some slits near the top and bottom to let air circulate. I just want to see if it is feeding a high frequency back into the loom.

[the evil twin]

Yeah. And put some slits near the top and bottom to let air circulate. I just want to see if it is feeding a high frequency back into the loom.

... as soon as you slit the Alfoil it negates the Faraday effect.

If you think it is the loom that is radiating (which it certainly could be) you have to wrap and earth the loom.
Wrapping the device will have no effect on the loom which will still be free to act as an antenna

[Kelvinator]

Build a faraday's cage around your whole car. then sit on the roof and use your uhf

[Cuppa]

It may be a little while before I try accessing the unit to earth it (or wrap it) as other things are taking precedence. Having removed the rooftop tent I’m currently in the middle of splitting up my portable solar panels (5 x 60w) & mounting them to the roof. It’s a job which is taking far more time than I’d considered it would. Using only Sikaflex 11fc to glue the mounts to the roof (rather than Sika’s far more expensive & harder to work with 252) has meant painstakingly taking off paint so I can glue direct to aluminium to achieve the strongest bond. The panels themselves are bolted to the mounts using riv nuts. (Believe me I’ve just about had enough of working on my knees up on top of the pod!). However I’ll certainly follow up on suggestions at some point, & report back. For the time being if I go out & need to use the CB if out 4wd’ing with others, pulling the radio fuse will suffice, but in the long term it’s a solution which wouldn’t work for long distance travel/communicating with other travellers, truckies etc.

[4bye4]

Maybe put an inline switch to save having to pull the fuse every time. Only as a temp measure I mean.

[GQ TANK]

I have used foil trick a couple times. Are you disconnecting the main fuse or the ignition sense fuse that is used to power the head etc?

Unplug the antenna lead on the am / fm radio.

Units must now meet the "c-tick" requirement BUT, as the levels being radiated might be under the minimum for a "c-tick" - it might still cause you interference. A -120db signal can cause you grief - especially if it is near your cb. Try walking around the vehicle with your hand held - how far from the head unit are you receiving the interference - you might be able to remote mount the cb.

When you are looking for a new unit, go to a vendor that has the units on display and take a hand held with you. You should be able to determine if the replacement will cause you grief.

We had issues with the patrol 4.2td computer causing interference in the VHF band a couple of years ago, we fixed the problem by going to the 3Ltd 9the computers are differant.

[Cuppa]

The fuse is the one from the bank under the dash to the right of the steering wheel. Switch is a good idea but the fuse is easy enough to access as a temporary measure. I’ll try with the handheld as a test unit as suggested, thanks.