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

[Agronaught]

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.

make sure it's a left handed knockometer

[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.

[Agronaught]

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.

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.

[Cuppa]

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.

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?)

[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

[TPC]

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

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.

[GQ TANK]

hmmmmmm very

[cgm]

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?

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[Agronaught]

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.

[Cuppa]

Cuppa did you ever do anything more with this?

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.