Poor UHF transmission

Submitted: Wednesday, Jan 21, 2004 at 00:37
ThreadID: 9906 Views:2109 Replies:6 FollowUps:1
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Wondering if anybody here has ever had transmission problems as described below.
Whilst on our Kimberley trip I believe it was the corrugations that could have caused a fault with the UHF.

Firstly, it was just a bit of static but eventually got worse to the point where I couldn't transmit or receive with the vehicle in front or behind me(or anyone).

But when the engine is turned off, presto, radio works perfect. I ripped the whole dash off today and upon pulling the radio out found that the little windy thing that holds the coax to the terminal on the back was loose. I wound it back on - tightly - and proceeded to test it with a local truckie. It seemed a bit clearer with the engine running but still not perfect.

Once again, perfect with motor off. This would lead me to believe that that some weird electrical interference has suddenly started up - maybe an indication of something in the electrics on the way out.
Can't be aerial or connections as it worked perfect when engine was off and although the windy thing was undone the plug was still all the way in to the socket unless engine vibration does something to it.

Enough said, any experience appreciated.

ChrisNice southerly coastal fishing trip someday.
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Reply By: joc45 - Wednesday, Jan 21, 2004 at 01:15

Wednesday, Jan 21, 2004 at 01:15
Not a great deal of info to go on, but the radio wasn't finding its DC earth via the coax cable, was it?
Check the viability of the main -ve DC connection.
AnswerID: 43765

Reply By: Member - Ken - Wednesday, Jan 21, 2004 at 08:41

Wednesday, Jan 21, 2004 at 08:41

I had my UHF aerial changed a couple of years ago due to a metal fatigue thing.

Everything worked ok for awhile until I noticed that the transmission side of things had virtually stopped. Just one of those things that gets progessively worse and you don't notice it until it virtually stops functioning.

Anyway, long diagnostic story cut short, I had virtually given up on identifying what was wrong when I just happened to give the aerial base spring a work out for nothing better to do and noticed ( again accidentally) that the coax was not moving up and down simultaneously with the aerial bending.

So I gave the coax a gentle tug and it virtually fell out of the base.

It was friction fitting that had got water in it had water in it and the connection had degraded to basically zero giving it a hit and miss effect.

I ended up taking it to a radio specialist place in Boxhill, Melbourne that does taxis and other commercial vehicles and after consultation with them, I put in a new different aerial base that had a factory fitted (soldered) coax.

Also ripped out the existing coax (It was cactus as well) and guess what. It has never worked better.

This may give you some thoughts on your dilema.


Ken Robinson
AnswerID: 43773

Follow Up By: Roachie - Wednesday, Jan 21, 2004 at 10:51

Wednesday, Jan 21, 2004 at 10:51
It's a fairly well known fact that around 99% of radio problems stem from the aerial. If the radio works okay with engine off, I would say it has nothing to do with the radio and everything to do with the aerial shorting out or not earthing properly, as mentioned by Ken.
If you can maybe go to a radio shop and ask to "borrow" one of their portable-type aerials with a magnetic base; plug it into the back of the radio and stick the thing on your roof and see if that works. I reckon there's a bloody good chance it will be nigh on perfect.
Let us know how you get on.
FollowupID: 306025

Reply By: Member - Des Lexik(SA) - Wednesday, Jan 21, 2004 at 11:30

Wednesday, Jan 21, 2004 at 11:30
Chris, another possible solution. As previously mentioned, the arial and cable get fatigued, and possible the wiring within the arial had broken apart so that whilst in motion, the vibrations are causing the static. If you can borrow another screw on arial, test it out and replace if that is the problem. Also if the base is not earthing correctly, remove the base mount, thoroughly clean including any rust and try again. Both solutions won't cost much if they turn out to be the problem. As stated previously, start from the arial and work your way back.Dare to Lead not to Follow
AnswerID: 43781

Reply By: jeff-wa - Wednesday, Jan 21, 2004 at 14:08

Wednesday, Jan 21, 2004 at 14:08
I agree, sounds like an earth problem, probally etierh in the coax or the connection to the arial, when the motor is idling, vibrations are causing it to intermitantly loose contact.
AnswerID: 43793

Reply By: Blinky - Wednesday, Jan 21, 2004 at 21:14

Wednesday, Jan 21, 2004 at 21:14
try this http://www.firestik.com/Tech_Docs/CBs_%26_RVs.htm
AnswerID: 43848

Reply By: Member - Nigel (QLD) - Saturday, Jan 24, 2004 at 01:03

Saturday, Jan 24, 2004 at 01:03
are you running decent power and earth leads to the battery? seems plenty of radios stuff up due to using existing accessory cabling.
AnswerID: 44176

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