Thread: UHF transmission problem

I would check the coax itself.

Unplug from the aerial & the back of the set, & then put a multimeter on the core & sheath. You should have an open circuit. If not, there is your problem.

If all is ok, then connect the aerial back up again, and check from the set end. Should be the same result.

Failing that, check to make sure that the earth is good.

If all else fails, it could be time to get the unit itself checked out.

No it will definitely be the unit. One of the solenoids has gone. Friends of mine had this problem for ages. We did about 3-4 long trips where it just wouldnt work despite lots of tinkering and replacing the cable and the aerial. It gave us the *****s.

If you think about it, if it were the cable or the aerial then there would be no explanation as to why it receives so well but doesn't broadcast! The problem is with the unit.

After much harassing, our friends finally went to a professional radio person who replaced the solenoid...cost about $150. They had a GME 3400 also.

Just take to a recommended GME repairer. Check the website -Australasian Contacts | GME for a contact in your state.

Angus

Test the cable

Basil135 & McDisco said it all

Mike

Originally Posted by McDisco

If you think about it, if it were the cable or the aerial then there would be no explanation as to why it receives so well but doesn't broadcast! The problem is with the unit.

Thanks Angus. The unit does broadcast perfectly within a small range. Would a dead solenoid be consistent with that or would it mean no broadcasting at all?

It was pretty confusing, them telling me they could not hear, and resorting to mobiles phones and personal abuse etc over whose unit was faulty or not pushing the talk button. We'd rejoin at the next stop park near each other and everything would be great again and the abuse would start up again in the carpark!

Check the simple things first before suspecting a serious problem. It could be something as simple as the coax rubbing through and 'earthing' on a part of the car. I've had this happen, and it's fairly common on 4WDs because of the vibrations etc.
The coax is the first thing I would check before moving on to other possibilities.

Murray

There are 2 main stages to the transmitter in your radio, the FM modulator and a power amplifier. The modulator stage changes the audio freqs into an FM signal at the correct frequency. This signal though is very low power (<100mw). The power amplifier stage then boosts this signal to the 5W output that goes to the antenna. If the power amp isn't being switched on by the PTT (push-to-talk) relay or the output transistor is blown, then all you are getting is the output from the modulator. This can be heard from nearby but not much further. My bet is you'll need to take it to someone for repairs.

Before sending the unit off, you probably should have the antenna checked using an SWR meter.
Using a multimeter is Ok for a basic check, but to check it properly you need a SWR meter.
The SWR meter will also test that the radio is outputting the correct "forward" power. If the "reflected" power coming back down the antenna is too high, it indicates there is something wrong with the antenna or cable. ( water inside the cable is a commmon problem - a multimeter test will probably not detect that)
Any radio shop / CB dealer should have an SWR meter. Or you may have a mate with one.

The other possibility is that you have a problem in your 12V power supply cable somewhere ( corroded connector etc ) - this will mean it works OK on the low recieve current but when you want the higher current for Tx it drops the voltage down. You can fairly easily test that using a multimeter - just measure volts at back of the the radio and compare voltage when receiving with voltage transmitting. - if it drops by more than half a volt there's a problem in your power wiring.

Originally Posted by JamesH

Thanks Angus. The unit does broadcast perfectly within a small range. Would a dead solenoid be consistent with that or would it mean no broadcasting at all?

It was pretty confusing, them telling me they could not hear, and resorting to mobiles phones and personal abuse etc over whose unit was faulty or not pushing the talk button. We'd rejoin at the next stop park near each other and everything would be great again and the abuse would start up again in the carpark!

It will still broadcast, just at reduce strength...hence why it only works over a short distance.

Our friends annoyed us cause we kept on telling them to get it looked at properly as their radio is one of the most important tools offroad (especially in Simpson where we were). But they were too cheap and kept on trying to fix it themselves.

Finally its fixed though...

Angus