Radio noise

[stickandrudderman]

Gents,
I've noticed something strange going on with my Falco's radio (SL30) and am looking for tips as to identifying the cause.
At my home base EGLD and when using Farnborough LARS (insert correct grammar for plurals here) my radio works fine on Tx and receive but when I switch to Cranfield I get a terrible noise when PTT is pushed and no response from Cranfeild. As soon as I switch back to Farnborough all is OK again. Any clues?

[mostlytossas]

Have the Cranfield frequency (along with all others) checked in the set. Depending on what type of radio you have fitted as some are worse than others,you will probably find the frequencies have wandered off a bit and the set needs re tuning. Usually more noticable on any frequency where the signal strength is lower such as distance from transmitter, terrain, etc.Another cause could be it is down on power. Often sets have dual power supplies ie 12volt+ and 12volt- powering them and one leg could be down often caused by capacitors in the set drying out. These will need replacing if the case.
The antenna can also be the culprit so have a SWER test done on that too.
Either way you need take your aircraft to a radio shop and have it checked out.

[Hasherucf]

I use a bird antenna analyser which gives a great graph of VSWR tests. You can see any dead spots over the frequency range you set . If it has a dead spot you can differentiate between the transmission line or antenna by using a dumby load in lieu of the antenna.

[dubbleyew eight]

jim weir diagnosed a similar problem in my radio.
the connector between the coax termination and the external aerial had become slightly corroded increasing the impedance.
increased impedance prevented the signal getting out into the antenna wire.
evidently it was radiating inside the aircraft and getting picked up by the mike boom cable, fed back into the first transistor in the radio and causing a horrendous squeal.

took the antenna off, cleaned off all the corrosion with brasso and screwed back together.
needs to be redone about every 5 years.
I seemed to receive ok but couldnt transmit.

[stickandrudderman]

Thanks for the replies so far.
After a bit more investigating I can offer a bit more detail.
The problem is more distortion than noise.
I tried several frequencies on the ground this morning and the lower down the frequency range I go the more distorted the sound becomes when I push PTT and the more noise too.

Hasherucf:

I use a bird antenna analyser which gives a great graph of VSWR tests.

I think you're on the right track with that and will try to find someone with that equipment.