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Reply with quote  #1 
To all Slingsby Guru's, here is one I could do with help with if anyone has had or heard of similar issues?

Aircraft Type: T67 / M260 Firefly

Fault: - VHF box 1 (top slot) when transmitting on frequencies within the 118.00 to 118,975 bandwidth, the ALT warning light flashes when you "speak" and increases in brightness/intensity based on the 'volume' of your voice. There are no ammeter fluctuations and/or drop in electrical services and the ALT remains online throughout.

NB - The light does NOT come on when merely pressing the PTT in the above frequency range and not talking............

Actions so far: - I have tried the same frequency range and diagnosis on box 2, I have swapped out the radios and it only occurs on the radio in the 'top slot' and only when speaking.............. Any ideas chaps?

Before I start ripping out cables and conducting RF tests if anyone is aware of known faults such as this any direction would be greatly appreciated,

Thanks, PM.
JHelps

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Posts: 20
Reply with quote  #2 
This seems to me an induced voltage issue.  Does it do the same thing across the band?  (ie the same thing at 118.00 as at 136.00?) Our radios are AM which can induce a modulation effect on a light source.  I would check grounds, etc to make sure they are all good.  As well check your shielded coax cable for good connections, perhaps the tray connector is bad.  There are also ferrite torroids that you can snap around the leads to the light that may help remove the induced RF.

I wish I had a definitive answer for you as I am having the same issue with my fuel gauges and have yet to resolve it.  The next steps for me are to try and get a sense of the RF in the area of the radio tray with a field strength meter to look for leakage and to install the ferrite torroids that I purchased, but currently the weather is too cold!  Her is a link to the discussion on my issue.

http://www.avcanada.ca/forums2/viewtopic.php?f=27&t=92571

Best of luck and I hope you find the problem as it will likely be the cause of my issue as well!
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