25 April 2018

Avionics: Silencing the hash of a USB socket.

Rather than use a cigarette socket in my plane since those are antiquated, I opted to install a dual USB power socket from Powerwerx for just under $25.


Like most state-of-the-art voltage converters, it's based on switching technology.  This creates RF noise.  In my aircraft, the GTR-200 transceiver would break squelch most times when the USB socket was under load and thus spill hash into the intercom (oddly, the GTN-650 had no issues), even with a high squelch threshold.  So I quickly fashioned a filter capacitor to see if it would help, full well realizing that you can't load switching circuits with excessive capacitive reactance.  


These two pictures show the capacitor installed on the back of the socket.


I went for a couple hour flight and was pleased to hear that my GTR-200 no longer suffered from the hash.  But, as I feared, the capacitor indeed caused the socket to misbehave and no longer provide a reliable output.  So my solution wasn't practical.

I saw that one parts supplier offers a similar socket for significantly more money (the OEM part is here).  The premium is due to the OEM providing for internal filtration.  The same part, from the OEM supplier, is available on Amazon for at least 30% less than the avionics parts supplier.  Thus, I obtained the Blue Sea 1045 to replace my Powerwerx socket (and not use the capacitor).


Turns out that the dust cover the Blue Sea socket comes with is too big to use (the F-01439 Seat Ramp Cover impedes its use).  So I just swapped dust covers with the Powerwerx socket.  Below the new socket shown with my Bluetooth audio receiver plugged in to it and the Music 2 In jack (I use 90 degree elbows to reduce the profile of the cables and thus reduce the chance of something breaking - that the particular USB elbow in the photo prevents the use of the other USB socket, so I later used a short 90 degree elbow USB extension cord).


 After adding it to my aircraft, I flew for a few hours without hash on the GTR-200. 

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