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GNC255 radio shorts nav antenna to ground?

agent4573

Well Known Member
I have a feeling this is normal, but wanted to verify. I've been checking all my antenna cables as I make them and noticed that if I test both ends of the NAV cable with it disconnected it's open between center conductor BNC back shell. Once I plug in the NAV cable to the 255 and check the other end, the center conductor has 0.3 ohm resistance to the BNC back shell. This is the only cable that acts this way, all the others remain open between conductor and back shell(comms,gps,transponder).
 
RF circuits

You can verify cables as not shorted using a ohm meter.
However, it is normal for many boxes and some antennas to measure near shorted with an ohm meter. Generally nothing to worry about.
 
Many radios and antennas have an inductor to ground to provide a discharge path for static buildup. This is a short at DC, but a high impedance at the working radio frequencies.

So, I would not make anything of it unless you have operational failures.
 
I have a feeling this is normal, but wanted to verify. I've been checking all my antenna cables as I make them and noticed that if I test both ends of the NAV cable with it disconnected it's open between center conductor BNC back shell. Once I plug in the NAV cable to the 255 and check the other end, the center conductor has 0.3 ohm resistance to the BNC back shell. This is the only cable that acts this way, all the others remain open between conductor and back shell(comms,gps,transponder).

Probably nothing to worry about -- just a side effect of the receiver architecture in the GNC 255.

However, if you want to be sure - measure the resistance between the center pin and the bayonet shell on the GNC 255 -- Open? Short? Resistance? How many ohms?

Whatever the answer is to the above, your test on the the cable in-situ should be the same.

Good luck!
 
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