TOPIC:

Hello,

I have had two situations involving ice loading on 6 meter antennas that have resulted in shorted output transistors. The last time (3 days ago) I even verified the SWR was below 2.0 (as indicated on Flex 6500 barefoot) before going to full QRO with the PGXL..but immediately on keying the PA transistors failed. Does the combination of ice and 50 Mhz RF present some special situation I need to be extra conservative about? Even if I am ultra conservative and QRT immediately if ice is a potential, how do I know when it is safe to resume QRO operations (since antenna feed points are a long way up and cannot visually confirm)? Any insight or recommendations would be greatly appreciated...I love the amp and just want to do what I can to assure reliable operations.

73s and Thanks in Advance de Tim (N0TB)

Hi Tim,

it is hard to answered precisely. Depends on antenna feed point and how exposed it is. Weather and snow at feed point is dangerous. I would not recommend any QRO operation if it is obvious that SWR increase, what prove that feed point is with snow or wet.

73
Ranko

Hi Ranko, Thank you for your quick response! It might be worth considering noting this in some form so that others can benefit from your suggestion. Obviously the high SWR protection circuitry works to some degree, do you feel that the icing presents some sort of "outside the design envelope" situation? Given that the time between the onset of the icing event and the "danger time" is fairly rapid (maybe <1 minute), one possible solution is to have the amplifier (in conjunction with flex xcvr) map and store the good swr curve of attached antennas and shutdown the amp when a significant deviation is detected..that way it may be possible to be proactive without having to actually look out the window and react manually....sometimes such icing events are not always predicted. Just trying to come up with ideas that could save final transistors....73s es Thanks again de Tim (N0TB)