Hello Chris,
These FETs are a good choice :-) You still manage to make them dead? And
your supply voltage is 50V? That's not ideal. You can use 320 V directly
from the mains, no heavy transformer needed, just a ferrite transformer
on the RF side, to decouple the RF signal from the mains.
I was running > 1.5 kW on 137 kHz (WSPR-15, no problem, not even in 100%
TX mode) with just 4x IRFP460A, which are not as good as yours. So i
don't really understand why you need a combiner at all. The 900V types
would be fine for a 3-phase PA running at 560 V DC in a H bridge
arrangement. A nice thought :-)
73, Stefan
Am 28.04.2017 13:36, schrieb Chris Wilson:
28th May 2017
Hi Stefan, remarkable work on VLF, congratulations!!
I see these with all FET's but I acquired very cheaply some Wolfspeed
FETs with a lot of overhead. These spikes sometimes kill lesser ones.
If you follow these links you can see the normal gate and drain
waveforms, and the drain waveform without a Varistor as an OPERA TX
period ends, i took the latter from a series of screenshots showing
the highest level the close TX spike reaches
http://www.gatesgarth.com/wolfspeed-scope-capture-50v.jpg
http://www.gatesgarth.com/wolfspeed-overshoot-50v.jpg
http://www.gatesgarth.com/wolfspeed.pdf
Best regards,
Chris 2E0ILY mailto:[email protected]
My part time LF grabber is at http://www.chriswilson.tv/grabber.html
Hi Chris,
Which type of FETs are you using?
The IRFP460A for example has a built in Z-diode which seems to handle
the spikes. Anyway i put a 150 Ohm / 220 pF (for LF) series RC paralell
to the Drain-Source...
73, Stefan
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