----- Original Message -----
Sent: Monday, January 16, 2006 12:35
AM
Subject: LF: Re: Re: Re: TA
Quoting Mal...
"This QRS business is severe on PA fets and some
psu's, especially the slower crawls. Anything beyond QRS 3 - 10 could be fatal
over long periods for most rigs. Any sudden antenna instability, windy
condx, showers then sunshine ie SWR variations are tricky at the vy slow
speeds, even the Decca Jeeps have been know to blow smoke in amateur
applications."
I don't buy that at all.
My station has run 24/7 for extended periods at
max power
What is max power, ie a 100 w or so or 1kw ? You
can get away with a lot at low power but at higher levels it is a
different story, also the protection circuit used plays a critical part, if it
works properly and closes the PA down at the slighest breeze then you will not
have a problem. Most amateur FET rigs do not have a lot of protection and are
therefore vunerable.
with a floppy vertical to deal with
the 'Pacific breeze' and rarely if ever have I lost a FET and never
a power supply... All my FET failures can be classed as operator error not
environmental factors... My only FET death this year was caused by arcing to
my nearby 80m dipole. It arced for a good 30minutes by the look of the
grab I was sent and then one of the FETs in the TX shorted...
Some operators around the UK are running the
DECCA amp at 1.2 kw, had you been using this power you would probably have
burnt the housed down instead of just one FET.
I will keep an eye out for SMOKE in your
direction, I am more likely to see this than hear you on cw.
The trick is ensuring good cooling and
sizing of the parts, particularly ferrites. If there is a danger to
the FETs its when you're doing that old switched carrier mode rather rapidly
and only if you haven't taken good care of the transients on the FET
drains ;-)
Sorry Mal but my observations during prolonged
and rapid weather changes don't indicate that amateur transmitters are so
delicate that they can't handle long QRSS dot modes... I've run my
sinewave (QRSS near-infinity) for weeks on end without trouble during all
kinds of weather events...
I have data if you want to see it...
I believe you but let me know what happens
when you get some real POWER into that wobbly antenna.
Scott
