Date: Tue, 9 May 2017 07:59:45 +0930
From: "Leigh Turner" <invertech@frontierisp.net.au>
To: "'AMPS'" <amps@contesting.com>
Subject: Re: [Amps] HV MOSFETs for RF
<Good point Peter; not an appealing scenario for your average punter...where
pragmatism and practicality rule the day.
Perhaps limiting the Class-A PEP to 10 Watts and having a PA bias mode
switch would be a good compromise for keeping the purists happy.
I think there's an unwarranted obsession with low transmitter IMD numbers in
the non-channelized HF ham bands where above a certain respectable number no
practical advantage is realized. In many cases poor Tx signals heard on air
are attributed to bad operator practice and maladjustment rather than
inherent transceiver design issues in respect of IMD; although a few
notoriously bad rigs are out there.
73
Leigh
VK5KLT
## leigh, no class A amp runs a lousy 8.9% eff. I see that the new
OM-600 SS
600watt amp is the only ss amp on the market without an ALC jack on the back of
the amp. The average operator will have fun times trying to get his 100-200
watt xcvr..
.....down to just a few watts to drive it. Dunno if henry radio is still
selling their pads
or not. Ideally, you find the imd sweet spot on the xcvr..then insert the
correct pad
for the SS amp drive level. A k3s sweet spot for imd is 30 w pep out. A 3-
6db pad is
then used, so 7.5 - 15 watts to drive the ss amp.
## what do you call acceptable IMD ?? I mean well away from the other
fellows freq.
And lets not make the classic mistake of adding the RX BW to the TX BW. IE:
Tx on say 3800 LSB. RX station listens on 3803 + 3797..and thinks the TX
station is 3 khz up,
and 3 khz down...using his 3 khz wide ssb filter. If the RX station had used a
200 hz filter,
he would hear the TX station down 3 khz.... but only 200 hz up.
## baffles me why I / K / Y cant produce ham gear with IMD thats as good as
their marine gear.
Sure, the marine ssb gear does not have a mic gain control + processor, but
its still tested with
a 2 tone signal, same as the ham gear. Its not like its gonna cost them more
$.
## The old yaesu 767 ham xcvr is a magnitude better than modern ham gear.
50% eff, and
100 w pep out from a pair of MRF-422s. My 1000-D uses the same pair of
MRF-422s..and runs
200w pep out at 50%. And 100w pep out at 35% eff. So what happened
there ?
The 767 was designed to operate at 100w pep out + 50%..and real low IMD, like
–46db pep IMD3
The 200w yaesus have good imd...at 100w out.... but then eff sucks..at 35%.
They already had it right the 1st time..with the 767. If they wanted a 200w
xcvr, they should used
4 x MRF-422s.
Jim VE7RF
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