Date: Sun, 29 Jul 2012 13:44:45 -0700 (PDT)
From: "Jerry Kaidor" <jerry@tr2.com>
Subject: Re: [Amps] Dedicated RF
A lot of new rugged devices have hit
> the market
*** Indeed. I was quite excited by the new Freescale devices - they have
a 1200W output one, protected up to 60-1 VSWR, and just $250 from Digikey!
Each device has a PAIR of RF FETs, suitable for a push-pull stage.
- Jerry Kaidor, KF6VB
## I see you just got sucked in by the BS hype. No it won’t do 1200w out.
Well, it will
in radar pulse mode, and even then the duration of each pulse has to be really
short. And
no, it won’t handle a 60:1 swr mismatch, that’s pure drivel.
## To get good IMD3 out of that device... and I mean, like –40db below one
tone, 9-46 db pep)
it has to be severely de-rated. Run it in CB mode..and IMD goes to hell.
Its maybe a 400-500w pep out device
at best.
## My problem with these SS amps is this. You require an RF deck that covers
1.8 to 30 mhz. Now
like Rob sez.. that’s a 16:1 ratio.... which is no small feat. You also
require a power supply. You also
require a 2000 watt CCS rated automatic ant tuner, so the SS amp doesn’t blow
it’s brains out.
## I don’t see any ferrite combiner’s that will cover 160-10m..and work eff.
On top of all that, the
RF deck also has to have a 2 kw CCS rated LP filter for EACH band !! Then
you gotta switch the entire
mess with 2 kw rated relays etc. Well, you could get away with a minimum of
7 x LP filters to cover 9
ham bands.
## BIG difference between a 1 kw CCS, class C FM broadcast TX... that sits
on ONE freq , and has 92% eff
vs a 160-10m amp, operates in class AB, that barely runs 50% eff, and MUST be
a linear amp. That’s a HUGE
difference in design demands. The single freq broadcast TX is a piece of
cake, and is much simplified.
## any tube amp doesn’t need a 2 kw LP filter, never mind 7 of the damn
things. A tube amp also doesn’t need
an automatic 2 kw tuner either.
## ever tried fixing a SS amp.....what a bitch of a job. A buddy had a
spike-transient come in from the street on his
240 vac line..and it took everything out, and I mean everything.... on his
megabuck ICOM SS amp. It had just gone out of warranty
and he was just livid.
SS amps are not ready for prime time...not yet.
Jim VE7RF
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