SPE should be in a good position to follow the 'multiple devices, under run'
approach. Their still current 2K-FA amplifier uses 6 pallets, each pallet
having a single 300 W, MRF151G, transistor. Then a combiner. There were some
pictures of the internals of this amp. on the FCC website when they were
going through type approval a few years back.
Unfortunately, SPE appears to be moving away from this approach - e.g. from
the six, oldie-but-goodie, MRF150 of their lower power amplifier (the 1K-FA)
to using only a single LDMOS in their 1K3 and 1K5 products. Sadly, many
users' see the rating, part of the amplifier model number, as something to
be chased, even on SSB. Some even report gleefully measuring power outputs
well in excess of the marketing department's rating. Independent test
reports suggest driving these amps. to circa 75%, or less, of the rating in
linear modes would make them much better RF neighbours.
I like the idea of four of the 1k8 LDMOS for a US legal-limit product. Being
generous, we could even allow the marketing department to call it a '2k'
product, before they feel tempted to conceive a model number with 7200, or
even 8000 in it! Four is a nice binary number for design. With care, and
enough copper and fans, it could even be CCS rated. As has been said, the
cost of the FET becomes less of a consideration when the product is in the
big $ class. User replacable pallets. Coverage to at least 70 MHz. Diplexed
output filters. Built in, -50 dB output sampler. etc.
Any manufacturers' willing to take up the challenge?
Regards,
Mark.
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Bill Turner
Sent: 23 April 2017 06:19
To: Amps group
Subject: Re: [Amps] Price per Watt Conversation
------------ ORIGINAL MESSAGE ------------(may be snipped)
On Sun, 23 Apr 2017 13:16:24 +0930, Leigh wrote:
>Solid-state QRO HF linear amps can be made to work very nicely
>particularly when conservatively driven and backed-off paralleled
>modules operating well clear of their 1 dB power compression points are
>combined and harmonic terminating diplexer LPF output filters are used
>to yield stable performance and good IMD specs.
REPLY:
I'm sure commercial manufacturers are well aware of this. The last thing
they want is a reputation for making lemons, a sure road to bankruptcy.
The more likely issue, IMO, is homebrewers who do not understand the
subtleties and who do indeed make lemons.
73, Bill W6WRT
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