on 9/18/01 10:34 AM, Michael J. Tubby B.Sc. (Hons) G8TIC at
mike.tubby@thorcom.co.uk wrote:
> There are
> the "FM service" transistors that end up in amplifiers with some bias on and
> called a "linear amplifier".
Well, this is done all the time. I designed several class A linear
amplifier modules that used "FM service" devices. As long as you properly
bias the device, it will be linear. Device construction is pretty much the
same between an "FM" device and a "linear" device.
The problem I (and others where I worked) discovered was that the FM service
parts basically didn't have very good small signal controls on them (we were
using a 25 Watt device backed off to less than a watt - needed it for the
IMD headroom - my board needed IMD of better than -75 dBc). The variation
in devices from lot to lot as far as tuning and performance was a problem.
So we convinced Motorola to come out with new, linearly spec'd devices which
where the exact same semiconductor die, but just tested to a different spec.
So it matters not how the manufacture "specs" the part but on how the end
user biases it.
73,
Jon
NA9D
-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)
Member: ARRL, AMSAT, DXCC, NRA
http://www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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