SB-104 (One Last Time)

[Kechkaylo Dave (ATLINKS)]

Dear Bill Coleman (and others):

Yeah, I hear what you're saying. The SB-104 DID draw upon the SB-303...in
the receiver. In the SB-104, the receiver front end dual-gate MOSFET design
was lifted from the SB-303, right up to the biasing arrangement on these
40673s, but without the RF amp, as this was where a lot of the IMD problems
crept in. Designing the front end preselectors on a 50-ohm basis is easy;
matching them to the relatively high input impedance of the 40673s over
several octaves was difficult. This in conjunction with the high noise
figure of these mixers and the inability to properly align the
8.395-8.895MHz 1st IF were the problems with the original SB-104 receiver.
The good design of the SB-104 was in the transmitter/display circuits.

As far as the Elecraft is concerned, there isn't anything new here. It's
lifted from previous, working, proven circuits and glued them together in
the right way (see them in the ARRL Handbook), and for this, they did a good
job (the PLL noise floor could still be improved upon, by the way). This
isn't a bad idea if you want this radio to land on its feet every time. I
could do this, and so could anyone else with several years experience in HF
transceiver design. But who wants to go into hock for all these parts,
particularly when the MC1350s (which already have), the MC145170 PLL, and
the 2SC1945s go obsolete or lifetime buy. Then what do you do? Who wants to
sort cheap 4.9152MHz microprocessor crystals? Can you say unobtainium again?
And oh boy...watch Motorola and Philips; they're obsoleting discretes faster
than you can design 'em in. Wasn't that way in the early 1970s!

My point is that there wasn't nearly as much to go by as a design reference
when the SB-104 was in its design phase, like there is today for the
Elecrafts of the world. Heck, just go out and buy several service manuals on
the best HF transceivers of today, and pick the circuits that turn you on,
then you're done! Now that's not a lot of work. So, the SB-104 still remains
a real piece of foward-thinking RF design for its day.

My last $0.02 on this subject.

Dave Kechkaylo, W8DLK

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