Projects for the winter


From: laura halliday (
Date: Sat Sep 13 1997 - 15:29:54 EDT

I've been ruminating on some things and may have come up with
an in-depth project for the winter - have a go at IF DSP. You
can probably blame Future/Active for this, who cheerfully sold
me an SD5400 quad D-MOS FET IC, the same as used in the front
end of radios like the Watkins-Johnson HF-1000 and other very
serious hardware. For the DSP end, a final IF in the 20-25 kHz
range, then a serious DSP (e.g. ADSP21061). Now I just have to
fill in the gaps between...

This could be *fun*. :-)

Looking at the specs of the SD5400, I see that the Rds(on) of
the individual FETs is some tens of ohms, just like the 74HC4066
mixers I was playing with at the beginning of this year. The big
difference (other than the price tag :-) is the switching time -
1 ns for the SD5400, 15 ns for the 74HC4066. That explains a lot
about the relative performance of these beasts at HF.

By way of comparison, an IRF510 has Rds(on) of 0.54 ohms, with
switching times on the order of 20 ns. Being a power device,
International Rectifier spec them differently: switching time,
plus rise and fall time.

A propos my sig - I'm amazed that my silly little sig quotes
are the object of such interest. They're my polite-but-firm
reminder that this is an international list, devoted to an
international hobby, using an international network to do it.
Another list I subscribe to has postings routinely in four
languages (English, German, Dutch, French), with occasional
postings in half a dozen more. I read them (or stumble through
them, depending on the language), and think nothing of it.
Only the Finnish postings remain more-or-less impenetrable.
Does this mean I'm weird?

As a corollary to this, I don't like my postings being an object
of curiosity just because of my sig quote - I'd rather people
read what I've said. Thus, email that only asks "what's your sig
say?" gets nuked on the spot.

Laura Halliday		"Les cigognes se sont envolees	Est-ce que nos promesses seront eternelles?
Grid: CN89mg		Les tournesols se sont refermes
(Chenevez/Laporte)	Peut-etre la vie est-elle encore belle."

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