Re: About a narrow filter at 10.7 MHz

It depends on what you need. Don't forget that the first single
signal
selectivity came to receivers in the thirties, via a single crystal
filter.
I'm suddenly blank about the name, but it was a balanced transformer
feeding a crystal on one side and a trimmer capacitor on the other.
You'd
trim out the crystal holder's capacitance with the trimmer.

Lamb? WAG.

Certainly it was described first by Lamb, or he actualy came up with
it, in that famous 1930's article about improving receivers. Basically
a
phasing crystal filter, which I suddenly was blank about when I posted.
I'm not sure I've ever seen it called a "Lamb filter", though perhaps
if you go far enough back in the books, it was once called that.

Michael VE2BVW

Actually, it wasn't. Don't recognize the famous 1930's article you refer
to,
but Lamb came up with the Lamb noise blanker. The principle of operation
being to turn off the IF strip while the noise pulse was present, the
"hole"
being less noticeable and annoying than a huge noise spike. Walter Cady
came
up with the single crystal filter in 1922. Incorporated in most superhets
during the years 1925 until the ladder, half lattice and full lattice
filters came along in the 60's.

W4ZCB

The QST article is pretty famous, and at the very least is credited
with bringing single signal selectivity to amateur radio (if not the
world).
I can't find a paper reference, but it might be an article titled
something like "What's Wrong with our Present Receivers" from 1932 (though
I thought the specific article had come later), and it may be
referenced in Byron Goodman's January 1957 article of the same name.

Everyone credits the article with bringing single selectivity to
amateur radio, and I can immediately find some web references that claim
(and I've read this somewhere in the paper literature) that Millen used
many of the ideas in the article for the HRO receiver. The noise blanker
may have been described in the same article.

And of course, it was lattice and half lattice filters that came along
in the fifties that allowed many to build SSB transmitters, if they
couldn't afford mechanical filters and didn't want to use phasing. I
never saw a reference to ladder filters (except for some oddball bit
in the SSB column in the fifties that had two serial crystals and one
going to ground where they joined) until the seventies, and it was more
like a decade later before they became popular in hobby circles.

Michael VE2BVW

Jeepers. This thread is getting as long as some of Cecils threads. I hope it
isn't as dumbfounding.

James Lamb, 3CEI, 1CEI and W1CEI, was tech editor for QST in the 30's. As
such, unlike todays offerings, he ALWAYS had at least one technical article
in each issue starting as early as March 1928. One of those articles was in
June 1932 and was titled "What's wrong with our CW receivers?" That article
had to do with audio selectivity and no crystal filter was mentioned. In
August 1932, he published another article, "Short Wave selectivity to match
present conditions". This was amateur radios first published introduction to
the single signal crystal filter

In this latter article, Lamb acknowledges the pioneering work of Cady in a
footnote, who published his discovery and design of the single signal
crystal filter in the Proceedings of the IRE over 10 years earlier in April
1922. Lamb only repeated Cadys work in QST. He may have brought it to the
amateur fraternity, but the world knew of it from the Proc of the IRE some
10 years earlier.

Lamb WAS responsible for the invention of the "Lamb noise silencer" which
bears his name some years later.

W4ZCB


.

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