On Jun 20, 5:20?am, "Harold E. Johnson" wrote:
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- Hide quoted text -

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I think that there is more to this story...

In his book 'Piezoelectricity' (originally published by McGraw-Hill in
1946; 2nd revised ed. Dover, 1964) Walter Cady indicated that he first
proposed the idea of using a crystal in a filter in 1921. He referred
to his Proc. IRE article, and his patent US1450246, filed Jan 28 1920,
granted April 23 1923. As far as I can see, the configurations
proposed by Cady do not include the center tapped transformer circuit
used by Lamb.

Cady went on (2nd ed, p 668): "Filters employing crystals were first
described by L. Espenchied". There is a reference to patent
US1795204, inventor Lloyd Espenschied of A.T.&T., granted Mar 3, 1931,
filed Jan 3, 1927. This showed the use of crystals in a ladder
structure.

Other work was also taking place at the same time. Robert Kinsman, in
his paper:
'A History of Crystal Filters, 1988 IEEE Frequency Control
Symposium,
pp 563-570,
provides some pointers. He refers to Cady's paper and Espenchied's
patent, and also a patent US2005083, inventor Clarence Hansell of RCA,
granted June 18, 1935, filed July 7, 1927. This shows the single
crystal filter in the center-tapped transformer configuration with the
capacitor to balance out the crystal shunt capacitance.

Kinsman does not mention a further patent: US1994658, inventor Warren
Marrison of Bell Labs, granted Mar 19 1935, filed June 7 1927. This
too shows the a single crystal filter with a center-tapped transformer
configuration.

To me, the fact that it took nearly 8 years for these patents to be
granted suggests that there were some major issues to be resolved.

There were also developments in the UK as described in the ''Amateur
Radio Handbook', 2nd ed., RSGB, 1940, pp 70- . I think that this
chapter was probably written by Ernest Gardiner, G6GR, who did much to
bring the use of crystal filters to the attention of UK amateurs in
the 1930's. According to the book, Dr. James Robinson, while looking
for a sharply peaked device to test his Stenode theory of reception,
intoduced the quartz crystal resonator into radio circuits. The book
goes on to say that Robinson publicised his work in the USA during a
lecture tour in 1930, and its potential use in amateur radio was first
recognised by American engineers and amateurs. The book then goes on:
"The excellent work of James Lamb in developing the practical
applications of the circuit is well known...". The folk lore in the
UK is that Robinson introduced the center-tapped transformer circuit
to Lamb.

Robinson was granted at least four US patents for his work, ie
US1821032, US1821033, US1898895 and US1908558. All four patents were
filed between 1929 and 1930, and all four show some form of a center-
tapped transformer crystal filter circuit. US1898895 is entirely
concerned with a specific embodiment. It was filed on June 9 1930,
but not granted until Feb 21 1933.

Two other points are worth noting:

1 Cady's book contains many references on the use of crystal filters
in receiving sets. There are five to acticles in by Lamb in QST, in
Aug 1932, Nov 1933, May 1935, Apr 1937 and June 1937. There is
reference to an article by Robinson on Stenode reception in Radio News
in 1931, pp590ff.

2. The filters invented by Espenschied were of too low a bandwidth
for voice use at a carrier frerquency of 60kHz. Warren Mason found a
solution in 1929 using a full lattice filter. To quote Kinsman:
"Mason expanded on this work in a landmark paper published in 1934."
and "... which was the basis for all crystal filter designs generated
in the next 20 years." The paper, 'Electric Wave Filters Employing
Quartz Crystals as Elements', was published in the Bell System
Technical Journal, Vol 13, July 1934.

73

John KC0G

The filters invented by Espenschied were of too low a bandwidth
for voice use at a carrier frerquency of 60kHz. Warren Mason found a
solution in 1929 using a full lattice filter. To quote Kinsman:
"Mason expanded on this work in a landmark paper published in 1934."
and "... which was the basis for all crystal filter designs generated
in the next 20 years." The paper, 'Electric Wave Filters Employing
Quartz Crystals as Elements', was published in the Bell System
Technical Journal, Vol 13, July 1934.

73

John KC0G

Thank you for the expansion. I have Kinsman, his work on monolithics alone
are worth the price of the book.

Regards
W4ZCB