Submarine Hull Is "Mike" - AmericanRadioHistory.Com

528 RADIO -CRAFT March, 1932
A New S. -W. Receiver
A discussion of a new short -wave receiver embodying a
unique feature in oscillator tuning. A complete and
timely discussion of this receiver is given below.
U1'1 A: the introduction of the eleven -
tuhe short -wave and broadcast
superheterodyne, known as the S -M
726SW, last June, it was felt that it
was the last word in short -wave-receiver design.
In spite of its relative simplicity in relation
to its performance, it was not as
simple as could be desired. Unfortunately, no
means
which
was known of, even undeveloped,
would permit of, for instance, a
simpler coil -selecting arrangement for the
short -wave bands; or which would permit
elimination of certain unpleasant, but not
really detrimental, sounds of the nature of
"burps" which occurred as the short -wave
dial was tuned because of a few unavoidable
reactions between harmonics of the broadcast
and short -wave oscillators.
As no method was known for eliminating
these two drawbacks -they were only slightly
unpleasant rather than really detrimental-it
was believed that nothing better
could be hoped for.
Ilut in November 1931, during the course
of development work in an attempt to
devise a better, or at least a simpler, system,
some experimenting was done with
autodyne first -detectors. While nothing
satisfactory resulted, an idea was found
by Kendall Clough, which now fully worked
President, Silver -Marshall, Inc.
By McMURDO SILVER*
out, bids fair to be one of the greatest
contributions to short -wave- receiver design
that has so far been found. It at once
simplifies the tuning of short -wave super -
heterodynes, el' ates most of the switching
necessary in sets not employing plug -in
coils, and dcxs away with all "burping" on
short -waves due to oscillator reactions. Six
months ago, this method had not even been
dreamed of- today. it is it practical, operative
reality in several thousands of sets now
in use.
While the autodyne detector system appears
attractive at first glance, it has two
drawbacks which render it worthless in a
"super." The first is its absolute inability
to discriminate against image- frequency
interference, since every signal is impressed
directly on the one tuned circuit of the combined
oscillator- detector tube. 'l'he second
drawback is that, since this circuit must be
tuned awl, y from the signal frequency by
the intermediate- frequency to produce the
necessary heterodyning action, and as on
short waves this I. F. will be quite high, much
loss of signal voltage results, particularly
on the lower signal frequencies. The autodyne
action is quite simple -but the new
Clough system is equally simple, has none
of the autodvne's drawbacks, and is in no
sense related to the autodyne system, since
it employs a separate and distinct detector
and oscillator with their separate tuned
circuits.
'l'he Clough scheme is to use only one
oscillator in the set, which must tune front
16.5 to 5.50 meters, or 18,000 to 550 ke.
Offhand, this sounds impossible, and it is,
for even the harmonics of the oscillator are
taw weak to be of direct use. The crux
of the idea lies in the use of a tube directly
coupled to the oscillator, which is so set
as to tune over the broadcast band of 550
te 1500 kc., this tube acting as a harmonic
generator and providing the necessary local
frequencies to heterodyne signals in the 16-
to 35 -, 3.5- to (i.5-, 65- to 100 -, and 100- to
200 -meter short -wave bands.
This system results in only one permanently
connected and aligned oscillator drcuit,
the harmonic generator tube providing
the required heterodyne voltages for the
short -wave bands. A single selector- switch
knob gives a choice of five separate coils to
enable the first -detector to cover the four
short -wave and broadcast bands. In the
final embodiment, one dial tunes the broadcast
band, this saune dial plus an auxiliary
trinuner tunes the short -wave hands, and
one five- position switch selects the five hands
at will.