Belt Valley times. [volume] (Armington, Mont.) 1894-1977, 1926-12-16
a sh0r.-wave supsrheterodyns.

Receivers used for the reception oi
short-waye signals generally make use
Of a regeneratlve detector followed by
one or two stages OF audIo frequency
application. In the majority Of cases
r. f. application is not resOrted to-
the reason being that the use Of r T.
stages becomes very difficult for the
high frequencies involved. In the
Radio Broadcast Magazine. however.
Is described by George J. Eltz, Jr., a
superheterodyne short-wave receiver.
efficient. and easy TO handle. This re-
eeiYer was first tried out just year
ago and has since been developed TO
that stage where It may be duplicated
by the average set constructor with
out fear Of any snags cropping up. It
employs two intermediate stages Of
r. T. ampllicatIon.
The superheterodyne used for the
reception Of short waves differs some
what from that used fol the recep-
ton OF broadcqsting,= although, of
course. the general theory is identical.
The superheterodyne method OF re-
| ception consists OF tuning TO the in
coming frequency, beating with # an
other frequency. and then simplifying
and detecting the beat note. The ac-
tual signal listened to has in II none
of the original frequency or the fire.
quency which caused the beat note.
In the reception of broadcast programs
or other signals between 1900 and $50
kc 600 and 500 meters) the beat note
selected is a frequency somewhere
between 30 and so kilocycles. This
relatively high frequency is selected
to prevent the Introduction of dIstor-
ton by elimination OF the side-band
frequencIes in the intermediate am
plifer and filter.
Reception Of Short Waves.
In the reception of short waves, par
tculariy the reception of c. W.. this
element of distortion may be dlsre-
garded, and such has heen the case In
this receiver, the assumption being
that most of the signals received viii
be c. W. The ordinary "super" used
for broadcast reception has two tun-
lngs first, the loop or antenna circuit;
second, the oscIllator circuit This
short-wave super has only one tun-
ing arrangement, In which Is COM
bined both the tuning operations indi-
Gated above. This method Of tuning
was selected because Of It's simplicity
and because It makes possible the
construction Of what Is practically
slHgle-eoRtrol set.
The intermediate frequency chosen
Is % kilocycles which, while too low
frequency for good telephone recep- |
ton, when simple tuned circuits are
used, Is satisfactory for c. W. or tele-
graph signals. The selection OF this
frequency necessItates detuning the
set % kilocycles from the incoming
signal, but at the frequencies CORE
spending to wave lengths OF 100 |
meters or under, this detuning is of
40 Importance in decreasing signal
strength.
The reader will recognize the de-
scription above as applying to- the
''autodyne" or f'selfheterodyneg type
OF super" The beat note of % kc. is
created In the same manner as In the
set. but az lower fre
Quency. For tlfe reception Of short
wave telephone signals, the ampllfica-
ton and detection OF the 22-kc. beat
note Is in the usual manner. When
c. W. signals are. to be received. an
other beat note must be created
either hY mems of another osCifiHtUr
tube or by a selfheterodyne beat note
In the second detector tube. The lat
ter method has been selected. a beat
note OF 1000 cycles being chosen as
the most satisfactory. This detuning
of the second detectOr circuit, while
L may appear to be inefficient because
II the low intermediate frequency, Is
not so bad as Il seems since the am
,lification In the intermediate circuit
s very great and there is plenty Of
snergy TO spare
Two Variable condensers.
In the accompanying diagram two
7ariable condensers are shown. but all
he tuning is done with the one In the
yrld circuit. The condenser In the
flatC NllEhAl tubot uC set Aul CuNA D0nu / n
Il freQuencies covered, for instance
rom 1893 kc. to 6,08S kc. Gao to As
neters), 6.663 kc. to 5.9o0 kc. CAS- to 80
neters), etc. This setting Is not crit
tssi. the only requirement is that the
ube oscillate strongly but not so vi0-
emily that It blocks. The variable
ondenser across the secondary In the
liter circuit Is not considered a major
ontrol.
The choke coll consists OF 100 turns
round on a wooden form inch In
lameter and 2 inches long. A honey
onb or similar coll Of 150 or $50
urns win also serve very nicely. The
transformers must be
apahle OF simplifying the rather low
frequency Of % kc. In this set. those
manufactured by the General Radio
ompany wers used. but there are
rubsbly any number OF others which
FAl serve TIE eella used h the an
mnua erId and Mate rlrrulfn are