Radio Broadcast - 1925, February - 113 Pages ... - VacuumTubeEra

Problems of Receiver Design
How the Super-heterodyne Combines Sound Elements
of Design Theory of Construction of the "Super"
WHAT MAKES THE WHEELS GO 'ROUND: X
BY WALTER VAN B.
ROBERTS
IN THIS interesting article, part of Mr. Roberts' series of clear explanatory articles
about radio and all its works, the author has not tried to cover the entire field of
receiver design, but he has explained some technical points about the super-heterodyne
receiver so well that no reader who prides himself on his theoretical knowledge should
miss it. This is the tenth article by Mr. Roberts which explains radio theory and practise
in his own clear fashion. This first appeared in our magazine for March, 1924.
THE EDITOR.
ALL transmitting stations used the same very accurately to special shapes, the two
wavelength (and took turns working) condensers that have to be changed in tuningin
different stations could be worked simul-
reception would be a much
IF
simpler problem.
For the receiving set might have taneously by a single knob, which leaves nothing
to be imagined in the way of simplicity of
as many tuned circuits as the designer had
any use for. The owner of the set would not tuning.
need to change any of the adjustments so there
would be no disadvantage, from the 78. BAND FILTERS
operating
point of view, in having a very complicated THE
circuit. The idea of the super-heterodyne is IF fixed frequency used is fairly low, the
fixed
simply this: build the very best frequency receiver can be made to
possible receiving
set to work on respond a equally well to a band of
fixed frequencies
frequency (what
ever frequency it is easiest to work sufficiently wide for high quality, and yet not
with),
respond at all to frequencies lying only slightly
then build a frequency changing device that
outside of this band. This is ideal selectivity
receives signals on a tuned loop or other antenna
and changes their frequency to that
and is achieved by the use of a band filter in
the
for which the receiving set is
designed. When
fixed frequency receiver. A band filter
tuning-in a station with this combination only
two adjustments are necessary: the loop
u
should
be tuned to the incoming radio waves, and the
frequency changing device should be set to
change the frequency to that at which the
receiving set is designed to work. Yet in
both sensitivity and selectivity this combination
has all the advantage given by the large
number of tuned circuits and many stages of
amplification that can be used in the fixed
frequency receiving set.
It is possible that other circuits may be invented
in the future that are cheaper or easier
to build than a super-heterodyne, but it seems
impossible that any could be made to work
better because the super-heterodyne can be
made ideal from the operating point of view.
By taking the trouble to cut condenser plates