March 1945 QST
of Contents]These articles are scanned and OCRed from old editions of the
ARRL's QST magazine. Here is a list of the
QST articles I have already posted. All copyrights (if any) are hereby acknowledged.
panoramic receiver is not a wartime development, experimental models
having been produced just prior to the outbreak of war. However, the
many uses to which it has been put have demonstrated that the panoramic
idea, particularly in the form of adaptors which may be connected to
any receiver, is going to be very important and useful in the ham station
of the future. In simple language this article reviews the general principles
upon which the panoramic system is based and includes also a picture
of the many ways in which it may serve the operator of a postwar amateur
See all available
vintage QST articles
A Review of Its Principles in Simple Language
Harvey Pollack,* W2HDL* Engineering Dept.,
Panoramic Radio Corporation.
At A desolate, lonely post
in the heart of the Allied lines in Burma, a Marine radio operator was
grimly monitoring the bands used by the Japs for field orders. Before
him were several communications receivers, each surmounted by a smaller
cabinet containing a cathode-ray tube. His alert glance shifted from
one to another of the fluorescent screens while he continually checked
the frequency sheet used by the various Allied mobile and fixed transmitters
in the area. The constantly shifting pattern of radiance was so familiar
to his trained eye that only cursory and occasional corroborations were
necessary; he knew almost instinctively that every station on the air
was that of a friendly post.
Suddenly, and without warning,
a small peak appeared on one of the screens where none had existed before.
It stood out like the shoe-button eye of a snow man.
muttered the operator. "And mobile, too. - Look at that peak grow! Only
thing that could come that fast is a flight of planes."
as suddenly the peak winked out and the scene was restored to its former
serenity. But the cat was out of the bag. The operator reached for the
land-line transmitter and spoke a few clipped words into the mouthpiece.
Almost instantly, at far-flung and widely separated aircraft
installations, a sharp alert was sounded as the men took their stations.
Long before the Japs came within striking distance, the Allied fighters
met them head on.
The Japs never had a chance.
What the Panoramic Receiver Tells Us
unit which makes such feats and many others possible is the panoramic
adaptor which may be added to almost any type of receiver. Technically,
panoramic reception is defined as the simultaneous visual reception
of a multiplicity of radio signals over a broad band of frequencies.
In addition, panoramic reception provides an indication of the frequency,
type and strength of signals picked up by the receiver. Deflections
or "peaks" appearing as inverted Vs on the screen of a cathode-ray tube,
as shown in Fig. 1, are indicative of the presence of signals. The character
of each individual deflection tells its own story. For instance, in
Fig. 1, a is a signal of constant amplitude indicating a steady carrier,
while b is a nonvarying signal whose strength is about twice that of
a. The signal indication at c is a peak which appears and disappears
so rapidly that the base line appears closed beneath the deflection.
This type of trace is produced by a very rapidly keyed c.w. signal.
With slower keying the base line would appear open. Incidentally, if
the keying is sufficiently slow the code can be read directly from the
screen, like a blinker, after a little practice.
Fig. 1 - Typical signal patterns on the screen of the cathode-ray
tube of the panoramic receiver. The peaks a and b indicate a c.w.
signal or unmodulated carrier. The closed baseline of c indicates
a rapidly keyed signal, while d's irregular shape identifies it
as a modulated carrier.
Fig. 2 - Graphic representation of the 3.5.Mc. amateur band with
the panoramic adaptor sweeping the 3.6 to 3.8·Mc. section. The receiver
is tuned to 3.7 Mc.
Fig. 3 - This is the same as Fig. 2 except that the receiver is
now tuned to 3.6 Mc., the panoramic sweep now covering a range of
3.5 to 3.7 Mc.
Fig. 4 - Sketches illustrating how "resolution" may be improved
by decreasing the sweep width. A indicates two signals very close
together in frequency with a wide sweepband, while B shows how the
same two signals are separated when the sweepband is reduced.
The signal at d is composed of separate parts. The smaller peaks are
produced by the sidebands of a modulated carrier, while the high center
peak is produced by the carrier itself. Hence, this is the picture of
a 'phone station. More often the sidebands will not be visible as separate
deflections, a 'phone station trace being recognizable rather by a deflection
which tends to vary in amplitude between the high center peak and the
low center peak.
The various frequencies shown may be compared
with reference to each other or to the calibrated dial of the receiver.
As an illustration, imagine that the receiver dial reads 5000 kc. Signal
c, the c.w. signal discussed previously, appears immediately above zero
on the scale. This scale reading indicates that the frequency of the
signal is that indicated on the dial of the receiver; in other words,
5000 kc. Another way of saying the same thing is that the frequency
difference between the receiver dial reading and the signal appearing
over the center of the scale marking is zero. It follows from this that
signal a is 100 kc. lower than signal c, or 4900 kc., while signal b
is approximately 65 kc. lower than signal c, or 4935 kc. Hence, while
signal c is heard on the receiver's normal output circuit, the other
signals will be seen distributed as shown in the diagram. They will
not be heard in the headphones, however, unless they happen to be close
enough to c in frequency to be within the receiver's normal band of
acceptance. Application to Amateur Bands
For the sake of clarity, let us choose the 3.5- Mc amateur band
for our discussion. This band extends from 3.5 Mc, to 4.0 Mc. and is
shown graphically in Fig. 2. Now let us say that the receiver has been
equipped with a panoramic adaptor which covers a maximum bandwidth of
200 kc. and that the receiver has been tuned to 3.7 Mc. All of the signals
between 3.6 and 3.8 Mc. will be visible on the screen of the cathode-ray
tube in the adaptor. The signal heard on the headphones will appear
at the center of the screen as signal c. Now to listen to signal a,
the receiver would have to be tuned to a lower frequency.
the receiver ·tuning is shifted, all of the peaks will move to the right
across the screen until signal a is heard. At that point, a will appear
centered on the screen as shown in Fig. 3. Signal c now has moved to
the right of the screen and is visible but no longer audible in the
headphones; b has passed through the center of the screen and might
have been heard for an instant as it passed the center point of the
screen. At the same time, new signals, d, e and f. which were not present
previously now have made an appearance at the left side of the screen
since the 200-kc. acceptance band has been shifted lower in frequency.
Because the signals in this part of the band all are c.w., the deflections
will appear and disappear in accordance with the keying. Should we now
tune to the 'phone band the signals will appear as peaks pulsating in
amplitude. This effect, as explained previously, is caused by the modulation.
Another feature of an adaptor
of this type is that the number of kilocycles visible at any time (sweep
width) is under the direct control of the operator and may be reduced
to any lesser value all the way down to zero if so desired. This control
provides the operator with a visual selectivity control of the most
flexible variety. As the sweep width is reduced, the resolution constantly
improves. The term "resolution" is used here in the same sense as the
word "selectivity" is used in discussing the frequency discrimination
of receivers. Fig. 4 should help to illustrate this point. Two signals
differing in frequency by 3 kc., let us say, will present the appearance
shown in Fig. 4-A if the sweep width control is set at its maximum point.
Now, as this control is backed off, the signals will appear to separate
and at about 20 percent of maximum they will appear somewhat as presented
in Fig. 4-B. This increase in visual selectivity may be carried still
further by a greater reduction in sweep width. Not only does this feature
permit visual inspection of signals which otherwise might interfere
with each other, but also it makes possible the analysis of signals
which are heterodyning one another. If we should be in the middle of
a QSO when QRM starts to wash it out, a quick reduction in sweep width
will disclose the side (high- or low-frequency) where the heterodyne
modulation is taking place. A break-in flash to the other end - such
as "shift two or three kc. higher" - will suffice to shift the QSO to
clearer channels. Superheterodyne Fundamentals
For the benefit of those who have permitted themselves to become
rusty in elementary superhet-receiver theory, let us first review the
principles upon which this type of receiver is based. Let us assume
that a radio signal whose frequency is 100 kc, is to be received. Referring
to Fig. 5, the 1000-kc. signal is fed into a tuned stage called the
converter. At the same time the h.f. oscillator of the converter feeds
a signal of 1400 kc. into the mixer section. When these signals are
combined in the mixer, a new frequency representing the difference between
the two original frequencies appears in the output. In this case the
difference frequency (or intermediate frequency) is 400 kc. Of course,
the original frequencies are still present, plus a fourth frequency
equal to the sum of the original frequencies, but the tuning of the
following i.f. amplifier is so sharp that only the 400-kc. signal is
permitted passage. Following the highly selective intermediate-frequency
amplifier, the signal is detected or demodulated, the modulation being
amplified through the audio amplifier to a sufficiently high level to
operate a speaker or headphones .
Thus we have:
frequency ....................................................... 1400
Signal frequency ............................................................
Intermediate frequency ...................................................
Now, should we desire to listen to a station at 1300
kc., we would rotate the tuning-condenser knob to the new position.
Since a ganged tuning condenser is usually employed, in so doing we
have changed both the frequency to which the converter is tuned and
the oscillator frequency and we now have:
....................................................... 1700 kc.
Signal frequency ............................................................
Intermediate frequency ...................................................
It will be noted that the i.f, has not changed because
we have maintained a constant difference between the signal frequency
and the oscillator frequency. Thus the tuning of the i.f. amplifier
may be fixed for all signal frequencies so long as the oscillator frequency"
tracks" 400 kc. higher (or lower if desired) in frequency than the frequency
of the incoming signal. In this case, the i.f. amplifier is tuned to
400 kc. and left there.
It is obvious that many signals differing
quite widely in frequency are inducing their respective voltages in
the antenna. Although the input circuit of the converter stage is tuned,
its selectivity is so poor that signals differing by several hundred
kilocycles from the one to which the receiver is tuned will appear at
the grid of the converter tube, with only slight attenuation below that
of the signal to which the receiver is tuned. Thus, with the response
characteristic shown in Fig. 5, the amplitudes of signals at 900 and
100 kc. are only slightly below the amplitude of the signal at 1000
kc. to which the. receiver is tuned.
Fig. 5 - Block diagram of the various
units comprising a superheterodyne receiver
with panoramic adaptor.
The accompanying graphs serve to illustrate
the tuning characteristics
of the principal units of the system.
Starting with the assumption that several signals of equal strength
reach the antenna, the signal to which the converter is tuned will be
the strongest, as we have seen, while the others which are off resonance
will fall off in relative strength to a degree depending upon the frequency
separation from the frequency to which the converter input is tuned.
Although it would be impossible to receive these signals simultaneously
by the usual aural method without interference, we shall see that this
can be done visually by panoramic reception. The Panoramic
A small portion of the voltage developed by
each of these input signals is taken from the output of the converter
and fed into the r.f. amplifier of the panoramic adaptor which is broadly
tuned with the i.f. of the receiver (400 kc.) as its center frequency.
It will be noted from Fig. 5 that the input circuit of this stage is
designed to have a response characteristic opposite to that of the input
circuit of the receiver's converter stage, the ultimate effect being
to compensate for the dropping off of signals off resonance in the converter
stage, so that all signals of equal strength at the antenna again are
essentially equal in strength at the grid of the adaptor r.f. stage.
The signal from the r.f. stage is fed into a converter stage
whose input circuit also is broadly tuned to accept all signals delivered
to it by the r.f. stage with as little attenuation as possible. The
local oscillator used in connection with this converter is normally
tuned to a frequency 200 kc. higher (or lower) than the center frequency
of the band accepted by the converter input circuit to produce an i.f.
of 200 kc. However, the frequency to which this oscillator is tuned
does not remain constant as it does in the receiver proper. Its tuning
continually is varied or swept over a selected range of frequencies
so that at some point in its excursion it mixes or beats with each one
of the signals appearing at the input of the adaptor converter to produce
the required i.f. of 200 kc. Thus when this oscillator's frequency is
500 kc., it beats with the 300-kc. signal to produce an i.f. of 200
kc. to which the following i.f. amplifier is sharply tuned. Similarly,
when the oscillator's. frequency. is at the other end of its range,
700 kc., it beats with a 500-kc. signal again to produce an i.f. of
200 kc. Cathode-Ray Indicator
of the adaptor's i.f. amplifier is rectified and the resulting d.c.
voltage is applied to the vertical deflecting plates of the cathoderay
tube. We know that with no voltage on either vertical or horizontal
deflecting plates the spot on the screen of the cathode-ray tube normally
will be stationary at the center of the screen. If, however, a varying
voltage is placed across the vertical deflecting plates, the spot will
move in a vertical direction, forming a luminous line if the variations
in voltage are sufficiently rapid to create persistence of vision. Therefore,
if we were to tune the adaptor's oscillator to beat with one of the
signals at the input of the adaptor, the out. put voltages of the rectifier
following the i.f. amplifier would follow a curve similar to the response
curve shown for the adaptor's i.f. amplifier in Fig. 5, and if this
voltage is applied to the vertical deflecting plates of the cathode-ray
tube, the spot will move upward from the center and then back to center
as the beat between the oscillator and the signal approaches the i.f,
of 200 kc. and then recedes after passing through maximum at 200 kc.
If the tuning of the oscillator in this manner is done repeatedly and
at a high rate of repetition, a vertical line would appear on the screen
of the cathode-ray tube.
Now, if at the same time a smoothly
varying voltage is applied to the horizontal plates, the spot will move
under the influence of a horizontal as well as a vertical force and
the resulting path will resemble the i.f. response curve.
In the panoramic adaptor,
the tuning of the oscillator is not done manually, of course, but this
is accomplished by a reactance modulator whose characteristics are such
as to sweep the frequency of the oscillator back and forth over the
proper range at a rate corresponding to the rate of oscillation of a
second special oscillator called the b.t.o. (blocking-tube oscillator).
Voltage from the b.t.o. also is fed to the horizontal deflecting plates
of the cathode-ray tube so that the spot when no signal is present at
the input of the adaptor is moved back and forth horizontally in synchronism
with the sweeping of-the adaptor's converter oscillator. If signals
are present at the input of the adaptor, they will cause vertical deflections
whenever the oscillator's frequency is appropriate to produce the required
200-kc. i.f, and these signals will then be reproduced in succession
as indicated in Fig. 5. Normally, the sweeping action is set at a repetition
rate of about 30 cycles per second, any rate which will maintain persistence
of vision being adequate.
Since the signal to which the receiver
is tuned corresponds to the center of the range being swept by the adaptor's
oscillator, it follows that any peak appearing in the center of the
screen is caused by the signal to which the receiver is tuned. Also,
since the amount of vertical deflection for any given signal is proportional
to its strength, strong signals will cause high peaks on the screen,
while the peaks of weaker signals will be proportionately lower.
It is not difficult to
visualize many ways in which panoramic reception may be applied in postwar
ham work. It is, of course; very easy to spot an unoccupied channel
on the screen of the cathode-ray tube, and just as easy to watch the
e.c.o. of the station's transmitter walk up to the vacant hole as the
operator tunes it to the proper frequency. Not only is the lining up
of stations in a spot-frequency net facilitated, but if net stations
or stations in a "round-table" are operating on scattered frequencies,
the control-station operator can keep tabs on all of them without disturbing
the setting of his receiver. This sort of visual reception is valuable
in many other practical operating tricks.
By the pattern on
the screen, it is possible to check percentage of modulation, comparative
signal strength, carrier shift and other signal characteristics. With
the sweep width reduced to zero, the panoramic receiver becomes an oscilloscope.
With a calibrated scale on the screen accurate frequency checks may
While it is not probable that many operators could
develop visual code-copying speed comparable with the speeds possible
by ear, it should not be difficult for any ham to develop his eye to
the point where he readily could recognize such things as the "CQ SS"
of a Sweepstakes contest!