March 1945 QST
Wax nostalgic about and learn from the history of early electronics. See articles
QST, published December 1915 - present. All copyrights hereby acknowledged.
"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 'V's on the screen of a cathode-ray tube." It is the
kind of display that
radar operators at Pearl Harbor were using when they mistook
wave of incoming Japanese bombers for a squadron of B-17s from the mainland. The
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
A Review of Its Principles in Simple Language
By 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.
"Japs!" muttered the operator. "And mobile, too. - Look at that peak grow! Only thing
that could come that fast is a flight of planes."
Just 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
The cathode-ray 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 "V"s 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 sweep band, while B shows how the same two signals are separated when the
sweep band 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.
As 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.
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:
Oscillator frequency ....................................................... 1400
Signal frequency ............................................................ 1000
Intermediate frequency ................................................... 400 kc.
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:
Oscillator frequency ....................................................... 1700
Signal frequency ............................................................ 1300
Intermediate frequency ................................................... 400 kc.
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
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
with panoramic adaptor. The accompanying graphs serve to illustrate
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
The Panoramic Adaptor
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.
The output 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
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
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
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 be made.
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!
Posted December 20, 2018