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 station. "
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.
A Review of Its Principles in Simple Language
By Harvey Pollack,* W2HDL
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."
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 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.
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.
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
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
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.
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 .......................................................
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:
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
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 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
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.
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
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.
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
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!