February 1963 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
1963 was five years since
America's first communications satellite, Echo, was placed in orbit. Echo was a
passive, spherical reflector that merely provided a good reflective surface for
bouncing radio signals off of. By 1963, the space race was well underway and active
communications satellites were being launched at a rapid pace. This 1963 issue
of Popular Electronics magazine reports on satellite signals being
received by other than their intended targets. Spotting and tracking
satellites has long been a popular pastime with two types of hobbyists: amateur
astronomers using telescopes and binoculars, and amateur radio operators using antennas
and receivers. Today's amateurs are picking up signals from spacecraft orbiting
Mars Reconnaissance Orbiter in 2018, and
China's Tianwen-1 probe in 2021) and are finding long-lost and presumed-dead (aka "zombie")
Earth-orbiting satellites (NASA's
and Cold War era military
LES-5 in 2020).
Eavesdropping on Satellites
By Tom Lamb, K8ERB
With at least six easy-to-snag NASA satellites
in the 136-137 mc. band, there's no time like right now to start pulling them in.
How? Well, a receiver offers no real problem-your present communications set can
be made to tune the 136-mc. band simply by adding a converter. And, you can either
modify an existing converter designed to cover the 2-meter ham band, or, better
yet, you can build the special "NASA 136" for this very purpose (for full details,
see the June 1962 issue of POPULAR ELECTRONICS, p. 39).
Fortunately, too, a large and elaborate antenna system is NOT necessary at these
frequencies. In fact, near overhead passes can be picked up with a 3' 7" dipole,
and you may even get satisfactory results with a TV antenna.
Start by listening for the Tiros satellites, since their signals are moderately
strong. With your antenna pointed SE or SW (in the U.S.), set your receiver for
c.w. reception, use a medium i.f. selectivity, and tune to 136.230 mc.
If your converter and receiver calibration aren't spot on, tune around the satellite's
frequency every five minutes or so, listening carefully for a weak carrier. An accurate
receiver can be left on the frequency until the carrier appears, although it could
take up to 12 hours for you to hear the first pass. A single, low-orbit satellite
can be heard for up to seven successive passes, followed by a 12-hour quiet period;
the exact sequence will depend to some extent on your location and system sensitivity.
Once you pick up the carrier, change to a narrow i.f., use a Q-multiplier, or try
any of the other tricks you may have for receiving very weak signals.
Identifying Satellites. All NASA satellites transmit a carrier (beacon) for tracking
purposes, and it's relatively easy to tell when you've picked one up:
(1) It will be accurately on frequency, but-
(2) A satellite will appear to be slightly high in frequency when approaching,
slightly low when receding. This Doppler effect will vary from nearly zero for a
distant pass to about 7 kc. for an over-head pass, and it's one sure way to identify
(3) Low-orbit (750-mile or so) satellites will be heard for only about 18 minutes
during each pass-usually considerably less.
(4) A satellite will usually be heard for several successive passes. (Since both
Tiros V and Tiros VI are on the same frequency, they confuse the picture somewhat-but
their transmissions will still be separated by the orbit period.)
(5) Most satellites are modulated by telemetry equipment. This modulation may
be quite weak, and audible only on near overhead passes.
Now that you know how and where to listen, you'll also want to know what satellites
to listen for. There are at least six, as we mentioned, of which the Tiros group
are especially good bets. Here they are, listed in order of ascending frequency.
Telstar. Frequency, 136.050 mc.; period, 157.7 minutes; altitude,
590-3500 miles. Telemetry on several very weak subcarriers. Long period and high
altitude make Telstar difficult to catch .
Tiros IV, V, VI. Frequencies, (IV) 136.230 and 136.920 mc.,
(V and VI) 136.235 and 136.922 mc.; period, (IV and V) 100.5 minutes, (VI) 98.7
minutes; altitude, 420-520 miles. Telemetry on weak subcarriers 1 kc. above and
below carrier. Tiros satellites are moderately strong and pass frequently. Weather
map pictures are transmitted on a higher band.
Ariel. Frequency, 136.408 mc.; period, 100.8 minutes; altitude,
247-750 miles. Telemetry sounds like clanking chains, out to ±15 kc. Ariel's modulation
is keyed from the ground and is not always present. Ariel is believed to have suffered
major solar cell damage from radiation belts and is transmitting erratically.
Alouette. Frequencies, 136.590 and 136.979 mc.; period, 105.5
minutes; altitude, 600 miles. Telemetry on multitone subcarriers out to ±20 kc.
A wide assortment of beeps and clanks makes Alouette one of the most interesting
satellites to log.
Other satellites in the NASA band are probably commanded from the ground and
are very elusive. But get Alouette, Ariel, Telstar, and Tiros (IV, V, and VI!) in
your log before you start thinking about snatching any of the hard ones!
PostedMarch 31, 2021(original