February 1963 Popular Electronics
[ Table of Contents] People old and young enjoy
waxing nostalgic about and learning some of the history of early electronics. Popular Electronics was published from October
1954 through April 1985.
As time permits, I will be glad to scan articles for you. All copyrights (if any) 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. 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. See all the available
Popular Electronics articles. 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 ap-proaching,
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 a satellite. (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 modu-lation 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.; pe-riod, 157.7 minutes; altitude, 590-3500 miles.
Telemetry on several very weak subcarriers. Long period and high alti-tude
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; al-titude, 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 suf-fered major solar cell damage from ra-diation belts and is transmitting
er-ratically. 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 as-sortment 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 think-ing about snatching any of the
hard ones!
Posted June 18, 2012
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