January 1970 Popular Electronics
[Table of Contents
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
is pretty cool. If I owned a good receiver, I would definitely give it a
try. In 1970 when this Popular Electronics article was written, a lot of
Hams were still using tube receivers so the recommendation to let the equipment
warm up for several hours prior to making the fine frequency adjustments
was good advice. Nowadays the warm-up time and stability of receivers should
permit 30 minutes or so to suffice (even ovenized frequency references need
time to stabilize when first powered up). Unless I missed it, the author
does not explicitly state that the frequency change measured over time is
due to gravity acting on the mass of the crystal reference, but I suspect
that is his intention since part of the experiment involves disconnecting
the antenna and shielding the receiver from outside interferers. Over a
period (29.5 days) we experience a leap tide and a neap tide which
maximizes and minimizes, respectively, the vector sum of gravity and therefore
should result in the greatest excursions. Maybe with a super-stable source,
a larger scale phenomenon such as a planetary
could be detected (but I doubt it).
See all the available
An Experiment with Gravity
By Commander Thomas Appleby
Sample graph shows the plot of frequency changes versus time. Note that
plotted line peaks out shortly after noon.
CHART THESE STRANGE FORCES WITH YOUR RECEIVER
We are all familiar
with the natural phenomenon known as gravity; but most of us tend to think
of gravity on the surface of the earth as being constant. In fact, it is
always changing in magnitude, due mainly to the forces exerted on the earth
by the sun and the moon. The variations are, of course, so minute that only
in the past few years have they been detected by specially designed, highly
sensitive instruments. Oddly enough, my years of research into the phenomenon
have shown that the average ham radio CW receiver can apparently "detect"
changes in gravity.
The effects of gravity on a receiver might account
for its drifting off frequency. Even after communications receivers have
had time to become thoroughly temperature stabilized, frequency drifting
and periodic returning are common occurrences.
of the effects the forces of the sun and the moon have on the earth's gravity,
you can experiment on your own. All you need is a receiver with an ultra-fine
scale on its tuning dial. (One that has 10 divisions for each minor division
on the main tuning dial scale.) Remember that gravity variations are on
the order of only 10-6
part of the weight of the mass in which they are produced. Although the
effect of the variations is greatly amplified by your receiver, the end
result is still minute.
To perform the experiment, disconnect the
antenna and any other leads that might pick up a signal at either 3500 or
7000 kHz. In the morning, set the tuning dial of your CW receiver to
either of the above frequencies and adjust the BFO for zero beat.
Allow the receiver to warm up for several hours. Then reset the BFO
for zero beat. Every half hour or so after this, see if it is necessary
to retune for zero beat. Record the new dial setting and make up a graph
similar to that shown here. The frequency changes you record will be very
small so use an expanded scale.
The recorded frequency variations
will increase or decrease, depending on whether the magnitude of gravity
is increasing or decreasing, respectively. You will notice that after the
sun or moon passes the zenith, the curve will begin to bend downward. Also,
the curve will change from day to day because of variations in the orbits
of the sun and the moon.
"A completely new branch
of astronomy is opening up with the recent discovery of gravitational waves
by Dr. Joseph Weber of the University of Maryland. The force of gravity
is the most fundamental and least understood force in the universe; confirmation
that gravity varies will be detected may well turn out to be as important
as the discovery of radio waves by Heinrich Hertz in 1887."
-The Industrial Bulletin, Arthur D. Little, Inc.
Posted January 7, 2013