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This Month’s Interesting Antenna-Related Web site:
This site discusses indoor antennas:
http://www.hard-core-dx.com/nordicdx/
antenna/hidden/indoor.html
will snap onto the fresh 9-volt battery which is
used to power the active antenna. No switch was
included in this design: the circuit was simply
un-snapped from the battery to turn it off.
The transistor can be an MFP-102 (Radio
Shack #276-2062), 2N3819 (Radio Shack
#276-2035), or similar N-channel FET. If you
substitute a P-channel FET then you must reverse
the battery polarity from that shown in the diagram.
Your local Radio Shack, Dan’s Small Parts
and kits, or other radio-parts supply store should
have the required parts.
Make sure all the wires and leads you connect
together are clean. You can scrape them with
a knife edge to clean them if needed. The unit
will probably work more reliably if you solder
the connections, but just twisting the leads of the
parts very tightly together will work if you can’t
solder. A small soldering iron is less likely to
overheat the components.
Carefully connect the parts as shown in fig.
1, and then recheck to see that the circuit is wired
properly. The position on the transistor of the leads
to the source, gate and drain varies for different
transistors, so check this in the data that comes
with your transistor.
The connection to the receiver antenna can
be via coax as shown in fig. 1, or you can use a
pair of wires twisted together to form a short cable.
The wire attached to the capacitor should run to
the center conductor of the antenna input terminal,
and the wire connected to the battery negative
(-) terminal should run to the antenna-connector
ground or shell.
Try lengths of from five to twenty feet or
more for the antenna wire. If it is too long, you may
notice problems with intermodulation distortion or
desensitization when strong signals are present at
your location. If your building shields the antenna
from signals too much for decent reception, try
putting a whip antenna in a window to replace
the antenna wire, hanging the antenna wire out a
window, or attaching the antenna wire to a wire
window-screen.
Happy monitoring!
Last Month
I said: “Let’s say that you are listening on HF,
and you receive a very short transmission, perhaps
just a dit of Morse Code. Then after only a fraction
of a second, say .13 second, you receive that
identical transmission again. Is it possible that the
short transmission wasn’t re-transmitted a second
time, but somehow, instead of traveling off into
space, it returned to your antenna a second time?
Could it even do this a third, or fourth time? Radio
waves travel in straight lines don’t they? So am I
just talking crazy, or could that really happen?”
Well, when propagation is right for it, signals
do actually go around the world in about .13 seconds.
And after doing this they sometimes arrive
back at your station with sufficient strength to
be heard. The antenna pioneer John Kraus has
mentioned that he used his famous bi-directional
W8JK beam to check for round-the-world band
openings by tapping the key, and listening for his
signal to return in this fashion.
Engineers for the radio pioneer, Marconi,
built a very large beam antenna in Australia
for Great Britain’s world-wide communication
system. When using this “Imperial Beam,” radio
operators could actually hear several round-theworld
passages of transmissions which they
sent from that beam: the signals made multiple
round-the-world trips and were heard several
times before they became too weak to be heard!
This Month
Okay, so we can receive a signal a second
time after it goes around the world and comes
back past our location again in about .13 second.
But what about receiving a transmission of our
own voice a few seconds after it was transmitted?
Sounds spooky, huh? Can it happen?
You’ll find an answer to this month’s riddle,
another riddle, another antenna-related web site
or so, and much more, in next month’s issue of
Monitoring Times. ‘Til then, Peace, DX, and 73.
* MFJ Enterprises, Inc., P.O. Box 494, Mississippi
State, MS 39762. phone: 800 - 647-1800
**Bilal Company, 137 Manchester Drive, Florissant,
CO 80816, phone: 719-687-0650
*** http://www.danssmallpartsandkits.net/
January 2005 MONITORING TIMES 63