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Minimal
Antennas and Grounds
Make it
cheap, simple and effective
By:
Daniel Grunberg (ce369@FreeNet.Carleton.CA)
Date: Aug 8, 1996
Original source: Usenet's rec.radio.shortwave
Modern
shortwave receivers, particularly modern portables, tend to
be very sensitive. Modern shortwave receivers most often are intolerant
of overly strong signals, even strong signals well away from the
frequency being tuned. For example, a local, strong MW station
might overload your receiver's front-end. The result could be
images all over the SW bands, or it could be an apparent lowering
of the receiver's gain.
Therefore, the best, and least costly, antenna is the least antenna
that can receive what you want to receive.
I'd try the following in turn, and stop when I was satisfied with
the reception I was getting.
1. The
receiver's built-in antenna.
2. Some
copper wire.
Up to twenty feet of wire (insulated or not) strung up as high
as is convenient, inside the house. Radio Shack has a reel-up
wire for this purpose (278-1374), which easily can be taken down
and stored when not in use. Ask about Radio Shack's return policy,
in case it doesn't work for you.
3. Grounding
the receiver and using antenna 1 or antenna 2 (above).
The following grounding methods may increase the received signal-to-noise
level, but they will not necessarily protect you, your house,
your property, or your receiver from lightening.
Almost any sort of external ground may help.
Improvised, less-than-ideal, external ground connections have
been known markedly to increase signal-to-noise ratios.
If your
receiver has an external antenna connector, an external ground
connection usually may be made via the sleeve of the connector's
mating plug (see illustration below). Inserting the plug into
the receiver's antenna connector will disconnect the receiver's
antenna from the receiver's front-end. A clip lead, from the appropriate
lug on the plug to the base of the whip antenna, can be used to
reestablish a connection to the receiver's whip antenna.
||__________
||__________||0 <--- to rcvr front-end
|| ^
to rcvr
gnd
You can
try to eliminate the the clip lead from the plug to the whip
antenna by cutting the antenna plug. What remains of the long
part near the wire terminals (which were not drawn on the left
part of the figure below) should be long enough to makes a non-intermittent
ground connection when it is inserted into the radio's antenna
jack, but should not be long enough to operate the antenna
jack's switch and disconnect the antenna.
The following figure shows what I mean.
The figure is not to scale, so no dimensions should be inferred
from it. [Actually, since I haven't tried cutting a plug, I
don't know what the dimensions should be.]
||______ ____
||______ ____||0
|| ^ ^
insert throw
this part this part
in receiver's away
antenna jack
The best
way to ground your reciever is to connect its ground to a
ground rod (Radio Shack has them, but I don't know the catalog
number) driven into damp soil, as near to the receiver as possible.
The next best external ground connection is to a ground
clamp mounted on a metal *cold* water line. Ground clamps and
ground rods often can be found in the electrical supply section
of your local hardware store.
Less satisfactory external ground connections may be made
(in the USA anyway) to a #10-24x1.5" screw or a #10-32x1.5" screw
that you have pushed into the small round ground-pin on a 120
VAC outlet.
Don't use the wall outlet ground unless you know
exactly what you are doing and you have
verified that the outlet has been wired correctly.
The diagram below is meant to represent a 120-VAC, 60-Hz,
grounded outlet like those used in all but the oldest house wiring
in the USA. The outlet has two parallel openings. Although the
parallel openings are of roughly the same size, it can be seen
that one of the parallel openings, the one shown on your left
in the diagram, is slightly longer than the other one. The outlet
has a third opening, the lowest one on the diagram, that is shaped
differently and is smaller than the other two.
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