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Dear MD, I hope I don't hurt your feelings but a "Balun" is a device for
changing a "Balanced" feedline (dipole) to an "Unbalanced" feed so as to match
the "unbalanced antenna input" found on most receivers. Balun is a conjunction,
combining bal and un to represent this balanced to unbalanced transition. Baluns
can perform other tasks also. Depending on the characteristic impedance of an
antenna "at the feed point" a Balun can be wound to form an impedance transition
(say from 200 ohms to 50 ohms characteristic impedance of the feedline.
The use of a Balun has other benefits also. To you as a listener, if you
use a balun at the feed point of your antenna and connect the coax cable you
ground the braid of the coax at that point. Also, when you connect the coax to
the receiver you ground (short out) the coax braid at that point also. The
effect is that the braid is now no longer a part of the antenna system and is
allowed to function as it was intended, to block noise from the coax center
conductor. To assure better noise rejection of the braid, and to keep it out of
the antenna system in an even more effective fashion you should provide a ground
for the braid outside & as close to the receiver as possible.
What you really are wanting to do is to 'Couple" your outside antenna to
the MW receive section of your receiver. First you need to check to see if the
receivers in question are using a built in MW antenna in the form of a ferrite
rod or a loop coil. The easiest check is to tune the receiver to any MW station
without any antenna connected. If you hear a signal then the receiver does have
a ferrite rod or a coil MW antenna to couple to. I'll bet that is the
case.
The easiest way to couple the external antenna to the receiver with a built
in MW antenna is to use another ferrite rod that is connected to the end of the
external antenna. Two very good examples would be to use an RF Systems AA-2 or a
Palomar LC-1 (both are ferrite rods that magnetically couple RF from the antenna
to the receiver, no direct connection needed. Both are carried by Universal
Radio). A better method would be to use a "magnetic loop" such as the Terk or
the Select-A-Tenna. Both have a mini jack for plugging in the external antenna.
The benefit of these last two options is that 1) they are tunable and 2) they
can be used alone for better nulls. One last trick that will always work is to
just wrap a few turns of the external antennas feedline around the receiver! It
too will inductively couple to the receiver.
I hope I didn't confuse you. Feel free to reconnect me.
73 John T. Wagner, Ohio
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