[Milsurplus] Coupling antenna to ART-13 on the ground

[J. Forster]

Even with the advantage of being inside a Faraday Cage, with certain
radios, there must have been some fairly strong fields. On the ARC-5 or
SCR-274-N, the transmitter binding posts were hooked to the Antenna Relay
and thence thoough the skin with open wires (OK, with creamic beads).

By contrast, the WS 19 Variometer output was mounted directly to the inner
skin of the AFV in many cases and must have had pretty low levels of RF.

-John

=============


> Hi Pete and the group.
>
> You should be able to get plenty of current in the wire.  The trick is
> getting that current to radiate out into space as opposed to lighting up
> the shack.  Unless your transmitter is right next to the
> bulkhead(oops....wall)where the antenna comes in, you might have too much
> of your antenna indoors.
>
> A trick I use for my TBX, which is made for a 24-foot vertical mounted
> right next to the transmitter, is to use a half-wavelength (electrical)
> run of coax out to a 24-foot vertical about 40 feet from the house.  This
> presents exactly the load that the transmitter expects, but with the
> antenna away from the house.  This trick works nicely because the TBX is
> only really useful on one amateur band(3.5Mc).
>
> Another trick is to use a 50 or 75 ohm coax-fed antenna like a dipole and
> run it into a 4:1 step-down transformer with a few hundred pF of series
> capacitance between the transformer and the transmitter.  I use 400pF on
> my TCS on both 3.5 and 7Mc on my TCS, maybe even 1.8Mc, I can't recall.
> That approach will work on multiple bands.  A single-band approach that
> works the same is to parallel 2x 1/4-wave lines and add the capacitor in
> series at the transmitter end.  That gets your antenna a quarter
> wavelength away from your transmitter.
>
> The guys running these in aircraft and ships had the advantage of metal
> bulkheads between the transmitter and most of the antenna, and much less
> in the way of sensitive electronics to be disturbed inside the "shack".
>
> RF
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