[Milsurplus] ART-13 Transmitter and BC-348 Receiver info

[Ian Wilson]

The parallel combination of a 'large' (at the frequency of operation)
capacitor and a 50 ohm load
looks like a series combination of a smaller resistive load and large
capacitance - in other words,
just what an electrically short antenna such as a trailing wire would
present. Since this is what
the various transmitter output circuits were designed to match to, they will
couple efficiently into
the transformed network. Note that only a small series inductance will be
required to resonate
away the large series capacitance. Using 1000pF across a 50 ohm load works
well with ARC-5
transmitters on 40m - about 10% of the variable inductor serving to resonate
the transformed C.

There are probably calculators on the web that allow you to see how
different choices of C affect
the transformed value of R, or you can use the series/parallel formulae and
calculate R the old way.
Since the transmitters can probably match effective R values in the 1-10 ohm
range, there is a
lot of leeway in the choice of C.

Using one of those largish square brown mica caps (1000pF or 1500pF, I
forget which) on 40m I
measured 50W output from an unmodified Command Set (OK, OK, I don't normally
drive them
this hard, honest).

73, ian K3IMW