[Lowfer] RF Ammeter recommendation

[Ed Phillips]

John Andrews wrote:
> 
> Ed,
> 
> > There's a pretty cheap way to go as well.  Use a (relatively) large
> > capacitor as a shunt, with a smaller capacitor in series with a
> > full-wave rectifier in parallel.  (Meter in the rectifier circuit, of
> > course.)  Analogous to a DC shunt and meter.  Simple and works OK.
> > Convenient for tuning and not bad for accuracy if you go to the trouble
> > of analyzing the calibration.  Compared to a thermal ammeter has the
> > advantage of a more or less linear scale.
> 
> I suspect that circuit would analyze out to be the same thing as the current
> transformer, just done with capacitance instead of coupled inductors. Sounds
> like a reasonable approach, assuming that the shunt cap can handle the
> current, and that you don't try to remote the thing. As long as the meter
> circuit is kept right at the antenna, it should be OK. Remote reading will
> add some unwanted capacitance from the antenna to ground, depending on how
> the wiring is run. I'd avoid sticking my finger in there while the rig is
> running.
> 
> John A.

	Correct on all points, particularly the last one.  As for capacitors
I've used polystyrene with good results.

Ed