🚀 go-pugleaf

In article <1992Oct15.032329.27616@am.dsir.govt.nz> srgxnbs@grv writes:

>basically I'd like to get a circuit which would allow me to power a remote
>transducer pre-amp (say 20-30VDC) and return the amplified signal (10kHz-
>1MHz) via a single 50 ohm coax cable.

	(I tried E-mail, but can't get through with the address given)

        It's really pretty simple; just power the preamp/oscillator with
a resistor/zener shunt regulator, and connect the AC signal
(through a transistor) to the coax.  The most convenient connection
is collector-to-center-wire, base to signal, emitter to resistor
to ground.

        Whatever the signal condition, the shunt regulator will
draw the current that the amplifier doesn't, so the current
in the central wire of the cable is fixed.  To this fixed
current you simply add some signal (modulated) current,
with that external transistor (or even just a small capacitor
to hold off the higher line voltage).

        Beware of oscillations in the coax cable, by the way;
you want to have resistor termination at both ends, or you
might end up with an accidental oscillator using the
cable as a delay line.

        John Whitmore