[Lowfer] Amplifiers for 136 kHz

[John Andrews]

Bill,

> Haven't figured out a way to drive a 100ft coax with a square wave having
an
> impedance near 0 ohms, unless I use a tuned circuit between the final and
> the coax to convert the output Z to 50 or 70 ohms. But that makes it two
> circuits to tune rather than one each time I want to change frequency. Any
> ideas?

You see, I ducked that here. I feed 10 milliwatts from the house into a 50
ohm resistor at the transmitter in the woods. That's 2 volts peak to peak,
which I run through a Schmitt trigger arrangement done with a 74HCT14
package that is the driver for the PA transistors. I'll dig up a diagram.

> Don't see too much of a handicap with an untuned final in the woods (well,
> not counting the loop tuning cap). Takes < 2 minutes each way to run out
and
> bring in the final box to the bench to make alterations and then return
it.
> I have a loop simulator coil and exciter simulator on the bench so there's
> no surprises when I re-connect it back to the loop and shack cables.

Of course, you'll be feeding a little more DC power out there, as well.

But it does provide good exercise to keep walking out there!

John A.