Hi Vic,
Have you thought of just switching the rx antenna out of circuit whilst
transmitting? Unless you are using fast break-in, a small externally
switched relay should solve your problem. If you are feeling
particularly paranoid:-), then use the same relay to earth the rx input
via a 50 ohm resistor at the same time.
gl, Trev G3ZYY
In message <[EMAIL PROTECTED]>, Vic Rosenthal
<[EMAIL PROTECTED]> writes
I am experimenting with using the K2 rant input (that's receiver
antenna, not verbal outburst).
I want to use my 20-meter quad as a receiving antenna when I am
transmitting on 160 with an inverted L. It is a lot quieter. The L is
right next to the quad, so a lot of voltage is induced in the quad when
transmitting with high power.
I tried putting a couple of back-to-back diodes and a 50-ohm resistor
across the quad feedline. I put my scope across it and found that the
signals from BC stations, etc. were well below the clipping level of
the diodes, and received signals were plenty strong with the K2 preamp
on. So far so good.
Transmitting resulted in the clipping level being reached with about
100 watts output (I have an external amplifier capable of 1500 watts).
All of a sudden, I realized that I have built a huge harmonic QRM
generator! If I use this setup, as soon as the diodes clip they will
generate harmonics all the way up into VHF, which will be re-radiated
by the quad (it will do a real good job on the 4th harmonic, near 20
meters, too).
Am I right? If so, this isn't a good way to do what I want. Does
anyone know a) how much RF voltage can be safely applied to the K2 rant
input when transmitting, or b) how to protect the input without making
harmonics? I thought of using the diodes after a lowpass filter that
cuts off around 2.5 MHz, but this is getting complicated.
--
Trevor Day
UKSMG #217
www.uksmg.org
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