[Elecraft] Using K2 rant input

[Vic Rosenthal]

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.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco