[Elecraft] K3 and K2 - concerns about power into RX ant

[Don Wilhelm]

  There have been several concerns expressed on the reflector about how 
much power is being sent into the K3 RX antenna (also applies to the K2 
with a K160RX option).

Rather than guess if that level is safe for the radio, why not just 
measure it?  It is easy to do.  Try this:

Do you have a wattmeter that is accurate at the 1 to 2 watt level?  If 
so, connect it to the receive antenna (make certain the antenna is 
terminated into a 50 ohm load either within the wattmeter or with an 
in-line wattmeter, connect the dummy load to the ANT side) - note that 
for this measurement, the receive antenna is the "transmitter".

If you do not have an accurate QRP wattmeter, then connect the antenna 
to a dummy load and measure the RF voltage across the dummy load with an 
oscilloscope or an RF Probe.  With an RMS reading RF Probe and a 50 ohm 
dummy load, 7.07 volts is 1 watt and 10 volts is 2 watts - with an 
oscilloscope (use a 10X probe), the peak to peak voltage would be 28 
volts for a 2 watt signal and 20 volts for a 1 watt signal.  If your 
dummy load is fully enclosed, you can gain access to the center 
conductor with a UHF TEE adapter.

The K3 generates a HI RFI message in the VFO B display if the level is 
about 1 or 2 watts, so we can likely guess that level will cause no 
harm, and it should be below the level where the COR activates.

If you have more than 2 watts from the receive antenna (from any 
transmitter running at its highest power and using any TX antenna) into 
a 50 ohm load, then I would recommend some secondary protection.  If the 
level with your highest transmit power is less than 1 watt, then I would 
not worry about it.

73,
Don W3FPR