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
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