Matt,
There is no provision for that as far as I know, however the 2N5109 used
in the K2 preamp stage is quite a robust transistor. For instance the
absolute maximum base to emitter voltage is rated at 3 volts and the K2
preamp design raises the emitter 1.3 volts above the board ground. It
would take a very healthy signal on the K2 input to produce greater than
3 volts peak at the base to emitter junction.
Even the K2 Receive Signal Tracing instructs one to inject a 0.14 volt
RMS signal for tracing purposes, and that is a very strong signal (I
calculate 39 mW).
The 1st mixer (a TOP1 diode ring mixer) is capable of handling very
large signals as well.
I would not drive a 5 watt signal directly into the K2 receiver and
expect no damage, but under normal operation there should be no problem.
If you are expecting an extremely large signal on the feedline while the
K2 is connected, I would suggest that some external protective device be
added to your station.
73,
Don W3FPR
On 5/2/2014 2:32 PM, Matt VK2RQ wrote:
When building the K2, one installs a couple of back-to-back diodes across the
input of the IF amplifier to clamp the input voltage. However, if there is a
large signal on the antenna during receive, what protection is there for the RF
preamp transistor and the first mixer? Does the micro controller monitor the
V_RFDET line on the antenna during receive, and switch out the preamp/switch in
the attenuator when a large signal is detected?
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