[Elecraft] K2 Preamp on and huge key clicks. Normal?

[Ron D'Eau Claire]

Yes! You were simply overloading the receiver. Your reading of "S9+40" even
if high, suggests that. 

That's why there's an on/off switch on the preamp. It's only needed up on
the higher bands where the noise levels are really, really low and you are
digging for a really weak signal. 20 is sort of a transition band. It can
have low enough background noise that some receivers will hear better with a
pre-amp, but I've not yet experienced that with the K2 with any sort of
decent antenna. 

Next time you are wondering, turn Off the preamp and turn up the gain to
hear the background noise on a frequency where there are no signals. Listen
to the background noise while you disconnect the antenna. If you hear the
noise level drop when the antenna is taken off, the pre-amp won't do a thing
to help you hear weak sigs. It only makes ALL signals louder, and can make
some signals overload the front end. 

Remember, the receiver is wide open - amplifying all signals over a very
broad range of frequencies that go well above and below the whole band -
until the signals get to the I.F. filter. Then, and only then, do the
signals off frequency get attenuated. So a big signal several hundred kHz
away can cause serious problems that seem to appear all over the band if
there is too much amplification before the I.F. filter. 

Sometimes it's the combined effect of two or three such signals.

The Preamp is provided because the noise generated in the early stages of
the receiver can mask very weak signals if the band noise is low. That's
most likely to happen on frequencies above 14 or 21 MHz, depending upon your
antenna and location. 

The noise generated in the receiver and band noise sound the same to your
ear. That's why you need to check by removing the antenna to see if the band
noise is stronger than the internal noise. If it is, don't use the preamp if
you want to preserve the ability of the K2 to handle the widest range of
signal strengths. If the internal noise is significantly stronger than the
band noise, you won't hear a drop in the level when you pull the antenna
off. Then it is possible that very weak signals might be covered up by the
internally-generated noise. The preamplifier is designed to contribute very
little noise of its own, so turning it on should pull very weak signals up
to over come the internal noise. Even then, you only need to use it when
digging for a very weak signal down near the noise level. If you want to see
its effect, if any, you can try disconnecting the antenna again with the
preamp on and see if the band noise drops. 

Ron AC7AC

-----Original Message-----

I made a couple of QSOs during the WPX and on Saturday night, when the
western US was the strongest on 20 m here, a couple of stations generated
huge key clicks in my receiver.  The whole band was trashed with clicks of
up to S8 from 2 stations about 1000 miles away; their signals on frequency
were about S9 + 40.

I sometimes noticed that issue before, mostly when I was mobile operating.
But this time, I hardly could do any contest exchange without retries.
Without thinking, I turned of the Preamp and the clicks where gone.  I
usually work with Preamp on, especially on 20, since I just use low wire
antennas.

Is this normal behavior of the Preamp?  If so, can someone explain to me why
this is the case?  Is the RX overloaded?  If this is not normal, where
should I start troubleshooting?

73, Andy, KU7T