[Elecraft] operating question about K2 pre-amp/attenuator

[Ron D'Eau Claire]

Hi, Matthew! 

The less gain you have before signals reach the I.F. filters, the greater
range of signals your rig can handle without overloading. Very strong
signals outside the I.F. bandpass can cause many problems if they are strong
enough to drive one of the stages into non-linear operation. The result may
be what sounds like signals that are not signals at all (so called
"birdies"), excessive background QRN and other noises that may sound like
someone's signal is splattering across the band and, in really extreme
situations, desensing of the receiver (all signals are reduced in strength).


However, too little gain ahead  of the I.F. filters may mean that the
weakest signals aren't strong enough to be heard above the internal
background noise created in the receiver, so a balance between some gain and
not too much gain in the "front end" (part of the receiver before the I.F.
filters) is required. 

Normally, the preamp would be used only on the higher frequency bands (above
10 or 15 MHz) where the band QRN is very low and you need the gain to be
sure weak signals are stronger than the internally-generated noise. That
depends on the background QRN at your location and the antenna you're using.
A simple way to see if you have enough "front end gain" is to set your K2 to
the narrowest I.F. filter setting you'll use, tune to a spot in the band
where you cannot hear any signals, just the background QRN, and disconnect
your antenna. If the noise level drops significantly, your ability to hear
weak signals is limited by band QRN and not the receiver gain. If the noise
level drops when you disconnect the antenna with the pre-amp off or the
attenuator on, those settings will provide maximum protection from overload
without compromising your ability to hear weak signals. Indeed, by avoiding
overload and the apparent band noise that can cause, you may hear weaker
signals with the pre-amp off and the attenuator turned on than you would
otherwise.

The K2 has excellent dynamic range characteristics, so you can use your
preamp much of the time without serious side effects, if you wish, but it's
not the best operating practice.  

Ron AC7AC



-----Original Message-----
Hi All,

My operating experience is fairly limited, so I have a question about
operating the K2.

What circumstances would cause one to turn off the pre-amp? And related,
what circumstances would cause one to turn on the attenuator?  Even my old
FT-101 had an attenuator to switch in, but I never came across a situation
where I thought I'd want to.

73, Matthew AE6UP