[Elecraft] K2 IF feed to 756 Pro or other spectrum displays

[Eric Swartz WA6HHQ - Elecraft]

Hi George,

In order to properly benefit from the K2's receiver performance you will
need to extract the IF signal -after- the crystal filter, which I think may
be a problem if you were looking to have a wider bandwidth RX for your 756
Pro. One of the key reasons for the K2's excellent RX front end performance
is the fact that we have our narrow crystal filtering immediately following
the first mixer IF amplifier, rather than after a wider roofing filter and a
second or third mixer as in the Pro. This contributes significantly to our
#1 rated close in dynamic range numbers. The term 'front end' is somewhat of
a misnomer in this case since the complete RX path through our crystal
filter stage is what sets our RX performance.

If you run the pre crystal filter IF signal to your 756 pro I expect you
will find the Pro easily overloaded and you will not receive any performance
benefit from its IF filtering in strong signal conditions. The DSP in the
Pro and most other rigs does not have as high a dynamic range as the K2.
Tapping the Pro in after the crystal filters will give you some interesting
possibilities though since you will benefit from our narrow crystal
filtering following the mixer cascaded with the additional DSP filtering in
the Pro.

It may be useful though if all you want to use the Pro as a pan adapter
spectrum display unit. For a spectrum display IF tap point it is important
to maintain the proper impedance match for the 2N5109 post mixer IF
amplifier transistor in the K2. If this match is disturbed you will find the
IMD dynamic range of the K2 degraded noticeably. I recommend using an extra
high impedance input buffer stage taking its signal from the output of the
2N5109. This will properly isolate your external IF devices from the K2.

73, Eric   WA6HHQ
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"George, W5YR" wrote:
> 
> Apart from enjoying the radio, my first project will be to extract the IF
> signal and feed it into my Icom PRO to evaluate the performance of the K2
> front end combined with the DSP IF and audio capabilities of the PRO.