[Elecraft] K3 and SDR Integration - Almost completed!!!

[Geoffrey Mackenzie-Kennedy]

Jack Smith wrote:

> In contrast, the K3, as I understand it, take an IF sample ahead of the IF 
> filter, with a source follower. Hence, a signal injected into the source 
> follower's output will leak back into the main IF path and be heard in the 
> receiver, reduced by the reverse gain of the source follower.  It would be 
> unusual, in my experience, to find a source follower to have much more 
> than 40 or 50 dB  reverse isolation at 8 MHz. If we assume 50 dB reverse 
> isolation, then the -40 dBm signal leaking out of the Softrock would be 
> fed back into the K3's IF chain at around -90 dBm, which is clearly a 
> problem.  One solution would be a second amplifier between the K3's IF 
> output port and the Softrock. This amplifier should be designed to have 
> high isolation and about 0 dB gain. Perhaps a grounded gate amplifier 
> would  be a good starting point.

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PA3AKE was using two grounded gate J310 FETs in cascade after each generator
for improved isolation while running IMD tests on H-Mode mixers. He reported
a reverse isolation of 75db and about 4db forward gain for each pair of
J310s at HF and 6m.

73,
Geoff
GM4ESD