Re: K3 and SDR Integration - Almost completed!!!
Posted by
Geoffrey Mackenzie-Kennedy-2 on
Jul 25, 2007; 6:37pm
URL: http://elecraft.85.s1.nabble.com/K3-and-SDR-Integration-Almost-completed-tp450573p450574.html
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.
------------------------------------------------------------------------
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
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