[hpsdr] JanOz-163 and SDR-1000 without INA163

[Ahti Aintila]

Phil,

Today I tried the balanced I/Q input to Janus taking the signals
directly from the sampling capacitors and without any amplifier. The
connecting cable was 1 meter long Cat 5e with 4 twisted pairs. The
unused pairs and the shield wire were connected to ground at both
ends.

The result are promising:
- testing frequency 3.7 kHz
- RFE included, no attenuator used
- noise floor -147 dBm/10,7Hz, Blackman-Harris window
- noise -132 dBm/500Hz
- no compression/clipping at -7dBm (max signal of my generator)

I had a lot of spurious signals visible, obviously due to common mode
and poor shielding of the cable. The spurious level was dependent on
the cable position on my working desk, so obviously better results can
be achieved with a more professional test set-up. Now I tried to
position the 500 Hz filter to the best position between the spikes.

Thanks for the good work!

73, Ahti OH2RZ

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