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

[Robert McGwier]

Ahti Aintila wrote:
> ***** High Performance Software Defined Radio Discussion List *****
> 
> 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)

This is very good news.  It will be a direct increase in dynamic range.


> 
> 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.

Why just use a twisted pair forcing all external signals to be common 
mode and eliminated so long as they do not clip the input amplifiers?

> 
> Thanks for the good work!
> 
> 73, Ahti OH2RZ
> 
> 

Nice job indeed.

Bob


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