[hpsdr] multiple rx in Mercury

[Bruce Walker]

Last fall, Kirk Weedman KD7IRS and John Melton G0ORX/N6LYT began an
effort to implement multiple independent receivers in Mercury.  With
their help, I revived this project a couple of weeks ago, and I
integrated some modules which Alex Shovkoplyas VE3NEA had written for
his multi-band skimmer firmware for QS1R.

At the moment, I have a version of the Mercury firmware which
implements four receivers, each of which should be of equal or better
quality (in terms of its decimation filtering) than the single
receiver in Mercury V2.9.  It is available for alpha testing from
repos_sdr_hpsdr/trunk/W1BW/MercuryNRx.  You will need to load
Mercury/Mercury.jic *and* the corresponding Ozy firmware from the
OzyJanus directory there.  The Ozy code implements the latest multiple
receiver USB protocol found in repos_sdr_hpsdr/Documentation.   I have
not tested whether this Mercury code will work with the released Ozy
1.7 code as a single receiver, but it might :).

At the moment, the only software I'm aware of which supports multiple
receivers in Mercury is John Melton's ghpsdr3, but I'm hoping that
making this test version available will enable others to add support
for it.  John and I have both been running the 4-rx code for the last
week without problems.  I've been feeding audio from four ghpsdr3
clients to hacked-up instances of WSPR to monitor and decode weak
signal digital transmissions on four bands simultaneously.

I'll continue to work to fit more receivers into Mercury, but more
debugging is required, and some sacrifice on the decimation filtering
will also probably be necessary....as I said, my intention for the
4-rx version was to be as good or better than the existing single
receiver, though I don't have any quantitative metric.

Please let me know if you try it out, successfully or unsuccessfully!

--bruce W1BW