[hpsdr] 8 DDC Skimmer Receiver firmware for Mercury/Metis

[Richard Koch]

Tnx Bryan.

I'm not doing any compensation for the rolloff. That's why this is mostly useful for
RX skimming purposes. There is still a lot of useful bandwidth for SDR skimmer clients
such as cw/rtty skimmer and sparksdr.

I was trying to get as many receivers as possible in the FPGA of Mercury with a goal
of hitting 8 for 8 band skimming. With the FIR it didn't have enough room for even 4.

-Rick / N1GP

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Very cool Rick!

If you're not using compensating FIR filters after the CIC filter in the DDC, how are you compensating for the rolloff in the CIC?

73,
Bryan W4WMT

________________________________
From: Richard Koch <n1gp at hotmail.com>
Sent: Tuesday, February 6, 2024 1:00 PM
To: hpsdr at lists.openhpsdr.org <hpsdr at lists.openhpsdr.org>
Subject: 8 DDC Skimmer Receiver firmware for Mercury/Metis

Hello list,

I've attempted to put some new life into my Atlas boards. I wanted to use
the Mercury / Metis pair to do some receiver skimming. I was able to get
8 DDCs working with one Mercury by using an NCO -vs- Cordic  (inspired
by the Hermes-Lite2 folks) and only using CIC filters in the DSP (no FIR).
It is also limited to a 0-30MHz range and is Protocol 2 based.

It seems to work pretty well for me and I thought I would put it out there
to share with the community, hopefully someone will find it useful.

I put the firmware up on the github TAPR site:
https://github.com/TAPR/OpenHPSDR-Firmware/tree/master/Protocol%202/Atlas/Skimmer_Receiver

-Rick / N1GP

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