[hpsdr] Metis functionality

[Jeremy McDermond]

On May 15, 2011, at 8:46 PM, Chuck wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> Several years ago, I bought Mercury-Janus-Ozy as at the time there was supposed to be support for recording entire bands (.5 or 1 MHZ or more) via the PC. It turned out that such a wide bandwidth was not possible.
> 
> I've not followed HPSDR in the meantime, but it seems from a few recent messages that Metis was introduced to overcome the bandwidth problem.
> 
> Unforturtunately, the Metis documentation tells me that it supports 100 / Gigabit Ethernet (and tells me how it was implemented) but it does not speak from a functionality point of view but rather an implementation point of view.
> 
> So: what data is being carried through Metis?

Currently, the same data that was coming through Ozy.  I/Q samples for the various receivers and the wide-band bandscope.

> Is there support at the PC end to store IQ files for later analysis?

This is dependent on the software being used on the computer.  I believe PowerSDR can record I/Q samples from the hardware.

> What are the limits of the bandwidth that Mercury / Metis can provide?

Metis has the potential of doing 1Gbps full duplex data bandwidth.  The ADC is a 16bit device.  That means you can fit around 60Msps down the wire.  If you do 2x(RF Bandwidth) sample rate, that means in theory you could shove around 30 Megahertz worth of bandwidth down the interface.  I did some back-of-the-envelope calculations a while ago and figured that we could put every ham band within the ADC's bandwidth into the gigabit connection.

Now, this is all theory.  The current code doesn't allow for such large datarates.

> Is the decimation FPGA controllable enough that I can choose what decimation I prefer?

The current FPGA code only allows three choices of sample rates, which determine the FIR used as well:  192000, 96000, 48000.  The FIR is equal to the sample rate.  This isn't to say it's set in stone.  That's why there's an FPGA, so that we can modify these values as we learn more by experimentation.

> Does PowerSDR support the playback of archived IQ files?

I believe it does.

> Chuck

--
Jeremy McDermond (NH6Z)
Xenotropic Systems
mcdermj at xenotropic.com




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