[hpsdr] Status of Hermes Gigabit

[Kok Chen]

On May 1, 2015, at 3:09 PM, Chuck Hutton wrote:

> With ham bands less than 400 kHz and 16 bit samples, we can live without GigE.
> But jump up to 17 bits or more (requiring 3 bytes) and / or move up to wider bands such as the medium wave band (let's say 2 MSPS) or wider ham bands and you will need GigE. 

The I/Q data from Hermes to the computer is already in the form of a pair of 24 bit numbers (>145 dBDR).  

The decimated Hermes I/Q data at 96 ks/s rate only has about 110 dB of SFDR and has lots of headroom (5 to 6 bits out of the 24 bits) left before we need to increase the I/Q data width.  

A faster sampling rate (e.g., 192 ks/s) actually reduces the numerical dynamic range requirement. The raw ("16-bit") ADC at 122.88 Msps starts with just 78 dB of dynamic range (about true 12.5 bits). 

Hermes' single signal "500 Hz ARRL" dynamic range of 125 dB is achieved when you finally decimate and demodulate inside the desktop computer at 500 s/s.

73
Chen, W7AY


 1430583201.0