[hpsdr] HERMES schedule question

[Graham / KE9H]

Alberto:

It is a matter of the software in the Mercury FPGA.  You can take the 
data out at 384 ksps
or 768 ksps or 1536 ksps or whatever, provided that you have the 
transport bandwidth
to get the data out of the board and up to the PC.

Nothing comes for free, and it is hard to fool Mother Nature, so this 
reduces the decimation
ratio and there are side effects involving loss of sensitivity and 
dynamic range, but that would
not likely be an issue in the broadcast band, where the atmospheric 
noise floor is so high.

192 ksps is a compromise between receiver dynamic range, sensitivity, 
dsp buffer sizes and
latency, and the width of the panadaptor display.  It is currently 
optimized for reasonable
sensitivity in the ham bands up through 10 Meters.

I hope you have better programs on the 540 to1600 kHz broadcast band in 
Europe than
here in the United States.  I cannot imagine wasting the disk space to 
record the AM
Broadcast band here in the US, much less wasting the time to listen to 
it another time.

--- Graham / KE9H

==

Alberto I2PHD wrote:
> On 6/19/2010 3:55 AM, Phil Harman wrote:
>> The receiver board (Mercury) incorporates a Digital Down Converter 
>> that takes the 1.966Gbps ADC data at 16 bits per sample and reduces 
>> it to 48/96/192ksps at 24 bits per sample.  This slower data is 
>> passed over the Atlas bus to either an Ozy board (USB interface to 
>> the PC) or shortly an OzyII  board (Gigabit Ethernet).
>> Hermes does the same except the functions of Mercury and Ozy are 
>> combined on the one board.
> Will Hermes too be limited to 192 kHz max downsampled frequency, or 
> there will be a provision for a more ample chunk of the spectrum
> available to the PC software ? This is one of the parameters that SWLs 
> use to judge if a given SDR is suited to their tasks.
> What they like to do is to digitize the entire MW spectrum (1600 kHz), 
> making a WAV recording of it, to then replay it leisurely.
> Presently only Perseus and the QS1r are capable of this.
>
> 73  Alberto  I2PHD

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