Re: SL settings for QRSS (was: Re: LF: RE: Todmorden receiver by Jack)

[JACK ASKEW <va7jx@shaw.ca>]

Thanks Wolf, lots to read up on, excellent information on learning

how to use SL for these slower speeds.  Also thanks for

pointing me to Stefan's site regarding the configuration

files for QRSSS, I wondered if anyone still had them available.

I recall playing with SL's ability to use VLF stations to lock onto but

they were too weak here in Canada. I do have GPS on my Tx now

but I still see some un-explainable instability over a period of 4-5hrs

but far less than 0.05Hz...so maybe not an issue when I was using

file 8270Hz_QRSSS_4mHz.usr. Not sure what equates to in QRSSS

though. I find that if I try anything like 'VLF_Soundcard_32K_47uHz.USR'

it takes several hours to load up in SL but I guess that stands to reason...I hope.

Regards

Jack Askew

---

From: "Wolfgang Büscher" <dl4yhf@freenet.de>
To: "rsgb lf group" <rsgb_lf_group@blacksheep.org>
Sent: Saturday, January 6, 2018 10:42:14 AM
Subject: SL settings for QRSS (was: Re: LF: RE: Todmorden receiver by Jack)

Hello Jack and all,

you wrote:

 >It comes back to using something like SL with its QRSS
capabilities. I wish I had a good file that worked at 8720kHz
for QRSS600 as an example. This would be a good start if nothing else.
<

It's not that difficult to set up. The key point in SL to get into the
microhertz-resolution is the decimation (of the sampling rate), along
with complex frequency to have a complex FFT spanning just a few Hz
around the "frequency of interest". The effect is similar as a
super-long FFT (concerning the frequency bin width, and thus the
"gain"). I think on Stefan (DK7FC's) site you can find some
configuration files for QRSSS.

Back in the "old days" of extremely slow Morse, I wrote this short
how-to (for Spectrum Lab):
http://www.qsl.net/dl4yhf/speclab/qrss_quickstart.htm
   (it shows how to pick one of the VLF transmitters to stabilize the
soundcard's sampling rate,
   a bit out of fashion since good GPSes with sync output became
available, but anyway..)

To make the FFT window even longer / frequency bins even shorter than
used in the default settings,
use the option 'complex input for the FFT with internal frequency
shift', as shown at
http://www.qsl.net/dl4yhf/speclab/settings.htm#fft_size

And, last not least, there an explanation of FFT length, decimation,
windowing functions, resulting resolution / effective receiver bandwidth
versus dynamic range, etc:
http://www.qsl.net/dl4yhf/speclab/fftinfo.htm

All the best,
  Wolf DL4YHF