Re: VLF: 8970 Hz transmissions, soon again here

[wolf_dl4yhf <dl4yhf@freenet.de>]

Hi Steinar,

Maybe I can help with that ... first of all, can you see the DHO38 signal as a 'hump' in the spectrum, center 23.4 kHz, with a few sidebands (caused by the MSK modulation) ? The MSK signal needs a reasonably good SNR to achieve a lock.

What the controls of the 'sampling rate detector' should look like is described in the manual, or here:

http://www.qsl.net/dl4yhf/speclab/frqcalib.htm#continuous_sr_calib_principle
I think Stefan's configuration already contains this (or a very similar) setting. For a quick start, all you need to know is that the 'Status' indicator on the lower edge of the window must turn GREEN after a few seconds (which means the sample rate detector successfully locked the sampling rate to the off-air reference). If it doesn't:

Scroll a bit down on that page. There is a screenshot of a 'scope' window. It shows the spectrum of the *squared* MSK signal. In that spectrum, there must be two very distinct peaks (separated exactly 200 Hz, which is the bitrate of DHO). Without those peaks, the decoder won't lock, and you will need to improve the signal/noise ratio from your VLF antenna.

Ok ?

73,
   Wolf  DL4YHF .

Am 26.11.2011 12:38, schrieb Steinar Aanesland:

Hi Halldór

My is grabber is up and running with "DFCW-6000.usr" now, but I am probably "completely blond" because i can't figure out  how to "use the sample rate detector to lock your sound card to a stable signal” .  I need some help here ;)

la5vna S




Den 25.11.2011 22:22, skrev Halldór:

 

Steinar

 

When starting my grabber Stefan and Chris thought me some tricks:

 

“and use the sample rate detector to lock your sound card to a stable signal”

 

That helps if you are using the 60000 window.

 

73

Halldór

TF3HZ

 

From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Stefan Schäfer
Sent: 25. nóvember 2011 20:33
To: rsgb_lf_group@blacksheep.org
Subject: Re: VLF: 8970 Hz transmissions, soon again here

 

Steinar,

600 s/pix. is a good start point for tmw but i would suggest to use a even narrower FFT bin width like 424 uHz. Also a well configured noise blanker can easily help to get another 6 dB S/N as we have seen in the past.

I attach you a "DFCW-6000.usr" which you can load into SpecLab. This was used successfully in many last experiments on many grabbers :-)

Not you have to wait some 10 minutes until the first pixel appears so do not wonder ;-)

73, Stefan/DK7FC

Am 25.11.2011 20:49, schrieb Steinar Aanesland:

Stefan

I had plans to use  600 sec/step 1mHz res. you will find  under "quick settings/Slow Morse(..)" in SpecLab, but f you have a better solution, I will be happy to try it.

la5vna S



Den 25.11.2011 20:26, skrev Stefan Schäfer:
> Thanks Steinar,
>
> But it will be a first pre-test, i may not get the maximum strength that i want but we'll see.
>
> How do you receive 8970 Hz on the software side? Do you have a "DFCW-6000.usr" for the SpecLab settings or how did you configure the software (which?)?
>
> 73, Stefan
>
> Am 25.11.2011 20:18, schrieb Steinar Aanesland:
>>
>> I will try to capture you Stefan , but I am afraid I got too much noise here to get a good result :(
>>
>> LA5VNA S
>>
>>
>>