Re: VLF: Software PSK modulation

[Markus Vester <markusvester@aol.com>]

Hi Domenico,

 

thanks for the VLF screen grabs!

 

I have uploaded my current VLF-grabber SpecLab settings:

http://df6nm.bplaced.net/VLF/vlfgrabber_settings_160119.zip

Beware though that several settings may a bit peculiar:

 

The opds/EbNaut saves have been included only in the "60000" instance, writing into a spectrum\data4H folder. In my case, parameters for sr.txt would be 

32000.15 31104 16384 8270

(ADC samplerate, decimation, FFT length, center frequency). The observed frequency range after decimation is only +-0.25 Hz.

 

To save some CPU, the narrowband instances are running only at 32 ks/s samplerate.

 

I am using a cheap "3D-sound" mono-input dongle, so a strong and clean 1pps pulse needs to be added on top of the RX antenna signal. After filtering (either DC-reject with a very short time constant, or bandpass), the pps pulse edges are completely removed by the noise blanker.

 

In the 60000 instance, the delay-line bypass factor (100) is used for extra gain, allowing more compact integer-number FFT data export.  

 

You will probably not need the FFT autonotch filter. I have inserted it hoping to remove wandering 33 Hz harmonics from the nearby railway, without taking out too much of the signal. It seemed to do some good, but I still find that my SNR for Uwe seems to be around 6 to 10 dB worse than on the DK7FC and OK2BVG grabbers. So far I have not yet been able to decode a VLF EbNaut signal.

 

The wideband instance calls a batch file for IrfanView png conversion, Dropbox upload and daily saves, a procedure you may want to adapt as well.

 

All the best,

Markus (DF6NM)

 

-----Ursprüngliche Mitteilung-----
Von: IZ7SLZ <iz7slz.domenico@gmail.com>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Sa, 23 Jan 2016 7:18 pm
Betreff: Re: VLF: Software PSK modulation

Hello Markus,

many thanks for sharing details of your very interesting experiment. As you known,  i have used your PLL method in my LF-EbNaut setup to generate a quite steady  modulating audio tone. But in my case, the feedback is taken at the output of the sound card before the ring-modulator that acts the bpsk.
If i have understood, you have now overcome the initial problem of this PLL that tends to cancels the psk modulation. That's good. I will try it in my next VLF local transmissions.

Since two days, i'm running a (temporarily !) VLF receiver/grabber with a resolution of 63 uHz:

https://www.dropbox.com/s/fsjkfuhggozzv5w/grabber.jpg?dl=0

Unfortunatly no signals on "dreamer" band in these two days of activity (made by you and Uwe)  was picked up. I'm working to improve reception trying to relocate the mini-whip. Next step will be to test a Loop antenna. By the way, the chances to pick up a VLF "dreamer" signal from Central Europe are very less here in my station in JN80 that is "urban-located" and fairly far from you.

I want to try to record and decode my local EbNaut signals on VLF. I made some reception test using Wolf's beta version that includes EbNaut facilities. I have succesfully tested it on MF during some test transmissions of IW4DXW. But i want test also your recording method that uses the FFT export file function of Spectrum Lab.
Taking in consideration that i'm using 48000 sample/s can you suggest the correct parameters needed for SL and for the sr.txt file used for the inverse-FFT program ?

Maybe someone else is interested at this method.

Thanks in advance.

73 and good week-end to all group

Domenico / iz7slz