Re: LF: All 73 Banders...

["Markus Vester" <markusvester@aol.com>]

Hmmm - capturing Bob's WSPR is a bit like crossing a four lane highway by foot: Once you've managed to find a gap between the DCF trails, you'll be hit by a Loran line on the next track...

 

Glad to see that Joe DF2JP managed to get some decodes, probably for the first time. His capture shows significant DCF77 "junk", the effect of which we have apparently reduced successfully.

 

Around midnight there were also some meager traces here, but simply not enough SNR to decode. I have marked the four tones with 0.1831 Hz spacing with green arrow heads on
 http://dl.dropboxusercontent.com/u/26404526/df6nm_74kHz_131214_0200_arrowheads.png
Unfortunately 74612 Hz would not be good here.

 

It's however strange that Hartmut and Victor didn't get any decodes, even though the signal seemed to be well visible for both. What looks like noise on Victor's capture must really be the WSPR-15 spectrum:
 http://dl.dropboxusercontent.com/u/26404526/pa3fny_74603_131214_0700_arrowheads.jpg

But both statiopns have a relatively strong Loran line, and Hartmut's directional antenna is pointing towards Sylt. However the nearby line frequency 74603.280 Hz should have been well outside the occupied spectrum of Bob's WSPR signal (74603.51 to 604.24), so it's not ovbvious why it should have prevented decodes. I'm speculating that the WSPR software finds the strong line, tries to sync to it, and then somehow excludes nearby real signals from further decode attempts. To prove the point and see how much spacing is needed, we could experiment with letting WSPR decode local audio signals in the presence of injected carriers. But systematic trials with WSPR tend to be time-consuming, even if such tests were accelerated by scaling to WSPR-2.

 

As Bob says, the best solution would be to move further out, avoiding the DCF77 sideband lobes alltogether:
 http://dl.dropboxusercontent.com/u/26404526/74kHz_spectrum_investigation_df6nm_131214.png
shows different parts of the spectrum in detail. My idea would be to move down by 300 Hz, ie 72.7 kHz dial and 74.300 to 74.325 kHz RF for WSPR-15. In that range, DCF noise is so weak that we would only neeed to avoid the more widely spaced Loran lines. I have listed and sorted the relevant GRI harmonics at
 http://dl.dropboxusercontent.com/u/26404526/Eu_Loran_frequencies_74300-74325Hz.png
 http://dl.dropboxusercontent.com/u/26404526/Eu_Loran_frequencies_74300-74325Hz.txt
but note that emitted levels are variable, and not every line will really be strong enough to cause interference.

 

Thus my suggestion would be to go to 72.7 kHz dial, and Bob sending on either 74304 or 74321 Hz.

 

Best 73,
Markus (DF6NM)

 

 

From: Bob Raide

Sent: Saturday, December 14, 2013 8:41 AM

To: rsgb_lf_group@blacksheep.org ; Bob Raide

Subject: LF: All 73 Banders...

I am authorized 68-76 kHz.  There must be clear freqs somewhere in that spectrum?  Let me know what most would like to try in UK/Europe-Bob WG2XRS/4 NY [WG4XRS for WSPR modes]