Re: LF: W4DEX at 8270 Hz - and VO1NA

[Markus Vester <markusvester@aol.com>]

Hi Paul,

superb! This is absolutely amazing work.

We can now clearly see the southwesterly origin of nighttime QRN, presumably South America. A similar effect is apparent on the wideband twin cardioids at DL0AO, with generally higher noise background from the west than the east. I am wondering if we are seeing the nonreciprocity here, suppressing distant QRN from Asia more than from the Americas. But it might also be related to absorption over a land versus sea path.  

Regarding the spectrogram implementation, three questions crossed my mind:

- The directional lobe seems rather sharp (also on the old two-loop spectrogram), slewing the pointer by say 45 ° lets a signal completely disappear. Linear cardioid magnitude 
  |B| = mu0 * | Ez/Z0 + Hx cos(phi) - Hy sin(phi) |
should be much smoother, so I presume you are calculationg brightness using some nonlinear function of angle? 

- What is the latency between the end of a one-hour buffer and the time the latest spectrogram comes online? Could downconvert-and-decimate be used to speed up FFT calculations for the narrow spectrogram?

- For the three input channels, are you still using three separate stereo soundcards with individual timing corrections, or one of the newer multichannel soundcards (e.g. Octo on RasPi)?

Best 73,
Markus

-----Ursprüngliche Mitteilung-----
Von: Paul Nicholson <vlf0403@abelian.org>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: So, 3. Dez 2017 13:06
Betreff: Re: LF: W4DEX at 8270 Hz - and VO1NA

Have a look at

http://abelian.org/vlf/fbins2.shtml

and swing the compass round to 280 degrees.

I've made no alterations to the display settings other
than to use 3-axis signals instead of 2-axis.

Compare with the 2-axis spectrogram

http://abelian.org/vlf/fbins.shtml

to see the difference the extra channel makes.

Still processing data in background to fill in the spectrogram.
It will slowly back date to 2017-12-01 14:00, in batches, you'll
have to refresh from time to time. It'll take a day or two to
catch up.

--
Paul Nicholson
--