Re: LF: More EbNaut 137.777

[Markus Vester <markusvester@aol.com>]

Hi Wolf,

 

at our distance, DCF39 is on the order of 3 mV/m. Assuming a best-case daytime band noise of ~0.05 uV/m/sqrtHz, a sensitive antenna could thus produce around 95 dB SNR in 1 Hz bandwidth.

 

But you asked for a weaker one... There's an unid carrier on 137689.45 Hz which is yellowish here and fading, so maybe from Italy or north Mediterranean area. It has always been visible on different QRSS-segment grabbers,  but for some reason became significantly stronger since Nov 6th (currently ~2 uV/m here).

 

Then of course there are Loran sideband lines. Lessay and Sylt are on multiples of 50000/6731 and 50000/7499 but not strong (some tens of uW at 137 kHz). Here they are only sometimes visible in QRSS-60 bins, but very reliable frequency markers in a sub-milliHz spectrum. Slonim is stronger at night and is on a convenient raster of 50000/8000 = 6.25 Hz multiples. 

Joe's PSK-modulated signal is spread over 0.5 Hz, and was thus hardly or not at all visible in any of my spectrograms. On the other hand, Domenico's transmissions were very conspicuous because he embedded his EbNaut sequences into relatively long segments of pure carrier.

 

High noise from an indoor loop might be caused by pickup from ADSL lines. The uplink spectrum sent by nearby modems starts above 138 kHz but there's usually spectral leakage into hour band. Though it is supposed to be a pure differential signal, the telephone lines are hardly perfectly symmetric, and the common-mode component radiates significant magnetic fields. Unlike the characteristic SMPS interference, ADSL is not so easy to identify because it usually sounds like plain white noise. You can use a portable AM-radio with a ferrite-loopstick, tune it to any clear channel above 140 kHz, and try to sniff around for telephone cables in the house or outdoors underground.

 

All the best,

Markus

 

  

-----Ursprüngliche Mitteilung----- 
Von: Wolfgang Büscher <dl4yhf@freenet.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Fr, 27 Nov 2015 7:14 pm
Betreff: Re: LF: More EbNaut 137.777

Greetings all,

Do we have a relatively stable, but not too strong 'carrier like' signal in the vincinity of 137 kHz,
to get a rough estimate of the local QRM level (by comparing that signal's SNR with the same receiver bandwidth, say 1 Hz) ?
I get the impression that mine, with a loop antenna (low-impedance, broadband) dangling under the roof, is far too high.
I didn't manage a single decode yet, which I first blamed on a bug in SL's timestamps (written into the decimated wave file), but since there was also not a trace of Joe's signal in a high-res spectrogram, I have my doubts..

73,
  Wolf DL4YHF .

Am 27.11.2015 um 10:49 schrieb Markus Vester:

A few more weaker decodes occurred here around midnight, ending before 1 UT. The spectrogram caught a short carrier around 0:20 UT (spectrum showing on https://dl.dropboxusercontent.com/u/26404526/EbNaut_spectrogram.png ).

 

   2015 Nov 26/27

 

start  Eb/N0  time offset
 UT      dB    seconds

 

2030     nil
2100     1.3     1.2  
2130     3.9     1.5
2200     5.4     1.9
2230     7.4     2.3
2300     8.4     2.5
2330     1.9     3.0
0000     2.2     3.4
0030     1.0     3.5
0100     nil
0130     nil

Best 73,

Markus (DF6NM)