Re: ULF: Carrier on 2470.01 Hz

[DK7FC <selberdenken@posteo.de>]

Hello Markus,

Hm, skywave cancellation? Then this must happen quite quickly. I would rather expect a slower dSNR/dt, like we can see at the VLF MSK transmitters. But maybe you are right.
So let's hope for some more weeks with such a low QRN levels. If you like, buy one of the accus i bought, then come here and we can connect them in parallel, to run the carrier for twice the time :-) Or we can do 3 dB QRO to see the fading more clearly, but then i need to build a stronger DC/DC converter.
Maybe next weekend we can try 1.97 kHz.

73, Stefan

Am 04.01.2019 14:33, schrieb Markus Vester:

Hi Stefan

> The trace appears to be a bit shorter...

This is interesting! The attached enlarged screenshot is a comparison from DL0YHF (top) DL0AO (bottom), with same timescale. We find that DL0AO was fading out towards the end, whereas the DL0AO trace seemed to be becoming stronger.

I suspect that this may again be due to skywave cancellation. During the afternoon hours (13 to 15 h local time), solar elevation slowly decreases and the height of the ionosphere goes up, increasing the path difference to groundwave. Thus the null will be moving out to larger distances where skywave is less steep, reducing path difference again. However the numbers don't quite match: For 300 km distance and 70 km iono height, Pythagoras calculates about 31 km or 0.25 lambda difference. So we would need to assume an additional -90° phase lag from the reflection.   

If I remember right, Jim's FDTD calculations also showed a sharp minimum at 2.5 kHz and 200 km. Thus we may be optimistic and hope that propagation will improve when you go to even lower frequencies. 

Best 73,
Markus (DF6NM)



-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Do, 3. Jan. 2019 19:53
Betreff: Re: ULF: Carrier on 2470.01 Hz

Here is a spectrogram  (attached) showing the reprocessed data of the VLF stream of DL4YHF.
The 2470.01 Hz carrier leaves a clear trace, not as strong as on 2970 Hz but clearly there. The trace appears to be a bit shorter, maybe due to higher QRN levels which were blanked or due to a loss of the reference signal (unlikely).
The first hour of the transmission produced a 18 dB SNR peak. Adding the second hour of the transmission made the result even a bit worse.
313 km distance on the 121 km band, that's ~ 2.6 wavelengths crossed...

73, Stefan




Am 01.01.2019 15:05, schrieb DK7FC:

Thanks Markus, ULF,

Again, congrats to the DL0AO crew for the latest record. We are operating on the 121 km band and crossed a distance of 283 km, or 2.3 wavelengths!! Certainly this has never been done before by amateurs.
DL0AO has now a new lowest frequency for a amateur signal detection :-)

Unfortunately i slept too long this morning and so i started the experiment to late. I see the QRN is already increasing now and it has been lower in the early morning. Maybe, the next weekend we could try 1.97 kHz but then with an earlier start time.
Here, the experiment is still running and i can hear the FETs beeping. Due to the relatively low ambient temperature, the accu voltage dropped to 11.5 V now and i have a remaining charge of 25.( AH or 21%. The antenna current dropped to 2.6 A now. 5 minutes left, then i will go QRT.

73 from the car,
Stefan



Am 01.01.2019 13:55, schrieb Markus Vester:

Again a very good signal at DL0AO, about 12 dB in 1.5 * 424 uHz:

https://vlf.u01.de/
https://vlf.u01.de/VLFgrabber/vlf5.jpg

We're also running a 47 uHz instance in the background, still showing yesterday's experiment: 
https://vlf.u01.de/VLFgrabber/vlf9.jpg

What a splendid start into the New Year!

Best wishes to all,
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Di, 1. Jan. 2019 13:40
Betreff: ULF: Carrier on 2470.01 Hz

Hi ULF,

Due to the recent success on 2970 Hz i am now TXing again on my ground
loop antenna. This time, since 12:08 UTC i am transmitting on 2470.01
Hz. Again the TX power is 520 W and i'm getting 2.75 A antenna current.
This time i need 1.72 uF for series resonating the antenna. As usual, i
intend to run the carrier for 2 hours.
Reports are very much apprechiated :-)
Unfortunately my own tree is shut down but i'm recording the stream of
DL4YHF and IK1QFK again. Also the DL0AO crew is watching and recording.
Maybe even Paul will get something significant?

With some luck, 2.47 kHz may propagate even better than 2.97 kHz ??
Optimism is the key word for the year!

Oh and attached is a spectrogram produced from the stream of DL4YHF,
showing my signal on 2.97 kHz. The SNR is far better than i ever
expected from such an antenna! See attachment. A long message could have
been transferred over this 313 km path!


Happy new year 2019 to all of you.

73, Stefan