Форум радиолюбителей ДВ

We sometimes find that the noise-blanker triggers on 50 or 100 Hz periodic interference from switch-mode power supplies (SMPS). The interference itself is reduced, but 100 Hz sidebands are created on strong signals. For example, in the attached screenshot from DL0AO, SMPS-QRM was present from 8:02 to 8:28 UT.

73, Markus (DF6NM)

Markus, email to QRP Lab about that problem, pse.

I did mention this to G0UPL a few years ago but have not received a response from him. Unfortunately I do not own an U3S kit myself, so I can't reproduce the problem here. However I have read that there are different "park mode" options which control the synthesizer frequency during key-up periods. Maybe you can tell the firmware to maintain a constant frequency, so that the phase will not change during a pause.

73, Markus

 

Еще спектр Оперы становится шире, если сигнал передается некогерентно, то есть каждая посылка имеет какую-то свою случайную начальную фазу относительно непрерывной несущей. Не знаю, принимаются ли в алгоритме U3S меры по обеспечению когерентности, если нет, то в причина может быть в этом.

Yes, unfortunately the U3S does not send Opera dashes with coherent phase. Opds can also detect incoherent signals, but sensitivity is about 3 to 4 dB worse.
73, Markus (DF6NM)

Hmm, normally R0 and R1 should both work the same way. It would only makes a difference if you have "Sync'd Resample" activated, but in this application we have selected "don't resample".

73, Markus

Hi Alex,
 
this is all very interesting!
 
> I still cannot explain this, why the signal is perfectly visible in the transition zone and is completely absent at the beginning of the far zone.
 
Well once again we see that the hardest part is getting out of the nearfield ;-) Normally we would expect a r^-3 dependence up to 5.7 km (18 dB drop at double distance). So yes, if you could **hear** the signal at 3.7 km, it should be detectable in some mHz bandwidth at 7.8 km.
 
Note that the pattern and orientation of the quasistatic magnetic field lines are quite different from the far field. There is also an axial component which is twice as strong as the transversal component, but disappears completely in the far field. This is probably what you picked up at the second location, providing another 6 dB signal strength and unusual RX-loop orientation. It is also possible that the signal was locally enhanced by reradiation from underground wires or metal pipes.
 
>  the frequency of the signal continuously and irregularly changes within small limits
 
This is normal behaviour of the PLL. Depending on the measured phase and small samplerate errors, it steers di.freq, such that on average the phase is held for the correct frequency (8270.00625). This was confirmed by the green trace, so I believe you were transmitting on the intended frequency.
 
> another laptop with rx-loop + DHO38-calibration.
 
Samplerate calibration based on DHO38 also has some difficulties. First it can be affected by soundcard glitches, wich cannot be corrected and can cause a residual phase change which will disturb the frequency. Using 1pps + GPS-phaselock is the only method available in SpecLab which can correct such glitches, because it knows absolute time and can calculate the phase which the signal should have, even after an interruption.
In addition, the DHO38 transmitter is not exactly on 23.4 kHz. When Wolf and I measured it ~ 12 years ago it was approximately 0.03 ppm high, which is why it is announced as 23400.00006 Hz in the table. But I do not know if this is still correct today.
 
> - should Input Calib and Output Calib be equal?
Normally yes. I know that there are some soundcards which have different ADC and DAC samplerates, but these seem to be rare.
 
> - do I need to enable the "resample to nominal output SR" checkbox?
No, this is not necessary for this application.
 
73 and good luck,
Markus

PS (off topic): Obninsk - the location of the world's first nuclear power plant, delivering electricity to the grid since 1954. Did you go to the museum? 73, Markus

Today is the second series. Moreover, the daily session

Sergey, do you want to try a daytime transmission now? Noise at DL0AO is very low, and the loop antenna is pointed in your direction.
73, Markus