Re: LF: XES Carrier tonight

[MarkusVester@aol.com]

Hi John and LF,

here is the result of last night's phase measurement on the WD2XES carrier:


<XES-GPS_060220-21_2234-0830.gif>

This panel displays three amplitude and phase spectra, differing only in the a posteriori frequency shift applied to the right (H-field antenna) channel used for phase reference. Each segment shows the whole night's data from 22:34 to 8:30, at 5 min/pix horizontally and 0.657 mHz FFT resolution (10 mHz/tick) vertically.

- left: no frequency shift applied. This is the normal colour-DF representation, referencing the phase of XES on the E-field antenna to that of the same signal on the H-field turnstyle. The westerly trace can be seen in blue against a background of purple-ish noise, originating partly from northerly Luxembourg-ICM on DCF39. Frequent grabber watchers will find it familiar ;-)

- center: frequency shift +0.309506014 Hz. Same as yesterday, this brings the 137577.00 GPS line to XES's frequency and measures the phase between the two.

- right: frequency shift -0.690493986 Hz, bringing the next GPS line on 137578.00 underneath XES. After applying an initial constant phase of 150° (reflecting the arbitrary start time of the recording vs. the 1 pps), the trace colours look very similar to those in the segment before. This proves that the phase measurement is not corrupted by soundcard samplerate errors, which would have caused phase drifts in opposite directions.

Ok, so here we have a validated and relatively simple (?) method to measure propagational phase variations, which can be done without a fully GPS-locked receiver. But, what's it good for?

Propagational phase and amplitude variations broaden the transmitted linewidth by a fraction of a milliHertz. Thus the stability of the channel sets an ultimate limit for extremely slow QRSS or PSK communication, and therefore the minimum transmit power requirement to overcome a given noise energy. Phase stability over an hour or longer suggests that we could still gain another 15 dB by going from 120s to 3600s symbol duration.

Both yesterday and today, there were two relatively long stable periods, separated by an interval of fading and more rapid phase changes. In yesterday's high-resolution spectrogram (top right), one can even find an interesting Doppler shift between the openings, where the line dips about 3 pixels (0.4 mHz) below the center frequency, and then slowly creeps back up. This is most likely a real effect, caused by changing ionospheric reflection heights. Such Doppler spectroscopy on LF could provide interesting insights into the lower ionosphere, as it does on HF for the upper layers.

Have started SndInput for another night, and also set up an experiment using SpecLab's 0.1 Hz amplitude modulator to shift a GPS line behind Brian's coherent transmission on 136317.9 / 318.1 DFCW - funny effects so far.

Best 73 to all

Markus, DF6NM


In einer eMail vom 21.02.2006 21:26:00 Westeuropäische Normalzeit schreibt w1tag@w1tag.com:

Thanks for the reports on the "dead carrier" last night. I've had a
request to repeat it again tonight, so XES will be back on
137.57730950601398944854736328125 kHz <g> again, starting at 2230 UTC.