[Lf] ... why wait for winter?

[Andre' Kesteloot]

MarkusVester at aol.com wrote:

> Hello group,
>
> yesterday night, the qrn seemed to be fairly moderate, so I decided to start
> spectrogram at 22:00 UT (5513 Hz, 512 pts, 30 s dwell, 128 averages,
> resolution bandwidth with windowing appr. 14 Hz). In the morning, I was quite
> surprised to see a fat trace of CFH 137.0 kHz beginning at 00:10. A first
> maximum occured around 00:55 with about 11 dBuV/m/14Hz, then the signal dived
> down for 15 minutes before it came back with similar strength. After staying
> fairly constant for about 1.5 h, it peaked to 13 dBuV/m/14Hz from 02:55 to
> 03:10, then decayed and became invisible around 04:10.
>
> SVX from Greece was strong all night until 02:40, with a pronounced
> double-minimum at 03:00 and 03:14 around sunrise. Starting at 23:45, there
> was another unidentified narrowband signal with dx-like fading on 136.3 kHz,
> up to 10 dBuV/m. The noise between the statics was around -10 dBuV/m/14Hz
> during the night, decreasing by 5 dB with daylight.
>
> For the calculation of signal strength, I have found a ratio of 7 dB between
> CFH's observed power density in 14 Hz and its total power, corresponding to
> an effective modulation bandwidth of 70 Hz. So the actual field-strength
> would be 20 dBuV/m in the maximum. Reducing the noise density to 1 Hz, I
> would see -10-11.5 = -21.5 dB/Hz, resultimg in an SNR of 41.5dB/Hz. The ERP
> of CFH is said to be around 10 kW, 40 dB above an amateur station's limit.
> That would leave us with 1.5 dB SNR in 1 Hz, or 11.5 dB with 10 s dots in 0.1
> Hz, even here in the middle of Europe. In other words:
>
> Had we tried last night, we would have made it across!
>
> BTW: Comparable observations in winter and early spring had shown a quite
> similar field strength, it was only the time window of common darkness which
> was much longer.
>
> Cheers
> Markus, DF6NM