[Lf] Spectran, Spectrogram and extreme QRS - a test ?

[Andre' Kesteloot]

Talbot Andrew wrote:

> I have not played with Spectran yet, but on the question of dot
> length......
> The optimum dot  will depend on the FFT and integration time of the
> software.  Ideally the dot length will be a multiple of the FFT period;
> three periods will give perfect resolution unless the software uses too
> excessive an interleave factor, two will be adequate but dots could get
> masked by impulse noise (an impulse can be several seconds in this
> mode).   What does the 0.03 Hz refer to, is it the FFT bin size or the
> minimum resolution which is usually two to three bins depending on the
> window employed.   I use either EVMSPEC for the faster rates, or the
> Dopplergram software for the EVM for slower monitoring,  both have rates
> at binary submultiples of 8000Hz.
>
> 30s dots is still fast CW as far as I am concerned !
>
> If your transmitter is REALLY stable, and I mean significantly better
> than 0.1ppm / 0.01 Hz and with the frequency known to this accuracy, I
> should be able to do an LF Dopplergram on your signal and see what day /
> night ionospheric effects are visible.  These effects do show up on the
> DCF 77.5 kHz signal and 137 should show a lot more.   Here the sampling
> rate of the signal will be 8000 / (2^18)  =  0.03 Hz and a 256 point FFT
> allows signal monitoring in a 240uHz bandwidth.  It won't take much
> notice of the 30 second dot period !
> Andy  G4JNT
>
> >Since we are used to 3 second dots with Spectrogram, it seems
> appropriate
> >to go to 30 sec with Spectran at maximum resolution.
>
> >Now, I want to arrange a test, if someone is interested, of course. I'm
> >planning to beacon for some days at low power, sending a message with
> QRS in DFCW
> >mode on 137.790 / 137.792, at 30 sec/dot, with 20 sec interval.
> >I will reduce RF power to 10 Watt, giving an approximative ERP of 10
> mW. With
> >this power setting my 900W TX will run unattended for days (I hope...)
> >, if you have a stable RX with a stable BFO !