A spectrum from the natural radio receiver at Sebring Florida
27.516N,81.517W range 869.4 km run by Joel Gonzalez,

 http://abelian.org/vlf/tmp/141204b.png

S/N is 12.6 dB in 55.5 uHz.

The noise level there is often quite high both natural and man
made.  A rough spectrogram shows quite a good nighttime S/N

 http://abelian.org/vlf/tmp/141204a.png

but only for a while.  A summer daytime test might do better
on that path with less background to compete with.

For comparison, here is W4DEX at Hawley Texas in similar
bandwidth during the day on 2nd June, range to Hawley is 1816km.

 http://abelian.org/vlf/tmp/w4dex_140603b.gif

Jim AA5BW wrote:

> I can run 10uW ERP at 8820 Hz for ~ 12 hour periods;
> oscillator stability may be ~100uHz.

I think you would need another 7 to 10dB ERP increase and
stability of order 10uHz to have a chance.

If you can't manage so much power but can do long transmissions,
it might just be worth trying the summer daytime T/A path.
It is long and stable and although attenuation is higher,
the background noise is lower.  Might just be detectable in
something like 25uHz bandwidth for a full day carrier.

But your 10uW ought to reach Forest VA 37.344N,79.288W without
difficulty.   Markus DF6NM achieves over 1000km with 10uW or
less, over a mostly land path - and gets across 14 character
messages at that ERP and distance.

For converting fT to uV and vice versa, on distant signals
I just assume free space impedance and use

   fT = uV * 3.333

and

   uV = ft / 3.333

The 3.333 is just 1/c combined with some powers of 10
to convert the micro and femto units.

--
Paul Nicholson
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