Paul, LF,
So, if we have the approx formula for VLF propagation and know the range of the
noise floor at 8,97kHz, then what would be the TX power i have to apply to a
300m vertical to reach Canada/USA, if there would be some well equipped
stations?
You know the details of my antenna and if it is enlarged to 300m, it will be
approx: C= 1750pF, R(coil, DC)=100 Ohm, R(other losses)~400 Ohm, => antenna
efficiency at 8,97kHz will be 0,0064%. In this case the limit will not be the
antenna voltage but the maximum available power, that is abt 600W. Would that
be enough? ;-)
BTW, yesterday i got the idea to built a second PA (to have one in reserve and
to:) to get a better operation of the generator: In the moment the PA works on
13,8V that is given bei a SMPS. If the carrier starts there is a power shift of
100% at since the SMPS always takes the needed power from the generator (even
if the 230V droppes to 80V), the fuel/speed regulation becomes unstable. I
often noticed a longer drive swing that can take up to one minute (depending on
the power and parallel switched batteries). That would become a problem if i
really want to take the maximum power the generator gives!
So, if i directly rectify the 230V (with a 300W halogen lamp in series. The
lamp will be short cut by a relay if the voltage across the C is >280V) and
apply a big C (i have some 350V/6000µF Elkos) and built a class D PA that
handles the 350V DC (i plan to use 2x STP10NK80Z FETs) i achieve the maximum
power the generator will give. The power regulation will be optimal since the
power decreases ~1/U^2. Even the small SMPS of the Notebook will be no problem
since it covers a wide input voltage range. When using a small 230V/10VA
transformer to generate 15V DC for the driver and use optical components for
keying and using the given isolating output transformer of the PA, there is no
danger to get a shock unless i do not touch the PA during operation. The FETs
are protected from overload power by the generator and since they have
integrated Z diodes, they will not be damaged by eventual voltage spikes... ;-)
73, Stefan
________________________________
Von: [email protected] im Auftrag von Paul Nicholson
Gesendet: Mi 17.03.2010 10:46
An: [email protected]
Betreff: Re: LF: Ionospheric VLF propagation
Alexander wrote:
> Certanly exponential factor exp(-r/a) should be present.
> I mentioned this before.
Yes you did! I am following your lead with this 1/sqrt(r)
thing and the exponential factor. And it is working - it is
giving the right answer for Stefan's signal!
3dB per 1000km (daytime) is mentioned in some literature but
I have to follow that up. Assuming that, we have the
estimate for daytime flux density at range r:-
B = sqrt( 9.5e-21 * ERP/r) * exp( -r/2.9e6)
> But this should be calculated. At the earth bondary one can
> use Leontovich bondary condition
Yes.
> But what to do with ionosphere boundary... To neglect dissipation
> in ionosphere looks not reasonable.
Yes too. The ionosphere boundary is more complicated. There are
two values for the refractive index - attenuation depends on
direction relative to Earth's magnetic field. The result is
phase and polarisation changes. I have some references to follow
up here too. But it is complicated and time consuming. It
would be nice to just use average figures for day and night
attenuation - surely good enough for 'amateur' work.
> To solve the problem (rather volumable problem) is nice task
> for physicist.
The hard work was done, decades ago, and appears to be fairly
well established. But it is a major job to go through the
literature and pick out what is relevant. It is a heady mix
of plasma physics, EM theory and ray tracing. There are one
or two textbooks - one I will order today.
--
Paul Nicholson
--
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