Dear Jim, group,
OK so far. And what do you think will be the most suitable TX antenna
type? The standard marconi as i will try it, with all its disadvantages
(high coil and earth losses, high voltages, high height needed...) or a
earth pole antenna that should (theoretically) form something like a
loop antenna? I am not very positive with these earth pole antennas, if
we want to reach more than 0,1...5km. If >100km is the goal, then i
expect the standard monopole antenna will be the best choice. A TX loop
antenna, out of a copper tube (say a tube >10mm diameter with 1mm
thickness) might be an interesting alternative since the skin effect is
not such a problem. But one can almost forget the radation resistance,
clear. It will be problematic but this is the challenge :-)
Someone of the group could start to check what is available with those
earth antennas. Not checking the web for literature, no transmission of
broad band audio signals but i mean rather trying narrow band modes with
an optimised antenna for one QRG. Those who have the place to reach a
distance of say >2km wire (hidden) and use a thick cable may reach more
since the "loop area" increases exponentially with the wire length. It
would be interesting if an improvement of the efficiency can be reached
when placing coils at both ends and so on. A quite interesting
alternative field...
73, DK7FC
Am 11.03.2010 00:37, schrieb James Moritz:
Dear Stefan, LF Group,
So far, I have not had time to make any detailed measurements and
comparisons - but the "quick look" screen shot attached was taken at
my home QTH on Sunday when both the QRN and the local mains QRM were
exceptionally low for a short period. The frequency range is 5kHz -
20kHz, and the FFT resolution is about 1.5Hz. The 3D waterfall shows
the alpha beacon "spikes" rather well. The continuous line just above
the highest alpha frequency appears to be a 15.625kHz TV line
timebase. Normally, frequencies below about 10kHz are filled with 50Hz
harmonics well above the QRN level, although the level varies greatly.
I did briefly try the RX at a /P location this afternoon - mains noise
was much lower than at home, but the QRN level was much higher today
than in this screen shot. However, since the 50Hz harmonics mainly
produce narrow-band spectral lines in the waterfall, these should not
be a great problem for receiving very narrow band QRSS-type modes,
providing the frequencies do not coincide exactly.
I'm not sure what to do about the TX side of 9kHz yet - I want to look
in a bit more detail at the technical problems that need to be
overcome before making a proposal for a NoV to Ofcom.
Cheers, Jim Moritz
73 de M0BMU
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