Hi Roger
The practicality of pumping 35A into a loop is not an easy task!
Couple this with the stability of most capacitors creates a real
engineering challenge for a loop on 9KHz, notE the BW and Q. Not to
mention really low ERP one would get.
This will be an engineering challenge for sure!
73 Scott
VE7TIL
On 3/18/2011 2:39 PM, Roger Lapthorn wrote:
Hi All
Just run Andy's spreadsheet for magnetic loops to see the sort of
figures we get at 8.9kHz. Assuming 100W and a loop diameter of 10m
with 3mm wire the efficiency works out at -87.4dB and the ERP
-67.4dBW (0.2uW). There is also the matter of the low loss
6211.7nF capacitor. With larger loop diameters, thicker wire (or
multiple paralleled wires) and maybe 200W then the ERPs are
starting to get more useful.
The Marconi does seem a better bet, even with all the issues with
losses in the huge loading coil, but a VLF TX loop doesn't look a
total "no-hope" approach. Larger loops, with improved
efficiencies, may be easier than kite or balloon supported ones in
a /P location.
And then there is the widely spaced earthed electrode antenna.....
but I won't start a discussion on the merits or otherwise of this
as I am about to go on holiday this weekend and will not be able
to respond to emails next week. We know from work by DK7FC (and
VLF professionals) that this does work as a radiating structure.
73s
Roger G3XBM
On 18 March 2011 14:09, Roger Lapthorn <[email protected]>
wrote:
Just wondering if anyone has done the maths to work out what
sort of ERP could be expected at 8.97kHz with, say, 100W to a
smallish loop antenna in the garden?
It would certainly avoid the need for very very large matching
coils and may be easier to engineer than a Marconi. Even an
efficiency of -80dB would allow 1uW ERP and, judging by
results from G3XIZ with around 2uW, this could be useful with
long stable carrier transmissions of several hours. Most of us
could run a loop with an area of 100sq m. with thickish wire
in our gardens. A loop might also be more practical for
portable operations perhaps with a triangle with one high
support.
Certainly my own results with WSPR at 136 and 500kHz with just
a few watts and quite thin wire and around 80sq m loop area
were encouraging. Mind you, 9kHz is very much lower than
136kHz, so the radiation resistance would be tiny I assume.
73s
Roger G3XBM
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