Hi Roger
Yes! It is as that's how we discover new things!
The practicality of a loop would depend on its size and the tuner
design. Stable caps would be needed and these caps would be very
expensive which resulted in my thoughts drifting to the concept of a
gyrator. Essentially an inductor used to simulate a cap with
suitable active components... Google 'gyrator'. There is some
precedent for this down in this frequency range... The trick would
be to design one that could handle the current. BUT it may solve
the stability/cost issue of using caps at the expense of
considerable engineering...
73 es GL
Scott
VE7TIL
On 3/18/2011 3:02 PM, Roger Lapthorn wrote:
Yep, I guess you're right Scott. And you know better
than most. Ah well, it was an interesting idea to toss around.
73s
Roger G3XBM
On 18 March 2011 21:53, Scott Tilley <[email protected]>
wrote:
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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--
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G3XBM GQRP 1678 ISWL G11088
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
https://sites.google.com/site/sub9khz/
G3XBM GQRP 1678 ISWL G11088
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