Andy, LF,
You wrote :-
"Now, I take two identical such loops and mount then on the same centre line
but at right angles to each other so there should be no coupling
between them, whatsoever. Now, I connect the two loops in series and
resonate the combination with a single capacitor of half the original
value."
I have been pondering about something similar as I have problems remotely
rotating yet another antenna.
My idea is to make the loops in the same way as you describe but feed the 2
loops to the two inputs of a balanced pre-amp like the G3LNP loop pre-amp
shown in the "LF Experimenters Handbook"
What are your thoughts on that please.
Gary - G4WGT.
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Andy Talbot
Sent: 21 July 2008 12:30
To: [email protected]
Subject: LF: Loop Conundrum
Was pondering this while out walking the other day, and couldn't come
to a satisfactory conclusion either way...
A small magnetic loop mounted vertically has a defined radiation
resistance that is a function of its diameter, a loss that is function
of its conductor and hence a loss or efficiency that is the ratio of
the two. It is resonated with a good quality vacuum capacitor, and
fed/matched by any suitable metrhod. Lets also leave aside all the
myth and folklore about small loops, and also ignore the environment
for now. It also as a radiation pattern with nulls.
Now, I take two identical such loops and mount then on the same centre
line but at right angles to eachother so there should be no coupling
between them, whatsoever. Now, I connect the two loops in series and
resonate the combination with a single capacitor of half the original
value. The resulting radiation pattern should have the nulls filled
in, and be a reasonable approximation to omnidirectional in azimuth.
BUT...
What is the resulting change in efficiency?
Argument 1:
Two identical loops = two times the loss R, but also two times the
radiation resistance (since they don't couple) so net efficiency
remains the same.
Argument 2 :
Chu-Harrington relates efficiency / Q / bandwidth / volume enclosed.
Therefore, as the enclosed volume has increased, the effciency ought
to rise.
Both arguments developed little side trendrils & thoughts as I walked
and pondered, and both appear valid in their own way. So
the floor is open for discussion :-
And where does the net radiation pattern fit into the equation? Does
it, at all ?
--
Andy G4JNT
www.scrbg.org/g4jnt
ps. Fascinating paper on EMP btw. - I was up way past midnight last
night reading it.
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