Why? I think you might need to look at the priorities first. Experience says
you will not notice the difference unless you have tackled the problem of
ground and environmental losses first (as Stefan has done) The improvement
obtained by improving the Q of the loading coil may probably only increase
the efficiency by a minute amount.
You say you have a Q of 200 now.... this indicates a bandwidth of about 2kHz
meaning you will probably need to retune across the band. A Q of 400 to 500
should be possible but unless the reduction in RF resistance is a
substantial fraction of the Rloss it is wasted effort. It also means that
your tuning will be very weather dependent. I feel that unles you have
situation of Rloss <15ohms you will barely notice the difference......except
a "flighty" system, difficult to keep peaked, and possibly a number of fried
PA devices when it goes wrong.
Litz will improve the Q slightly, coil form factor needs to be right as
well, and Litz is a devil to work with (note "proper" Litz has strand
numbers are twisted in powers of 3, anything else is just bundled and will
not achieve the theoretical advantage) If you miss one strand out of the
soldered connection of the Litz you will lose a lot of the advantage.
Top loading may well turn out to be more effective, but it all depends on
your partcular location, and you need to make measurements of the antenna
systtem, and possibly the field it generates, not guess (though that is very
seductive :-)) but in my experience is usually wrong! )
You are right in that the best way is to make incremental improvements to
the antenna, but be very critical, weighing the cost in effort and cash for
the improvement .......what works for others may not work for you.
Best of Luck
Alan
G3NYK
----- Original Message -----
From: "Dimitrios Tsifakis" <[email protected]>
To: <[email protected]>
Sent: Friday, February 15, 2013 12:31 AM
Subject: LF: how to increase the Q of my loading coil?
Hello group,
I would like to increase the Q of my loading coil for 475 kHz. . It
consists currently of a 20-litre plastic bucket with standard house
240V electrical wire (with PVC jacket). I measured the Q and found it
to be about 220 (XL is about 2 kohm). I do have some Litz wire I can
use. I also have a piece of large diameter (25 cm) storm water pipe,
which I think is made of PVC. Would you recommend using a PVC former
or should I look for a more exotic material (glass/porcelain)? Would
you think the inter-turn capacitance is very detrimental and some
exotic winding technique would yield better results?
I understand that ground losses are bigger in my case than the
inductor losses, but I would like to address the inductor first.
73, Dimitris VK1SV
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