On 10/19/2015 3:34 AM, Brian Howie wrote:
In message , bilou
writes

"Brian Howie" wrote in message
...

I've a 5 foot Octagonal loop for MF. The shield is copper water pipe,
with
a gap , 7 turns inside plus a coupling winding. It does a good job
eliminating local noise (mostly ASDL hash from the phone lines) compared
with a vertical. However the capacitance between the shield and turns
seems to load it quite a bit meaning I can't get the tuning range I'd
like.

Brian GM4DIJ
--
Brian Howie
Hi
My own experience is that ,at least for receive, multi turn loops are
useless.
Instead you can use a single turn one with a good coil in serial.
The tuning range for a given variable capacitor is much greater
especially if ,at low frequency, the coil is using ferrite .
Switching the coil can increase the tuning range easily.
The coil, with a secondary winding,is also very useful to
adjust the coupling to the receiver.

I'd have thought I'd get a better signal from more turns, but maybe
better coupling and a higher Q from your suggestion would do the same.

I can't imagine why more turns won't help a receiving loop. I guess it
depends on what is limiting reception. Adding a coil may improve the Q
or it make make it worse depending on the Q of the coil. More turns
won't help the Q of a receiving loop, other than reducing the
significance of the resistance of connections and other components.
More turns *will* increase the signal strength.

How does the coil affect the tuning range of the cap? A cap is limited
by the ratio of the minimum to maximum capacitance. The ratio of
frequency is limited to the same ratio.

--

Rick