On 10/19/2015 3:50 PM, bilou wrote:
"rickman" wrote in message
...
On 10/19/2015 3:34 AM, Brian Howie wrote:
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.
In a multiturn loop you get huge capacitance between turns.
For a given variable capacitor it appears in parallel.
The Q of that big coil might be higher but as you need to add
fixed capacitors to the variable one to get useful tuning range
you loose almost what you gain.

I sort of lost the thought here. If you up the inductance of the loop,
it lowers the required tuning capacitance, so why would fixed capacitors
be needed? Are you saying the parasitic capacitance of the loop is
enough to significantly reduce the tuning range of the variable cap?
Maybe, but there are construction methods that minimize the parasitic
capacitance of multi-turn loops. Wide spacing is important. I've seen
spiral loops wound on wooden frames that look like God's Eyes, very
attractive.


I saw descriptions using a 128 pairs telephone cable and spending
several days to wire it as a 256 turns loop.
A bad idea IMHO.

I'm not sure what problem you would be trying to solve by using a 256
turn loop. There are middle grounds...

--

Rick