On 10/20/2015 10:35 PM, rickman wrote:
On 10/20/2015 9:21 PM, amdx wrote:
On 10/20/2015 1:56 PM, rickman wrote:
On 10/20/2015 10:44 AM, amdx wrote:
On 10/19/2015 10:53 PM, rickman wrote:
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...


Often a 60kHz WWVB time receiver.

So why would that be a "bad idea"?


Ahh, you ask "what problem you would be trying to solve"
I should clarify, a resonant antenna for 60kHz, and that requires a
large inductance. Or at least that is one approach.

But the context was that a 256 turn loop was a bad thing. I'm trying to
understand what that was about. I don't need to know when it is a good
idea... well, I guess even that is interesting. But I think the way a
256 turn loop would be made for a WWVB receiver is around a piece of
ferrite. But who knows, maybe a large loop of telephone cable would
work well too.

It obviously works. It is not ideal because it would have a lot of
interwinding capacitance. Also the interwinding capacitance is not a
quality capacitance thus the Q is lowered.
It could be built with space between wire and layers, and 256 solder
connections is not a great idea when trying to insure high Q.
As far as "bad idea", all it has to do is receive enough signal
to keep the clock accurate, more than that is interesting, but useless.
Mikek