On Mon, 31 Jan 2005 21:49:21 GMT, "Highland Ham"
wrote:

Example : To make a 4 turns loop as above you would need 2*4 equals 8 metres
of 8 lead ribbon cable using end of lead 1 and 8 as ends of the loop , join
ends of lead 2 and 3 , 4 and 5 , 6 and 7.

Loops made of multi conductor cables in this way tend to have a very
large capacitance between turns and in the worst case the loop will
have a self resonance frequency below the desired frequency band. Even
if the self resonance is above the desired band, the amount of
external tuning capacitance is greatly reduced.

When a wide ribbon cable is available, it can be a good idea to use
only every other lead and let the intermediate leads floating to
reduce the capacitance between turns.

Paul OH3LWR

Example : To make a 4 turns loop as above you would need 2*4 equals 8
metres
of 8 lead ribbon cable using end of lead 1 and 8 as ends of the loop ,
join
ends of lead 2 and 3 , 4 and 5 , 6 and 7.

Loops made of multi conductor cables in this way tend to have a very
large capacitance between turns and in the worst case the loop will
have a self resonance frequency below the desired frequency band. Even
if the self resonance is above the desired band, the amount of
external tuning capacitance is greatly reduced.

When a wide ribbon cable is available, it can be a good idea to use
only every other lead and let the intermediate leads floating to
reduce the capacitance between turns.

Paul OH3LWR
=============================
Paul , Tnx for the above advice ,although for a loop made with flat multi
ribbon to be tuned to 60 kHz , the self-resonance freq will highly likely be
higher than 60 kHz . The ribbon I have is 15 leads wide ,hence for higher
freqs I could leave out every other lead .
Tnx again , this is good education .

Frank GM0CSZ / KN6WH

Beyond 3 or 4 turns on a single-layer coil, the coil's resonant
self-capacitance is not very much related to capacitance between adjacent
turns.

This is because the individual between-turn capacitances are all in series
with each other and the resultant rapidly decreaes.

For a 10 turn coil the end-to-end capacitance due to adjacent turns is only
1/10th of the individual turn-to-turn capacitance.

Coil self-capacitance soon becomes a linear function only of coil diameter
and length of the coil former.

It's rather complicated but the resulting self capacitance is much smaller
and the resonant frequency is higher than what you think it might be just by
considering the individual turn-to-turn capacitances.
----
Reg, G4FGQ

Well, Mr. Anderson, thank you very much for your detailed reply. This all
sounds very interesting but I think it's going to have a low benefit-to-work
ratio, especially with the long project list I already have. I was hoping I
could down to the passive re-radiator store and pick up something that you
would work. Oh well.

Thanks again,

Vic