Ian White GM3SEK wrote:
The bunched choke is the one that has a Fmax/Fmin frequency ratio of 6.
A certain amount of mental gymnastics allowed you to claim that 1.5, 2.1
and 2.7 are all approximately equal to 2... so how about 6?

It is a known fact that the VF of these chokes changes
with frequency so they don't behave exactly like a
transmission line. Bunching probably changes the VF
considerably more than a helical wound choke since
the first turn and last turn may be on top of each
other.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Ian White GM3SEK wrote:
The bunched choke is the one that has a Fmax/Fmin frequency ratio of 6.
A certain amount of mental gymnastics allowed you to claim that 1.5, 2.1
and 2.7 are all approximately equal to 2... so how about 6?

It is a known fact that the VF of these chokes changes
with frequency so they don't behave exactly like a
transmission line. Bunching probably changes the VF
considerably more than a helical wound choke since
the first turn and last turn may be on top of each
other.
--
73, Cecil http://www.w5dxp.com

I've never actually really compared bunching to helical wound.
The one they specify to build for my triband yagi is a helical
coil. On that antenna, I've used both methods, but not at the
same time to really compare. I didn't notice any real noticable
difference in operation though. I was just looking at the small
choke in my trunk for 2m. It hangs from the trunk lid, and is
tie wrapped. It was about 2-3 diameter, and about 4-5 turns
or so, bunched together. For the purpose I used it for, it
worked great. But it could well be possible what you say about
the higher frequency operation. I do know a bunched choke is
a whole lot better than no choke at all.
MK
MK

wrote:
I've never actually really compared bunching to helical wound.
The one they specify to build for my triband yagi is a helical
coil. On that antenna, I've used both methods, but not at the
same time to really compare. I didn't notice any real noticable
difference in operation though.

You wouldn't notice much difference for a single band
and maybe not even for a tribander. The helical has a
greater bandwidth than the bunched. For instance, at:

http://www.k1ttt.net/technote/airbalun.html

there's an 8 turn helical Vs 8 turn bunched. If the
target choking impedance is 500 ohms minimum, the helical
covers 6-24 MHz, a 4:1 ratio, while the bunched covers
4-10 MHz, a 2.5:1 ratio. The helical also has about two
times the maximum choking impedance as the bunched one.
--
73, Cecil http://www.w5dxp.com