David G. Nagel wrote:
Chris W wrote:
I have been looking at the MFJ-1622 antenna. Part of the
instructions for antenna set up, which you can find here....
http://www.mfjenterprises.com/man/pdf/MFJ-1622.pdf
say to roll up about 30 feet of coax into a 12" diameter coil. This
they label as a choke. This just seems like a "duct tape" solution to
me. Is there a better way to accomplish the same thing? Would a few
ferrite beads on the coax do the trick or do I just have no idea what
I am talking about?
P.S. please check out my new Ham Radio Repeater Database web site.
http://hrrdb.com

Chris;

Your best choke is about 30 feet of coax rolled up into a 12" coil.

This is not a duct tape solution but one that has been used for
decades. It is the cheapest and easiest choke you can use. Others are
better but not easier.

Agreed.

The coil only *looks* crude - especially if you actually do use duct
tape. But looks can be deceptive.

With the right length of coax, number of turns and method of winding,
such a simple coil resonates with its own self-capacitance and is
unbeatable as a single-band choke. With about the same amount of care, a
slightly different coil can be selected to give an adequate common-mode
impedance across several bands. The design data has been in the ARRL
Antenna Handbook for many years, and there's more data about
solenoid-wound chokes on the web.

The really crude solution is to use just "a few ferrite beads" without
giving any thought to which ferrite beads, or how many, or why.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek