jawod wrote:
Ian White GM3SEK wrote:
For a more broadband solution based on coiled coax, I'd agree with
Cecil's suggestion of cascading a large coil for the lower bands with
a smaller coil optimized for the higher bands. It would also be
possible to cascade a large coil with a small ferrite choke.


Ian and Cecil,

I think you both should disclose any ties you might have to the cable
industry. (hi)


Somewhere in there is a very bad joke about "cable ties"...

Cable is much less expensive over here than large ferrite beads imported
from the USA; hence my interest in the coiled cable chokes.

I haven't been able to find out the proper placement of ferrite beads.
Are they placed ANYWHERE along the cable. Do you calculate the
transmission length for voltage peaks?


The place to start is where the common-mode current would be launched
onto the coax. In an antenna fed with coax all the way, that would be
the feedpoint. In an antenna fed partly with coax and then with parallel
line, it would be at the transition point.

But if the system is physically asymmetrical (eg if the feedline runs
back horizontally below the antenna) a single choke may not be enough to
solve the problem. In that case, the next place to think about would be
a quarter-wave closer to the transmitter.

....Doorbell...

Someone stopped by for a long Sunday afternoon chat, and in the meantime
Cecil has provided the rest of the answer.


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