John,
It's very difficult to get decent common-mode impedance across a 4:1
frequency band with an air-cored choke - they are too "High-Q".
A further problem caused by their high Q is that their impedance is
almost totally Reactive away from the SRF. Depending on the impedance of
your common-mode path, the choke Reactance can actually increase the
common-mode current. Check out an EZNEC example which illustrates the
problem, towards the bottom of this page:
http://www.karinya.net/g3txq/chokes/
As Jim said, Ferrite-cored chokes with a predominantly Resistive CM
impedance are a much better solution.
73,
Steve G3TXQ
On 17/11/2010 05:30, John Molenda wrote:
Does anyone have the dimensions for a air-core choke balun to be use
for 160 - 40 mtrs . thanks John kb2huk
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