[TowerTalk] Balun Recommendation

Fri Apr 20 08:47:54 PDT 2012

The really lesson in all this is: Never make an absolute statement.

A simple case that would disprove your 'always' is a coax to waveguide
conversion where you have the shield connected to the outside of the
waveguide and about 1/4 wave of the center conductor sticking into the
waveguide to excite it.  You can change the swr all over the place and not
have common mode currents on the coax.  

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net

-----Original Message-----
From: Steve Hunt [mailto:steve at karinya.net] 
Sent: Friday, April 20, 2012 14:55
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Balun Recommendation


For a fixed feedline Zo, a change in SWR *always* indicates a changed load
impedance; and a change in load impedance always causes a change in choke
dissipation unless the system is perfectly balanced, in which case you don't
need a choke.

So, the only case where there is no relationship between SWR and choke
dissipation is one of perfect balance, which I have yet to encounter in a
practical antenna system.

Steve G3TXQ

On 20/04/2012 15:40, K1TTT wrote:
> I would go with something like this:
> In SOME cases SWR may be an indicator (but not direct cause) of 
> changes in the common mode current that a choke would see.  In other 
> cases it has no relationship to it.

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