Re: [TowerTalk] Remote balun 4:1 or 1:1 ?

[Bill Coleman <aa4lr@arrl.net>]

On Sep 9, 2004, at 11:38 PM, Steve Forst wrote:

> Tried running  ladder line into the shack, but too much RFI.    Most 
> sellers
> of remote baluns offer 4:1  baluns for connection between coax  from 
> the
> tuner and  450 ohm ladder line  to the  antenna.

The key thing here is that it doesn't matter what the balun ratio is so 
much for two reasons.

First, you're not running the transmission line in a matched condition 
-- it has a complex impedance on it, that changes with frequency and is 
no where near the characteristic impedance of the line.

Second, the transformation ratio of a balun only applies for resistive 
impedances. Because the impedance is complex, who knows what the 
transformation ratio might really be.

> The guys at DX Engineering  have a 1:1 balun for this purpose, which 
> they of
> course  say works better  They also  say to use 300 ohm line instead 
> of the
> 450 line.

A lot of the 4:1 baluns used a voltage balun design on a powdered iron 
core. Voltage balun designs are old and do not do too much to enforce 
current balance.

Current baluns do a better job of enforcing current balance. A typical 
current balun consists of a ferrite core or a series of ferrite beads. 
It suppresses common-mode currents while not affecting differential 
currents.

My recommendation -- use a 1:1 current balun. Also, use whatever 
transmission line has the largest conductors. The object is to minimise 
loss. Since the losses at HF are mostly resistive, a larger conductor 
will show less loss in the transmission line.

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk