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Re: [TowerTalk] Balun Recommendation

Subject: Re: [TowerTalk] Balun Recommendation
From: Steve Hunt <>
Date: Thu, 19 Apr 2012 20:23:29 +0100
List-post: <">>

That sounds like a very similar analysis to this one from Jim:

"What if the choke is on the output side of an antenna tuner (for 
example, up in the air at the feedpoint, or somewhere along the line) 
and the tuner is stepping up the impedance to match a higher impedance 
load? An impedance step-up of 4:1 doubles the voltage, which increases 
dissipation by 6dB, so our worst case CW or SSB dissipation is back to 
10 watts. Increase the impedance to 400 ohms and CW/SSB dissipation 
rises to 14 watts."

Steve G3TXQ

On 19/04/2012 12:42, wrote:
> Hi All, this is an observation from an innocent bystander:
> With constant power level, if the antenna Z increases, The voltage 
> increases as well, right? Conservation of energy then requires the 
> current to decrease, right?
> The rf voltage on the coax shield where it connects to the antenna 
> would be the voltage referenced to ground at that half of the antenna. 
> The choke current would be that voltage divided by the choke impedance 
> (also referenced to ground), Is that right?
> So, one might think that a higher Z antenna = higher E = higher choke 
> current? If so, power loss is then I^2 X whatever resistive loss is 
> present in the choke.
> 2X Z = 1.414 X voltage = 1.414 X choke current = 2 X loss. if the 
> above is true?
> 73,
> Gerald K5GW

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