[Milsurplus] [ARC5] Smart People: Antenna Matching Mystery

[Peter Gottlieb]

It's not voodoo, just electrical engineering, and pretty well understood. 


Peter

> On Aug 7, 2017, at 11:50 AM, arc5 at ix.netcom.com <arc5 at ix.netcom.com> wrote:
> 
> 
> 
> Sent from my Ain't Smart Phone.
> 
> 
> ------ Original message------
> From: J Mcvey
> Antenna Matching Mystery
> 
> ...The 50 ohm coax at the terminal causes a host of reactance and reflection issues by itself.
> Bet if you added coax length, the situation would change to something else, maybe better, maybe worse!
> 
> RF is spooky stuff!!
> ----
> You are so right.  I switched the coax jumper to a long one, coiled into a big spool "shield RF choke."  It completely changed the tuning.  RF is Electronic VooDoo.
> 73 Dave S.
> 
> On Monday, August 7, 2017 10:13 AM, Ian Wilson > wrote:
> 
> 
> I have noticed that the roller coil has distributed capacitance, so it
> does not always behave as a simple inductance even at lowly RF.
> 
> To a reasonable approximation, it could probably be modelled as
> "a few" L-C sections. 4 would be a good starting point.
> 
> 73, ian K3IMW
> 
> On Mon, Aug 7, 2017 at 6:57 AM, David Stinson <arc5 at ix.netcom.com> wrote:
> OK y’all- here’s a mystery (at least to me),
> Series circuit, designed to match a normally 5-12 Ohm
> Aircraft radio output to resistive 50 Ohms.
> Follow me here:
>  
> Series circuit:
> PA Tank coupling link – Roller coil –
> 120pFd ceramic cap mounted at antenna post –
> 50 Ohm Load = 25 W out.
>  
> PA Tank coupling coil –  120pFd ceramic cap mounted
> at the input of the Roller Coil – Roller Coil –
> 50 Ohm Load = 15W out.
>  
> The ceramic cap is near chassis ground both ways,
> so it’s not circulation currents.
> The PA tuning cap setting does not change,
> so it’s not de-tuning the PA tank.
>  
> Why the difference between these two series circuits?
>  
> 73 Dave AB5S
>  
>  
> 
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