[ARC5] Smart People: Antenna Matching Mystery

[J Mcvey]

Agreed on the distributed capacitance.Also, complex impedance circuits can often interact and setup in different modes.I just had that situation with an "over coupled" matching system that would give me unexpectedresults if it wasn't tuned to perfection. Ideally, it should sweep with two humps on either side of f0, but it would also have other quite different scenarios when the tuning was a bit off.I think it came down to how much reactantance was being reflected into what. 

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!!
 

    On Monday, August 7, 2017 10:13 AM, Ian Wilson <ianmwilson73 at gmail.com> wrote:
 

 I have noticed that the roller coil has distributed capacitance, so itdoes 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 OhmAircraft 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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