[Elecraft] Can I measure antenna impedance with K2?

[Wes (N7WS)]

Excellent!

On 8/1/2014 12:56 AM, Jim Brown wrote:
> Much confusion and misunderstanding about impedance matching at the output of 
> an RF power amplifier. The output impedance (source impedance) is NOT 
> necessarily the same as the rated Load impedance. Rather, the rated Load Z is 
> the Z that the output stage is happy driving based on its dynamic 
> characteristics (what we old farts, raised on hollow state devices called the 
> "Load Line"), and will often be LESS THAN the rated Load Z.  Yes, the matching 
> network should be tuning out the reactance, and it should be providing the 
> resistive load Z that the rig wants to see, but this Z will rarely be the 
> source Z of the output stage, and will often be much lower.
>
> But the real question here is, why expect a transceiver, designed nearly 20 
> years ago, to be suitable for measuring the impedance at the transmitter end 
> of a piece of coax connected to an antenna when so many EXCELLENT devices 
> capable of that measurement are available at remarkably low cost, and with 
> great power and flexibility?
>
> There are the AIM products, OK but expensive for what you get, and my 
> favorite, the German designed, UK built, VNWA, a 1.5 GHz Vector Network 
> Analyzer that cost me $750 delivered to my home in W6 three years ago with 
> calibration loads.
>
> I export data from this unit in Touchstone format (a plain text format for 
> data exchange) to SimSmith (freeeware, excellent) and let it compute the 
> complex Z at the antenna end of the coax, having measured the length of the 
> coax using the TDR capability of the VNWA.  I can also expert data from the 
> VNWA on this sort of measurement to AC6LA's excellent Excel spreadsheets, and 
> also the data on a sample length of any piece of transmission line (coax or 
> other) to compute fundamental properties of the transmission line. I can also 
> use SimSmith to design matching networks using stubs and discrete components.
>
> http://k9yc.com/PacificonSmithChart.pdf
>
> So with all of this analytic capability with very good accuracy available at 
> very low cost, why would you want to use a K2 and far less elegant methods to 
> do much less?
>
> 73, Jim K9YC
>