[Elecraft] [K1] Question about antenna tuners that I should not have to ask but do.

[Don Wilhelm]

Doug,

I think you are "doing it the hard way", but what you have proposed 
along with some math will result in the correct information to give you 
the impedance at the shack end of your feedline.  That is if and only if 
the KAT1 tuner has tuned to an SWR=1.

To figure the impedance at your antenna feedpoint, you will have to know 
the type of feedline as well as its length and feed that information 
into the formulas or an application such as TLW - (transmission line for 
windows).

The easier way is to beg, borrow or steal an antenna analyzer and 
measure the impedance at the shack end of the feedline.  You will still 
need to apply the feedline parameters to determine the antenna 
impedance, and the feedline will act as an impedance transformer.

BTW, 24x10 is 240pF.

73,
Don W3FPR

On 9/28/2015 7:37 PM, Douglas Hagerman wrote:
> Does anybody have a “worked example” of how to use the L and C values reported by the K1 internal antenna tuner to analyze an antenna? I feel pretty guilty asking this, because it’s sort of a “please help me do my homework” question. And I am supposed to know how to do this homework.  :-)
>
> I have a space-limited dipole for 20 meters with drooping ends. The KAT-1 tuner will tune it. What I want to know is whether to use a 4:1 or 1:1 balun, or no balun, at the antenna.
>
> If the tuner reports 24 “x10” pF, is that 240 pF or 2.4 pF? A straight reading suggests that it’s 2.4 pF, but I don’t see how the tuner circuit can provide so little capacitance. But C4 (82 pF) plus C5 (150 pF) gives 232 pF which could 240 pF if you include some parasitic capacitance, maybe?
>
> Next, I need to figure out the circuit. If the tuner reports nt 2, I think that means that the coil is next to the tuner’s antenna connector, and the capacitance is in parallel with the radio connector. I guess that is designed to be 50 ohms of pure resistance, so I have a nice little circuit with one of each part. I can figure out the various reactances, etc., and combine them, but am not sure I’m doing it right. That should give me the reactance at the tuner’s antenna connector.
>
> Then I have about 12 feet of RG-8x coax, so I can use a Smith chart to work out how the reactance at the tuners’s antenna connector is transformed to the antenna connection, but there is always the confusion about which way to go around the outside of the chart. And then take into account the 4:1 balun that’s on there. In theory, all of this should tell me the antenna's impedance at the point where the balun connects, which should suggest whether it would be better to use a 1:1 balun instead.
>
> Does anybody have an example of this sort of calculation? I have looked in the Antenna Handbook and other sources and they all dance around it; I’m looking for something practical and cookbook-like.
>
> Or I could spring for a 1:1 balun and try it.  :-)
>
> Thanks!
>
> Doug, W0UHU.
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to w3fpr at embarqmail.com