I think I see where the confusion has arisen. Here we are talking about a K2 with integrated KAT2 ATU. So, when I used the term "rig end of the feedline", I was referring to where the feedline connects to the KAT2 BNC connector at the back of the K2, which is the output or antenna side of the KAT2 ATU. In order to make the impedance where the antenna connects to the KAT2 output look like 50+0j ohms, the KAT2 will use an LC network to transform the impedance. The impedance of this LC network together with the 50ohms of the K2 final PA output will be equal to the complex conjugate of the impedance you will see looking into the shack end of the feedline leading to your antenna.
For example, to keep the maths simple, let's consider a case where the impedance at the end of the feedline in the shack works out to be 50+j100ohms. That is, the antenna is slightly inductive. In order to transform this impedance to 50ohms, you could connect a capacitor in series that has a reactance of 100ohms to cancel out the inductive reactance of the antenna+feedline. If we look at the impedance of our matching network plus radio, we see the capacitor in series with the 50ohm transmitter, so the impedance looking into the "ATU" plus transmitter is 50-j100 ohms. This is the complex conjugate of the impedance looking down the feedline towards the antenna, which we already see is 50+j100ohms. In a more complicated scenario, the resistive component at the shack end of the feedline may not be 50ohms, and our matching network will be more complicated, and we will connect some reactance across the feedline and/or transmitter to achieve the required impedance transformation. If you go through the maths, you will again find the impedance looking into the ATU+transmitter is the complex conjugate of the impedance looking into the feedline+antenna. 73, Matt VK2RQ > On 1 Aug 2014, at 7:29 am, Per-Tore Aasestrand <p...@ieee.org> wrote: > > Hi Don, > > I still doubt that this is correct. > > The L/C values given by the tuner, are the values as seen from the tx side. > It is the values that will make the tx happy. It does not say much about the > impedance at the rig end of the feeder. > > In order to change the VSWR on the feeder itself, one has to put the matching > network (tuner) between the antenna and the feeder. > > BTW, the tx is probably not conjugate matched by the tuner. Conjugate > matching does not apply to transmitters or power amplifiers. But I realize > there is a huge dissension in this area too. ;-) > > Per-Tore / LA7NO > > > >> On 31 July 2014 22:42, Don Wilhelm <w3...@embarqmail.com> wrote: >> Per-Tore, >> >> Yes it is correct. He stated that it is the impedance at the rig end of the >> feedline. >> That will not likely be the feedpoint impedance of the antenna. That >> impedance can be found if you do the calculations for the impedance >> transformation of the feedline (for which the length of the feedline must be >> known). >> >> 73, >> Don W3FPR >> >> >>> On 7/31/2014 4:23 PM, Per-Tore Aasestrand wrote: >>> Hi Matt, >>> >>>> Of course you realise that the output impedance of the ATU will be the >>>> complex conjugate of the impedance at the rig end of your feedline. >>> I wonder if this is correct >>> >>> IMO, the task of the tuner is to make the tx happy, so it can look into the >>> load it is designed for. Thus, it will translate the impedance as seen from >>> the antenna connector into something as close to 50 ohm as possible. The >>> tuner will not change anything on the feeder. With or without the tuner, >>> the feeder will have the same VSWR. >>> >>> Per-Tore / LA7NO >>> >>> >>> >>> >>> On 31 July 2014 22:02, Matt VK2RQ <matt.vk...@gmail.com> wrote: >>> >>>> Of course you realise that the output impedance of the ATU will be the >>>> complex conjugate of the impedance at the rig end of your feedline. >>>> However, if you want to know the impedance of your antenna, you need to >>>> realise that the feedline is acting as an impedance transformer, and you >>>> need to take into account factors such as length of feedline, frequency of >>>> operation characteristic impedance and velocity factor of the feedline, >>>> etc.. >>>> >>>> 73, Matt VK2RQ >>>> >>>>> On 1 Aug 2014, at 1:02 am, TF3KX <kristi...@gmail.com> wrote: >>>>> >>>>> Thanks. Yes, I can determine the tuner settings (L/C-values, etc.) and >>>> from >>>>> the network equations derive the impedance these settings match into. It >>>>> would be neat if the K2 had enough CPU power and memory to carry these >>>>> calculations out for me and just display the R+jX. Perhaps a good project >>>>> for a small program or an app... >>>>> >>>>> 73 - Kristinn, TF3KX >>>>> >>>>> >>>>> >>>>> -- >>>>> View this message in context: >>>> http://elecraft.365791.n2.nabble.com/Can-I-measure-antenna-impedance-with-K2-tp7591798p7591803.html >>>>> Sent from the Elecraft mailing list archive at Nabble.com. >>>>> ______________________________________________________________ >>>>> Elecraft mailing list >>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>>> Help: http://mailman.qth.net/mmfaq.htm >>>>> Post: mailto:Elecraft@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 matt.vk...@gmail.com >>>> ______________________________________________________________ >>>> Elecraft mailing list >>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>> Help: http://mailman.qth.net/mmfaq.htm >>>> Post: mailto:Elecraft@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 p...@ieee.org >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:Elecraft@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 w3...@embarqmail.com > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@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 arch...@mail-archive.com
