>From what I calculate, 22 +j8 ought to be relatively easy to match, if the >KAT3 schematic is correct. A low-pass L with series L = 1.48 uH, C = 1967 pF >gets it to 1.009:1, assuming no strays and Qc = 1000, Ql = 200.
If my paper and pencil addition is correct, the available C ~ 2600 pF allows a match to a load of ~16 +j20. (with L ~ 0) Since I prefer matching at the antenna, I don't have a KAT3, so this is all a paper guess. Wes N7WS --- On Sun, 1/31/10, Kok Chen <[email protected]> wrote: > From: Kok Chen <[email protected]> > Subject: Re: [Elecraft] KAT3 antenna tuner > To: "Elecraft Reflector" <[email protected]> > Date: Sunday, January 31, 2010, 1:27 PM > > On Jan 31, 2010, at 1/31 10:34 AM, Roger D > Johnson wrote: > > > I started on this topic because the tuner failed to > find a good > > match at > > 1800. > > To see the approximate range of the internal K3 antenna > tuner at 1800 > kc, take a look here > > http://homepage.mac.com/chen/Technical/Tuner/tuner1.8.pdf > > (warning, it is a very large 9 MB PDF file (lots of > points), if you > download as PDF and view with a PDF reader, you can > rescale, etc > faster than viewing from a web browser). > > Each dot indicates the impedance at the antenna port when > the radio > port of the tuner is set to 50 ohms. So the tuner > should tune an > antenna that is the conjugate of where a dot lands on the > Smith Chart. > > The green points are for the case trx > series L : shunt > C > antenna, > and the blue points are when the tuner switches to trx > > shunt C > > series L > antenna. > > > My VNA shows the impedance at the TX connector as > 22+j8 which should > > be well within the proper range. > > > The conjugate of 22 + j8 ohms appears as 0.44 - j0.16 ohm > on the > normalized Smith Chart in the PDF file. That is just > barely inside > the coverage region of the tuner. > > You might try manually setting the tuner to the trx > > shunt C > series > L > antenna position, turn C to the max > (1200+600+300+...) and then > manually adjusting around the small values of L for lowest > SWR. > > From my fiddling with the values, a 50 ohm source appears > to prefer > large shunt C followed by a small series L on the way to a > 22 + j8 > ohms antenna . It could be possible that other > circuitry is > preventing you from reaching precisely that area of the > tuner. > > One thing you can do is to move the impedance of what you > see at the > end of your current transmission line. Since you have > a VNA, you > might want to play with changing the line length of the 50 > ohm > transmission line (or use a short length of a different > impedance line > to transform the impedance that you are currently seeing) > so that its > conjugate is more inside the dotted region of the PDF > file. > > Also, since you have a VNA, why not temporarily disconnect > the > transceiver output from the tuner, replace it with a 50 ohm > resistor > and look at antenna port of the tuner with the VNA? > You can then see > the conjugate of the impedances which your tuner can > transform into 50 > ohms. > > 73 > Chen, W7AY > > P.S. Anyone who wants to run this program for other > frequencies just > send me a note and I can either send you the app or the > Xcode project. > You need to be running at least Mac OS X 10.5 (also works > fine on > 10.6). If you want to modify it for the KAT100 L and > C values, you > will need to change the component tables in the source, and > recompile > under the Xcode IDE. > > Some caveats: the chart shows the combinations of C and L > values > without taking into consideration any strays. It also > does not take > into consideration the effects of the KBPF3. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
