Jeff, Any antenna tuner, including the MFJ, the KAT3, or any other does not actually "tune" the antenna. It adds a network of inductance and capacitance between its input and output to allow the input impedance to be near 50 ohms resistive while the output impedance will be whatever it was to start with.
What I am trying to say is that an SWR meter placed at the output of the KAT3 will not change before, during, or after tuning the KAT3 (unless there is something wrong in the antenna system) - nothing is changed on the output side of the tuner. The only thing that will change is the impedance looking into the tuner input, and that is the SWR indicated by the K3 using its internal wattmeter. The KAT3 arranges its internal inductance and capacitance so it is a transmission line transformer of the proper ratio to produce a 50 ohm match to the K3 PA to operate into. Take the small MFJ tuner between your SB200 and the K3 away, it serves no purpose that I can think of. With the SB-200 and the high power tuner both set to bypass, the KAT3 should be able to match the antenna. When you put the SB-200 in-line, you should set the KAT3 to bypass, and if the amp input circuit does not offer a low enough SWR to properly operate the K3, then whatever problem that exists should be fixed in the amplifier. The large MFJ will have to be tuned manually to match the output of the SB-200 to your antenna - the same as the KAT3 did for you automatically when the SB-200 and large MFJ tuner were bypassed. BTW, the easiest way to adjust a manual tuner is to connect an antenna analyzer to the tuner input and then tune until you have a low SWR or ideally a R=50, X=0 impedance indication. After that, connect the tuner to the SB-200 and operate (on that band or band portion) without touching the tuner settings any further. As long as your antenna does not change, you can record the tuner settings for quickly resetting the tuner when operating on that frequency the next time. 73, Don W3FPR W7BRS wrote: > Elecrafters, > > I know this is off-topic, but the range of ham-smarts on this list is > pretty good so I'll throw the question here and hopefully get some of that > ham-smarts too. > > OK -- K3/100 with KAT3 is the rig. > > I have it connected through a tuner and then to the SB-200 and then Dipole > > K3/100/ATU <-> MFJ tuner <-> SB200 <-> Dipole > > If I use Auto mode on the KAT3, put the MFJ tuner in Bypass and hold TUNE > then the KAT3 goes and brings the SWR (according to the display) to a > favorable value (1.0 to 1.2). I use a MFJ tuner between my Rig and Amp > because the Old Bard told me to. Actually my setup is different than > what I just described, but I'm simplifying this for the question at hand. > > [ What I really do is K3 <-> Small MFJ Tuner <-> SB200 <-> Big MFJ Tuner > <-> Dipole ] > > On the watt meter of the (small) MFJ Tuner, the indication is I have a non > favorable SWR, more reflected power than had I put the KAT3 in bypass and > manually tuned the MFJ Tuner to a favorable SWR (1.0 to 1.2 or so). > > So, can someone explain in basic terms what's happening when I use Auto > mode on the KAT3 and see favorable SWR on the KAT3 (via K3 display) but do > not see favorable SWR on the MFJ tuner? > > This is not a round-about way of expressing a problem with the K3. On the > contrary - I couldn't be more pleased with the KAT3 performance and so > forth. > > I'm asking this question as a data-point before I decide to build the KAT2 > for my finished K2. > > Thanks in advance, > > -jeff > > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
