Hi! In my experience, the counterpoise can be a tricky thing. Keep in mind that minor changes in ground current can lead to substantial swings in antenna impedance. That translates directly into changes in SWR. For instance, I use an MFJ Artificial ground to tune a counterpoise for my 85' EFW. There are some bands that I simply cannot match with a low SWR if I do not have my counterpoise adjusted to see maximum current. On other bands the peak is rather broad and it isn't as important. Using end fed wire radiators can be VERY effective, but they tend to take more effort for multi-band operation if you care about keeping the ground current optimal for maximum efficiency.
It is not necessary to use an AG for series capacitance and inductance if you are willing to either use a separate wire per band or adjust the length of your counterpoise by either trimming it or folding it back onto itself. The AG is, of course, more convenient and allows one to use the same 'poise for more than one band- within reason (I use a separate 'poise for top band and 80 meter ops). To get the length right (the point at which the 'poise sees maximum current) you will need some method of monitoring the current. My MFJ AG has a built-in meter for this. You can also use a small light bulb at the rig as an indicator and tune for max brightness. Of course, what you are theoretically going for is a counterpoise of 1/4 wl, but it is not as exact as this and some form of adjustment is helpful. QSYing within a band can sometimes require a slight adjustment in ground current as well if the antenna exhibits a high "Q". For antics of the pedestrian mobile sort, I would probably use the cut-and-try method to get the right counterpoise length per band if the SWR was giving me trouble. One other thing worth noting is that I have found with my KAT2 and KAT100 auto-tuners that small amounts of either capacitance or inductance added in series between rig and antenna can work wonders in helping the tuner find the right L/C combination on problematic bands. I have a 335 pF air variable with banana jacks soldered onto frame and stator that I use for this, as well as a goofy looking toroid wound on a T94-2 core that is tapped at regular intervals with more banana jacks. 73, Mychael AA3WF K2 #1025 _______________________________________________ Elecraft mailing list Post to: [email protected] 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
