Tuner
Although the ICOM AH705 tuner handles all the matching now, I'll describe the tuner I needed to use with my previous rigs in case anyone is still interested in a homebrew external tuner.
It's a C-L-C type setup with a series connected capacitor, a parallel coil, and another series connected capacitor. The switch and the tuner are mounted as one unit as shown in the five pictures that include a simple schematic diagram. All the parts are very very non-critical, including the switch which is just a cheap rotary switch salvaged from the junk box. One rule of thumb is that as you go lower in frequency, the caps and coil will need to be larger, so if you plan to use it down to 1.8 MHz you'll need something similar to the values shown in the picture. But if you only plan to use it for the higher bands, you can get away with using smaller values. Once you initially find the correct settings for the coil and caps on each band, you can quickly return to those settings. Initially to find the correct settings, I start with the caps at mid range and change the taps on the coil for the lowest SWR. This may get you anywhere from 1:1 up to 5:1 or so. Then, if you're not already there, change the tuning of the caps to get down to 1:1. Mark those settings, and you're all ready for some quick band changes in the next contest, especially if you use a multi-pole switch to change the coil taps as I do. Remember these tune-ups must be done on the air, so take every precaution not to interfere with someone. NOTE: The schematic pictured is of an older tuner and indicates a different coil, but the general idea is the same.
