Tuner

A simple and inexpensive antenna tuner for AM and SW bands

YYYYY
   YYY
    Y
    |            L1             L2
    |
    +------((((((((((((((((((+-ccccccccc-+-----+----> Ant
    |       | | | | | | | | | i          |     |
    |           ^------------------------|     |
C1 =/=                                        =/= C2
    |                                          |
    |           i = open switch setting        +----> Gnd
    |               to shunt entire coil       |
-----             assembly into circuit    -----
   ---                                        ---
    -                                          -

L1 is 36 turns of wire on a toilet paper roll, tapped every 4 turns.
L2 is a ferrite loopstick or can be made from 90 turns of light hook-up wire wound on a 6-9 inch ferrite rod from an old table radio.
C1 and C2 are both 365 pf variable capacitors.

This type of tuner is called a Pi -section coupler and works particularly well with short verticals and a good ground especially on the tropical band, but also does well with longer antennas at other frequencies. The circuit above appeared sometime back in the 1960s in Popular Electronics when I built it for use with my Heath-Kit AR-3 Receiver and QF-1 Q Multiplier. I lived on a city lot which didn't have room for me to stretch much wire. I simply attached a vertical piece of wire on the outside walls of the house to about 15 feet. The signal went from antenna to tuner through a short piece of coax which was well grounded both at the antenna and tuner ends, to the cold water system of the older house.

If you can't find the 365 pf capcitors, a couple of old tube radio BCB capacitors wired in parallel work well too. See also the S-A-T Clone article and links to Mouser and Dan's on this page. The ferrite rod antenna from the same BCB radios can also be used in place of the loopstick. You can read more about this and other kinds of ATUs in the ARRL Handbook the ARRL Antenna Handbook, and also in Joe Carr's Receiving Antenna Handbook.