Product Details:
Low Frequency Variometer. A unique design of an old standby, a motorized variometer. This unit allows variable coupling between 2 series inductors to achieve a limited inductance change in an antenna matching or tuning circuit.

The input to the unit is via an "N" female connector mounted on the bottom of the enclosure. A short length of coax connects to the circuit. The circuit consists of an input transformer with 11 taps. This connects to the 2 series coils in the unit and on the output there is a power sensor. On the top of the cabinet there is a giant 6" in diameter 4" high glass bowl feedthru insulator with a 4" corona disc. Connection is to a 3/8" threaded stud. There is a spark gap.

The inductors are #13 or #14 served Litz wire wound on a giant 6-1/4" form. The smaller 220 µH inductor consists of 44 turns tapped every 4 turns allowing switch selection of 11 different inductances in 10 µH steps. The large inductor is 150 turns of the same wire on the same form with taps at 5 turns, 5 turns, 10 turns then each 15 turns for remainder of the coil. This coil is 2200µH and the taps allow selection in approximately 220 µH steps. These taps are brought out to threaded studs on a fiberglass panel which allow the output lead to bypass turns on the top of the coil. Although both coils are in series they are separated by 1-1/8" on the form.

Inside the form there is an aluminum cylinder 5" in diameter, 1/4" thick and 1" long. This cylinder is mounted on a 1/4" shaft which is coupled to the knob on the internal panel and a 12 vdc motor. There is no control circuit for the motor; it runs whenever power is supplied at 5-1/2 rpm. Rotation of this cylinder changes the coupling between to 2 coils. The position of the cylinder may be manually adjusted by the knob on the internal panel.

On the fiberglass panel there are also ten 30k ohm, 10 watt wirewound resistors connected in series. These are apparently provided a swamping resistors to reduce the Q of the circuit. A combination of these resistors may be selected by interconnecting the desired number of them across the large coil via jumpering to threaded studs.

The external control connector on the bottom of the enclosure provides motor power, output power signal and external input of forward and reflected power supplied to banana jacks on the internal panel. The motor switch on the internal panel switches off external power to the motor. There is also an interlock switch activated by the hinged lid.

The unit is contained in a 20" x 24" x 13-1/2" aluminum weatherproof enclosure with a hinged lid. The lid may be secured by a padlock in addition to the 7 stainless steel clips.