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A Versatile Tuner for SOTA Activations by KX0R



because I’m going to build the above KX0R-tuner, I bought different poly-varicons (in Germany) and measured quality factor. The results were as follows. Q is Q of the resonant circuit build with a coil, not only the capacitor-Q. Measured for full and half capacitance (of the high capacitance part).

ebay.de, oppermannelectronic: “Folien Drehkondensator mit 4mm Messingachse 21mm Kondensator CAPACITOR”
Text says: “2 x Ce= 360 pF, Ca= 15pF und 2 x Ce 30 pF, Ca 9 pF”
Measured: 5…350 pF resp. 4…24 pF, with all trimmer capacitors set to minimum.
Labeled: “ELS”, “Made in GDR” [GDR = German Democratic Republic = DDR], “07 89”
Q = approx. 430

ebay.de: m-o-s_2010: “Drehkondensator 60 pF + 140 pF”
Labeled: “TT”, "TTWM"ä
Q = approx. 200

ebay.de: m-o-s_2010: “4-fach Drehkondensator 22 pF + 22 pF + 90 pF + 150 pF”
Labeled: “NCE”
Q = approx. 330

www.ak-modul-bus.de: VCAP4 Drehkondensator AM/FM (2 x 265 pF + 2 * 20 pF)
Labeled: “WP”.
Q = approx. 150
BTW: They sell very nice extension spindles (“Verlängerungsachse für VCAP4…”), see my last image!

Measurement method:
VNWA, measuring s21, poly-varicon + coil connected between coax inner conductor and ground in series configuration.
Measurement of resonant frequency and 3-db bandwidth, no correction for the 2x 50-Ohms-source-resistances.

Resonant frequency: 3…14 MHz, depending on capacitance and number of coil windings.
Coil: 1.0 mm enamaled wire wound on 38 mm diameter, self supporting, spacing of winding very approximate 2 mm but varies largly because of self support.

BTW, reichelt.de has water proof toogle switches, for example: RND 210-00450.

Hope it helps,
vy 73 Axel DF1ET

Edit: Added labeling of ak-modul-bus varicon.


A drop of sewing machine oil (or WD40 perhaps) applied with a needle to the rotator where it meets the housing will make it turn a lot more easily.
73 de OE6FEG