KARC Tuner Project (update 2012)

With 2012 Field Day coming up, a number of KARC decided to build antenna tuners for themselves, Based on the 2010 BOM a new build project was formed five interested members. Kimo, KH7U, agreed to handled procurement for the group. In the two intervening years costs had increased and alternative vendors identified. Kimo did a good job of reducing the number of vendors and simplified shipping. The KARC FD Tuner project continues and now a total of 10 have now been built by club members.

Martin's (KH6MB) tuner design, with carbon fiber poles and fine cooper clad wire for antennas simplifies station setup and produces excellent results from beach front sites. Much better results with much less effort! (To display a section of interest, click on the + sign to display the information.)

    Circuit Diagram

    Assembly Photo

The rotor shaft of the capacitor should attach to the 50 Ohm side. This keeps the high voltage away from your hand while tuning. Keep about 2 inches spacing between the inductor and the capacitor. The red wire and the brown wire from the inductor to the ground connection on the coax connector are #12 or #10 gage wire. This is where all the current is. The blue wire is #16 gaga. One goes to the antenna the other to the ground mat. These are low current lines. Note the orientation of the inductor; wider spacing wire turns towards back of unit.

    Bill Of Materials

P/NDescriptionQtyCost per KitVendorContactManufacturerNotes
NBA-10142Box, Enclosure1$52.71$16.00Mouser Electronics1-800-346-6873Bud IndustriesCost for Qty 5
Ship UPS 2 day
NBA-10980-PLPanel, Enclosure 10.5" x 6.74" Plastic1$7.26included
523-83-1R83-1R SO-239 UHF Fem Conn.1$3.28AmphenolCost for qty 1
RI-20Inductor 0.1 - 20.0 µH 4500Vpk1$90.00$24.00Palstar, Inceva@palstar.com
PalstarShip UPS
CustomCapacitor 5.5 - 83 pF 4500Vpk1$65.00included
Custom¼" shaft coupler for one each for
capacitor & inductor
450-1722-NDKnob, Switch ¼″ shaft1$3.60$1.50Digi-key1-800-344-4539TE ConnectivityShip by
 US Mail
450-1750-NDKnob, Switch, skirt & no. 1-10, ¼″ shaft1$7.68included
H782-NDPan head Screws 4-40 × 3/8″4$0.28B&F Fastener Supply
H724-NDNuts 4-404$0.20
H713-NDPan head Screws 6-32 × 3/4″10$1.00
H730-NDSplit Lock Washers 6-3210$0.20
H735-NDSplit Lock Washers 6-324$0.16
H725-HDNuts 6-326$0.48
Rod ¼″ diameter × 1-2″2$2.00 Hardware Hawaii   
Wing Nut 6-322$1.26 Local Hardware
Solder Spade Lugs 6$1.00  
Hook up WireAR$1.00  
Total Costs >> $237.11$41.50 Total is $278.61 vs. estimate of $262.00 ea.

Note: The knob for the inductor should be the larger one for easier gripping. (the inductor is harder to turn). The knob for the capacitor should be numbered to aid in dialing in predetermined amounts of capacitance (based on your know antenna requirements). Nicer knobs are available but they can be very expensive.

Some of the miscellaneous hardware can be purchased locally in small quantities but we had to order knobs and ended up buying the hardware in packages of 100 from the same vendor (Digi-key) and had it shipped with the knobs.