HF/VHF Portable Mini Tuner

By Guy, de ON6MU

Schematic fig1

Parts list

• alu box of 70mm X 40mm X 33mm

• 2 female PL 259 chassis

• C1 = variable capacitor of at least 300pF or better 500 pF

• S1 = 10 or more position rotary switch

• L1 = 0,7mm insulated copper wire, 6 turns par connection closely together, 9mm outside diameter (8mm inside)
  taps every 6 turns and the last two sections (L1' and L1'') 4 turns spaced at 1mm and 3turns spaced by 2 mm.
  The first two sections has a ferrite core inside.
  Could be that lower frequencies needs higher inductance, experiment with by adding a core in the last few sections (see fig2)

• I added two bolts on the alu-box chassis to - if needed - connect the tuner to ground or for using a counterpoise.

• R1: 1.5k carbon 1/4w; optional to allow drain of possible static build-up on the antenna (or use a 10mH inductor)

• R2: 2 x 470 carbon 1/2w parallel; optional to have some little protection during switching when using a carier, as the switch could open the the connection for a fraction of a second during switching.
  

The coil

• Wind 6 turns x - 2 connections on your switch (in this project a 10-position rotary switch is used, being 8 times 6 = 48 + 4 + 3 = 55 turns) over a 7mm screwdriver (or simular obkject hi) and make a tap every connection. Solder each tap.

• Solder each tap to each connection of your switch and stretch L1' (being 4 turns) at 1mm spacing and L1''(being only 3 turns) at 2 mm spacing. You can replace L1'' by 3 turns of silver wire to allow better Q on higher frequencies (VHF).

• Minituner insides...

Fig.2

• Alex VE7DXW changed 5 of the lower 6 wdg air coils with 1 wdg, 2wdg, 4wdg, 4wdg, 6wdg ferrite core coils, which gives higher L values
  Thanks Alex!

Specifications

• manual operation

• frequency range (depending on the coil min & max inductance):
  160m...6m
  (Up to 150Mc if: L1'' is silver(plated) wire, High Q switch, minimum capacitance of C is small enough and close connections are used in respect to 50 Ohms impedance)

• 10 Watt +-

• direct feed through

• small and compact design ideal for low power QRP transceivers, like the Yaesu FT-817, or of course for receivers...

• connection for counterpoise/ground

Notes:
If you elect to use an antenna tuner, it is extremely important that you understand exactly how to use tuners and what they can and cannot do. A few watts of RF can easily become lost in an incorrectly adjusted antenna matching device. The whole idea of a QRP station is to keep things simple and economical, so I cannot overemphasize the priority of a clean, efficient connection of the amplifier output to a resonant antenna.

Homemade aluminum box

Don't forget to check these out:
.ON6MU Homebrew projects
.Radioamateur related projects

.ON6MU Ham mods
.Modifications of transceivers


73"

Home