HF/VHF Portable Mini Tuner
By Guy, de ON6MU
RE-AT2HF6/P 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' = 4 turns spaced at 1mm, and L1'' = 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 (non-inductive resistor, metal film); 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 (non-inductive resistor); 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. Recommended NOT to
switch when transmitting. Tune on receive to the biggest
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 object 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). Place a ferrite core inside the low end of the coil (defines the lowest usable frequency).
changed 5 of the lower 6 turns air coils with 1 wdg,
2wdg, 4wdg, 4wdg, 6wdg ferrite core coils, which gives
higher L values
(depending on the coil min & max inductance):
(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, and of course receivers...
connection for counterpoise/ground
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 TRX output to a resonant antenna.
forget to check these out:
.ON6MU Homebrew projects
.Radioamateur related projects
.ON6MU Ham mods
.Modifications of transceivers
Homemade aluminum box