- The KC5LDO SPC Tuner - * Practical Wire Antennas by John D. Heys G3BDQ; * The ARRL Handbook 1995; * QST (The Rollerless Ultimate) November 1973.
Built properly, it will match a very wide range of impedances. It also maintains
good harmonic attenuation.
The best part of this project was that it could be built at home with very basic
tools. All of my components, with the exception of the SO239 connectors and
four rubber feet, came from the junk box. The .040 inch plate spacing on my
capacitors are more than enough for the 125 watts I intend to use. For higher
wattage output use capacitors with wider spacing. Surplus parts are always
welcome when home brewing.
The cabinet caused some trouble because everything I found was never quite
right. While talking to a co-worker one day, I mentioned this dilemma and he
nonchalantly said he would make what ever I needed. Having past experience
at a sheet metal shop and still having access to this shop, it was no problem for
him. The housing is .074 inch thick aluminum.
Amazing how easily some problems can get solved!
Due to RF floating around inside the cabinet, it has to be rather large. My
components led me to the conclusion that the smallest cabinet I could use would
be 14 inches wide, 17 inches deep and 7 1/4 inches tall. There should be ample
spacing around all of the coils and capacitors. Being mounted too close to the
cabinet will affect their performance. My tuner works exactly the same whether the
top cover is on or off.
I assume this means I allowed for ample room.
|
|
 |
Use the formula to figure out the number of turns required if doing so.
|
|
 |
|
|
 |
|
|
 |
|
|
 |
|
|
 |
C2 - dual gang air variable capacitor with approximately 200pf. per section.
Mine has 12 plates per section, also with .040 inch spacing.
SO239 - two needed, my preference is silver plated with Teflon insulators.
Don’t be cheap here.
L1 - Coil should have an inductance of between 25uh. and 28uh. for 10 - 160
meter use.
I made my own air wound coil. I used 14 gauge enamel covered
copper wire bought from a shop that rebuilds electric motors. The coil is 30 turns,
2-1/2 inches in diameter and 3-1/2 inches long. Tap the coil every 2 turns.
L2 - This coil is used for the high bands. It will affect 10 and 12 meters the most. Due to parts layout and stray capacitance from wiring, it is hard to say that one size coil here will work for everyone. After making four coils, the one that worked for me is made from 12 gauge tinned copper wire 5/8 inch diameter, two turns spaced to 1-1/2 inch long. You may have to add a turn or increase the inner diameter. Do this if the SWR will not come down low enough on 10, 12 or 15 meters.
J1 - a ceramic feed through bushing for single wire use.
2- insulated ceramic shaft couplings
1 - ceramic rotary switch, preferably with silver contacts.
I needed 15 contacts for my tuner.
Misc.- 1/4 inch shaft and coupler for rotary switch, knobs, a cabinet with four rubber feet and necessary screws, washers and nuts.
|
| |||
SPC Tuner |
Power Generator |
Receiver |
Portable Vertical Antenna |
View Guestbook