L – Network Tuner
This page consist of two versions of the L – Network Tuner. The very first design being that of a higher wattage one, then as you look further down this page you will find a much lower wattage version.
In the past all my inexperienced radio stations operated with a maximum power of 100 watts, This all switched this past Father’s Day when I was introduced with an Ameritron AL-811H amplifier.
Since all my antenna tuners were built to treat 100 watts it was time to buy a tuner that could treat the 800 watts or build one. The evident choice was to construct a fresh tuner.
My antenna system covers 80 through Ten meters with a SWR of Two.Two to 1 or lower. It was plain to see a elementary tuner could lightly bring the SWR down to acceptable levels. I also wished to construct a tuner that was smaller than most commercial made kilowatt tuners.
The L-Network tuner is a ordinary impedance matching network that consists of one variable inductor and one variable capacitor. The L-Network tuner has often been described as a one band tuner made to work with random wire or vertical antennas. With decent components it will match a broad range of impedance. The L- tuner can match high to low or low to high impedance simply by reversing the coax cable connections. Since I was only worried with a match on the 80 and 40 meter bands, the L-tuner seemed the prefect choice.
My tuner is built in an old Heathkit audio generator cabinet with measurements of 13 in X 7 1/Four in X 7 1/Four in. The front panel is made from aluminum stock. The Hammarland capacitor measures 500 pf. with both sections tied together. Plate spacing is .100 of an inch. The coil form is Trio inches in diameter and wound at 8 turns per inch with 12 ga. wire. Total coil is 26 turns. .
I made my coil taps at 1 turn embarking at the end closest to the antenna connector. I did this for 6 turns and then made taps every Two turns. This was done purely on guesswork. You could use an alligator clip and low power to find that ideal spot for your antenna system and then make your tap with a switch. I was fortunate and only had to switch one tap. My vertical antenna is lightly tuned for all bands in the 80 to Ten meter range. The band switch is a 17 position Centralab and utilizes silver contacts. Silver braid measuring Trio/16 inch broad was used for tap switch connections. All other wiring was done with 12 ga. nude wire.
The L-Network tuner was flawless for my situation. It treats the amplifier’s 800 watts using very little inductance and capacitance. I am not sure of the tuners limitations, but it seems to work well when SWR is within a reasonable range. Elementary in design, low on parts count and with the ease of operation makes this tuner a real winner.
A Homebrew Coax Switch
After building the L – Network tuner I determined it would be best that I had a coax switch box that could be securely used with the 800 watt amplifier. Time to dig into my junk box once again.
This is what I came up with and if you have any questions about it’s construction, drop me an E-Mail and I will gladly provide you with more details.
The Transmatch or Tuner Revisited
Transmatch is actually the decent name. It’s an L version built just like the one above
on this webpage. The only difference is that this one is made for 200 watts maximum.
So if QRO is not your method of operating, then this little brother to the big one shown above just might be the one that will meet your needs.
Here are the specs:
Chassis size: Ten” X 7.Five” X Trio”
Variable capacitor: 500 pf. with .020 of inch plate spacing.
Coil information: Two inch diameter, 42 turns of #16ga. silver tinned wire tapped at Three,8,16,Nineteen,23,27,30,33,35 turns.
The finished project.
So, no matter if your pleasure is QRO or QRP, if you need a real good L Transmatch, then either one of these projects should meet your needs.
Foremost is to love the building of projects and I hope we meet on the air.
73, James – KC5LDO
Articles written by James Tobola – KC5LDO
and reproduction, publication, or duplication of this article, or any part thereof,
in any manner is prohibited without the express written permission of the author. ©,2013