Tuner


This project was to build  T type matching device out of 
junk box supplies.   The criteria are as follows:

1)  Match unbalanced loads such as 50 ohm coax/transmitter to a vertical antenna (at antenna) or reduce reflections from coax fed antennas to the radio (in the shack).

2)  Make it suitable for outside or shack use

3)  Handle 1500 watts
of RF

4)  Use antenna analyzer for adjusting

5)  Concerned with 80, 40 and 30  meters

The box is homebrew using 1 /8" and 3/16" aluminum sheet and 3/4" x 1/8" aluminum angle stock.  Aluminum can be cut very nicely cut with most carbide tipped rotary saw blades in a table or miter saw.  Use eye protection as small aluminum fragments are dangerous.  I clamped the angle pieces to the sheet metal pieces and drilled with a bit suitable for a 6x32 tap.  Then I drilled the the sheet metal holes out to 9/64" and tapped the angle pieces.   This method keeps the holes perfectly aligned.  At the final assembly I put on a thin coat of RTV at the joining areas to eliminate hair line entrance areas for moisture.

When connected to the vertical,  I needed an easy way to disconnect the feedline from the house and to connect my analyzer to readjust for frequency changes.  I added an SO-239 connector to the front panel and disconnected the rear
panel connector.  If the unit is used in the shack, it is a simple matter to reconnect the rear jack.  The feed through insulator is quite large with a 3/4" porcelain through section and a large outer apron.  Using a step drill I drilled the hole to 5/8", marked and drilled mounting holes for a SO-239 and using the step drill enlarged the hole to 3/4".  When the feed through insulator is used, its large skirt covers the SO-239 holes.  If the unit is used to feed a coax, it's a simple matter to remove the insulator and put in a SO-239.

No need to discuss wiring.  I used a 500pf input capacitor, 20mH roller inductor and a dual section (1000pF?)  output capacitor in a T configuration.  Actually, it can easily be rewired in any configuration.  I also used reduction verniers to make tuning a bit easier.

The  last piece of the puzzle was how to protect the front panel when in outdoor use.  In my case the front panel is 19" rack mount stock and over 3/4" extends on the sides and 3/8" on the top.  I built a 3 sided frame with a slot all around to slide over the panel out of cedar and put a piece of weather resistant plywood used for soffets in it for the front.  The bottom is open to allow the coax entrance.  So far it is working well.


This unit is obviously homebrew.  The capacitor verniers and knobs don't match and the old can of black crinkle paint I used on the panel didn't crinkle.  But regardless, I have a quality unit that works and all from accumulated "stuff".