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Two new projects from the workbench of Jake, N0LX. July 2, 2005
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project #1 33-foot, Shortened 1/2-wave vertical for 40-30-20 meters
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project #2
Matching unit for 40-20 meters
See more photos and details at bottom of page.
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ANTENNA:
* 33-foot tall vertical
* Electrical halfwave for 40-30-20 by using taps on coils.
* Held aloft by an MFJ 33-foot fiberglass pole.
* Wire is 20-gauge stranded (insulated) in three sections: Center section is 20 feet in length, the two end wires are 6.25 feet long.
COILS:
* Coils were made using #18-gauge stranded (insulated) wire.
* Wire is wound around 1-1/4" PVC tubing.
* Covered with black electrical tape
* An alligator clip allows for shorting the coil to change bands:
20-meters: Antenna is full size, so there is a tap at the bottom to bypass coil.
30-meters: 11 turns up from bottom with a tap. See note*
40-meters: 23 turns for full coil. Clip is fastened back on itself, unused. See note*
* Note: Based on tests I conducted, if I were to make another antenna I would add an additional turn for both the 30- and 40-meter coils. So 12 turns for 30m, and 24 turns for the total on 40m.
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QRP MATCHING UNIT FOR 40-30-20-17 METERS
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The photo on the left, below, shows the inside of the tuner. It consists of an AM radio tuning capacitor and a toroid coil with five secondary windings to match 50 ohms input. A rotary-dial switch, seen in the photo below, right, selects the secondary taps. The antenna plugs into the red banana jack on top, while the black banana jack on the side is for later counterpoise/ground experiments. For now, I use no counterpoise, and it seems to work fine.
Note for my own reference, #0 on the switch connects 1 winding of the secondary coil, #1 gives two turns, #2 gives three, etc. up to #4. That is five turns of the secondary. #4 through #9 are shorted together.
I found a 1.0:1 match with the following settings:
40-meters = #1 switch setting selected
30-meters = #2 " " "
20-meters = #3 " " "
The toroid is a T68-2 from Amidon. There are 34 turns in the primary, with an inductance value of 6.5uH, and 5 tapped turns in the secondary.
The capacitor had a measured capacitance of ~ 6-135 pF.
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This whole project came about because I have placed an order for my first ever CW-only rig, the 40-meter ROCK-MITE from Small Wonders Labs. I wanted an efficient but compact antenna for 40 meters so I came back to my favorite vertical design, the shortened, endfed halfwave.
How well does it work? I tested it two evenings ago on 40 SSB. With 5 watts from an FT-817 and the antenna set up in my very small front yard between the house and two trees, I was heard in Oregon and Indiana from here in Golden, Colorado. The funny part: the OR station, running 800 watts, had just commented to his friend on how, "it would take some real power to make it through my noise level tonight." That's when I broke in and worked him.
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UPDATE: After posting this page, I again set up the new antenna and tuner in the front yard, but this time on 20 meters. Same 5 watts, sideband. My first contact was Jack, XE1/W5FG in Mexico, then Pat, XQ1VLY 5,500 miles away in Chile!
A final confirmation that it all works.
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