Jeremy, N1JER, hasn’t been a ham long, but he’s really gotten into it in a big way, building kits and homebrewing QRP stuff. His latest creation he calls the “Toilet Paper L-Network Tuner.” The name comes from the material he used for the coil form.
Here’s what he posted to the qrp-l.org mailing list:
- Uses the standard L-Network out of the 2008 ARRL handbook, pp. 19.44 and 19.45.
- Borrows the switched inductance coil idea from KD1JV’s ALT, and KI6DS’s SLT.
- Uses an air coil formed around a Toilet Paper roll with multiple tap points.
- Uses a varicap out of a junk AM/FM radio I found on the street.
- Uses 1 insulated binding post, and 1 binding post that connects to the chassis for ground.
- Uses an array of inexpensive switches that are soldered together.
- I used a formula to have each switch control a coil that is
progressively smaller. In order from left to right ~7uh, ~4uh, 2uh,
1uh, and 0.5uh. I didn’t measure the actual values, but did pay strict
attention to how the coils went on the TP. Each coil can be turned on
independently so I can have 2+1+0.5 = 3.5uh.
- Total cost was about $11 USD. (including value of junkbox parts).
- Using a 51ft wire with a peak at about 30ft and a 33 ft ground wire.
- I get a solid dip at 40m. (Tested using KD1JV ‘Tenna Dipper the LED gets very dim, but I don’t know the actual SWR).
- Using same setup 30m on 20m the LED can go completely out.
- On 80m there is a very slight dip, but I wouldn’t think good enough to operate.
- I made one contact with this using my 40m 3w Wilderness SST, ~750 miles.
Have a great day everyone,
Jeremy Chase, N1JER