N1JER Does it Again!

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:

I shot a video documenting this project, and have posted some photos.

Overview:

• 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.

Details:

• 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).

In use:

• 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
http://jeremychase.net