K4HB Homebrew Projects

Low Band Antenna System
(Constructed Jan 2011)

This antenna system uses common radials for two inverted Ls. One is for 160 meters, which is 70 feet vertical and 60+ feet horizontal. The other is a 40M/80M dual bander, which is 3/4 wavelength 40M and 3/8 wavelength 80M. The vertical length is 60 feet and the horizontal is 30+ feet. There's 32 radials which are 108 feet. The dual bander 40/80 is the AE6C design, which was featured in July 1991 QST. Switching the inverted Ls is done with vacuum relays and controlled remotely. When I first tested the common radial system for both inverted Ls, the UNUNs caused the antenna not in use to be at ground potential. This interfered with the antenna in use. Had to add more relays to take the UNUN not in use completely out of the circuit. The antenna switching relays are in the enclosure with the UNUNs.

The feed point tuner, which is controlled remotely, uses a Jennings motorized vacuum capacitor and a motorized inductor built by Collins in 1957. The inductor was part of the Collins 180L-2 automatic tuner, which was used in aircraft. Vacuum relays are used for Bypass/Tuner, Hi-Low Z, and an extra 1K pf fixed capacitor. Forward and reverse voltage to the motorized components and voltage to the vacuum relays is supplied from a local power supply with the use of a relay network. The tuner, which can be bypassed remotely, is not necessary for some frequencies in the CW portions of 40M, 80M, & 160M.

The parts came from several sources. The motorized inductor, motorized vacuum variable capacitor, and vacuum relays are from Max-Gain Systems. The UNUNs were built by Balun Designs. Transformers, common relays, diodes, etc, are from Mouser. Hit a snag when looking for an enclosure for the controller. I needed one just the right size to hold all components and also fit in the space available. So I looked through my old junk and found an old TV test tuner that I built when TVs had mechanical tuners. It was sold by Radio Shack but was no longer available. And it was a perfect fit. So I cut the face off and replaced it with plexiglass that I painted black. You can see in the controller pics that the face is thicker than the rest of the enclosure. Had to do some packing, but all components were mounted OK. Sometimes, you gotta do what you gotta do.

The controller controls all functions in the housing, which is mounted on a tree 100 feet from the shack. It also controls the remote antenna switch, (Pictured) which consists of vacuum relays and is mounted outside the shack. The remote antenna switch selects from 3 dipoles, 2 inverted Ls, and a dummy load.

A camera is mounted inside the housing so the tuner is observed from the shack. I captured a video of the tuner in operation, as viewed on the monitor inside the shack. The clip is at the bottom of this page.

Dual Inverted L