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ADDING 160 METER COVERAGE TO HF AMPLIFIERS

  ADDING 160 METER COVERAGE TO HF AMPLIFIERS   (updated original manuscript, article published in January 1989 *QST*) by Richard L. Measures, AG6K, April 1988 WHY? If you have ever tried to use the 80 meter phone band for local communications on winter evenings, you probably experienced situations where under 200Km propagation was almost nonexistent. The group of friends that I talk with on 80 meters was plagued by these "winter doldrum" conditions so a few of us put up 160 meter antennas to see if the situation could be improved. We discovered that, when the 80 meter band was essentially useless for short-haul propagation, the 160 meter band provided good communication. There were tradeoffs to using the 160 meter band: Most of us had to put up compromise antennas that would fit on a city lot -- like the end-fed Marconi . These antennas were not as efficient as full-size dipoles. The only practical way to compensate for the lack of efficiency was to increase power. Another pr...
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A Balanced Balanced Antenna Tuner

  A Balanced Balanced Antenna Tuner By Richard L. Measures, AG6K   The published version of this article appeared in the February 1990 issue of QST Magazine. This is the pre copy-edited version, updated in May, 2003. ........................ JPG of a remote controlled, balanced L-network tuner built by Mike, WA1SEO. Antenna tuners are like shovels. It takes more than one kind of shovel to be able to efficiently perform a variety of jobs. For example, a snow shovel isn't suitable for digging holes in hard ground. A tiling spade could be used to shovel snow, but it wouldn't be very efficient. Similarly, no single antenna tuner circuit can do everything extremely well. A balanced load tuner should be designed, from the ground up, for the job that it is intended to perform. This article describes a circuit that does a good job of feeding an open-wire transmission line [ladderline]. It is not intended to be used for unbalanced loads such as a coaxial transmission line or for end...
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AG6K SB-220 Amplifier Circuit Improvement

  Updated 29 August, 2001   The Heathkit SB-220, two 3-500Z, amplifier made a notable impact in the world of amateur radio. It was the first, reasonably priced, intelligently designed, SSB-CW, HF-amplifier that was sold to the amateur radio community. Unfortunately, this amplifier kit is no longer being manufactured. The SB-220 has some excellent design features and a few design weaknesses that are easily corrected. In this article, I will discuss both topics and the cures for its weaknesses. HV Power Supply Before the arrival of the SB-220, there was a popular notion that a legal-limit SSB amplifier needed a heavy-duty power-supply that required two grown men to move it about. Heath engineers knew that this idea was based more on amateur radio folklore than on sound electrical engineering principles. They also knew that the average duty-cycle of a human voice was only about 15% when no carrier was present, as is the case for SSB operation. So, why build a 100% duty-cycle, AM,...
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