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From: Mike Coslo on Sun 4 Mar 2007 22:56
" wrote: Besides old ARRL Handbooks prior to the 1970s, I'd suggest finding the site that has digitized copies of GE Ham News. Those were (bi-monthly?) hand-outs by GE to push their tubes (naturally) but they contained lots of different ham projects (using tubes, of course). Got it! Thanks a lot Len - I googled them up, and have enough reading material to keep me busy for a while. the site is: http://bama.sbc.edu/ge_ham_news.htm Thanks for the reminder on BAMA contents. BAMA has more than just old tube equipment manuals. :-) Good site! On the general subject of tube PA matching to load, some remarks: The automatic antenna tuner might have its beginning at Collins Radio of the 1950s decade. Reference is the T-195 transmitter, part of a set that used the special version of the R-390 series called the R-392, designed and built for the USMC, first fielded in 1955, intended to be Jeep mounted. The basic whip antenna matching was a servoed single variable L and a single variable C to a conventional PA output tank...so-called Ell-network, switchable to the four possible L-C connection possibilities. On an Army demo in late 1955, I was most impressed when the demonstrating officer simply removed half of a whip section (!), hit the tune function, and the servo system re-tuned to this new antenna impedance in seconds. :-) Warren Bruene must have had a hand in that Autotune labeled antenna matcher because it has the first instance I've seen for the "Bruene detector" in the transmission line to get both amplitude and phase of the RF. Slight variations of that exist today, generally with a toroid for current output and a small capacitor for voltage output, both combined into dual diode detectors. Today's antenna auto-tuning subsystems use binary-progression switched single inductors and single capacitors with the servo system basically a microcontroller plus small frequency counter (sometimes) that can determine which L or C to switch and remember the frequency and setting. SGC (Stoner Goral Company) in the Puget Sound area of Washington state has at least three models for both maritime and amateur radio HF use. The Big3 (Icom, Yaesu, Kenwood) have them, either built-in or as out- board boxes. Several independent USA companies have them. ALL (no exceptions) antenna tuners have limits on their impedance matching capabilities, whether "Pi-L" output tanks or big boatanchor style structures that look very impressive. There are few overall advantages in any configuration with the possible exception of Simplicity of the single L, single C variety now common to today's autotuning matchers. ALL, even the popular Pi-network, have limits that can be proven mathematically; if the math doesn't fit, no amount of publicity or historical references will make it fit better. If you or anyone else would like an algebraic-only math explanation of the four combinations of single L and C matching combinations...with their limits of load impedance variation, I'll be happy to forward them by e-mail attachments. No binary files here and the equations, figures are better shown in the PDF format. 73, |
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