TIGHAR
Amelia Earhart Search Forum => Radio Reflections => Topic started by: h.a.c. van asten on May 11, 2011, 06:22:48 AM
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ChVar. The 13C PA band coil sets were delivered with a condenser , p.e. "4000 mmF . The available schematic does not show this capacity. 1. Was the condenser connected parallel ovver the coil poles, parallel to a part of the coil , or how ? 2. Was the condenser a single double pole , or 3 pole design with the central pole earthed ?. I do btw not think that a 100-50 W PA dissipation played a major role for range. illustration : during the Battle of Britain , Aug- Sep 1940 , the entire communications circuit over southern England was handled by TR9-D HF transceivers installed in all fighter airplanes (Spitfire , Hurricane) and all interceptors (Beaufort etc.) . TR9-D RF output was 0.5 Watts (PA anode current 25 mA) from dry battery powered valves (Xosc-PA mode , AM) and the system worked flawless day and night. Aerials were long single wire , frequencies 4.3 - 6.9 mc/s . The receiver was of Det- 2 x AF fashion. The HF system became obsolete , only after the introduction of TR 1143 VHF radios (USA SCR 522) later in the war. The WE radio o/b NR 16020 was comparable to the BC 375-191 (MO-PA) in powerful installations of WW II USA B-17´s etc. Probably the laesio enormis of the Earhart crew was to rank DR-Celestial in the primary , and RDF in the secondary row of importance from the beginning , not against the end of the flight.
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ChVar. The 13C PA band coil sets were delivered with a condenser , p.e. "4000 mmF . The available schematic does not show this capacity. 1. Was the condenser connected parallel ovver the coil poles, parallel to a part of the coil , or how ? 2. Was the condenser a single double pole , or 3 pole design with the central pole earthed ?
h.a.c. van asten ,
I have to assume that you're asking about the capacitor labeled "C (C10, C11 or C12)" in this diagram (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/ElectraRadios/FigureB.html). The value of this capacitor was 4000 pF when used with the 7B coil for 3000-4000 kHz (and with the 7C coil for 2000-3000 kHz.) The diagram should make clear that it was a 2-terminal component, series-connected between a tap on the coil and the antenna connection point.
(Capacitor C13 in the diagram was also 4000 pF.)
Chuck
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Ch.Var. In the schematics I saw so far I couldn´t identify this condenser (the captions unreadable). The PA layout is very much alike the one of the British TR9 (HF) transceiver of 1934-36 as used in many early WW-II aircraft , evidently a designer´s fashion of the era , also found in the English 38 and 22 transceivers , probably to turn the output circuit to more broad band characteristics for easier adaptation to a variety of antenna lengths and possibly to avoid harmonics break through.
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General . The ´Donut´ theory / practice , why did it apply to 6,210 kc/s , not to 3,105 kc/s when A/c was in the roads of Howland ?