Re: Marconi Q meter exciter
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On Sunday, 16 July 2023 at 00:25:54 BST, Morris Odell <vilgotch1@...> wrote:
"It seems that there is a significant voltage drop in the connection consisting of a short (about 100 -150 mm) cable and two BNC connections.? I'll have to re-think the coupling from my amplifier into the TF1245!" ---------------------------------------------------------------------------------------------------------------------------------------
There is no significant voltage drop in the cable.? The polythene dielectric cable inside the TF1245 is about 90mm long.? The electrical length is insignificant at 50kHz, so the input impedance at the front panel is about 0.5 Ohms and almost wholly resistive, but at 50MHz the impedance is about 0.53 + j7 Ohms and maybe 0.7 + j20 Ohms down a further 150mm of cable with the same velocity factor.? The TF1246 therefore needs to develop enough output voltage to provide the injection current required.? I'm guessing that the length of the "special" Marconi cable and equipment layout was chosen to be short enough to ensure the TF1246 could always supply enough current to the TF1245 even at 50MHz.
PeterS????????? G8EZE
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