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SWR meter as power meter
On Tue, 30 Nov 2010 13:50:35 -0800 (PST), JIMMIE
wrote: Owen, the meter is just a 1 to 100 linear scale meter on on 100 uA movement. Ive used it for years just to "guesstamate" VSWR. Not really as inaccurately as one may think. My thought was to cal a scale for the "full scale set" knob so that when the meter is adjusted for full scale the knob position will indicate power. Part of the reason for doing it this way is that it is a nice large good quality meter and I dont want to risk damaging it by taking it apart. I may have other uses for it later on. Im thinking "linear scale capacitance meter similar to the heathkit model. I intend to use an NE555 osc instead of vacuum tube osc should I do this . Jimmie Hi Jimmie, On reading this, several thoughts came to mind. You write about having used a linear scale to guesstimate SWR. Sounds good and it immediately leads us to an existential question: "What value is there in knowing the value of SWR?" The first motivation following a glance at the SWR meter is to LOWER the SWR, for whatever value it may reveal. In this sense, the value is a trivial consideration - relative indications are enough to achieve the goal. Using the feed from a Bruene style detector pair into a Log-Amp will give you a power response in a linear scale. If you want to know the SWR with accuracy, you can throw the reverse switch for the second power reading and compute, or you can throw the reverse switch and start twisting nobs to make the power indication go away. consider: http://rfdesign.com/mag/503rfd33.pdf Says it all in one page - with pictures, schematics, and math too. I don't quite catch the drift of the "capacitance meter" paired up with NE555 osc. I presume you mean to construct a DC-Freq converter? 73's Richard Clark, KB7QHC |
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