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Using Tuner to Determine Line Input Impedance
On Jun 3, 4:19*pm, Owen Duffy wrote:
dykesc wrote in news:22d6efc6-76ca-487a-9fc1- : ... I am concerned about an RF field from a local broadcast that may be causing issues with using the low power MFJ 259B. When I use the auto tuner I am tuning at 10 watts so plenty to counteract any local rf on the antenna. I really need to back calculate an impedance from the inductor, capacitor, and final swr from the auto tuner. Why didn't you say that the first time? Guess I was in a hurry and just wanted to know if I could back calculate the impedance (R +- jX) my auto tuner is seeing based on the inductor, capacitor and final swr values it displays after a "match is achieved. I would still like to do this. Dave gave me a link and of course I can do it manually with a Smith Chart (I think lol). Tom Rauch (one of the designers of the '259B) posted this info re interference: "BC interference causes the bridge in the analyzer to remian (sic) unbalanced even with very low SWR, so the analyzer will read a fixed minimum SWR when BC interference. It will read that way on any frequency from dc to daylight. For example if the unit falls asleep the SWR meter won't drop to zero. That's an indicator of BC interference or external voltages being applied to the measurement port." Owen Thanks. Now there's a bit of info I didn't have. So if the 259B is behaving normally, when it enters "battery save" mode the swr value should drop to zero. If not, there are external voltages on the antenna port. I think I will check this out with a 100 ohm resistor across the antenna port. 2.0 should drop to 1.0 or zero when "battery save" kicks in. By the way, the broadcast station is FM at 105.5 MC. |
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