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Why is my dipole low impedance?
In article , Lumpy wrote: I'm a little stumped. I'm sure I'm missing something obvious but I just can't see it. Silly question - have you calibrated your MFJ meter against a known-good load recently? The fact that you get the same impedance reading when you add 50 feet of coax (which is pretty close to a quarter-wavelength) is a red flag. Since the added cable is roughly 1/4 wavelength, you'd expect to see a *big* impedance transformation - a load of 6 ohms at one end, would be transformed up to around 450 ohms at the other end. Since you're getting the same reading with, and without the quarter-wavelength cable extension, I'd be very prone to suspect that your measurement tool (the MFJ meter) is frotzed. The MFJ-259 and -269 meters use "zero bias" Schottky diodes as part of their power-measurement circuitry. These diodes are relatively delicate, and can be damaged if the meter inputs are exposed to more than a relatively small amount of RF. Even keying up a transmitter on one antenna, while having the meter hooked to another (nearby) antenna at the same time, can hit the diodes with a high enough voltage to pop 'em. Reportedly, the -269 meter can also be damaged if you turn the UHF feature on or off at the wrong time or with the controls in the wrong settings. Check your meter with several loads - a 50-ohm dummy load, 25- and 100-ohm test loads, open circuit, and short circuit. See whether it reads close to the correct value or not. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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