I've been getting what appear to be erroneous readings on my MFJ-269
impedance analyzer when measuring the input impedance of the elements in
my short vertical array for 160 meters. I've ruled out BC interference
by using the MFJ-731 BC filter. I am also seeing a real resistance
reading (e.g. 250 + j 1000) when measuring a 100pf capacitor at 1.8 MHz.
The reactance magnitude (1000 ohms) is in the ballpark, but the
resistance reading doesn't make sense. Over the weekend I ran through
the calibration procedure that is available from the MFJ website. When I
looked at it on the specA, harmonics looked fine (better than 25dBc at
VHF/UHF and better than 40dBc at HF) and the output level was very flat
from 1.8 MHz up through VHF/UHF. One thing that alarmed me was that I
had to rotate trimpot R72 all the way to its stop to get Vz to full
scale (in this case Vz=FFEh was the best I could do). Similarly for the
steps where Vz was specified to be set for CCCh, I was a little bit
short even when R72 was on the stop. This makes me think that one of the
detector diodes in the bridge might be damaged. I suppose it might also
explain the erroneous real resistance value for the 100pf capacitor
measurement.
Anyone out there have similar problems? I am thinking that this unit
needs to make the trip to Starkville for repair.
Thanks,
Mike W4EF.............
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