[CQ-Contest] Correctly measuring coaxial phasing lines with an MFJ 269
Bob Shohet KQ2M
kq2m at kq2m.com
Sat Dec 3 12:35:10 PST 2011
Help!
It has been a few years since I have had to measure/cut a phasing line with the MFJ269
and I can't find my earlier notes.
I know the formula for length of one half-wavelength is 492/freq. x Vf.
I have a 170' piece of Buryflex Foam 50 ohm Coax
Questions:
In order to find the Vf I believe that I need to do the following:
1) Connect one end (through a PL259) of the coiled coax into
the MFJ269 and short the other end.
:
2) Measure for lowest Resistance and X (Impedance).
Following this procedure, I get the following minimum values
of R of 12 and X = 0 at
11.54 mhz
13.89 mhz
16.19 mhz
18.54 mhz
Then dividing 170 by 6 (half wavelengths) and then dividing by (492/13.89), gives me a
Vf of 0.800 close to what it should be. Same result if I divide 170 by 7 and then divide by
(492/16.19).
I note that the dips occur about every 2.33 mhz and 6 x that = 13.98 mhz.
Is this correct? Please advise, Tnx & 73
Bob
Bob Shohet, KQ2M
kq2m at kq2m.com
www.rlsfinancialgroup.com
Bob Shohet, KQ2M
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