[TowerTalk] Measuring 1/2 Wavelength coaxial lines with an MFJ-259

Robert L. Shohet kq2m@mags.net
Sun, 23 May 1999 20:29:09 -0700

I am in the process of making up feedlines for some monobanders that I
am putting up and have come across a vexing problem with the MFJ-259.

Here's what happens...

I measure an odd multiple of 1/2 wavelength for let's say 21.250.

At the 3rd harmonic, instead of seeing an swr "dip" at 63.75, I might
see the dip at 64.25 instead (3rd harmonic of 21.417).  At the 5th
harmonic instead of seeing the "dip" at 106.25 Mhz, it might dip at
107.30. (5th harmonic of 21.460)

Why does this happen?  Shouldn't the 3rd and 5th harmonics be exactly 3x
and 5x the original frequency?

More importantly, which freq. do I use as the correct measurement for
the 1/2 wave coaxial line, the 1st, 3rd or 5th harmonic or some

Would appreciate replies from MFJ users and guidance on what to do.

Tnx for your help and 73.

Bob KQ2M

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