[TowerTalk] Measuring coax loss with MFJ-259B

[Pete Smith]

Last summer, I put in 2 x 190-foot runs of LDF4-50A from the base of my tower to alongside the house.  From there, I run RG-213 about 45 feet into the shack.

I decided to measure the loss in these feed-lines, so as to have a point of reference, using the Coax Loss function of the 259B.  Measuring at around 30 MHz, I was surprised to read large cyclical variations in the loss reported with relatively small changes in frequency.  For example, one of the feedlines (they have slightly different-length "pigtails" on the tower end) shows as much as 2.0 dB loss at ~30.3 MHz, but at 30.1 the reported loss is 1.2 dB, and at 32 MHz it is back up to 2 dB.

Naturally, I was expecting a gradual increase in loss with frequency, but this change seems both abrupt and cyclical in nature.  Anyone have any clues on what is going on?  Defective meter (it otherwise seems to work fine)?  Defect in the flexible coax causing an impedance mismatch?

73, Pete N4ZR
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