N8UR/4 Feedline Measurements

I just installed some modest antennas on the roof of my new lab/hamshack (er, I mean house...) and wanted to document the feedline length and performance while things were fresh. These are screenshots from an Agilent 8712ES network analyzer in "cable fault" mode, showing any impedance bump in the cable including the big one at the end that represents the antenna. I also measured the return loss of the two ham antennas.

The cable fault measurements were all made with an assumed velocity factor of 1.0 and a cable loss of 0 dB. Thus, the cable lengths shown are the electrical length. The physical length is equal to the electrical length times the velocity factor, which is nominally 0.85 for LMR-400 and 0.84 for LMR-240UF. A piece of LMR-400 from the same spool used for these lines confirmed an actual velocity factor of 0.85 for this batch of cable; measurements of its characteristics are at the bottom of this page.

The first marker on the cable fault plots is set to the impedance bump that (more or less) represents the antenna at the end of the line. The second marker shown in most of the plots is the connection between the main feedline and a short LMR-240UF jumper going to the antenna base.

Full analyzer data is here.

Discone -- LMR-400 (Cable #2)

Cable Fault Measurement

Return Loss -- 30 - 1300 MHz

Return Loss -- 30 - 500 MHz

Dual Band Vertical -- LMR-400 (Cable #4)

Cable Fault Measurement

Return Loss -- 144 - 148 MHz

Return Loss -- 420 - 450 MHz

Aeroantenna GPS -- LMR-400 (Cable #3)

Cable Fault Measurement

Motorola Timing2000 Antenna -- LMR-400 (Cable #5)

Cable Fault Measurement

Spectracom WWVB Antenna -- LMR-240UF (Cable #1)

Cable Fault Measurement

Cable #6 -- LMR-400

These are measurements of the leftover piece of cable from the spool used for the other feedlines. It's now serving as a jumper between the surge protector at the basement entry point and the HP 8-way GPS splitter that feeds the GPS units in the lab.

According to the length markers printed on the cable with a tape measure for interpolation, this piece is 46.58 feet from N connector to N connector. Assuming a velocity factor of 0.85, the electrical length is 54.80 feet. The length measured by the VNA is 54.76 feet, so the correlation is very good (and well within the uncertainties of the tape measure, much less the analyzer!).

Cable Fault Measurement (Far End Unterminated)

Cable Fault Measurement (Far End Unterminated, Zoomed)

Cable Delay -- Time vs. Frequency

Cable Transmission Loss

Cable Return Loss (terminated in VNA port 2)

Inside Cables

These are length measurements of the cables used from the entrance point to the various radios in the basements.

Cables A and B, which connect to the two GPS antennas, were trimmed using the VNA to be the same electrical length. If you do this, remember to allow for the length of the connector to be added after trimming. The crimp-style N connectors I use add about 0.5 inches each. Cables D and E, which go to the ham station operating position, were trimmed by eye so they ended up with about an inch difference in length.

Cable A (LMR-400, to Clock Room)

(This is the same as Cable 6 characterized above, with an N connector added to the far end.)

Cable B (LMR-400, to Clock Room)

Cable C (LMR-240UF, to Clock Room)

Cable D (LMR-400, to Ham Station)

Cable E (LMR-400, to Ham Station)