Following the Pinecone Amateur Radio Club’s Field Day operation, it was necessary to check one of the coax cables for power handling. At some point it’s integrity was called into question, it was labeled “Check for Loss”, and set aside. I took on this task with my handy RigExpert StickPro which made quick work of it once I refreshed my memory of how to use it (beyond simple SWR measurements).
When performing feed line measurements, I avoid coiling it to avoid capacitance between turns. It might not matter for TDR measurements, but it can affect SWR measurements.
Unfortunately the length of coax I was working with did not have any identifying
markings on it. Had they existed, I would have been able to look up the velocity
factor of the cable. Fortunately, the StickPro has a Cable Length (cLen)
function that allows you to plug in either velocity factor or length, and
compute the other. Long press the arrow keys to switch inputs, update the length
in meters, and hit ▶ to make the velocity factor measurement. I broke out a tape
measure and measured 70’ 8", or 21.54 meters. From this, I was able to compute a
velocity factor of 0.78. This velocity factor matches the specs of other
RG-8X cables.
With the velocity factor computed, enter this into the analyzer’s configuration to use it across different modes. Hold ▶ to enter the menu, and press ▶ again to “Adjust user settings”. The “Cable vel. factor” is on page 10/13.
After configuring, it can be interesting to check TDR measurement to see where
the cable is “open”. You can check this cable length measurement against your
manual measurement.
Measure the cable loss (cLoss) by following the onscreen instructions. Leaving
the cable open is easy. I created a short by holding a paperclip across the far
end of the cable.. Maybe I’ll make a short from a barrel connector at some point.
The StickPro computed the following cable loss measurements:
| Frequency | Loss (dB) |
|---|---|
| 4 MHz | 0.34 |
| 8 MHz | 0.57 |
| 14 MHz | 0.78 |
| 22 MHz | 1.03 |
| 30 MHz | 1.24 |
| 144 MHz | 3.00 |
| 440 MHz | 5.75 |
These measurements match the specs for RG-8X cable. Mission complete, the cable can be returned to service!