Recently the feed-line to my 144 MHz antenna started to go bad – at first it just had elevated SWR but was still useable, but eventually the SWR rose to the point that the transmitter started to reduce power. Just before the September ARRL VHF contest I pulled it down and replaced it with a temporary line for the contest.
In the meantime, I asked the folks on the Badger Contesters and Northern Lights Radio Society email reflectors how one should go about troubleshooting a bum feed-line. A number of helpful ideas were offered, but the one that most intrigued me was using a time domain reflectometer (TDR) to "ping" the line and find out where physically on the line the problem is located. I assumed that such a device would be prohibitively expensive (and the commercial devices are!) But then I found the YouTube videos by W2AEW documenting how to build one for just a few dollars (presuming one has access to a good, fast oscilloscope, which I do), so I thought I'd give it a try.
Here are all his videos (so far) on this specific topic:
Not as neat as W2AEW's, but it works. |