Way back in the dark ages on 2013 when I got my technician ticket, one of the very first home brew projects that I made was the typical J-Pole made from copper tubing. I mounted it on a 20 foot mast made from the top pipe on chain link fences. I used that antenna for all of my UHF-VHF activities. Considering I have been net control for a local net since Oct 2015, that antenna was used a lot. As time went by my signal got weaker and weaker. It happend so slowly that no one really noticed it. Then this past summer a good friend was moving across the country and was selling his ham radio gear. I was able to obtain a real nice Diamond 718 Repeater/ Base Station antenna, I plan on doing a review of it shortly.
|Diamond 718 Repeater/ Base Station Antenna|
Wouldn't you know, I just happen to have a piece of coax laying around.
|DX Engineering RG8X Coax.|
The first thing that you need to do to measure the length of a piece of coax is to short out the coax being measured. So I made me a little jumper wire by using a couple of alligator clips and a short piece of wire. Back in my teenage years I used alligator clips for something else, but we will not discuss that here.
Next I hooked the jumper to the end of the coax by connecting the center wire to the outer shield. The other end I hooked the coax to the MFJ-259C. I then turned on the MFJ-259C amd started off at the lowest frequency range and started adjusting the frequency higher. While I did this I watched the Resistance Meter (this is the meter on the right that is labeled IMPEDANCE. I was looking for the needle to dip down to zero ohms. It finally did this at 10.991 MHz. Next I looked up the velocity factor for my coax and found that it is 82 percent. Then I took the frequency and divided by 492 and then multiplied the answer by the velocity. The answer is the number of feet in the coax. In my case it said that my coax was 36 feet long. This is enough to let me set my 2 meter yagi up and hopefully use it on SSB for the ARRL's January VHF Contest.