This time of year a post on how to check the integrity of a coaxial cable run is appropriate – masts are down, pre-launch checks are underway.
When you use a multimeter to check that you have no short circuited connectors in your cable run you should be aware that the cable must be disconnected at the antenna as well as at the radio.
Most vhf antennas show a short circuit to a multimeter – see the first picture – so the cable, when connected to the antenna, will also show a short circuit whether it is or is not actually short circuited. This short circuit reading at the Metz, and other quality antennas, does not mean the antenna is faulty. This is the correct reading.
So, if you’ve just come down from connecting your antenna at the masthead and you haven’t checked the cable run yet, you’ll need to shinny back up the mast and disconnect it.
Only then can you proceed to check that you don’t have a short circuited connector or a corroded section of cable. In fact, it’s a good idea to check each connector at the time you fit it, before you solder it, to avoid much frustration later on.
I’ve written before about troubleshooting your vhf antenna system and about the ease with which a PL259 connector can be inadvertently short circuited during fitting but I felt the need to emphasise the point about disconnecting the antenna before checking the cable run after a couple of people thought they had a ‘short circuited’ antenna. No, it’s supposed to be that way. A faulty Metz! Heavens forefend!