Originally Posted by StanleyCup
I was struck by lightning and it zapped the VHF radio and some of the electronics. Don't think it was a "direct" strike because steaming and anchor
lights still work, as do some of the instruments (depth/speed, etc.) ...
.... Are VHF coax cables that have conducted a lightning strike usually unusable? Is what I am suggesting feasable? Advisable? ...
... And if this might work, any good way to test the cable? ...
Given the many possible variables, the word “usually” is meaningless, when discussing lightning damage. Even similarly described “lightning events” can vary greatly in their etiology & consequences.
Utilizing an Ohmmeter (continuity tester), you can perform a basic DC Continuity (Open) & Short Circuit test
on your “suspect” coax cable. These tests will reveal "gross" damage only .
If the antenna line has been damaged, it is possible that:
1. Either the inner conductor or the shield are “open”.
2. The shield could be shorted to the inner conductor.
1. OPEN (Continuity) Test):
Test both conductor & shield. With the antenna disconnected, and the inner coax conductor shorted to the outer shield, there should be zero resistance. You could determine which comnponent is open (the inner conductor is more likely to be open than is the shield); but it doesn’t really matter - the cable is “toast”.
2. SHORT Circuit Test:
With the antenna disconnected (open coax cable ends), there should be NO CONTINUITY between the inner conductor and the outer shield. A higher resistance will indicate degraded insulation
. A lower resistance will indicate a short.
As previously mentioned, an Output Power and VSWR meter (designed for Marine
VHF: 156 - 160 mhz) is a useful tool for testing connected antennas.
See: Shakespeare ART-2 ($50), or ART-3 ($100), and others such as MFJ (259B?) ...
See the excellent short tutorial “VHF Marine Antenna Fundamentals
” ~ by Al Corkins
VHF Marine Antenna Fundamentals
What are the Chances of Lightning Striking Your Boat?
The following statistics are based on all of the BoatUS Marine Insurance claims for lightning damage over a five-year period. The percentages suggest the chances of the various types of boats being struck in any given year.
Auxiliary Sail 0.6% Sixty out of 10,000
Multi-hull sail 0.5% Fifty out of 10,000
Trawlers 0.3% Thirty out of 10,000
Sail Only 0.2% Twenty out of 10,000
Cruisers 0.1% Ten out of 10,000
Runabouts 0.02% Two out of 10,000
BTW: Thunder is more than just a rich source of loudness
(audible up to about 25 miles).
It can also tell you interesting stuff
, such as how close you came to being hit by lightning.
Since light travels at 186,000 miles per second, you see the lightning the instant it flashes. But sound, including thunder, travels about a mile in five seconds
(1000Ft/Sec, 340m/sec) near the ground, at normal temperatures.
Lightning closer than about three miles away is a warning to take shelter immediately. Successive lighting
strikes are often two to three miles apart. If the first stroke is three miles away, the next one could hit you.
If you don't hear it, you got hit, so never mind.