Birdman
Veteran Member
Lets keep it simple, forget the theory behind all this, lets just define what you have, and define how to test it, without trying to describe the theory behind it. Which I believe is what the OP is interested in, antenna theory, vSWR, an antenna analyzer.... are all great, but you could read 50 books written by RF engineers over 20 years and still know next to nothing about rf theory. ;-)
I'm a licensed amateur radio operator, and know a tiny bit about antenna's. I'm no expert by any stretch, but maybe this will help.
Easiest test, plug it in, and try it! "Most" (not ALL) modern VHF radio's will protect themselves from a bad antenna. They will shutdown or reduce output power significantly if they sense a bad or no antenna connected. So worse case, it won't work, or won't work very good. Throw away and go buy a new antenna. Best case, it works great... Plug it in, tune to a known working WX radio station in your area, if you hear nothing, the antenna is not working, do not transmit on it. If you do hear WX, great, but it still does not mean the antenna is good, but it's a good start. (sometimes wx stations are so strong depending on where you are, you can receive them with a broken or no antenna!). Now tune to a local channel people use, like 68. NOT 16 which is for emergencies/CG. Ask for a radio check. If you know somebody else within 5 or 10 miles on the water, call them via phone ans ask to test it with you on ch 68 (or other ch). That way you know you not just being ignored. Some people hate answering "radio checks", mainly because many people do them all day long and on the wrong channels (like 16!).
A more robust test:
Looking at the picture of the antenna ends that screw together, you have an inner element (the actual part of the antenna that does the radiating), and an outer shield or dielectric (the fiberglass). The metal and threads used to screw the ends together, is really not part of the "radiating antenna", just the inner element is (the copper part). And the fiberglass is just a protective cover.
The first thing you need to do is clean off those ends, get all that grease and dirt off them, you want them spotless (you can add some dielectric protective grease later). Then, with the antenna separated, and NOT connected to the feed-line (coax cable), test it with a simple electric voltage meter to ensure it is not shorted out. To do this, put the meter on the continuity setting, make sure it works buy touching the two meter leads together, most meters will beep when touched together to indicate continuity (meaning, voltage can flow between them). Now hold one of the leads of the meter to the center element (copper part) of the antenna, being careful to not let that lead touch the outer part of the antenna (metal part with threads on it). Around the outside of that inner copper element you will see a small blackish area (grease), that is the area keeping the element from touching any other metal (the part with the threads) which would short out the antenna. Now take the 2nd lead from the meter, and touch it to the outer metal part with the threads, being careful not to touch the inner copper element, or the 1st lead your still holding. You should NOT hear a beep from the meter. In other words, there should not be continuity between the outer part of the antenna connectors, and the inner copper element. If the meter beeps, the antenna is shorted and likely garbage. Do this test on EACH section of the antenna (3 pieces I think you said?).
Next, you can get yourself a marine VHF swr/wattage meter to test if the antenna is ok, they cost about $100 at west marine, Shakespeare makes a simple easy to use one. Connect it inline between the radio and the antenna, and follow it's simple directions to test the swr of the antenna (as noted ideally it will be 1:1, but definitely should be less than 2:1). If it reads 2.5:1, or 3:1, or even 5:1 then something is wrong (either the feed-line or antenna is bad most likely).
In any case, TAKE THE PENNY's out, and do not put anything else in there. And CLEAN those connection points out first, wipe with a rag, then spray crc or wd40 on it, wipe clean.
Hope that helps...
I'm a licensed amateur radio operator, and know a tiny bit about antenna's. I'm no expert by any stretch, but maybe this will help.
Easiest test, plug it in, and try it! "Most" (not ALL) modern VHF radio's will protect themselves from a bad antenna. They will shutdown or reduce output power significantly if they sense a bad or no antenna connected. So worse case, it won't work, or won't work very good. Throw away and go buy a new antenna. Best case, it works great... Plug it in, tune to a known working WX radio station in your area, if you hear nothing, the antenna is not working, do not transmit on it. If you do hear WX, great, but it still does not mean the antenna is good, but it's a good start. (sometimes wx stations are so strong depending on where you are, you can receive them with a broken or no antenna!). Now tune to a local channel people use, like 68. NOT 16 which is for emergencies/CG. Ask for a radio check. If you know somebody else within 5 or 10 miles on the water, call them via phone ans ask to test it with you on ch 68 (or other ch). That way you know you not just being ignored. Some people hate answering "radio checks", mainly because many people do them all day long and on the wrong channels (like 16!).
A more robust test:
Looking at the picture of the antenna ends that screw together, you have an inner element (the actual part of the antenna that does the radiating), and an outer shield or dielectric (the fiberglass). The metal and threads used to screw the ends together, is really not part of the "radiating antenna", just the inner element is (the copper part). And the fiberglass is just a protective cover.
The first thing you need to do is clean off those ends, get all that grease and dirt off them, you want them spotless (you can add some dielectric protective grease later). Then, with the antenna separated, and NOT connected to the feed-line (coax cable), test it with a simple electric voltage meter to ensure it is not shorted out. To do this, put the meter on the continuity setting, make sure it works buy touching the two meter leads together, most meters will beep when touched together to indicate continuity (meaning, voltage can flow between them). Now hold one of the leads of the meter to the center element (copper part) of the antenna, being careful to not let that lead touch the outer part of the antenna (metal part with threads on it). Around the outside of that inner copper element you will see a small blackish area (grease), that is the area keeping the element from touching any other metal (the part with the threads) which would short out the antenna. Now take the 2nd lead from the meter, and touch it to the outer metal part with the threads, being careful not to touch the inner copper element, or the 1st lead your still holding. You should NOT hear a beep from the meter. In other words, there should not be continuity between the outer part of the antenna connectors, and the inner copper element. If the meter beeps, the antenna is shorted and likely garbage. Do this test on EACH section of the antenna (3 pieces I think you said?).
Next, you can get yourself a marine VHF swr/wattage meter to test if the antenna is ok, they cost about $100 at west marine, Shakespeare makes a simple easy to use one. Connect it inline between the radio and the antenna, and follow it's simple directions to test the swr of the antenna (as noted ideally it will be 1:1, but definitely should be less than 2:1). If it reads 2.5:1, or 3:1, or even 5:1 then something is wrong (either the feed-line or antenna is bad most likely).
In any case, TAKE THE PENNY's out, and do not put anything else in there. And CLEAN those connection points out first, wipe with a rag, then spray crc or wd40 on it, wipe clean.
Hope that helps...
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The results can very easily be mis-interpreted to be a bad antenna, when in fact it's really a bad feed line, or vice-versa, or any number of other things...
