vhf testing and antenna/coax replacement

[Norton]

My old Midland vhf started having problems transmitting. I started doing some research to buy a replacement and came across threads suggesting that a proper antenna and coax setup were much more important factors than the actual radio choice. I also saw other threads saying that fiberglass antennas and coax had a life span. I have a metal whip antenna mounted on my mast, not a fiberglass antenna, and am wondering if there is a life span for whip antennas? Should coax and or antenna be replaced periodically? I have gotten responses to my radio checks, the bridges opened when I called, so I know I am transmitting with the new radio. I receive the weather service. Is this as much testing as is done for most vhf setups? I am wondering what other methods some of you use to test the effectiveness of your radio. My anchor light needs repair and would probably have not worried about the antenna setup, since it seems to be working, except that I can kill two birds if necessary when I deal with the light.

 

[George]

Similar Problem

*o I have a similar problem and what I'm going to do is install a Antenna/Radio Tester. What info I have comes from www.hamiltonmarine.com. ( this instrument measures the watts your rig is delivering as well as the efficiency of your antenna system. Required on vessels carrying over 6 passengers. (I would think paying passengers).It should save me problems in the long run.George

 

[Ken Palmer]

Time to check coax connectors

The ss whip antenna on top of your masthead will last a very long time as well as the coax inside the mast. Damage is done by UV, so the coax isn't in the sun, and the only part of the whip that will deteriorate is the rubber part that covers the nut at the top of the antenna coil where the whip slips in.You should check coax fittings at both ends of the coax by doing a "twist" test, "pull" test, and visual inspection. The twist is done by holding the cable in one hand and twisting the connector body with the other hand. There should be no slipping of the connector on the cable. The pull is done by slightly pulling the connector while holding the cable. Again, there should be no slipping.Look for any corrosion at the center pin on the connectors and the receptacles. You should also think of the meter that George mentioned. At $45, it is a good indicator if your transmit power is being radiated by the antenna.As far as the radio, there have been many improvements in VHF technology over the years. I just bought a digital select call VHF with a wireless remote mic/remote control. That is really slick. I have the radio below at the nav station, and the mic with me on my belt or hanging near the wheel. Radios are also a lot smaller now with added sensitivity. Transmit power remains at 25 Watts maximum by law.Good luck with your task.

 

[Gregg]

Try an SWR meter

An efficient antenna system is at least as important as the radio you hook up to it. Try inserting an SWR meter between the radio and antenna. This will give you an idea of power output (more is good), reflected power (less is good), and the standing wave ratio (SWR - less is good). SWR of less than 2:1 is preferred. You can get an SWR meter at the famous shack of radios, (get one for the VHF band - marine VHF is 156-157 mhz.) or maybe you have a friend who is a ham radio operator.Your metal whip should not be a problem, unless there is some corrosion where it is mounted to the coil. The coil (round metal base of the antenna) could eventually need replacement; sometimes the wire inside breaks. But marine antennas are pretty well sealed, and there isn't a whole lot of vibration. Coax connectors should be checked; sometimes they're not soldered properly, more so when done by the dealer than the antenna manufacturer. Unless your coax is real old, it should be OK. I've had coax on the roof of my house for 15 years and it's good. If you can disconnect the coax from the antenna and the radio, put a multimeter on a connector center pin and sleeve, and the multimeter should read open. Try the SWR meter first - it will tell you a lot.

 

[georich]

vhf / antenna / coax testing

The metal whip antenna should last a very long time. The 3db metal whips are the best for sail boats and rarely fail. Enviormental factors, heat & cold cycles & salt air and moisture can affect the coax and connectors. Your best bet is to buy or borrow an SWR meter for VHF freqency (also called VSWR) and check while your mast is still up. This meter measures how much of your radio's power is reflected back down the coax when you transmit. Bad connections, corrosion and coax dammage can cause a large amount of radio energy to reflect back into your radio decreasing it's efficiency and possibly dammaging your radio.If the meter indicates a problem, replace the coax and connectors when you service your anchor light. Make sure you buy 50ohm coax and not the 75ohm stuff for cable TV. Be sure to wrap exterior connectors with electrical tape or heat shrink tubing. You'll be set for a long time.If you have any friends who are ham radio operators see if they'll lend you a hand. Ham's love to work on radios.The new VHF radios have some great features that we didn't have in the old days. Enjoy. Buddy Richardson, N3RKVs/v Cowardly Lion

 

[Jeff M21319]

Well, I was hoping to add something...

to this thread but it seems you guys have beat me to it! All the info above is correct and there's not much more to say. A VSWR meter is a pretty handy tool to have, without it you have no way of knowing what is really going on with your antenna. One thing I might add is if you decide to replace your coax, I'd suggest you upgrade to RG-8X, which is only slightly larger in diameter but has a bit less loss than standard RG-58 and it doesn't cost much more. Be really careful when soldering on those PL-259 connectors, if you haven't done one before it might be a good idea to have someone in-the-know show you the proper method. Good Luck!JeffS/V Katrina MarieKD6KNA

 

[Norton]

Good answers create more questions

Thanks for the input. I may have a line on a meter to borrow. I have a few questions about what the three different numbers mean in terms of evaluation. If I test output at the vhf or mast base connection this parameter will tell me that the vhf output is proper, not antenna output correct? Subtracting reflected power from output gives me the power output of the coax/antenna? If I had the meter at the top of the coax it would be giving me the power the coax delivers to the antenna and I would subtract reflected power from the output number to get antenna output? Or does it not matter where you put the meter? Do you check output power at the vhf without the antenna connected first, and then with it connected? What are the differences in what reflected power and SWR numbers are telling me in terms of evaluating my equipment?Sorry about the rambling, I have never used one of these meters and am thinking I can test sections of the system if the intial tests indicate a problem.

 

[Jack Swords]

water

One problem with coax that has not been addressed is that if not sealed at the ends it can wick water into the cable, forever changing the impedence of the cable. All coax, sealed or not, should have a drip loop at the top of the mast so that water does not tend to enter the coax. Water can ruin even new coax. The SWR will indicate problems. Jack WA6WTH

 

[Jeff M21319]

Using a VSWR meter...

isn't really all that difficult. The meter should be inserted between the radio antenna jack and the end of the coax. You'll need a short 'jumper' cable with PL-259 connectors at both ends to make the connection. Make sure you connect the meter properly, as it will not function if connected backwards. You would then switch the radio to an un-used channel, set the SWR meter switch to 'Forward' and key the mike. Adjust the knob on the meter so that it deflects to the 'set' line at the right side of the meter scale. Then, switch the meter to 'reflected' and you will see what your VSWR is. Anything under a reading of '2' is considered acceptable, but it is possible to tune the antenna to get it even lower by adjusting the length of the whip in small increments. However, remember that the SWR will vary dependeing upon what channel you are transmitting on, so it is best to reach a compromise that results in an acceptable SWR for all channels. While this is a 'thumbnail sketch' of how to use the meter (getting proficient with this tool and learning to 'tune' antennas takes a bit of practice) at least you'll have enough info to see if things are working correctly. If you'd like a more detailed example, let me know!Hope this helps,Jeff

 

[Tom S]

SWR Meter for VHF is $50 at West Marine

Buy it once and you'll have it for the rest of your life. Its a pretty good investment (Click to link to product)http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&productId=21217.Can't add much more to whats been written, though I heard you typically only insert these SWR meters temporarily and they are not recommended for permamanet installation (I think you lose some potential power), but I would think there are some expensive ones that could be used permanently.