VHF Radio Questions/Problems

[Tmacmi]

I am replacing my VHF radio with a new one that has its own GPS.

The current doesn't appear to be working and I want to figure out if its a radio problem or antenna problem before I install the new one. It worked during the shake down cruise with the PO.

1) I've turned it on and confirmed it has power. I've tuned it to the weather stations and can't hear anything.

2) I've read a few on-line items and have read that you can stick a short wire into the center female antenna hold and check for reception that way.

I've tried that and have not heard anything back. Any advise?

[AA3JY]

Try Simple problem first..turn down your squelch till noise..then up slightly to cancel the noise..then try monitoring the local WX freqs. that are close to-your area..

[Tmacmi]

Originally Posted by AA3JY

Try Simple problem first..turn down your squelch till noise..then up slightly to cancel the noise..then try monitoring the local WX freqs. that are close to-your area..

Yep, tried that. No joy.

[AA3JY]

Try unscrewing the barrel of the VHF connector..pull out the Center connector just slightly..leave a slight open gap between the barrel connector and radio. Try listening again..

[tkeithlu]

I ran into somewhat similar problems a few years ago. In my case, it turned out that I left the sat phone sitting on the VHF. It was charging, and cut out all transmission.

I chased it down by spending $95 on a spare VHF and $15 on a spare antenna. Back and forth narrowed down the problem.

It wasn't $110 wasted. The spare VH and antenna is in storage on the boat, waiting for the day a lightning transient fries my electronics. In Florida, that's a reasonable risk to mitigate.

I have a suspicion that your antenna is grounded. VHF radios are pretty bullet proof. Buy yourself, or borrow, a VHF antenna and try again with AA3Jy's suggestion.

[Brian.D]

Even if the antenna is shorted and/or grounded, that should not make a difference on receive. A paper clip can be used with limited success in receiving.

Another test to confirm if the receiver is even working is to use a handheld at close proximity to the main radio. If you key the handheld and it does not break squelch then the radio is differently faulty.

But it could be something as simple as the center conductor on the SO-239 within the radio is broken off. This will not allow any RF from the antenna to access the receiver circuits. But the handheld test will pass and confirm the receiver circuit is functional.

I would recommend trying to break the squelch with a handheld radio. That will confirm the functionality of the circuity in the receive path.

[continuouswave]

Originally Posted by Tmacmi

The current [boat VHF Marine Band radio] doesn't appear to be working and I want to figure out if [the cause is] a radio problem or antenna problem.

You have three components in the system:
--radio
--transmission line
--antenna

With no test gear, you can only test using the three components, and you do not know if any of them work properly.

The suggestion to test for radio reception by disconnecting the transmission line from the radio will removed the transmission line and the antenna as part of the system.

If you are in South Haven, Michigan, the NOAA Weather Radio station WXN99 is the closest station. You use their off-air signal as a test signal to determine if the radio receiver is working.

First, verify that other boats near to you can receive WXN99 with strong signals.

Use a temporary antenna consisting of a piece of wire about 18-inches long connected the center conductor of the SO-239 connector on the back of the radio chassis.

Tune the radio under test to WXN99 at a frequency of 162.425-MHz. Note that many VHF Marine Band radios cover the NOAA weather frequencies with their own channel numbering system. For advice on typical channel numbers used for weather radio see

continuousWave: Whaler: Reference: Assesing Antenna Performance

If the radio under test is typical, then WX-4 may be 162.425-MHz.

If the radio under test cannot received WXN99 with a temporary antenna, the results are ambiguous. The radio could be out of range. The temporary antenna could be too poorly located.

If the radio under test can receive WXN99 then you have established at the minimum that the radio can receive very strong signals.

Another NOAA Weather Radio station that may be delivering a strong signal to South Haven is WWF34 at 162.475-MHz. Check for reception of that signal, too.

Here are predicted coverage maps:

WWF34 = https://www.weather.gov/nwr/sites?site=WWF34

WXN99 = https://www.weather.gov/nwr/sites?site=WXN99



Another method to test the radio in isolation from the transmission line and the antenna: move the radio to another boat nearby, connect it to that boat's power and antenna transmission line. Repeat the test for reception of WXN99.

There is no effective way to test the transmitter output power of the radio without some test gear.

There is no effective way to test the transmission line without some test gear.

There is no effective way to test the antenna without some test gear.

If the boat is a sailboat and the antenna is located at the masthead, the most likely problem will be in the antenna itself, or in the connection to the transmission line, or in the transmission line.

[Tmacmi]

Thank you for the detailed response regarding weather stations. That actually helps a great deal. I tried to find which station had the best coverage and couldn't.

I am guessing that the testing equipment is a vswr. Not a cheap thing.

[S/V Illusion]

Originally Posted by Tmacmi

Thank you for the detailed response regarding weather stations. That actually helps a great deal. I tried to find which station had the best coverage and couldn't.

I am guessing that the testing equipment is a vswr. Not a cheap thing.

An SWR meter isn’t expensive, however, as you apparently can’t receive, it is useless in terms of identifying the cause of that problem.

Either 1. try a different radio fed by the existing antenna or 2. try the same radio into a different antenna.

[prajna101]

I dont think I am going to hijack this thread, its pretty similar question. I have two very nice handheld VHFs and one main one with an antenna on mast head 70 ft up. My handhelds get better RX and TX than my main. My main does work, Its just odd that my handhelds have significantly more reach. I have just let it be so far, but would love to get it fixed. But I just don't know how to troubleshoot. There was some good stuff in this thread related, but not quite.

The radio works. I can send and receive. It just doesn't do it as well as I think it should.

Any ideas?

[rslifkin]

Originally Posted by prajna101

I dont think I am going to hijack this thread, its pretty similar question. I have two very nice handheld VHFs and one main one with an antenna on mast head 70 ft up. My handhelds get better RX and TX than my main. My main does work, Its just odd that my handhelds have significantly more reach. I have just let it be so far, but would love to get it fixed. But I just don't know how to troubleshoot. There was some good stuff in this thread related, but not quite.

The radio works. I can send and receive. It just doesn't do it as well as I think it should.

Any ideas?

Depending on the quality of the cable run up your mast and condition of the connections, it's very possible that you're losing a lot of signal in the cable run. A good, heavy cable run up the mast with an antenna up top and good connections should be worlds better than a handheld.

[Jammer]

Originally Posted by prajna101

I dont think I am going to hijack this thread, its pretty similar question. I have two very nice handheld VHFs and one main one with an antenna on mast head 70 ft up. My handhelds get better RX and TX than my main. My main does work, Its just odd that my handhelds have significantly more reach. I have just let it be so far, but would love to get it fixed. But I just don't know how to troubleshoot. There was some good stuff in this thread related, but not quite.

The radio works. I can send and receive. It just doesn't do it as well as I think it should.

Any ideas?

1) It's usually the feedline or the connectors. High-quality feedline components, installed with knowledge and care, can still fail, especially after a period of years in the weather. There are many installations using substandard materials or workmanship and of course those fail sooner.



2) Temporarily connecting a known good antenna to the radio using known good feedline is one of the best diagnostic techniques. You can clamp the antenna to a rail while testing and then keep it as a spare or as part of your emergency kit. Or you may find that it works well enough that you lose interest in climbing the mast for further troubleshooting or repairs.



3) You can also connect your known-good handheld radio in place of your fixed radio as a diagnostic technique. In most cases you will need an SMA to SO-239 adapter. These are available for a few dollars on eBay and elsewhere. The ones with a short pigtail work best and won't stress the connector on your handheld.



4) A skilled person can find out everything there is to know about an antenna and feedline system with a VNA in a matter of minutes. VNAs used to cost thousands of dollars but you can now buy the NanoVNA on eBay for $50 and they'll fit in your shirt pocket. You will also need some adapters and cables. There are websites, books, and videos explaining how to use them.


5) All of these techniques can be used on individual parts of the system e.g. if you have a separate piece of feedline between the radio and the foot of the mast, you can disconnect the feedline at that point and substitute in the known-good antenna, the known-good handheld, or the VNA and further isolate the problem.

[continuouswave]

Regarding possible problems with antennas, particularly antennas mounted at the top of a sailboat mast:

Antennas at the top of sailboat masts are exposed to very rapid movements and high winds, and those antennas are more prone to failure than antennas mounted lower on the boat. To reduce weight aloft the antennas mounted atop sailboat masts usually use a small diameter whip radiator, which as its name implies, can whip or move rapidly, creating further movement and possible problems.

The high mounting improves the radio horizon compared to much lower antennas. The result is that an antenna mounted atop a sailboat mast may still appear to work on receive quite effectively, even when the antenna has serious problems and might not even be connected to the transmission line.

The behavior of an antenna on receive or transmit is the same. However, it is very common that antennas that are completely useless for transmitting will still provide useful reception. The explanation is quite simple.

When an antenna is used for transmitting, there is a limit to the transmitter power being applied, that is the amount of amplification of the signal that is applied before reaching the antenna. Typically 25-Watts is the maximum power. In contrast, when an antenna is being used for reception, there is no limit on the amount of amplification permitted in the receiver. It is not unusual for a receiver to have an enormous amount of reserve gain in its amplification system which will automatically be applied to amplify a very weak signal delivered to the radio from a practically non-working antenna system. Thus while the behavior of the antenna is symmetrical on both transmit and receive, the amount of signal amplification is not the same in each case. The receiver is permitted to amplify the signal as much as it can in order to raise its level to be sufficient for demodulation.

It is quite common for radios on recreational boats to be connected to antennas that are barely functional and for the radio to appear to work based on reception of signals, albeit usually strong local signals, while transmitting with that antenna will produce very poor signals that can only be heard by local stations at very short distances.

ASIDE: in the very early days of commercial radio broadcasting, there was a distinct difference in the distribution of amplification in the radio signal transmission system. In the 1930's a pioneer broadcast station, WLW in Ohio was transmitting at a carrier power of 500,000-Watts. This permitted its signal to be received on low-cost receivers of that era that were very primitive and lacked sensitivity. The distribution of gain in the system was heavily weighted on the transmitter side.

[Bycrick]

Another big difference in the antenna system between transmitting and receiving is that, when receiving you only care about the signal strength in volts (typically microvolts). The input impedance of the receiver is high enough that essentially no POWER is involved. So almost anything used as a receiving antenna will probably work.

But to transmit, you have to have power, so the transmitter, cable and antenna need to present the same impedance. If they don’t, then some of the transmitted power ends up being converted to heat rather than being radiated.

Just because you can receive a signal is no indication that the antenna system will actually radiate anything useful.

[ka4wja]

Tmacmi, (and prajna101),


1) Continuouswave gave you a great description of the situation / answers to your questions....and he, and S/V Illusion, gave you some steps to do some testing...and, there's not too much more to add...except a few specifics here...



2) But, I'd like to add a few comments / recommendations that I feel should help...


a) Using your own words / your information....your Spirit 28 is a 1979 boat....so, if your VHF antenna and antenna cable/connectors is even half as old, my very first recommendation is to simply replace the VHF antenna and all VHF coaxial cable 'n connectors with new / hi-quality (not marine store crimp-on crap)...


It's good that you're replacing the VHF radio (as I suspect your old one was not a Class D Marine VHF-DSC-FM radio?), so you might as well replace all the coaxial cable and connectors, and VHF antenna as well... (BTW, if your old antenna is still good, you can save it as a "spare"...)




b) No need to spend $$$ (~ $100) on a VSWR/Power meter that is accurate at VHF frequencies...


I know, I know....this is contrary to my usual advice/recommendation....but, with an old radio being replaced, and we assume an old antenna and old coaxial cable (and connectors), in my opinion, you are much much better served by just replacing everything!!



So, unless you are certain that your VHF antenna, and especially the VHF coax and connectors, are all 100% working fine (which we are not), your $$$ are best spent on a new antenna, and again especially new cable and connectors!!!




c) Next, I'd like to point out the unfortunate facts that many of our "modern conveniences" of our lives these days (smart phone chargers, LED light voltage regulators, "smart devices", etc.) can be producers / radiators of RFI (Radio Frequency Interference), which can have significant negative effect on other systems on-board, primarily radio communications systems.


Now, some may think that since you have a 28-footer, and might not have a masthead tri-color light, that you might not have any of these RFI-producing devices close-enough to your VHF antenna, to have a detrimental effect, so no worries there...but..


But, you may just have some "charger", "power supply", LED light, etc. that does produce enough RFI to effect your VHF reception....(of course if you have old, poorly-shielded, coax and/or poorly-shielded connectors, etc. on your VHF system...then even if you don't have any RFI-producing device close to your VHF antenna, you can still have RFI-caused VHF reception issues...)


Please have a look here:
https://www.dco.uscg.mil/Portals/9/DCO%20Documents/5p/CG-5PC/INV/Alerts/1318.pdf?ver=2018-08-16-091109-630


And, here:
https://www.cruisersforum.com/forums/f14/tri-color-wiring-in-mast-235079.html#post3155087





3) And, specifically in regards to prajna101....as others have pointed out, it's likely that your antenna isn't even connected at the masthead, and/or the antenna (and/or masthead connection) is damaged....


Now, you could buy a decent VHF VSWR meter and jumper cable, and if you compensate for the loss in your transmission line, you could test your system out....and determine if you have a coaxial cable, connector, and/or antenna issue....but...
https://www.dxengineering.com/parts/dmn-sx40c
https://www.dxengineering.com/parts/dwa-cn-501v

BUT....

Similar to Tmacmi's case, you might be better better off, replacing your masthead VHF antenna and all your coaxial cable (and connectors)....although, in your specific case, before you buy an VSWR meter, and before you buy a new antenna and/or hire a marine radio tech to replace your antenna...I'd first recommend:


a) First, before anything else....have a close look at the coax and connector right at the back of your VHF radio...making sure this connection is good (yes, a visual inspection won't tell 'ya much, but sometimes there is something obvious)...


b) Then, take a close look at your VHF masthead antenna with a good pair of binoculars....(although your standard 7 x 50's are good, if you can borrow someone's higher power pair for a couple minutes, that might be good)....look at the VHF antenna and see if you can identify it....(usually easy if its new)....

If you can identify it, look up its specs on-line....the spec you're looking for is, if it "DC grounded" yes or no?? (Shakespeare specifically shows this for most of their antennas)

Knowing this spec, can allow you to use a simple multi-meter (ohm-meter), to measure across the center-pin and the shield....and depending on what your meter registers and what it is supposed to show, can point you to where your problem is...
{Also, when looking at your masthead antenna thru the binocs, you should be able to see if there is weather-proofing on the cable/connector/antenna junctions....}


As an example:


If you have a Shakespeare 5215, 5400, etc....this antenna is NOT a DC grounded antenna, and therefore will show an "open" connection (at least a few 100-thousand ohms), when measuring across the center-pin and shield of the coax cable...if you see a short-circuit (or intermittent), or a measurement of only a couple thousand ohms.....you have a cable or antenna issue (probably a cable / connector issue)

https://shakespeare-ce.com/marine/product/5215-ais-with-vhf-squatty-body-antenna/


If your antenna is spec'd as "DC grounded", it will show a "short circuit" when measuring across the center-pin and shield of your coaxial cable....and as such, if you measure a "short circuit", from the cable as it comes off the back of the VHF radio, you may have a good connection to the antenna, OR you may have a "short circuit" in your coax cabling!




c) Next, have a look in your bilge, at the mast step....where you'll likely have a coaxial cable junction (usually a PL-258 "double-female-connector", between two PL-259 male connectors)....

This is a very common failure point....usually, poorly assembled (and/or poorly weather-proofed) connections here...

Taking this junction apart, inspecting them, cleaning as needed....and then measuring the cable, using your multi-meter....

Measuring between center-pin and shield of the cable going up the mast, AND the cable going to the radio (disconnected from the radio, of course).....you should have an "open circuit" on the cable going towards the radio....and whatever your antenna spec's say, is what you should read on the meter, when measuring the cable going up the mast...


Doing these tests, you should be able to narrow down the problem to either:
1- "in the mast and/or at the masthead" (could be cable, connector, or antenna...or all three!)

2- "in the bilge and/or in the cabin" (could be cable or connectors)



d) Depending on what your simple multi-meter tests show (compared to what your antenna specs say the tests should show), you might need to go up the mast (actually having a trained marine electronics tech, go up the mast), and repair your masthead VHF cable connections and/or replace your VHF antenna...

{note: if you, or someone you hire, is going up the mast to repair / replace things....or even just to check things out....have a spare antenna ready-to-go....'cuz it's a relatively cheap thing to replace, compared to the costs of other things on a boat!! so, unless you find a cable/connection problem in the bilge, you're going to be well served by replacing the masthead antenna....although, this should not be done, unless you verify all your cable/connections are good, and/or all have been inspected and repaired/replaced as needed...that means replace the antenna AND replace/repair (or at least clean and verify as good) your masthead coaxial cable connector, just replacing the antenna, without verifying proper connection or replacing connection, is a waste!}



While I'm not familiar with the age of your Beneteau 462 (but, doubt it's as old as Tmacmi's Spirit), replacing old VHF coaxial cable, old connectors (with properly installed new connectors, of course), and replacing your old VHF antenna, are never bad ideas....and if you can replace your VHF mast coax yourself (not hiring professionals to go up/down your mast, etc.), using professionally installed connectors (whether locally assembled or pre-made cable assemblies, such as from DX Engineering), this entire operation will cost less than $200, all-in...

https://shakespeare-ce.com/marine/product/5215-ais-with-vhf-squatty-body-antenna/


https://www.dxengineering.com/parts/dxe-213udx075


https://www.dxengineering.com/parts/dxe-213udx025



(FYI, if you don't have the room in your mast conduit for the larger RG-213, you can use the smaller RG-8x, and only loose a bit more signal....still better than what you have now!)



Finally, please have a look at this thread, where you'll see some info on cable losses, margins, etc...as well as lots on VHF Radiowave Propagation!

https://www.cruisersforum.com/forums...ge-149499.html






I hope this helps

fair winds.

John