How to measure/diagnose/cure weak VHF output?

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jfm

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I suspect my VHF output is weak. For the last 2 weeks cruising in company, other boats owned by friends have only been able to hear me when very close. Even my tiny handhelds work better. Receiving seems better, though not great. I have not accidentally selected 1w transmit; the 25w is clearly showing in the display

Also my boat doesn't show on marine traffic despite ais transmit being activated, and using the same antenna as the voice VHF. This suggests my ais transmissions also have weak range and are not reaching the base stations, which points to a problem with the antenna or antenna wiring. That all looks ok on visual inspection

The position of the antenna is ok: my previous boat worked fine and shows reliably on Marine Traffic

I think this problem has existed since boat was new ( boat is 2013 squadron 78 with garmin 300vhf and garmin 600 ais. Boat antenna is in the standard position)

So, what do you think might cause this? Loose connections? Faulty antenna? Is there a meter I can buy that measures the output signal strength? Thanks for any ideas
 
Hi John, I have an AIS 250 installed and used the inbuilt splitter to run the AIS off the existing VHF antenna. Having read the manual, I decided to install a separate antenna for the AIS as Raymarine suggested VHF range could be adversely impacted using the splitter. That's where I'd start, disconnect the AIS and see if your VHF range improves when the radio is the only thing connected then take it from there depending on the results.
 
I recently had my Raymarine 240E repaired - it was ok on 1W, but transmitting on 25W sounded like the daleks were invading.
Quite hard to test without the right kit, and it turned out that water intrusion had killed the base unit at some point (a FW drip that was later repaired), causing a very weak signal on transmit.
 
An SWR meter will show you where the power is getting lost if you insert it between the antenna and the coax and work your way back to each join.
Removing the splitter would be my first test though.
 
Presumably to test the output the coax needs plugging into an oscilloscope or trace analyser. Suspect most water front marine engineers might not be up to that level of electronics diagnosis.

I'd look very very carefully at the joints with specific regard to water ingress and stray wires from the outer shielding.
 
My very first action would be to start at the beginning. Is the entire set up receiving a good healthy 13.8 volts and sufficient amps to power the system. It is not unknown for the original installation to have not been put in properly in the first place. A quick test call across the car park at the factory is a little less demanding than calling a boat 5 miles away with all the other systems drawing power.
We need decent connections on everything, a loose terminal butt connector or fuse etc which has come loose over time or a little corrosion on a earth bus may let the radio work perfectly OK on RX but when you want to TX either on your VHF or perhaps AIS the volts will drop away pronto.
Only then would I work up the food chain looking for obsqure and exotic faults.
Aerials go wrong very rarely,plugs are more usually the problem.
Can you get to back of radio ?.Even the cheapest of budget multimeters will indicate if there is a big voltage drop (a bad thing) when you transmit on the radio. You should see a constant 13.8V (ish) and it should only drop by a volt or two max when you key the mic. If the volts drop right away it is power problem.If all Ok search elsewhere.

We had a chap in yesterday with a "feed back " problem on his radio, apparently this problem had occurred on this radio ever since we had sold it to him, despite it being installed in two or three different cars over several years.
Obviously we had been selling duff gear.
After a quick look it turned out to be a poor electrical connection.
Radio OK on RX but when driver transmitted, volts disappeared, set turned itself off and bleeped when in came on again.
Quick squeeze with a set of crimps...and Hey Presto the long suffering driver was able to use his radio without "feedback".
Just call me Sherlock Pro Bono blimming Holmes.:)

Ps.Testing for short circuit across the aerial plug will only lead to confusion,it can indicate a short.It is the way some aerials are designed.
 
Last edited:
SWR meters can only test within the system (ie. break a cable and see whats happening at that point)

Something like this measures outside of the system.

http://www.radioworld.co.uk/MFJ-801...y_hwl_rD5hrFprBdwRraWevTlnEMB9jA0QhoCIZjw_wcB

http://www.radioworld.co.uk/MFJ-802...ISP3pH7bNUAyE2cIUwDqSuDslNoiwgfnnGhoCBf_w_wcB

http://www.ebay.co.uk/itm/like/2513...ff3=1&ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=108


Be careful however. As these are simple, cheap instruments they are affected by a lot of factors including your own body and the reading is really only an indication, not an absolute.

They can also be measuring a signal that you do not intend to measure (Bluetooth/WiFi/Cellular/RF noise).

I had an incident many years ago with a professional field test meter. After the big radar at Heathrow was installed controllers in the old tower were concerned they were being irradiated. Therefore we brought in a meter to measure the field in the glass house. Sure enough the meter went off the scale! After a bit of hurried and concerned investigation the stray RF was traced to a faulty fluorescent tube in the room underneath the measuring point.

Martin
 
This might help: http://www.saltyjohntheblog.com/

First job is to identify whether it's an antenna or radio problem. Take your radio to a known good antenna or bring a known good antenna to your radio.

If it's the antenna, then quite likely to be a corroded or shorted connector - disconnect at antenna and splitter and check there is no circuit between PL259 body and centre pin. If you can get both ends of the cable close enough to each other you can also check for continuity between centre pin and centre pin, and braid and braid. Usually only possible with a short cable run.
 
Checking antennas and cables for me is the 2nd step.. first you need to decouple the radio from the AIS as previously advised to take that out of the equation, it's a very quick and simple job to do. just disconnect the antenna from the AIS, disconnect the cable between the radio and AIS and reconnect the Antenna to the radio, 2 minute job

If the radio is still not performing as expected, then further diagnose with any of the above approaches but as mentioned, it's usually a connector issue or a capacitor in the radio. iCOM recently repaired mine due to a dud capacitor. the radio could receive fine but would only transmit a strong signal on certain channels

p.s. I think John has Garmin throughout on his boat rather than Raymarine
 
oGaryo said:
Checking antennas and cables for me is the 2nd step.. first you need to decouple the radio from the AIS as previously advised to take that out of the equation
Click to expand...
+1.
Actually, I would use separate aerials regardless of whether that's the (only) problem or not - as you also did.
 
Just a comment on AIS
As you know we all use class B and there are limitations
Class B only transmits about every 30secs - much less often than class A
In my ecperience, ship to ship class B AIS is very poor
If you are using poor AIS transmission as a test that your system isn't performing, I suggest that you do some other tests

My VHF system is built round the Simrad RS 87 which I don't rate ag all
I have just removed it to send it off fir repair - only transmits - no receive
 
mlines said:
SWR meters can only test within the system (ie. break a cable and see whats happening at that point)

Something like this measures outside of the system.

http://www.radioworld.co.uk/MFJ-801...y_hwl_rD5hrFprBdwRraWevTlnEMB9jA0QhoCIZjw_wcB

http://www.radioworld.co.uk/MFJ-802...ISP3pH7bNUAyE2cIUwDqSuDslNoiwgfnnGhoCBf_w_wcB

http://www.ebay.co.uk/itm/like/2513...ff3=1&ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=108


Be careful however. As these are simple, cheap instruments they are affected by a lot of factors including your own body and the reading is really only an indication, not an absolute.

They can also be measuring a signal that you do not intend to measure (Bluetooth/WiFi/Cellular/RF noise).

I had an incident many years ago with a professional field test meter. After the big radar at Heathrow was installed controllers in the old tower were concerned they were being irradiated. Therefore we brought in a meter to measure the field in the glass house. Sure enough the meter went off the scale! After a bit of hurried and concerned investigation the stray RF was traced to a faulty fluorescent tube in the room underneath the measuring point.

Martin
Click to expand...

Never needed to use a field strength meter. I built antennas and aerial systems when I worked in small scale broadcast systems (and still do occasionally) a SWR meter will work fine. If you really want to measure from the outside in then you should use a spectrum analyser. Those MFJ devices are so basic, they are not even worth trying.
 
jfm said:
I suspect my VHF output is weak. For the last 2 weeks cruising in company, other boats owned by friends have only been able to hear me when very close. Even my tiny handhelds work better. Receiving seems better, though not great. I have not accidentally selected 1w transmit; the 25w is clearly showing in the display

Also my boat doesn't show on marine traffic despite ais transmit being activated, and using the same antenna as the voice VHF. This suggests my ais transmissions also have weak range and are not reaching the base stations, which points to a problem with the antenna or antenna wiring. That all looks ok on visual inspection

The position of the antenna is ok: my previous boat worked fine and shows reliably on Marine Traffic

I think this problem has existed since boat was new ( boat is 2013 squadron 78 with garmin 300vhf and garmin 600 ais. Boat antenna is in the standard position)

So, what do you think might cause this? Loose connections? Faulty antenna? Is there a meter I can buy that measures the output signal strength? Thanks for any ideas
Click to expand...

JFM,
Some quick checks I would do in your situation.
1. from description suspect you are right that problems points to cabling or antenna since both VHF & AIS appear to have similar issue. (most likely cabling joints)
Confirm by checking range on low power 1W it should be greatly reduced also if its antenna and cabling. Test/compare using handheld to a handheld in bowels or onshore, then your VHF on 1W to a handheld in same location.

2. If confimed low range then check antenna cabling for any obvious damage/corrosion/ingress.
If you have splitter mentioned in previous posts I would disconnect "antenna side" cable and disconnect cable at the antenna to isolate the cabling. Then put a multimeter "measuring resistance" across inner pin of cable and the brade to check for short cct and try to isolate.

3. Even if no obvious short I would still double check all my connectors as most common fault is leakage due to faulty N type connectors caused by weathering and/or poor installation.

If all seems ok,

4. Test VHF system by removing splitter and connecting direct to antenna. You generally lose aroung 3dB through these splitters and they are the next most common fault.

Next it may be time to delve deeper,

5. You can pick up a a wattmeter for £25-£35 which would go inline and measure power at various points in your system.
 
Many thanks everyone for this really useful info, and sorry for my slow reply

The 12v power supply is good - no problems there. JTB has kindly offered me the use of his SWR meter so I'll apply that as soon as I get the opportunity, and check all the antenna connections. I'll report back. Thanks again everyone
 
Hi JFM
Im assuming your using Garmin,
I thought the garmin 300i was combined antenna (built in ais. No sperate antenna for ais or splitter)
I assumed it would be a single cable to vhf antenna with your black box radio unit doing the rest.
 
Robg71 said:
Hi JFM
Im assuming your using Garmin,
I thought the garmin 300i was combined antenna (built in ais. No sperate antenna for ais or splitter)
I assumed it would be a single cable to vhf antenna with your black box radio unit doing the rest.
Click to expand...
hi Rob. Nope, the 300i is AIS Rx only. I have 600 which is Tx and is in a separate grey box from the 300 VHF set. Iirc the splitter is integrated within the 600; there isn't a separate splitter unit. You connect a short coax lead between the 300 and 600 then you plug the main antenna into the 600. I think...

I had identical gear on the last boat and it was fab. I've likely just got a bad connection on this boat and I need to find an hour or 2 to track it down! I'll report back
 
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