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VHF reception.

Old 04-25-2008, 04:02 PM
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Default VHF reception.

I put a new Standar Horizon VHF on my boat last year with a Shakespeare Galaxy 8' whip. I noticed last year that I was able to transmit to friends several miles away but not receive them well. I am finding that again this year. I notice Channel 65 for some reason always sounds like the squelch is turned up or someone has a keyed mike. Today when I docked my boat and shut off my Raymarine C80-gps fish finder and radar I noticed that 65 did not sound keyed. I couldn't really check the radio because I am too far up a river to find anyone to do a radio check. Is it possible that the GPS is causing the receiving problems? My VHF antenna is mounted around 4' away from the GPS antenna which is flush mounted on the cabin roof. The radar is usually off so I don't think that is a problem. I am also wondering about the connection to the antenna. I appreciate any input..Artie
Old 04-25-2008, 05:50 PM
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Default RE: VHF reception.

A bad antenna connection would be the first suspect. A bad solder joint at the connector on the end of the coax is deadly. Most likely that is your problem. Most returns of radios to the shop result in "no problem found" because the problem is the antenna connection. It is worth it to solder on a new connector as a first step in diagnosing the problem.

After that, make sure the power supply is solidly connected. If those are not the problem, there is not much else you can check. There could be a break in the antenna cable along the way. Try connecting another antenna and cable and test it. Even better is get an SWR meter and a dummy antenna to test with. Not too expensive online. Don't ever key the mike with no antenna connected! That will fry the radio.
Old 04-26-2008, 01:45 PM
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Default Re: VHF reception.

I went to the boat today and went over all the wiring. I took the antenna wire out of the harness it was in and ran it direct to the back of the radio. All connections were good on GPS and Radio. When the GPS is on there is nothing but static on channel 65A the second you shut off the GPS the static stops. Somehow the GPS is interfering with the VHF reception. Any thoughts?..Artie
Old 04-26-2008, 07:32 PM
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Default Re: VHF reception.

The GPS antenna is a receive only antenna so it is strange that it is interfering with your VHF reception, does this happen on only one VHF channel, or across all the VHF channels?

Even though the GPS antenna is a receive only antenna, it does contain active components that can cause RF emissions.

The best way to check you VHF antenna/line is to put a test set like a Bird wattmeter in line with the antenna lead and transmit into the antenna, if the SWR or reflected power is low I would believe the VHF/antenna/line is OK

Has this always happened or did it just start up?

Jim
Old 04-26-2008, 10:17 PM
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Default Re: VHF reception.

I noticed last year when i put the radio in that I could transmit alot greater distance than I could receive and suspected a problem. A friend of mine monitors channel 65 and I went fishing with him this year. The whold time on 65 it sounded like someone had a keyed mike. When I got to the dock I shut the GPS unit off and the static on 65 stopped. I turned the GPS unit off and on a few times to make sure. Nothing but static on 65 while the GPS is running.
Old 04-27-2008, 04:15 AM
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Default Re: VHF reception.

Fireguy

If you are convinced that your VHF antenna connections are good, ie coax to connector, then you need to check your "grounds" and make sure these are good. Two problems that can occur are loose and/or corroded connections, another could be that there is too much of a load on the guage of wire coming from your batteries resulting in a poor ground and noisy connection.

I would test this by first replacing the antenna coax connector, if that doesn't solve the problem, I would then run a temporary power connection from the VHF to the battery, if that cleans up your channel 65 then you know your problem is in the DC power system.

Hope this helps

joe
Old 04-27-2008, 06:00 AM
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Default Re: VHF reception.

First make sure your radio is in the "US" position, and that you are actually receiving "65A".

In the "International" position, Ch 65 would be set to receive 160.875, which is allocated outside the marine band in the States. A legal signal on 160.875 could cause the signal you're reporting.

Of course, in the US, 65A is allocated to "Port Operations," and would not generally be available for non-commercial use, but that's another subject....
Old 04-27-2008, 09:23 AM
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Default Re: VHF reception.

Borrow a handheld VHF and see if the noise increases as you move closer to the GPS unit. Disconnect the GPS antenna from the GPS and see what happens.
Old 04-27-2008, 09:50 AM
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Default Re: VHF reception.

It is definately on US i checked it yesterday. I am not getting good reception on all channels and intermittent noise when the GPS is on. I dont usually go on 65 but a few guys who are from my dock do. I will try disconnecting the GPS antenna and the handheld those are good ideas. Thanks for the input so far.
Old 04-27-2008, 03:02 PM
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Default Re: VHF reception.

You just need to get somebody to put a test unit in line with your VHF and antenna to find out for sure if you have any issues. Than go from there, otherwise you are just shooting in the dark.

Jim
Old 04-27-2008, 03:20 PM
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Default Re: VHF reception.

Went by the boat again this evening. I unplugged the GPS antenna and still same problem with GPS on stops when you shut GPS off. I checked the sheild on the Power cable to the GPS and its grounded. I emailed both Raymarine and Standard Horizon. I will wait to see what they say. Thanks for your replys...Artie
Old 04-27-2008, 10:58 PM
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Default Re: VHF reception.

Sounds like a possible "birdie". All electronic devices can create a radio signal. This is why so many things have FCC approval stickers on them, even if they are not radios.

Your GPS could be throwing out a birdie on channel 65A. The birdie is in the circuitry of the GPS itself, not the antenna. This would explain why it is there when the GPS is on - antenna connected or not. If you had a frequency counter you could confirm this on your own.

If this is the case, Raymarine should correct the problem for you. You may end up with a new GPS.

I suspect birdie because the interference is limited to one channel. If it were wide band (across all VHF channels) then it would likely be something else.

Get a radio tech to check your antenna. There is a simple piece of equipment that they can use to test forward and reflected power. If the antenna is the problem then it will show up fast. Also have them solder on a new connector just for good measure. Connectors go bad. It is normal.
Old 04-28-2008, 03:54 AM
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Default Re: VHF reception.

I do not believe the interference is limited to one channel. I think its obvious on one channel. I am not getting good reception on all channels. I am going to solder a new connector on the VHF antenna because i cut the old one off to pull the wire out of the harness to rule out it being too close to the power wire for the GPS. The birdie theory sounds possible. Artie
Old 04-28-2008, 05:17 PM
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Default Re: VHF reception.

Thanks for your replys. I took the GPS unit up to Raymarine in NH today and they did in fact find it was the problem. The couldnt get a hand held within 6 feet of it without interference. They opened the unit up and tightened all the grounds and placed suppression ferrites inside the unit and changed out the back case. They said the back case is painted on the inside with special paint that contains emissions. He said he was then able to hold a handheld VHF right up to the unit. Thanks again..Artie
Old 04-28-2008, 05:49 PM
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Default Re: VHF reception.

Very interesting . Thanks for posting the followup on the confirmation of the problem and the solution. Nice you were able to drop in on the RayMarine compound.
Old 04-29-2008, 05:55 PM
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Default Re: VHF reception.

More bad news. I installed the unit again tonight and same thing as before. I guess I will head back to Raymarine tomorow.
Old 04-29-2008, 07:45 PM
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Default Re: VHF reception.

Don't mean to hijack the thread but I am having a similar problem. Everytime the motor is running I get a constant buzz from my VHF on all channels. I shut the motor off and it is fine....does anyone have any ideas on what could be causing this?
Old 04-29-2008, 08:10 PM
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Default Re: VHF reception.

That sounds like a ground problem to me.
Old 05-02-2008, 05:45 PM
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Default Re: VHF reception.

Just an update for anyone who cares. I finally have the problem completely resolved. Raymarine replaced the C80 and the problem was around 80 percent better. I was able to squelch out any interference but there was still some from the C80. I spoke with a gentleman at Voyager Marine in Essex Mass who suggested I move the antenna. He stated the display can throw off a frequency and he had me test this by facing the unit away from the antenna which in fact stopped the interference so I moved the antenna 3 feet toward the aft end of the cabin roof and the problem is completely gone. Thanks again for your reply's.
Old 05-03-2008, 06:09 PM
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Default Re: VHF reception.

glad you got your problem solved. However...
A properly designed unit should never do this - at all. A nice Black Mark is deserved for the C80.

Woody

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