VHF Distortion

[dragula65000]

I Have an Eclipse GX1000 VHF radio on a center console. I have an antannae made for CC's and is 4'long, mounted on the holding bar around the windshield. I also have a lowrance GPS, and the antannae for it is about a foot or so away on the same bar. I also have an am/fm radio onboard as well. When the GPS is on and the VHF, I get static on the channels and worse when the GPS map is up, but not so bad when only the sonar page is up.
When I transmit with the am/fm radio on, I get feedback thru the speakers, and when the am/fm is off, I get feedback thru the VHF itself while transmitting. I don't think I can transmit at all, but can recieve. I have each component on its one wire, not wired up to each other, but all wired to the same power point. I tried a seperate connection and still the same problem. It worked great before, but now is slowly going south. When the GPS is off, VHF is fine, but distortion is there. I am pretty sure it has to do with the GPS antannae. Any suggestions?

 

[NYBo]

Re: VHF Distortion

I get feedback thru the VHF itself while transmitting. I don't think I can transmit at all, but can recieve.

I'm confused by the first sentence I quoted, but putting your whole post post together leads me to believe your VHF radio or its antenna cable is bad.

 

[Bluesail661]

Re: VHF Distortion

It sounds like you might have a couple of issues. The first is the VHF itself.

I would suggest having it bench tested to confirm it is working correctly. An electronics shop should test to see if it is putting out it's full power of 25watts. They can do this by hooking it up to a BIRD watt meter and another antenna or a dummy load and keying the mic. If your antenna is bad which it sounds like it might be, the result might have damaged the radio. They can also test the antenna to see how much of the power is actually making it out of the antenna and how much is actually being reflected back into the boat. This may be the reason for the feed back and why you can rx transmissions but cannot transmit. The signal is not leaving the boat and the VHF wants to put out 25watts when you key the mic so it has to go someplace.

Regarding noise when the GPS is on... Couple of things to try. First, separate the VHF power from that of the GPS. Problem still there? If so, check the case ground on the GPS and make sure it goes to an earth ground and not just to DC ground. If all else fails, simply hang a wire over the side so it touches the water and connect the other end to the GPS earth ground. If the problem remains, it may be nessesary to move either the GPS or the VHF away from each other. It sounds like the display is emitting some RF that is interferring with the VHF. Is this a CRT(TV TUBE) type display or an LCD (flat screen)?

Hope this helps,

Chuck

 

[twistedshadows]

Re: VHF Distortion

back in school when doing my avionics class i remember that each antenna has to be spaced a certain distance apart based on its broadcast range. gps being a very high frequency receiver needs less room then a vhf if i remember correctly. so maybe you just need to move the the antenna's away from each other (should be very easy to test). as previously stated could also be feed back in the power or grounds on ether unit. i dont think the gps even if it is a tube display would put out enough energy to cause the kind of distortion the op is talking about. could also be a damaged unit as stated or even the antenna or cable (id do a quick check with a multi meter to make sure the cable isnt shorted) if the cable or antenna are messed up i would defently take the unit to a shop to make sure it wasnt damaged.
joe

 

[dragula65000]

Re: VHF Distortion

Well I tried it this past weekend. I have each component with a seperate ground, and with the engine running, I'm able to transmit with the outboard running just fine, and range is around 4 miles clear on both ends. I get the LO BATT status when the engine is off and the GPS battery status tells me I am getting around 11 volts, so I'm thinking without the outboard running, stereo on, and GPS on, I figure the amp draw is too much for the battery. Not too sure, but on both high and low selection with the outboard running, I have no problems, except for a little static when the GPS is on. I have a bigger battery with a higher amp reserve, so I'll try that next. It is a 2 month old radio and antannae, so I doubt its that, but with boats ya never know.

 

[LippCJ7]

Re: VHF Distortion

Did you terminate the coax or are you using factory terminated coax? can you disconnect both ends and check continuity? One more thing do you have a roll of extra coax near the same electronics or the associated cabling of those electronics your having an issue with? Your battery could very well be an issue but these are other things I would check as well. 4 miles on VHF is nothing you should do much better with 25 watts in my experience on open water.

 

[dragula65000]

Re: VHF Distortion

AS a matter of fact, I have extra wire tucked down underneath the console. I didnt cut it becasue I plan on possible getting a t top, and that antannae wire is near the gps wire, so I may move that as well. Never even thought of that.

 

[twistedshadows]

Re: VHF Distortion

yes two antenna wires running next to each other WILL cause distortion, hell a antenna cable next to anything with varying current will cause distortion (like speaker wiring).
joe

 

[ChampionShip]

Re: VHF Distortion

If you still have an issue with voltage it may be a good idea to run a 2nd battery for your electronics- from the sound of it I would run the gps/sonar and am/fm on its own battery and the outboard/vhf on one.....however you want to rig it.

I had an issue with noise in my vhf when I added a 2nd sonar to my boat this year, the fix was my wrapping my vhf antenna with adhesive backed silver foil hvac tape.....just needed something to insulate the noise and it worked like a charm.

 

[dragula65000]

Re: VHF Distortion

I'll be moving the antenna wire, coating it with the tape, and figurin out something with the batteries so that should all fix the problem. Thanks a bunch.

 

[Bluesail661]

Re: VHF Distortion

Based on what you describe above, you have some kind of voltage drop when the engine is not running which means your battery is done or you have a poor connection someplace in the system which is masked when the engine is charging at its normal rate.

You still seem to be getting some noise from the display on the GPS. My guess is that anytime you change screens on the GPS, the static on the VHF drops out until the GPS screen fills again. Check the earth ground and ensure this is properly connected to a proper earth ground.

If you change batteries, make sure that what ever you have charging it is up to the job. Adding battery capaicty is ok if you can charge it. I don't think the electronics you mention should have mutch of an effect on a good battery.

Hope this helps,

Chuck

 

[wire2]

Re: VHF Distortion

The working frequencies of those 3 units are vastly different; broadcast FM is 88-108 MHz, VHF radio is 156-174 MHz and GPS is 1575 MHz. There should be little interference between them, although you are pushing it a bit with only 1 ft between 2 of the antennas.

I'd start with an SWR meter on the VHF radio antenna to see how good (or bad) the SWR is. 4 miles range suggests it's far from 1:1
If it's greater than 2:1, temporarily remove the other antenna, see if it improves.
Also undo the PL 259 conector, see if there's any corrosion in there.

Then it's a good idea to have a ferrite choke on the each + power lead (red wire) on each unit to trap RF from the 12v wiring.

One other thought; 2 antennas in close proximity will affect the directional characteristics of each. A shorter antenna will act as a director to the longer one, the longer one will act as a reflector for the shorter.

 

[LippCJ7]

Re: VHF Distortion

Well? come on man this is an electrical problem we need updates!!