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Old 11-24-2005, 05:19 PM
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Default GPS causing interference in VHF radio

I have a new Uniden 525 radio and a Garmin GPS Map 230. If I turn the GPS on it is causing static on the radio. It is not constant static but rather a short crackle every couple of seconds. It is also causing any reception that is less than asuper strong signal to just get garbled in static.

Here is what I have tried so far:

1) Changed the connector on the radio antenna cable.

2) Removed a splice in the GPS antenna cable and put on a new connector

3) Moved the electrical connections for the radio to another bussbar and rerouted the wires away from the GPS.

4) Put the interference reducing magnets on power and antenna leads for both radio and GPS.

None of this has worked. I have narrowed it down to the GPS coax cable because when I disconnect the cable from the GPS the interference stops even if the GPS is still on. So I don't think that it is an electrical issue.

My problem is that the GPS and radio cables run together through a T-top tube from the electronics box to the antennas on the T-top. Due to the design of the tubes there is no easy option for me to seperate the two wires other than runnning one of them throught the bilge and up a tube that is on the opposite side of the boat. Not an easy thing to do.

Any suggestions on how I can fix this? It is driving me nuts!!
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Old 11-25-2005, 09:22 AM
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Default Re: GPS causing interference in VHF radio

Everything you have done so far is exactly right.

Are there any ground studs, lugs, or wires on the two pieces of equipment? If there are, before you go any further, make sure they are all grounded.

You need to learn two things, Where is it coming IN, and where is it coming FROM.
solving either one will solve your problem.

For both pieces of equipment, it will be either the Antenna, the cables, or the Chassis.

Try disconnecting your VHF antenna and see if the problem goes away.
Do NOT transmit, but it will be fine to just receive and listen.

If the problem goes away, you are actually picking it up off the air, if it does not go away, then disconnect the cable from the back of the radio, if it still does not go away, it is coming right into the chassis, or other wires, Look into other things, like speaker wires, DSC interface wires, Maybe a hailer, or an intercom?

If it is the Antenna, I would run a temporary antenna and cable from your radio, just to see how far away from the GPS you have to get before the problem goes away.

Next thing to know is where is it coming from? GPS antenna, or GPS cable, or GPS box
Try wrapping your GPS antenna with tinfoil. It is a RX only antenna, so it won't hurt it. Be sure the foil is grounded.

You can also use the foil to wrap the radio or GPS chassis. If that cures it, then take things loose and see how far you have to relocate them to make it go away without the foil.


It helps if you wear a tinfoil hat yourself while you do this, actually, That part is not true, but all the rest is.

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Old 11-25-2005, 01:19 PM
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Default RE: GPS causing interference in VHF radio

FWIW, I had a similar issue with a Uniden radio. Eventually I switched to a Standard Horizon and the problem disappeared. That may or may not work for you, but I thought I'd pass it along.
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Old 11-25-2005, 03:10 PM
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Default RE: GPS causing interference in VHF radio

Yep- probably the Uniden.

They have HORRIBLE noise suppression and adjacent channel rejection specs.

Quick check is to turn up the squelch when the GPS is off. Turn it up just until there is no noise. Then turn on the GPS. If the VHF makes noise again (exceeds the set squelch), it is definitely the radio. You can try additional noise suppressors, live with it, or ditch the radio.

I would get an Icom or Standard and consider that Uniden a lesson in what not to buy for a VHF.
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Old 11-26-2005, 11:24 PM
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Default Re: GPS causing interference in VHF radio

vvreddy- FWIW, I believe what you are describing is most often caused by a F/F or depth sounder signal. Is it possible your "GPS coax" is picking up the signal from one of those and transferring it to the radio cable nearby? If so , isolating/rerouting the transducer cable or using seperate power sources for sounder and GPS/Radio may help.
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Old 11-27-2005, 03:18 PM
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Default Re: GPS causing interference in VHF radio

Thanks everyone for the suggestions.

dwg2116, I have established that it is coming in from the GPS antenna cable. When the GPS is on and I disconnect the cable the static stops. I will try the relocating but it is going to be a pain.

TTaxi, it isn't the F/F as it makes no difference in the static whether it is on or off.
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Old 11-27-2005, 08:46 PM
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Default Re: GPS causing interference in VHF radio

Quote:
vvreddy - 11/27/2005 3:18 PM Thanks everyone for the suggestions. dwg2116, I have established that it is coming in from the GPS antenna cable. When the GPS is on and I disconnect the cable the static stops. I will try the relocating but it is going to be a pain. TTaxi, it isn't the F/F as it makes no difference in the static whether it is on or off.
You may be right, but not necessarily,

The Antenna itself has circuitry in it, possibley a pre amp, possibly also some sort of data communication going on between the main unit and the antenna. When you remove the cable, you also remove the power source and "power down" the antenna, so it is hard to tell if it was the cable, or the body of the antenna that was allowing a signal to radiate.

If it is indeed the cable itself, that is a relatively easy fix. if there already is a shield, make sure it is grounded. If there is not a shield, you can add one. Put the whole cable inside a tinned copper braid, and add heatshrink over the top of that. volia, sheilded cable.

However, I will bet, that the interferance is antenna to antenna. Your VHF cable is already shielded, so if the GPS cable was the source, the VHF cable itself should not be very susceptible, and since the whole shebang is inside an aluminum tube, it shouldn't get outside the T-top tube to affect the VHF antenna itself anyway. All that was assuming you do have a good ground on your VHF.
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Old 11-27-2005, 09:09 PM
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Default Re: GPS causing interference in VHF radio

got any splices in these wires?
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Old 11-28-2005, 09:32 PM
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Default Re: GPS causing interference in VHF radio

dwg2116, you make some good points. Couple of things--- I don't see how I would ground the shielded cables (for VHF and GPS), they just connect tothe antenna on one end and the units on the other. I presume the grounding is provided by the units? There is no connection to ground the radio either, other than making sure that the negative has a good connection. I presume that's what you mean by grounding?

Glen E, I did have a splice on the GPS cable which I removed and attached a new gold plated connector.

I wonder if Unidens are just crappy radios like a couple of the others said

This is a brand new UM 525 which is one of their higher end models.
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Old 11-29-2005, 11:17 AM
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Default Re: GPS causing interference in VHF radio

Quote:
vvreddy - 11/28/2005 9:32 PM

dwg2116, you make some good points. Couple of things--- I don't see how I would ground the shielded cables (for VHF and GPS), they just connect tothe antenna on one end and the units on the other. I presume the grounding is provided by the units? There is no connection to ground the radio either, other than making sure that the negative has a good connection. I presume that's what you mean by grounding?
Yes, you "should" have good grounds through the units power cables, but obviously not good enough, or something is not connected. Also, some power wires, particularly the GPS can be very tiny. RF noise likes a very large conductor to travel down, it may not even attempt to drain down something small like a 22 ga wire.

Perfect would be a dedicated RF only ground strap mounted on your boat, but odds are zero that you have anything like that. If you have a DC ground bus in your console, that will be an adequate place to go to. using just regular old 12 ga. stranded house wire, you can hook temporary jumpers from the outside shells of the antenna connectorcables to the ground, then, use a square of aluminum foil and wrap the GPS antenna, and ground that also. you can even wrap the chassis itself of the VHF, and the GPS.

Now obviously, you are not going to leave any of this in place, but it will help you find out exactly what it is that is causing your problem. Remember, the GPS is radiating, and the VHF is receiving, It is best to block the source, rather than the "victem" but you can do what ever works.

Once you find it, then you make a nice neat, clean fix with marine appropriate materials.

assuming it is antenna to antenna, it may help you to know that antennas couple very well when they are side by side, they do not couple well at all then they are one above the other. A short extension of your VHF, or a lowering of your GPS could be the answer.
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