gps interfering with vhf

[Lowranger]

My GPS, a 10 year old Lowrance Global Map 1000 fixed chartplotter, is creating a pulsing, musical interference on my new VHF(Horizon Intrepid). It did the same thing with my old Horizon Explorer. This forces me to turn the squelch way up. The GPS receiver(antenna?) is a 5 channel Lowrance(Rockwell type) that is mounted on the port side of my C-Dory Cabin Cruiser. The display itself hangs from an overhead shelf. It's receiver and power supply leads run to port. The VHF is mounted atop the shelf. It's antenna and power supply leads run to run to starboard. The Shakespere 8' f.g. antenna is mounted to the starboard side of the house. Question? Is the VHF picking up this noise through it's power leads, antenna leads, or it's housing? Are their filters for the power leads, antenna leads, or both that I should be using? On a boat this size(22') electronics are crowded but I've tried to keep the wiring/antenna leads seperate. Interestingly, my fishfinder(20 year old Lowrance X-50) is directedly beneath the VHF but causes very little interference. Suggestions? Pete

 

[kd6nem]

Re: gps interfering with vhf

You're thinking along the right lines. Try whichever suggestions are easiest/cheapest first and work through one step at a time to identify and solve the problem. If your antenna coax is cheap and not well enough shielded that can create problems. Are you using the same coax as before? If this is the case and it is easily replaceable do so. When finished use amalgamating tape to waterproof the connections. Borrowing another coax for test purposes can be cheaper than buying before trying, though it shouldn't be too terribly expensive. The braid is rated in percent shielding, and the cheap stuff is common but not worth having. Do not run too much extra coax if you can help it. Another thing to try is to put filters inline with the power leads. Wrapping a donut torroid 4 or 5 times (at least) with the power wires works well so long as you can convince the connectors to go through the center of the donut. Mount the filter as near as possible to the VHF rig. Right where it goes into the box is ideal. The other culprit might be the remote display. Try temporarily moving it and see what happens. You are wise to try to keep your antenna coax separated from everything else. If you have any wires to the remote (or anything else) tied up and running alongside your coax even a short distance separate them. They may need some space between them. Any time two wires (with other than direct current) run together parallel for very far the signals tend to bleed together. Crossing at right angles, shielding, or separating are the answers for this, although twisting actually is what is used inside phone and computer cables. Twisting tightly is probably not the way to go in your case. There are more extreme measures like bandpass filters but it is more likely something simpler like what is mentioned above.<br /><br />Let us know what you find out!

 

[Lowranger]

Re: gps interfering with vhf

B.P., Thank you for the indepth reply. I'll follow your suggestions and see how it goes.