Troubleshooting
Two Fish Finders Interfering? How to Fix Sonar Crosstalk
Adding a second graph at the bow, a live sonar unit, or a buddy's portable on the same boat is one of the most common upgrades in fishing. It is also the most common way to suddenly get a screen full of junk: diagonal streaks, rain-like dots, curved spokes or pulsing bands that were not there before.
That noise is usually sonar crosstalk: one transducer hearing the pings of another. It is fixable in almost every case, and most fixes cost nothing. This guide explains what is happening and walks through the fixes in the order that usually solves it fastest.
How to tell crosstalk from other noise
Several different problems put junk on a sonar screen. Crosstalk has a recognizable signature, and confirming it first saves a lot of time.
| Noise type | Typical look | Quick test |
|---|---|---|
| Sonar crosstalk | Regular, repeating lines, dotted "rain", curved spokes or bands, often drifting diagonally | Turn the other sonar off; noise vanishes |
| Electrical noise | Random speckle across the whole screen, often worse when the motor runs | Turn off the trolling motor or outboard; noise drops |
| Aeration / turbulence | Dropouts, a lost bottom, clutter near the surface, worse at speed | Slow down; picture recovers |
| Surface clutter | Dense band near the top of the screen | Raise surface clutter filter; band shrinks |
The off-switch test is the most reliable. With both units running, watch the noise; then power off (or disable sonar on) the second unit. If the pattern disappears within a few seconds, you are looking at crosstalk.
Why two sonars interfere
A transducer sends a pulse of sound and then listens for echoes. It cannot tell whether a returning sound came from its own pulse or from another transducer nearby. If another unit is pinging at the same or an overlapping frequency, its pulses arrive at random times relative to your own, so your unit draws them as marks at random depths. Because both units ping at steady rates, those false marks often line up into slanted lines or repeating patterns.
CHIRP sonar sweeps across a range of frequencies instead of using one fixed tone. That improves target separation, but it also means a wide CHIRP band can overlap another unit's frequencies more easily than two old single-frequency units did. Imaging (down and side), 2D sonar and live forward-facing sonar can all interfere with each other if their frequencies overlap, even across brands.
Fixes, in the order to try them
- Turn off sonar you are not using. Many anglers run a bow graph only for maps or live sonar while the console unit is still pinging 2D, down imaging and side imaging in the background. Every active channel is a potential source of crosstalk. Disable the channels nobody is watching, or set the unit to "sonar off" if it is only a map display.
- Separate the frequencies. If one unit runs a high CHIRP band, set the other to a medium or low band, or to a fixed frequency well away from it. The goal is no overlap. Check each unit's manual for the exact ranges it uses.
- Turn on interference or noise rejection. Most units have a filter (names vary: interference rejection, noise rejection, ping interference) that discards pulses that do not match the unit's own timing. Start at a low or medium setting; a very aggressive filter can also hide small real targets.
- Change ping speed. On units that allow it, adjusting ping speed on one display can break up a regular pattern. It does not remove the interference, but it can make it less distracting.
- Increase physical separation. Transducers mounted side by side on the same transom are the worst case. Moving one to the trolling motor, or spacing transom transducers further apart, reduces how much energy each one picks up from the other.
- Use a same-brand network. On many systems two displays from the same brand can share one transducer over the network, or coordinate their pings. One transducer feeding two screens removes crosstalk entirely between those two.
A common, clean setup is: console unit runs 2D and imaging from the transom; bow unit runs live sonar or nothing but maps. If the bow unit also has a trolling-motor transducer, set it to a band that does not overlap the console's active band.
Live sonar and traditional sonar on the same boat
Forward-facing live sonar transducers transmit a lot of acoustic energy in a fan shape. Many anglers see bands or streaks on their 2D or imaging screens while live sonar is running, and sometimes the reverse. Because live sonar systems use their own frequency ranges, the fix is usually the same: avoid overlapping frequencies on the traditional unit, turn on its interference filter, and switch off imaging channels you are not using while you watch live sonar. Some systems also offer settings specifically to coordinate live and traditional sonar on the same network; check your system's documentation for the exact option name.
If you fish with a partner whose boat runs live sonar nearby, you may also see their pulses on your screen. There is not much to do about that except moving away or filtering.
Portable units and a friend's graph
Ice anglers and kayakers sharing a spot see crosstalk often, because many flashers and portable units ping on the same common frequencies. On the ice, holes a few feet apart with two flashers on the same frequency can make both screens unreadable. Options include:
- Switching one flasher to its alternate frequency, if it has one.
- Using the interference rejection setting most flashers include.
- Spacing holes further apart.
- Agreeing to run one unit on a narrower cone, which focuses energy and listening into a smaller area.
When it is not crosstalk
If the noise stays with every other sonar on the boat switched off, look elsewhere:
Electrical noise
Trolling motors, bilge pumps, fuel pumps, alternators and some LED lights can push electrical noise into the sonar. Signs: the noise changes when a device is switched on or off. Fixes include running the fish finder from its own battery or a clean dedicated circuit, separating the transducer cable from power cables, and checking the ground connection.
Aeration
Bubbles across the transducer face cause dropouts and clutter, mostly at speed. That is a mounting issue (transducer height, angle, or location behind a strake or rivet line), not interference.
Cable damage
A nicked or crushed transducer cable can let water in and cause intermittent noise. Inspect the full length, especially where it passes through hatches, under seat bases and through cable clamps.
Planning a two-unit boat to avoid crosstalk
If you are about to add a second unit, a little planning prevents most of the headache:
| Decision | Lower-crosstalk choice | Why |
|---|---|---|
| Brand | Same brand, networked | Lets units share a transducer or coordinate sonar |
| Bow unit's role | Maps or live sonar only, or sonar from the console | Fewer active transducers in the water |
| Transducer spacing | Transom plus trolling motor, not two on the transom | More distance, different aim |
| Frequencies | Different bands per unit | No overlap to pick up |
| Power | Clean, fused circuits away from motor leads | Rules out electrical noise as a second problem |
Networking requires compatible cables and sometimes a network hub or adapter; check which network type your units support before buying.
Wrap-up
Crosstalk is a nuisance, not a defect. In most boats, switching off unused sonar channels, separating frequencies and turning on interference rejection clears the screen in a few minutes. If you are planning a two-unit setup, keeping both units in the same brand's network and giving the bow unit a clear role prevents most of the trouble before it starts. And if the noise survives the off-switch test, look at power, cabling and aeration instead.
FAQ
Can two fish finders of the same brand interfere with each other?
Yes, if both are pinging on overlapping frequencies from separate transducers. Same-brand units are easier to fix because they can often share one transducer over a network or coordinate their sonar.
Does interference rejection hide real fish?
At aggressive settings it can filter out small or faint targets. Use the lowest setting that cleans up the screen.
Why do I only see interference when another boat is nearby?
Their sonar is reaching your transducer. Changing your frequency band and using interference rejection usually helps; moving a little further away helps most.
Will running live sonar ruin my side imaging picture?
It can add bands or streaks if frequencies overlap. Turning off imaging channels you are not watching and using interference rejection on the traditional unit is the usual fix.