Doc Sonar Cross talkWhy does my GPS/Sonar Unit screen show vertical lines on it after I turn on my other GPS/Sonar Unit? When 2 sonar units are sending sound at the same frequency you can get cross talk. Each transducer is sending (pinging) and receiving sound; sometimes the one unit will hear the other sonar’s sound and you will see vertical lines.

Since the cone shape of the sound from a transducer gets larger as it goes deeper you will get more overlap of cones in deep water. In shallow water, you will get less or no crosstalk because of the shorter distance.

The arrows are pointing to the vertical lines. The sensitivity is set high to demonstrate the cross talk.

Sometimes you get crosstalk and sometimes the screen is clear even though the depth hasn’t changed. The reason for this is the transducers are each sending sound at different times and sometimes the difference is enough so that they don’t hear each other. On a Lowrance unit you can change the ping speed in the sonar menu. Sometimes this helps, but the best way is to turn off one unit. On a Lowrance unit you can select stop the chart on the LCX/LMS/HDS units which will eliminate the cross talk. By selecting stop the chart unit will stop the transducer from pinging.

Doc Sonar Stop Chart


Doc Sonar Stop sonar

On the Lowrance HDS units you can connect them with an Ethernet cable and see the same transducer readings on both displays with no crosstalk. For example, you can use the transom transducer searching for fish and switch to the trolling motor transducer when you begin fishing. Your partner in the back of the boat can see a clear screen on the console while you watch the bow screen. The bad news is when you see a fish and park the boat on the fish, he knows what you doing since he can see the fish on the console screen!

Another choice on the Lowrance HDS models is you can select 83 kHz for one unit and 200 kHz for the other and eliminate the cross talk since the difference in frequency is enough to eliminate cross talk. This is a splitscreen of 200 on the left and 83 on the right from the same transducer showing no crosstalk.

Doc Sonar Split Screen

How do I get my Lowrance HDS unit to show temperature and time on the screen? You have to add overlay to a screen. If you add it to the sonar screen you won’t see it when you have the chart/sonar as split screen and you will have to add it to the splitscreen also. This allows you to have different overlays on different splitscreens.

Select pages, menu, edit overlay

Doc Sonar Main Menu Lowrance HDS unit

Then select menu, add, and add whatever you want.

Doc Sonar Configure

Is it possible that my Lowrance HDS unit has water inside it? I thought they were waterproof.
Yes it is possible.

Lowrance GPS/Sonar units have a long history of being waterproof and rarely have fogging issues, but Lowrance had a problem with seals in 2009 which caused water leaking into the units. This has been corrected and if you have water in a unit contact Lowrance Customer Service.

For more information on Lowrance StructureScan or for educational DVD's by Doc Bruce Samson on sonar units, GPS units or Lowrance HDS Units go to