fish finders agree no feed back.

[WYIfish]

I bought a Humming bird finder, a high end model. I got it to up grade the old 15 year old garmin 400 (that still works quite well). I set them both up in the yard to test both for feed back in the eskimo shelter and got none 4 feet apart.  Lacking any feedback on the lawn-would I expect any in the ice?

[hardwater diehard]

NO ...is the short answer ...the "feedback" occurs when the signal bounces back or out .I do not think air is the greatest medium for that ...The Hummingbird should have an adjustable IR setting ...i.e on the Vexilar it is achieved by pushing the gain button . Once you find out how and how many modes (Vexilar has 10 or 20 depending on the model) you have you can cycle through them ..note you may not get rid of it in its entirety but can reduce it enough so you can fish.. also if two or more fisherman are close and experience interference ONLY ONE SHOULD CYCLE THROUGH THEIR UNITS IR FUNCTION.