To judge why one sonar system can pick-up a target and another cannot starts with putting these testing standards in place. Any one of them not being in place will not make for an accurate test:
A. You must test in same holes with same targets.
B. You then need to use identical transducers, this means you must use the same transducer on both units. You can never expect different 9, 19 or 12 degree transducers all to perform the same.
C. The transducer and target must be in exactly the same positions in the hole.
D. FL-8 and 18 sonar systems have different receivers than the FL-12 and FL-20 so it may require a higher gain setting to get the same signal display but the adjustment is seldom more than 15% difference in gain adjustment up or down. The FL-12 and FL-20 are designed this way for enhanced Interference rejection.
Classic problems with target and signal ID:
My friend sees his lure on his Vexilar and I cannot?
#1. Are you using the same lures? Different lure shapes result in a different bounce-back signal, which may or may not be stronger or weaker than your friends lure.
#2. Are you using the same type of transducer? A 19 degree transducer is not as intense a signal as a 12 degree, so you may need to turn up your gain. Adjusting your gain control up to 15% will often result in finding even the smallest targets.
#3. Be sure to wipe the face of your transducer on your pant leg. Your transducer can develop a layer of dirt on the face, so simply wiping on your pant leg will increase your transducer sensitivity.
#4. Straight hole? If your Ice-Ducer is not pointing straight down your hole, you may not see your lure.
I have three holes and I want to put my sonar unit in the middle and watch both lures, my friend can do it with his, but I cannot on my unit what is wrong?
#1. Hole placement must be identical as your partner, since a hole even 6 farther apart will effect target ID. Your transducer should be placed below the bottom of the ice to insure the transducer is shooting straight down the hole. Even the slightest change in your transducer angle will result in a lost target.
#2. You may need to increase your gain to increase your area of coverage or signal strength to see lures in your hole while your fishing partner might not due to the differences in transducers.
#3. Clean the surface of your transducer and be sure it is placed in the same position in the hole as your fishing partner.
#4. Are you using the same lures? Different lure shapes result in a different bounce-back signal, which may or may not be stronger or weaker than your friends lure. Note that minnows may swim your hook out of the transducer cone as well.