Yes, this is normal -- IF you have your sounds set to "conductive," and you run a fully open screen. In "conductive sounds," this means that you have set the machine up to key on the CO number (the second number in the ID number pair) when assigning tone. The lower the CO number, the lower the tone, and vice versa. So, a 28-46 nail, and a 12-46 quarter will sound essentially the same, tonally, since the tone is keying off the 46 CO number when using conductive tones. It is in the FE number where a nail will ID differently from good (coin) IDs.
SO -- the way to run the machine "open," and effectively separate iron targets from "good" targets, is to run the machine in COMBINED tones. In combined tones, you set up 5 bins -- four horizontally from left to right, across the top half or so of the screen; these are your "conductive" bins. Then, you set the lower half or so of the screen (from, say, the 20 FE line on down to the bottom of the screen) as your "ferrous" bin.
For that ferrous bin, you then can set it up audibly/tonally as a "low tone" (iron grunt). So for instance, you might set it at, say, 75 Hz, for the tone.
Now, above your lower "ferrous" bin, you have your four "conductive" bins, from left to right, which sit above that lower "low tone" or "iron" bin, that you can then assign higher tones to.
So, for example, let's say you set things up in the following manner, in your Combined setting. First, you set your "top" four bins up like this -- bin 1, you set from conductive numbers 1-10, and you assign it a 200 Hz tone; bin 2, from CO 10 to 30, and you set it at 400 Hz tone; bin 3, from 30 to 40 CO numbers, assigned 600 Hz tone; and finally, bin 4, 40 to 50 CO, and you assign it 1000 Hz tone.
Now below, on your "iron" bin (the lower portion of the screen), let's say you set that bin starting at the FE 20 line, which would then extend on down across the rest of the screen. This bin then would then include roughly the whole lower half of the screen (20 to 35 FE lines).
So NOW, set up in this way in Combined tones, let's say you hit a nail, that IDs 28-46. With the machine set up as above, in combined tones, you would get the low (75 Hz) tone for this target, because the 28 FE number assigned this target would place the target ID it in the bottom half of the screen (below your 20 FE line, since 28 FE is of course "below" the 20 FE line that you set as the top of your "iron" bin). So, in this case, with the target giving the low-tone grunt you assigned, it immediately becomes obvious that it's iron.
Then, let's say you hit a quarter, and it reads 12-46. NOW, your target would report a high tone (1000 Hz as per the tone you assigned to your fourth "conductive" bin), as the 12 FE number of the target places it ABOVE your "iron" bin, and the 46 CO number places it in the fourth "conductive" bin, from left to right (the highest tone) you had set up. In other words, the target would plot in the upper-right-hand side of the screen. Likewise, let's say you hit a nickel, at 12-13. It would report in the mid-low tone bin (400 Hz) that you set up, as again, the 12 FE places it ABOVE the bottom "iron" bin, and the 13 CO ID places it in your second (from left to right) "conductive" bin.
Does this make sense to you?
Steve