In the Sensitivity Zoom window, you see the signal strength (signal%) at a percentage of when the detector overloads. So Carl says it really isn't signal loss. This isn't on any specific frequency - the reading is on the incoming signal before it has been separated into the 3 frequencies. The goal is to keep the ground signal about 20% so that you still get depth and can still see shallow targets without overload. Signal% doesn't indicate signal "loss", but rather the amount of residual signal present. If ground + null are the cause, then this doesn't take away from sensitivity. Instead, it takes away from large/shallow target response, manifested in a signal overload. None of these are losses, but rather they reduce the available dynamic range. The lower this % number the stronger the signal will come through or be received.
The Noise% measures the External Interference. 0% or a low number indicates very little external noise and low ground interference, thus allowing for using a higher preamp RX Gain. A high % reading of Noise of 50% or more would require you to:
If your noise is EMI, you can try; 1) Freq Offset, 2) Decrease RXG, 3) Salt Mode, 4) 22.5Khz Single frequency, 5) Filter change, 6) Smaller coil.
Cranking up the Gain or Sensitivity can obliterate a good signal with an increase in noise. Particularly small and deep targets get the worse treatment. EMI shows up as chatter and reduces the low end, the minimum detectable signals. Ground causes overload or makes GB difficult and the reduction is on the high end, large/shallow target overload.
The V3 (not V3i) recommended a preamp gain to keep the total residual signal level below 10%. The signal is coming off the preamp or the first stage. I would go no more than 30-40% MAX. Quite often EMI will be the limiting factor. If EMI is the limiting factor, run the preamp gain as high as you can, but keep it stable. Also, when EMI limits the max gain TX boost becomes an effective way to get some extra depth. The rule of thumb is that, to gain another inch of depth the gain must be doubled. This means that increasing the gain from 14 to 15 will not improve depth much at all whereas increasing the gain from 2 to 4 should gain another inch. So 4 to 8 gains another inch and 8 to 16, oops there is no 16, another inch. So don't get crazy on setting the RX at the upper levels because it provides diminishing rewards. In some cases the added noise will actually negate the increase. So in my opinion, higher RX and more noise and signal loss would be about the same as lower RX with less signal loss. If you are hunting in a clean area with only deep targets, then run the gain just below the overload point for max depth. But if there are a lot of shallow targets, then this will result in a lot of audio overload signals which might be annoying. The bottom line is, with any coil, run the gain as high as you can for stable operation, just as you'd do with any detector.
If you have ground coming in at -94(VDI) with a signal strength of 2% and another ground coming in at -91 with a signal strength of 7%, it would seem to me that the ground coming in at -91 is more mineralized even though it is a less negative VDI. 0-10%=low mineralization, 11-25%=moderate and 25% on up = high. Try to keep it at 20% or less.
On the noise I never actually saw a number given. I just adjust RX, filters etc. to lower it.
