I had a conversation with a distributor who mentioned the SL gets about 20% less depth than the TDI. Is this true??
Well, it can be for certain reasons and here are some of them.
First, the SL has a relatively short battery life so many people run their batteries as long as possible. Also, they usually run the Ni Mh units rather than alkalines. Now, the NiMh batteries have a lower voltage to begin with, so they will produce less depth. Next, trying to squeeze more time out of either them usually causes more depth loss as the batteries run down. Bragging on how long the batteries last is great if you are trying to promote some battery setup, but if you are serious about getting the maximum depth or number of targets you can find, then maximum power is needed and not maximum battery life.
A couple of things can be done regarding the battery life and one is to go to Li Ion batteries such as the RNB system. The run time is longer and the voltage is higher with their new 3100mah system for the SL. Another alternative is to go to a 4 cell setup made by Reid and sold on Ebay. This system kicks the voltage up to the TDI voltage and uses the new Panasonic 3400 mah batteries. In either case, run time should be better than 4 continuous hours before you should consider changing to a second set. One might be able to get 5 to 6 hours out of them before they die but again, after a certain time, even the Li Ion batteries begin to sag and depth is lost. Personally, I prefer to change batteries once I notice little things indicating the batteries are declining.
Another issue is noise. No, you normally don't hear it easily on the SL but failure to properly set the frequency will cause depth loss. This depth loss will happen on both the TDI and SL if the minimum noise setting isn't used, so take time to listen carefully to the threshold and adjust the frequency for the least noise.
A couple of years ago I notice the noise reduction design in the SL caused a small depth loss, maybe a typical 1/2" or so on a coin size object. Well, I came up with a fix only to have the factory say it would cause a sound on the upswing of the coil. I couldn't duplicate the noise but did abandoned my idea. Later, I was asked to help find a solution to a hiccup signal happening on the SPP being sold in Australia. Well after considering several more complex designs, I went back to my original idea I had and tried it. What I found was the hiccup was gone on half of the tones. After analyzing the signals, I realized the other half had the hiccup because of another component and I couldn't figure out why it was there. I removed the part and everything seemed fine, but ultimately another quirk reared its ugly head as the result of my mods.
Often times a detector will have a power on reset used to clear any and all quirks that could happen at start-up. As it turns out, if there is a POR (power on reset) on the SL, it didn't work and what could happen was when the detector was initially turned on a useless filter wasn't reset and could cause an audio response that lasted a few seconds. This happened as the result of all my mods when using only certain coils.
The simple solution was to remove the worthless extra filter by simply shorting out a capacitor (cap) which I did, but doing so increased the gain. Increasing the gain didn't place the typical presets in the exact spot and increase the noise some. So the distributor in OZ complained and as a result the cap was left in. With the cap still in, some coils would and still do cause the audio start-up signal. To stop this signal one only has to bob the coil and the filter is reset and causes no more problems until the next time the detector is turned off and on. The reason there is no more problems after start-up is because there is a reset function built in that resets three filters any time a signal caused by a target or the ground occurs and that happens all the time.
Anyway, for those of you who heard of the Australia problem of a hiccup, you now know how it came to be fixed. One other positive feature of the fix was the depth loss occurring because of the noise reduction design was gone. Since the SL has the same gain as the TDI and the depth loss caused by the noise reduction was gone, the only reason the SL didn't match the TDI for depth was battery voltage. Change that and the SL should match the TDI.
One other idea I had was to use this useless filter to add a second filter with the same time constant as the ones in the autotune circuitry. This would add a second filter which could help with really bad ground conditions. By using something simple like a 3 position switch one could have the useless filter in just like it is, or switch to a second filter design, or finally eliminate the filter all together. Believe it or not, I used something like this on my very early low powered PI years before the TDI was thought of. At some point I will try this idea, but only when time permits.
Well, that is all for now, but as you can see, there are still things to try on the TDI series to add features and this little post mentions some of them.
Reg