There has been some discussion on the forum since the release of V3 regarding Recovery Delay and how to set it .... I have set up a chart showing RD time settings for four (4) coil sizes - 4", 6", 9.5" and 10", deployed at sweep speeds ranging from .5 ft/sec to 5.0 ft/sec. The "average detectorist" swings somewhere between 1.5 ft/sec and 2.5 ft/sec. At 2.0 ft/sec it will take 2 seconds to swing a 4' arc in one direction.
First off, definitions: Recovery Delay settings are just as the name implies - the delay time that you are imposing on Spectra before it can process a second target after the first target has been processed. Another term would be Signal Processing Delay, or how long Spectra has to process the first target, and then be ready to process a second target. When I "explain" this time, I like to use the analogy that a target is processed in four steps .... (1) It is acquired (2) target data is calculated (3) target data is displayed (4) target is released and housekeeping done in preparation for the next target. Steps 1 - 4, added together = Recovery Delay.
Lower numbers = SHORTER delay. Higher numbers = LONGER delay.
Optimized Recovery Delay is a function of Sweep Speed, Ground Filter, Mineralization, Coil Size and to some degree, RXG and Disc Sensitivities.
The premise that the attached chart is founded upon is that (1) the coil can't see anything before or after it is over the target (discounting edge effect for purposes of this discussion) and (2) a full coil width's separation will minimize masking. You may find that you can actually reduce your delay times a bit from the settings in the table. They are given a 5% margin to address edge effect. I used the middle of the road 7.5Hz filter.
Faster RDs are best deployed in high trash areas. Slower RDs will provide more depth, up to the point that the coil is no longer over the target. Increasing / decreasing RD around the "recommended chart setting" will not add or subtract inches from your target depth, unless of course you adjust "too far" in one direction or the other. EG: A RD = 0 will make a quarter "chattery" at about 3", so that's "too short".
Coil size. Just want to touch on this .... A 4" coil (4X6"DD shooter) will pass over a quarter in less time then a 10" coil (10"DD) if both are moved at the same sweep speed. Thus, it has been my suggestion that if one is making a significant change in coil size, it may be worthwhile to adjust the Recovery Delay accordingly.
The chart is purely mathematical. I have sampled the data using all four coil sizes and varying sweep speeds and the performance matches the numbers. Please note that the sweep speeds are "Mississippi's", they are not timed with a laser and the coil wasn't moved by a highly consistent mechanical arm.
The quickest way to arrive at your "optimum" RD (IMHO) would be to place a two coins, one coil's width apart and swing the coil at your speed until you got two hits from the unit. If you know your sweep speed (and most people think they are sweeping slower then they really are) then the chart will "get you in the ballpark" and minimize your tweaking time. It will also provide a "sanity check" for your program settings as you develop them, or perhaps help you understand other people's program settings.
To estimate your sweep speed, lay off a line 4 feet long. Stand in the middle and sweep your coil from end to end, counting "Mississippi's". A 2 ft/sec sweep speed should take you 2 seconds to cover that 4 feet in one direction. I have seen many a surprised detectorist when they discovered that their sweep was closer to 4 ft/sec !!!
Hope this is helpful .... Da FoX