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Questions about Filters, Scan Speed, Recovery Speed, Response Time, etc.

December 15, 2019 07:22PM avatar
From Todd's Original Post .. w/replies in blue:

Can you state the missing details in my chart below?

…………………………………….# of Filters…..Scan Speed…...Recovery Speed…...Quick Response (Yes or No)
#1..Tesoro Bandido II µMax...……….2...……..Slow-to-Moderate......Fast...………….............Yes
#2..Tesoro Compadre...………………2...……..Slow-to-Moderate...…Fast...…………............Yes
#3..Teknetics Gamma 6000...…….....2 ..………….Slow……………....Fast...……….………….Yes
#4..White's Classic II...………..……...2 ...….....Slow-to-Moderate..…Fast...…………….........Yes
#5..Garrett Ace 250...…………….…...2 ……………Slow……………...Slow...…………….........No
The Scan Speed, which I describe as Allowable Sweep Speed, is related to the so-called 2-Filter design and is influenced by the overall circuitry design. It is also related to the severity of the ground mineralization and make-up. Sweep Speed has several 'parts' or 'factors' related to understanding it and does cause confusion for many people ... until they learn each particular detector. Your list of 5 different models is a good example of some circuitry design differences.

ALL five models are based on a 2-Filter design. (For readers who are lost already, I'll get to 'Filters' in the following reply.) By design concept, a 2-Filter detector is designed to be worked at a slow-motion sweep speed in any ground make-up, and especially slower when dealing with higher ground mineralization and tough challenges like black sand, pea gravel or a rock-based surface material. The Teknetics Gamma, and most of the comparable circuitry designs by FTP, and the Garrett Ace 250, and other models in that series or earlier GTA series, and many others makes and models, require a slower sweep speed to work. Even in some moderate ground mineral conditions they have to be worked at a slower sweep speed. Increasing the sweep induces too much ground signal too fast for that model's circuitry to process, filter, and still pass along a target signal.

There are, or have been, some detectors on the market that actually have a more 'controlled' sweep speed and must be worked not too slow and not too fast or the detector performance is terrible. However, there are some 2-Filter designs that are more forgiving in moderate to a little more mineralized environments, such as most of those made by Tesoro, using Jack Gifford's design, and the very comparable White's Coinmaster Classic and Classic SL series designed by Wm. Lahr for White's.

Those models I corrected above because they are a 2-Filter and allow a nice Slow-motion sweep-speed. But even though a 2-Filter design, they have a little better 'enhanced' performance in that they can also use a Moderate sweep-speed in some tougher conditions and still provide adequate performance and not lose functionality as quickly as most types that have a more regulated Slow-motion design. Of course we get back to terminology we all use, but not all might understand. I can say I use my Bandido II µMAX or modified IDX Pro at a Slow to Moderate sweep speed, but other people hearing me say it or reading this post might not know my definition of Slow to Moderate.

Recovery Speed is on your list, but it's also difficult to answer unless first defined. It's also misunderstood by many people in this great sport because they think it means an ability to unmask closely-located targets. Some detectors do well, and some don't. Search coil size and type can also be important considerations, and that's why I asked about search coils in my first response. I could have expanded the questions to include what type of site conditions are these different detectors you listed going to be used?

All of them have performed quite well for people who used them in an 'average' urban Coin Hunting application where very few nails and other iron are encountered, and coins and other metal objects are not too closely spaced. When the site conditions get more difficult, then you see the benefits of a well-designed detector and coil combination over those that are slower and lack the ability (in circuitry) to process signals in close, rapid encounters.

You listed "Recovery Speed" and then "Quick Response" but there are three considerations when trying to 'separate' close targets or 'unmask' close targets, especially when some of them might be ferrous junk and positioned too closely to a desired non-ferrous keeper. That is the 'Handling' or 'Processing' done to restore the detector and be abl to respond to a nearby target. When searching an area we might encounter a coin. The first thing in order of occurrence is we can hear a Response. It might be 'average' or it might be a Quick-Response, or it might be a Slow or Delayed Response. Then, when the search coil is swept across the coin, we might hear a Fast-Recovery. That's when the detector has processed a target and restored to a functioning point to then Respond to the next coin we might encounter.

That Recovery-Time can be Faster than normal or Slower than normal, if not whatever 'normal' might be, and for 'average' Coin Hunting applications almost anything will do. To see this effect, use two identical coins, such as a 2 Pennies and lay them on the ground, or floor, and measure them to be exactly 2" from coin-edge to coin-edge. Only a 2" space between only these 2 coins. Then, use a detector with any available search coils and sweep across the two coins. The coil might have to be worked about 1" to perhaps 3" above the coins, not much more, and listen for a Quick-Response from the first coin, and then see if there is a Fast-Recovery Speed to let the detector/coil respond to the second coin.

Most detector / coil combinations will do that, especially with a smaller size coil. Sometimes a Concentric or Double-D might outperform the other type ... dependent upon the circuitry design. Use 2 Pennies and try that with each of your 5 detectors and any coils you have for them. Check their required Sweep Speed, Quickness-of-Response, and ability to Recover-Fast and respond to the 2nd coin. They might all work OK and show that they just might make a useful urban Coin & Jewelry Hunting set-up. So, was that an example of 'separation' or 'unmasking' ability? Yes, to a very simple degree, because only two targets were close together that needed to be detected and processed to respond.

Make sure you measure only 2" exactly between the edges of the coins. Don't have them any farther apart.

Note, too, that such an encounter might require a slower Sweep Speed to separate these 2 coins into 2 signals, and a faster sweep might not allow functional target-signal processing. You'll often see a pronounced difference in performance that favors a smaller-size search coil, and when site conditions get worse and there are multiple targets in close relationship (accepted and/or rejected), it helps show the differences.

Now, just one more quick-and-simple Response-and-Recovery test. Get two more identical coins such as using 4 Pennies. Lay them out in a straight line as before, and keep an exact 2" space between each of these four matched coins. Use the same detectors and the same search coils and do it all over again and see what happens ... or doesn't happen. There are now multiple coins evenly spaced, and depending upon the search coil size and coil type (Double-D or Concentric), there will be more than one coin at a time under the search coil diameter, and likely 3 or even all 4 of the coins might be covered by the search coil, or close enough to the Tx and RX winding to have an influence. That's a lot more 'information' for the detector to process in order to provide a workable response.

Remember to sweep the coil's center-axis along the row of coins at a uniform coil height. And don't pre-guess the results or that a coil type, like Double-D, is always going to work better and a Concentric coil won't. I use this 'test' often when I compare detectors, and repeated it again last night before I got to this reply. With 4 Wheat-back Pennies on my den floor, the following combinations I have did NOT handle this and FAILED to give me 4 separate target hits. My Fisher F44 w/7" Concentric coil and Makro Racer 2 w/7" Concentric coil.

Of my other detectors, all ready-to-use with their set-up, I DID get 4 separate audible hits. I'd even check with a faster sweep speed to see which set-ups provided me the better 4-hit performance when the sweep speed was increased from the slowest possible. Here they are in the order they gave me the best Sweep Speed performance from slower to the fastest they could handle it. Some are very close to being tied, but this is how well I heard them. Remember, these about in order! They are:

XP ORX w/5X9½ DD .. Nokta FORS CoRe w/4.7X5.2 'OOR' DD .. FORS Relic w/5" DD .. Nokta / Makro Simplex + w/11" DD .. White's IDX Pro w/6½" Concentric .. Teknetics T2+ w/5" DD .. Tesoro Bandido II µMAX and Silver Sabre µMAX w/6" Concentric .. XP ORX w/9" DD.

As I stated, ALL of them gave me 4 clear hits and several were almost too close to tell from another so I based my order of finish on the audio tone or clarity.


In the far left column of my chart (# of Filters) I entered number 2 for all detectors listed, as I believe they are generally thought of as being 2 filter detectors, although I suppose there might actually be additional filters performing other tasks in the circuits.

Please let me know if any of the detectors listed are generally thought of as having more than 2 filters and what the number should be.
We seldom read anything about modern detectors being labeled with a "filter" reference. Initially, back in '78, we didn't immediately have a references but it came up to help describe why our earliest motion-based Discriminator (the Bounty Hunter Red Baron) designed by George Payne, had to be swept so very briskly in order to reject the ground signal and reject trash signals and pass along a desired good target signal. That term was '4-Filter.'

Hobbyists wanted a slower sweep detector, and one that would recover faster since most of the 4-Filter designs had a longer "ring-time" before they would recover. In '82 we got our first Slow-Motion / Quick-Response detector (Fisher's 1260-X) designed by Dave Johnson., He used the term 'Double-Derivative' which translates to, and was most generally referred to as, '2-Filter'.

Metal detectors have many more 'filters' at work in their circuitry design, but this was a references to how they were designed to handle the Ground Balance and reject or Discriminate the ground signal and restore to a functional condition. A 4-Filter detector required a fast Sweep Speed and handled the ground mineral better and could provide a little better depth in bad ground, but that had a slower Recovery-Speed making it difficult to hunt in a trashier environment. The 2-Filter design did 'OK' when it came to handling bad ground, but did allow a Slow-Motion sweep speed, and also gave us a Quicker-Response and Faster-Recovery ... based upon circuitry design.

The Fisher concept worked okay, but didn't handle iron trash very well, such as iron nails, as was more of a 'ticky' or 'popping' sort of audio on them. In '83, Jack Gifford, of Tesoro introduced a new model that was a Quick-Response and Fast-Recovery design that did handle iron much better (that was the Inca) and it started a surge in the industry to make a popular, easy-to-use slow-motion design. Tesoro set a high standard other tried to match.

Each model had its strengths and weaknesses. There was a new 'filter' offering in 1987-'88 when Compass engineer John Earle designed a new model series (the original Scanners) that used what he termed a 'Vari-Filter'. By his description, that design was a 3-Filter concept and gave us sort of a blend of the better parts of 4-Filter and 2--Filter designs. The detector could be swept at a faster Sweep Speed, but also at a slower speed. And it didn't lose performance in more mineralized ground like the 2-Filter, and it also gave us the 2-Filter Quick-Response and Fast-Recovery performance. A happy blend, and a new terminology of 'filters'.

We didn't see that used again, in a popular make or model, until White's brought out a new design developed by Dave Johnson (the MXT), and with that model's popularity, and the increasing number of slow-motion 2-Filter designs, we saw the end of the 4-Filter detectors. Most manufacturers don't use the filter references any more because it can be confusing, and mainly because we've moved on from analog circuitry detectors to those that are digital designs and a lot of the 'processing' is done in software.

All I was asking is for you to advise the missing data in my chart if you can.
I did so above.

As for the make, model and size coil for each detector, just base your answers for the missing data on the standard coil that comes with each detector when bought new, as I have listed below. The only coil change I will make occasionally is switching to the 5" DD Teknetics sniper coil on the Gamma 6000.

#1..Tesoro Bandido II µMax......8" Round Brown Donut, Concentric Discriminator, Monolithic Shielding.
#2..Tesoro Compadre...............5.75" Round Solid Concentric.
#3..Teknetics Gamma 6000......8" Round Spoked Concentric.
#4..White's Classic II......….......8" Round Black Solid.
#5..Garrett Ace 250...................6.5" x 9" Open Elliptical "Proformance".
So readers understand, the 5.75 reference to the Tesoro coil was a dumb marketing move, like White's made just about that time. White's used 5.3 for a search coil that is a measured 6½" in diameter. Tesoro used 5.75 for coils that measure 6" in diameter.

My 'answers' in the graph you originally posted and in the additional information I provided, was to describe the results we might get afield. Not just Sweep Speed or Response Time or Recovery Time, but also the 'processing time required to provide above average Processing and Recovery & Response time to best handle dense target encounters.

In conclusion, will my post be editable for me to make changes and additions? Otherwise, as another option, I could copy my post for reference and then it could be deleted entirely from the forum and I could re-post it with the changes and additions after you reply with the missing data.
Here is some missing or corrected data, as well as my other comments so readers might better understand what detectors they have or what they are capable of.

If you're OK with this reply, I can do a cut-and-paste and put it in your original post and delete the rest. Just e-mail and let me know what you'd like done.


Todd's 'Signature' is below

Teknetics Gamma 6000, Tesoro Bandido ⅡµMax and Compadre, White's Classic Ⅱ, Garrett Ace250 and Pro-Pointer AT Pin Pointer, Treasure Products Vibra-Probe 570, Cen-Tech Pinpointer, Lesche Digger, Tabdog Digger Replica, Detect USA RatphonesMax Headphones, Janster Coin Probe.

Edited 3 time(s). Last edit at 12/21/2019 12:02PM by Monte.
Subject Author Views Posted

Questions about Filters, Scan Speed, Recovery Speed, Response Time, etc.

ToddB64 130 December 15, 2019 07:22PM

Re: Questions about Filters, Scan Speed, Recovery Speed, Response Time, etc.

ToddB64 28 January 22, 2020 09:25AM

Simple answers.

Monte 19 January 22, 2020 03:17PM

Todd had good questions and I hope my reply helps readers. N/T

Monte 44 December 21, 2019 12:05PM

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