How to deal with EMI

[cddz75]

Today I went out for a quick hunt around town with a buddy. I was using 8khz frequency, no matter what I tried would allow me to get the sens above 70. I switch to basic2 which uses 8khz as well and it stabilized. The only real difference was the Disc level. So I went back to my zero disc full tone program and increased the disc to 10, at that point it finally calmed down. I pulled the coil cover off and checked, clear of debris. Why would increasing the Disc cause the interference to go away?

 

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[Tedyoh]

Not sure but I'm going to try that, have a few annoying spots on our properties.

 

[ggossage]

Usually a change in freq provides relief...for me, the higher the better (usually). I'll have to remember your disc idea for next time.

 

[BARKER]

Hi; Although this one is for the Engineers here my own experience has been that I lower the Sensitivity. Leave the Disc alone. It has "absolutely" no bearing on EMI's. Then
re Ground Balance your machine. This has worked for me many times. If you turn the Disc to 10 you lose everything including coins and a LOT of Depth ok. Leave the Disc alone PERIOD ok. The first few steps I laid out should work for you. There are times when you may have to repeat the first steps a few times but it will work ok. PEACE:RONB

 

[cddz75]

Hi; Although this one is for the Engineers here my own experience has been that I lower the Sensitivity. Leave the Disc alone. It has "absolutely" no bearing on EMI's. Then
re Ground Balance your machine. This has worked for me many times. If you turn the Disc to 10 you lose everything including coins and a LOT of Depth ok. Leave the Disc alone PERIOD ok. The first few steps I laid out should work for you. There are times when you may have to repeat the first steps a few times but it will work ok. PEACE:RONB

That is the question I was asking about. I am not new to the hobby. Not sure How using a Disc of 10 on the XP would prevent me from finding coins. Ground balancing had no effect on the interference, nor did changing frequencies. I just found it odd that switching to a program on the same frequency with the only real difference being the level of Disc used.

 

[can]

I am new so I am not even sure what you are talking about. You might have already seen this, but then again it might be helpful

 

[Tedyoh]

Disc at 10 is fine for coins. You may lose 1/4 inch in depth compared to Disc at 0

 

[cddz75]

Disc at 10 is fine for coins. You may lose 1/4 inch in depth compared to Disc at 0

Yea, that is what I figured. Never on any detector have I had to resort to using disc to stop the chatter.

In fact, just tested it here in front of my computer, disc had no effect on the EMI. Must have been site specific.

 

[Pointman]

The only thing that seems to work for me is to keep the machine on tracking GB and I change the frequency in the offset settings (seems like when I use the built in frequencies I still get chatter until I SLIGHTLY change them in the offset). Lowering the reactivity seems to help as well. I am not sure why. Worse case, I will put the machine in 3 tones in order to give my mind a break from all the squeaking.

 

[jvav]

Did the program that had the disc at 10 have a higher TX power setting? I find sometimes turning that down helps.

 

[vferrari]

Can't really argue with someone when something works for them (even if physics or the design specs say it shouldn't). However, in the strictest sense, adjusting discr should not have any effect on EMI. Regarding discrimination - unless you are explicitly searching for ferrous/iron targets (e.g., not coin shooting), then discr should be set somewhere between 8 and 10 (even for most relic hunting). This enables most ferrous junk to be filtered out while still allowing some ferrous targets to be heard (provided iron volume is not set to 0) and enables the ferrous/non-ferrous horseshoe icon to work properly.

Regarding EMI and the Deus:

First and foremost - Get the basics right- initialize the coil (turning on the control unit) with the coil raised in the air (away from the ground plane) and obviously away from metal objects above the ground (cars are obvious, but also watch out for re bar and metal siding on structures). Don't hunt with your batteries on the edge of dying. And, finally, properly Ground Balance your machine using whatever method and mode you prefer.

If you get all those right, that's most of the battle against having a chatty, unstable machine. They may seem obvious, but you'd be surprised how even the most experienced md'ers (Ahem) sometimes forget when they are in a hurry to hit a search area.

If still chatty after that, then you might want to try frequency offset - note that since frequency offset makes the coil run less efficiently, XP locks Tx power to 2 when using frequency offset (see Tx power discussion below). Also, frequency offset is not even available when running at 4khz. If offset doesn't work then try switching to one of the other 3 frequencies.

Your next tweak should then be sensitivity - the sweet spot on sensitivity (from a depth perspective) is 88 - 92 since much above 92 you don't get much benefit because the sensitivity vs. depth curve flattens out. If you lower sensitivity from this point then depth does drop off pretty linearly, but if you can afford the depth hit, go ahead and lower sensitivity to reduce chatter (try just reducing it one number at a time until the noise stops). An expert setting under sensitivity is Tx power. Tx power does obviously affect depth capability. Tx 2 is typically fine. Run Tx 3 if you can if the soil is not too mineralized (of course this increases battery drain). Tx 1 can be used if even Tx 2 is noisy due to very high mineralization. Bottom line though is that Tx power is not really something you should need to tweak because of EMI. Also note that Tx power is fixed at 3 for the 4 khz frequency setting which could make 4 khz unusable for highly mineralized soil conditions. [Edit: BTW - how can you ascertain ground mineralization? Check the height of the single bar graph on the far right of the display. Don't confuse mineralization with ground conductivity, which is displayed numerically and is used to aid in properly ground balancing the machine.]

[Edit: Thought I might add the following regarding Tx power and preset modes: Tx is set at 3 for RELIC only (which is not a great setting if you are relic hunting in highly mineralized ground as I mentioned previously since minerlization tends to diffuse the higher Tx signal making audible target identification harder, i guess similar to having reactivity set too high as discussed below); Tx is set at 2 for all other preset modes except for WET BEACH where it is set at 1. FWIW]

Reactivity can have an indirect impact on the noise performance of the Dus and a direct impact on depth performance . Reactivity should be run at 1 or 2 unless you are in a really trashy area and you need max recovery speed but you shouldn't go higher than 3 because depth suffers as you increase reactivity (plus the audio gets choppy making it hard to catch the target). While reactivity does not affect EMI performance directly per se, You need to watch out because an expert setting under reactivity is Silencer which XP incorporated to reduce iron chatter noise susceptibility. Silencer is pretty straight forward in that -1 = no noise reduction 0 = some noise reduction with minimal impact on depth and the higher values 1 through 4 progressively increase iron noise immunity at the expense of depth performance. Silencer should not be set above 1 unless iron noise/trash is such a problem that you need to go to 2 and sacrifice the depth (similar to reducing sensitivity but with a much greater and coarser impact). Ideally you should leave silencer at 0 if possible. -1 and 0 have practically no depth performance difference, so it just makes sense to leave silencer at 0 unless you want the extra millimeters of performance and speed afforded by -1 (you get faster response because there is less filtering and signal processing) or if you want to be sure you don't miss good targets that are lying right next to iron. If there is a lot of iron trash, however, lack of any silencer filter might drive you nuts. HERE IS THE THING THOUGH - XP SET UP SILENCER DEFAULT VALUES FOR EACH REACTIVITY SETTING AND WHENEVER YOU CHANGE REACTIVITY SILENCER REVERTS TO THAT DEFAULT SETTING WHICH CAN BE AS HIGH AS 3 FOR REACTIVITY SETTINGS 0 AND 1. So whenever you change reactivity, be sure to check and readjust Silencer to a lower value (0 or 1) as appropriate.so you don't loose depth. Also note that Silencer is set to 4 (!) for the following preset programs: DRY BEACH and BASIC 2, set to 3 for G-MAXX and RELIC , set to 2 for BASIC 1, GM POWER, and PITCH, and -1 for DEUS FAST (now that DOES make sense) and WET BEACH. Go Figure. [Note that I edited the above slightly from my original post to more accurately reflect the reason for the Silencer, to reduce not EMI but Iron Chatter, and to identify when you might want to run with Silencer off = -1].

A combination of the above tweaks should handle 99% of the EMI situations you may encounter. Understanding what the settings do and how they work in concert is key and the best way to do that is experiment and test. Hope this helps and HH.