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EMI
Posted by deadeye
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There is one yard that I have detected in that has real bad EMI or something else. I have tried a Titan 3000, Garrett 2500, White DFX, V3, AT PRO, 75 LTD and Racer 2 in the yard. There are no wires going over the yard, they run to the back of the yard about 50 yards away from the front where I am trying to detect. Of all the detectors I listed the only ones that I could find anything with, was the AT PRO and the 75 LTD, all of them give erratic beeping but the AT PRO and 75 LTD was not as bad. I didn't try to make changes on the DFX when I tried it. On the racer 2 I could hear a pulsing sound. On the AT PRO and the 75 LTD I could get them to quiet down some by using frequency offset, on the Racer 2 I could not.
By changing to a smaller coil on the all the detectors helped some, but I still had problems.
How can sites like this be hunted?
By changing to a smaller coil on the all the detectors helped some, but I still had problems.
How can sites like this be hunted?
EMI can be caused by both near-proximity sources and more distant sources, and often we can't determine what causes an EMI issue.Quote
deadeye
There is one yard that I have detected in that has real bad EMI or something else.
Of all the detectors I listed the only ones that I could find anything with, was the AT PRO and the 75 LTD, all of them give erratic beeping but the AT PRO and 75 LTD was not as bad.
On the AT PRO and the 75 LTD I could get them to quiet down some by using frequency offset, on the Racer 2 I could not.
By changing to a smaller coil on the all the detectors helped some, but I still had problems.
How can sites like this be hunted?
The offending contributor might be a full-time functioning annoyance, or it could be a radio or power transmission source that only operates on certain days or times of day. Thus, we might try searching an EMI challenging site at different times of the day, or night, or day of a 'business' week or weekend. I know there was one particular park in the greater Portland, Oregon area that gave all my detectors EMI fits, be it mildly annoying or very bothersome and unusable, on most days of the week except Sundays, Holidays when banks and schools, etc. were closed, or often no EMI problems after about 7 PM. I simply avoided it except on the favorable times w/o EMI.
As you noted, two of the models seemed to have a less annoying EMI pulsing when you changed the frequency. Using detectors with a significantly different primary frequency can sometimes help. Not a slightly shifted frequency, but a designed frequency that was different. I have had EMI issues with some detectors operating in the 13 to 15 kHz range at times in the past, but gone to a 6.59, 7.8 or 10 kHz model and had less or no EMI problems, as an example, so that might be what is required.
Oh, it has worked the other way, too, where the lower frequency models were more bothered than a higher frequency model.
Most of the places I detect are rural and I seldom deal with EMI. Only in a few urban locations do I encounter a problem, then, if I do have an EMI issue, I simply select a make and model detector that is least effected or not at all, and that is often determined by the operating frequency. Also, as you noted, smaller coils can also be an advantage, and I use them the most anyway. Naturally, you can reduce the Sensitivity/Gain and see if that helps at all.
Monte
Don't know about all the detectors you mentioned, but I do hunt with an F70 and have dealt with this problem in the past.
There is one site I used to hunt with the most EMI problems I have ever experienced and they were constant and consistent because I hunted there many times.
It was at the entrance area of an old park right next to the street with power lines running through the area, large old homes just across the street with WiFi I assume and I could never find it but somewhere in the vicinity was some sort of large piece of machinery that caused that thrumming, pulsing effect you only get near big stuff like huge air compressors...or running train engines.
Very difficult but because of the history I just kept coming back until I figured out how to succeed.
The higher end Fishers have a rep for being noisy and they can be if you turn up the settings but turn them down and they will be quiet...but I never tried that here.
What I did try was exactly the opposite and the way I hunted was in all metal, sense and thresh turned up all the way too and the jumping was horrendous but surprisingly the Fishers seem to stop all the jumping and nonsense when the coil passes over something good and even in this site that happened.
I ran over a couple of good targets in this area doing this, the good repeatable signals were fleeting but I did notice them and stopped and went back to move the coil around the area to examine them further.
Upon closer examination these good signals calmed down when the coil passed over them so I suspected something good even though there was jumpy behavior all around it.
I found many clad coins in this problem area this way and a few other older cool targets too that were non ferrous which was good because this area was infested with trash and iron.
Another technique was using disc not exactly low settings but sense up to at least 80, Thresh at -1 to -2, DE speed and disc was probably somewhere between 4 and 23 because that is what I used the most back then.
I know now that monotone and low disc at 0 or 1 would probably work even better but using these settings I still came across jumpy behavior galore but calmed way down when I ran over great targets and on most I was using the big DD coil, also.
Using disc I eventually found my greatest coin spill with an early wheat in the the teens and 3 IH's going back to the 1880's and about 8" deep.
Another was a gold ring sitting between two pieces of iron and yet another was using disc in the low 20's, sense all the way down to 30 to have the effect of shrinking that scanning field on the big coil to laser like proportions.
Still some interference even at that low sense settings but in the very entrance part with all the EMI and about 100 years of trash I still managed to pluck out some hidden and masked clad plus a very nice merc dime.
Don't think I would have found that coin spill deep at this low sense setting but in the trashy are it was just perfect to find a 4" deep dime.
All of this is just to say that by learning the behavior if your chosen detector more than well you might be able to notice a second more hidden language...something I know the Fishers possess but other types and brands just might also.
In your place I would wade into that site with the F75 knowing what I know about Fisher behavior, but heavy EMI should never detour you but motivate you to find the key and solve the puzzle instead...and I believe there us always an answer but you just have to figure it out.
Edited 4 time(s). Last edit at 05/09/2016 03:32PM by diggwr27.
There is one site I used to hunt with the most EMI problems I have ever experienced and they were constant and consistent because I hunted there many times.
It was at the entrance area of an old park right next to the street with power lines running through the area, large old homes just across the street with WiFi I assume and I could never find it but somewhere in the vicinity was some sort of large piece of machinery that caused that thrumming, pulsing effect you only get near big stuff like huge air compressors...or running train engines.
Very difficult but because of the history I just kept coming back until I figured out how to succeed.
The higher end Fishers have a rep for being noisy and they can be if you turn up the settings but turn them down and they will be quiet...but I never tried that here.
What I did try was exactly the opposite and the way I hunted was in all metal, sense and thresh turned up all the way too and the jumping was horrendous but surprisingly the Fishers seem to stop all the jumping and nonsense when the coil passes over something good and even in this site that happened.
I ran over a couple of good targets in this area doing this, the good repeatable signals were fleeting but I did notice them and stopped and went back to move the coil around the area to examine them further.
Upon closer examination these good signals calmed down when the coil passed over them so I suspected something good even though there was jumpy behavior all around it.
I found many clad coins in this problem area this way and a few other older cool targets too that were non ferrous which was good because this area was infested with trash and iron.
Another technique was using disc not exactly low settings but sense up to at least 80, Thresh at -1 to -2, DE speed and disc was probably somewhere between 4 and 23 because that is what I used the most back then.
I know now that monotone and low disc at 0 or 1 would probably work even better but using these settings I still came across jumpy behavior galore but calmed way down when I ran over great targets and on most I was using the big DD coil, also.
Using disc I eventually found my greatest coin spill with an early wheat in the the teens and 3 IH's going back to the 1880's and about 8" deep.
Another was a gold ring sitting between two pieces of iron and yet another was using disc in the low 20's, sense all the way down to 30 to have the effect of shrinking that scanning field on the big coil to laser like proportions.
Still some interference even at that low sense settings but in the very entrance part with all the EMI and about 100 years of trash I still managed to pluck out some hidden and masked clad plus a very nice merc dime.
Don't think I would have found that coin spill deep at this low sense setting but in the trashy are it was just perfect to find a 4" deep dime.
All of this is just to say that by learning the behavior if your chosen detector more than well you might be able to notice a second more hidden language...something I know the Fishers possess but other types and brands just might also.
In your place I would wade into that site with the F75 knowing what I know about Fisher behavior, but heavy EMI should never detour you but motivate you to find the key and solve the puzzle instead...and I believe there us always an answer but you just have to figure it out.
Edited 4 time(s). Last edit at 05/09/2016 03:32PM by diggwr27.
|
Re: EMI May 09, 2016 04:22PM |
Registered: 12 years ago Posts: 6,830 |
deadeye Wrote:
-------------------------------------------------------
> There is one yard that I have detected in that has
> real bad EMI or something else. I have tried a
> Titan 3000, Garrett 2500, White DFX, V3, AT PRO,
> 75 LTD and Racer 2 in the yard. There are no wires
> going over the yard, they run to the back of the
> yard about 50 yards away from the front where I am
> trying to detect. Of all the detectors I listed
> the only ones that I could find anything with, was
> the AT PRO and the 75 LTD, all of them give
> erratic beeping but the AT PRO and 75 LTD was not
> as bad. I didn't try to make changes on the DFX
> when I tried it. On the racer 2 I could hear a
> pulsing sound. On the AT PRO and the 75 LTD I
> could get them to quiet down some by using
> frequency offset, on the Racer 2 I could not.
> By changing to a smaller coil on the all the
> detectors helped some, but I still had problems.
>
> How can sites like this be hunted?
Well, for one if you could identify EMI source,,, maybe would help.
Things like electric fences,,invisible dog fences-- drive most detectors nuts.
Even an aircraft at 30,000 ft overhead,,, could as it flies over and nearer drive a detector nuts.
Some sites due to EMI,,,are just limited to shallower detecting when it comes to EMI,,,just do the best you can,,some detectors may do better than others,,,my experiences running most of the flagships,,,if minelabs with noise cancel can't hunt a site--- few if any others will be able,,,,,meaning depth limited is what a person is looking at running lower sensitivity, tx boost, etc
Smaller coil is one possible work around,,,,and not all detectors with small coils are created equal with both separation and depth.
DST upgraded F75 with small coil would be one of my recommendations.
CTX 3030 with 6" coil another
Etrac with 5 or 6" coil another.
I am sure there are others.
-------------------------------------------------------
> There is one yard that I have detected in that has
> real bad EMI or something else. I have tried a
> Titan 3000, Garrett 2500, White DFX, V3, AT PRO,
> 75 LTD and Racer 2 in the yard. There are no wires
> going over the yard, they run to the back of the
> yard about 50 yards away from the front where I am
> trying to detect. Of all the detectors I listed
> the only ones that I could find anything with, was
> the AT PRO and the 75 LTD, all of them give
> erratic beeping but the AT PRO and 75 LTD was not
> as bad. I didn't try to make changes on the DFX
> when I tried it. On the racer 2 I could hear a
> pulsing sound. On the AT PRO and the 75 LTD I
> could get them to quiet down some by using
> frequency offset, on the Racer 2 I could not.
> By changing to a smaller coil on the all the
> detectors helped some, but I still had problems.
>
> How can sites like this be hunted?
Well, for one if you could identify EMI source,,, maybe would help.
Things like electric fences,,invisible dog fences-- drive most detectors nuts.
Even an aircraft at 30,000 ft overhead,,, could as it flies over and nearer drive a detector nuts.
Some sites due to EMI,,,are just limited to shallower detecting when it comes to EMI,,,just do the best you can,,some detectors may do better than others,,,my experiences running most of the flagships,,,if minelabs with noise cancel can't hunt a site--- few if any others will be able,,,,,meaning depth limited is what a person is looking at running lower sensitivity, tx boost, etc
Smaller coil is one possible work around,,,,and not all detectors with small coils are created equal with both separation and depth.
DST upgraded F75 with small coil would be one of my recommendations.
CTX 3030 with 6" coil another
Etrac with 5 or 6" coil another.
I am sure there are others.
|
Re: EMI May 09, 2016 04:42PM |
Registered: 14 years ago Posts: 3,028 |
I have noticed in some places that EMI is bad at some times of the day and not other times. The yard that I am talking about, is bad every time of the day. There is an electric fence about 50 or 60 yards away. I had the 75 LTD upgraded, so I will give that a try. I have detected a lot closer to an electric fence with no problems at other places.
I am not giving up on the place, I just need to figure out how to get past the problem.
I am not giving up on the place, I just need to figure out how to get past the problem.
|
Re: EMI May 09, 2016 05:47PM |
Registered: 14 years ago Posts: 3,028 |
DirtyJohn Wrote:
-------------------------------------------------------
> Who'd of thought a few years ago that an F75 would
> ever be mentioned in a thread talking about EMI
> resistant detectors.
>
> HH
> John
I was thinking the same thing.
DST was quite an improvement in terms of audible EMI.
-------------------------------------------------------
> Who'd of thought a few years ago that an F75 would
> ever be mentioned in a thread talking about EMI
> resistant detectors.
>
> HH
> John
I was thinking the same thing.
DST was quite an improvement in terms of audible EMI.
|
Re: EMI May 09, 2016 07:52PM |
Registered: 10 years ago Posts: 214 |
I've wondered about EMI sources and have heard the usual stuff like cell towers and wireless access points. What I don't get is how those sources could be a big problem when they operate at a far higher frequency. I've been near cell antennas and my detectors have run just fine. Wireless APs run around 2.4gHz or 5 gHz. What I suspect for most EMI sources is some sort of transformer or anything that produces some sort of electric arcing which would probably produce noise on a wide range of frequencies like trains (elec drives), blenders, power tools, etc. Since I have been more into urban detecting recently, it seems traffic control boxes or even radio operated remote controlled sprinkler systems will drive most of my machines nuts.
|
Re: EMI May 10, 2016 05:08AM |
Registered: 14 years ago Posts: 8,155 |
NASA-Tom Wrote:
-------------------------------------------------------
> One of the biggest offenders of EMI is........
> underground power wires.
>
> Then................... it's the 'above ground'
> leaking transformers and/or wires.
Yep forgot about one spot even my cz's get a waiver of emi. It where and old late 1800's early 1900's railroad building sets on one side of a railroad track and the newer one is on the other side and the old one has and underground cable between the two.
The old one is full of electrical switch gear etc. Still cz's are by far the least effected, t2 can't stand it.
------------"Cz's still bad to the bone".------------
Living on a big ass Astroid.
The woman that got my rib,I want it back.
Edited 2 time(s). Last edit at 05/10/2016 02:51PM by supertraq.
-------------------------------------------------------
> One of the biggest offenders of EMI is........
> underground power wires.
>
> Then................... it's the 'above ground'
> leaking transformers and/or wires.
Yep forgot about one spot even my cz's get a waiver of emi. It where and old late 1800's early 1900's railroad building sets on one side of a railroad track and the newer one is on the other side and the old one has and underground cable between the two.
The old one is full of electrical switch gear etc. Still cz's are by far the least effected, t2 can't stand it.
------------"Cz's still bad to the bone".------------
Living on a big ass Astroid.
The woman that got my rib,I want it back.
Edited 2 time(s). Last edit at 05/10/2016 02:51PM by supertraq.
I live in an area of a old coal town...Seem like the owners threw the ashes in the yard and old coal burners were inefficient thus are tough to hunt with any detector as unburnt hard coal...yep even CZ's.......Find another yard ought to cover it as some places just are not huntable due to unknown or unseen sources..
TabWhisperer Wrote:
-------------------------------------------------------
> I've wondered about EMI sources and have heard the
> usual stuff like cell towers and wireless access
> points. What I don't get is how those sources
> could be a big problem when they operate at a far
> higher frequency. I've been near cell antennas
> and my detectors have run just fine. Wireless APs
> run around 2.4gHz or 5 gHz. What I suspect for
> most EMI sources is some sort of transformer or
> anything that produces some sort of electric
> arcing which would probably produce noise on a
> wide range of frequencies like trains (elec
> drives), blenders, power tools, etc. Since I have
> been more into urban detecting recently, it seems
> traffic control boxes or even radio operated
> remote controlled sprinkler systems will drive
> most of my machines nuts.
You're right, it isn't the RF. However most cell sites are slam full of AC/DC converters, rectifiers, generators, amplifiers, ac to DC powerplants, Hvac units, etc. Also all cell sites have underground power/telco (the main culprit for detectorists), large buried ground rings that can be half an acre, etc.
AM is paticularly nasty however . The whole tower is an actual antenna, some with voltage up to 50,000 watts. I've seen towers a mile away from them that can actually shock you if you touch them with a wrench. They have to have detuners installed to divert the electrical charge in the air.
Edited 1 time(s). Last edit at 05/10/2016 04:21PM by deadlift.
-------------------------------------------------------
> I've wondered about EMI sources and have heard the
> usual stuff like cell towers and wireless access
> points. What I don't get is how those sources
> could be a big problem when they operate at a far
> higher frequency. I've been near cell antennas
> and my detectors have run just fine. Wireless APs
> run around 2.4gHz or 5 gHz. What I suspect for
> most EMI sources is some sort of transformer or
> anything that produces some sort of electric
> arcing which would probably produce noise on a
> wide range of frequencies like trains (elec
> drives), blenders, power tools, etc. Since I have
> been more into urban detecting recently, it seems
> traffic control boxes or even radio operated
> remote controlled sprinkler systems will drive
> most of my machines nuts.
You're right, it isn't the RF. However most cell sites are slam full of AC/DC converters, rectifiers, generators, amplifiers, ac to DC powerplants, Hvac units, etc. Also all cell sites have underground power/telco (the main culprit for detectorists), large buried ground rings that can be half an acre, etc.
AM is paticularly nasty however . The whole tower is an actual antenna, some with voltage up to 50,000 watts. I've seen towers a mile away from them that can actually shock you if you touch them with a wrench. They have to have detuners installed to divert the electrical charge in the air.
Edited 1 time(s). Last edit at 05/10/2016 04:21PM by deadlift.
|
Re: EMI May 11, 2016 03:20PM |
Registered: 14 years ago Posts: 353 |
deadeye Wrote:
-------------------------------------------------------
> I have noticed in some places that EMI is bad at
> some times of the day and not other times. The
> yard that I am talking about, is bad every time of
> the day. There is an electric fence about 50 or 60
> yards away. I had the 75 LTD upgraded, so I will
> give that a try. I have detected a lot closer to
> an electric fence with no problems at other
> places.
>
> I am not giving up on the place, I just need to
> figure out how to get past the problem.
The easiest way is ask the owners of the electric fence if they will turn it off for a few hours. See if it is the offender.
Gonebeepin'
------------------------------------------------------------------
Just one more good target before I go.
-------------------------------------------------------
> I have noticed in some places that EMI is bad at
> some times of the day and not other times. The
> yard that I am talking about, is bad every time of
> the day. There is an electric fence about 50 or 60
> yards away. I had the 75 LTD upgraded, so I will
> give that a try. I have detected a lot closer to
> an electric fence with no problems at other
> places.
>
> I am not giving up on the place, I just need to
> figure out how to get past the problem.
The easiest way is ask the owners of the electric fence if they will turn it off for a few hours. See if it is the offender.
Gonebeepin'
------------------------------------------------------------------
Just one more good target before I go.