EMI ferrite core cable attachments

[sovereignelite]

Does anyone have any experience with these little cheapy cable clasps that are supposed to inhibit electromagnetic interference: specifically Sovereign models?

 

[rl48off]

Not me.

 

[Tin Fin]

I've not used any on the Sovereign, but I have used them on radio equipment, tv's, and other electronic stuff - they make a difference most of the time. Placement can be key, but so can the type of ferrite core that is used. Using a torrid, you have to wrap the wire through the torrid - I don't want to do that with the GT. The snap-on style made for computers might help some, but I would have to play with it some. As it is, most of the time, EMI isn't much of a problem for me except in a couple of areas, and I don't think it would help in those locations. I have several around; if I get a chance to work with them to see if there is any improvement, degraded signals, or other differences, I will get back with you on this.

 

[dewcon4414]

Many have tested them.... but few find them effective. If they made a vast improvement i know a couple of the companies that have EMI issue would already have them on their machines. I believe they are also called torids ..... take a look: http://www.minelabmods.com/joomla/index.php?option=com_content&task=view&id=44&Itemid=42

Dew

 

[sovereignelite]

Many have tested them.... but few find them effective. If they made a vast improvement i know a couple of the companies that have EMI issue would already have them on their machines. I believe they are also called torids ..... take a look: http://www.minelabmods.com/joomla/index.php?option=com_content&task=view&id=44&Itemid=42

Dew

So it looks like Minelabs already have them internally. Interesting read. Thanks!

 

[Tin Fin]

Most electronics have the toroid's in them - the only time I have used them is for RFI on TV's and radio. Sometimes they help, sometimes not. But, in wrapping a wire through the toroid, inductance becomes a factor. That's why I never messed with them on a detector to start with.

 

[Critterhunter]

The primary source of EMI is it being picked up by the coil, because coils in effect are just giant antennas. So to reduce EMI coil selection is more important IMO. You can do that by using a small coil, or egg shaped coils appear to be less prone to EMI. I've always heard this, and I can say that indeed the 12x10 allows higher sensitivity settings around EMI than the 10" Tornado or the Ultimate, or at least it always panned out when I'd swap coils at the same site on the same day, the 12x10 usually allowed higher sensitivity settings. And this is without moving the coil, because you have to hold the coil still to see if chatter or nulling is due to EMI, where as when moving the coil on the ground those things might be being caused by ground mineralization.

If you do a search in the modifications forum, I think you'll find some discussions on the topic, as about a year or so ago I remember some talking about the subject.

As Tin Fin said, I'd be more worried about coiling the coil cable around the shaft, as that creates a inductive field, and inductors try to inhibit current flow. That's just one of the reasons why I run the coil straight up the shaft until behind the grip, mainly to get it away from the coil as fast as possible, but in reality It's still being coiled around my upper metal shaft behind the grip. I've read of people who coil the cable in a non-tight stand alone loop, and then hang that from the shaft via velcro, for this very reason.

Another approach is to shorten your coil cables. I plan to perhaps do that as one of my winter projects. I only want the coil cable long enough to reach the control box on the shaft without the meter in between, with just enough length to wrap it about 3 times around the shaft, so I've got extra slack to fix a short should I ever get one. Even though I always have a meter on my land shaft, I want enough coil cable length to insure ability to use it without a meter for re-sale purposes.

As for my Digisearch meter, it too has a ton of extra coil cable length, because it's made that way so if you are using it you can also still hip or chest mount the control box, because that's why the coil cables are so long on the Sovereigns in the first place- designed for land/water hunting. So not only do I have a ton of extra coil cable because the coil plugs into the meter and not the box, but I've also got a ton more from the meter to the box. Just way too much for comfort IMO.

The only coil I plan to keep at stock length is the 10" Tornado, because that stays on my water shaft and I need it long for chest mounting, or for in the future when I mount a waterproof box on a back shaft extension to throw the control box into when I'm water hunting. If I end up replacing the Tornado with the S-12 for water use, I also want to keep the Tornado at stock length because I plan to then trade it off as it has no use for me on land where I only use the 12x10, or my future 13" Ultimate or 8" Tornado sometimes.

From what I gather non of the stock or aftermarket coils for the Sovereign have shielding in the cable, due to the unique pre-amp on the RX winding in the coil which boosts the very weak received signal before sending it up the coil cable. This stronger signal makes it less prone to being washed out or contaminated by EMI noise, so I guess that's why they don't shield the cables on the Sovereign, while it's typical to do on all other detectors as they don't feature a pre-amp like this in the coil. I believe Ralph at Sun Ray did say early versions of the S-12 didn't have shielding in the cable, but the later versions (which have a different color cable) have shielding, but only because they needed those for making the Etrac/Explorer versions of the S-12, so I guess it just made more sense to order one type and use it on the Sovereign/Excal version coils as well. I think he noted that they never really saw any difference between the older non-shielded version and the newer one.

All that said, way I look at it never hurts to hedge your bets. By shortening the cable it should equal less EMI potential, less weight/mess on the shaft, and also gaurd against the induction issue of coiling the cable around the shaft.

Another area of concern for EMI is the circuit board in the control box it's self. There was a ran of ealier XS models I believe (not all of them), that didn't have shielding inside the control box. I remember running across posts where people were installing their own shielding. If anybody does that make sure it isn't going to touch anything and short out, and ground the shielding to the main negative trace ground coming from the battery. I noticed in my GT that the shielding only goes around the circuit board left to right from top to bottom, but the front and back ends are open, much like a "tube" of shielding around the control board. I would think EMI could easily enter from the front or back ends of the control box for that reason. I've been playing with the idea of installing some shielding to insure further against it. Next time I have my GT apart I might tackle that idea.

I remember when I first started investigating the Sovereign as a potential purchase, in my research I ran across a number of posts about EMI problems. I was concerned with that, but in truth I don't really find it any more prone to EMI than any other machine I've owned over the years, except of course my Explorers because you can dynamicly noise cancel them. I suspect many of the EMI issues I ran across posts on were either due to the non-shielding production run of an older Sovereign model (think it was the XS, and it wasn't every one, just some that weren't shielded), or perhaps was due to the older non-Tornado coils that perhaps were more prone to soaking up EMI than the newer Tornado versions. Even with the stock 10" Tornado I find the GT very well behaved around houses and such most of the time, but yes sometimes I have to lower the sensitivity a good bit if switching noise bands doesn't help. Not always though.

 

[deepdiger60]

The external ones dont work at all on detectors you would be wasting your money buying one, Minelab takes care of EMI problems internally but still not 100% .

 

[dewcon4414]

Looks like Critter has been reading some of the answers on Toms site when the subject was discussed.... i read those as well. Not many believe they help.

Dew

 

[Neil]

Looks like Critter has been reading some of the answers on Toms site when the subject was discussed.... i read those as well. Not many believe they help.

Dew

yep

 

[Critterhunter]

Dewcon/Neil, I don't believe I've ever read any ferrite discussions on there that I remember, as for one thing I haven't been on that forum for all that long. I have read them on other forums though over the years. On that forum though, I did bring up a related subject for discussion and opinions- horizontal versus vertical coil orientation when noise cancelling the FBS units.

I say that people holding the coil vertical when noise cancelling are changing the conditions of the EMI, because far as I've always figured changing the orientation of an antenna can change the strength of certain frequencies received, just like in adjusting rabbit ears on a TV.

You can see that in how a detector often gets noisy when it's laid down with the coil now vertical while you are digging a target. That's why I brought the subject up to see if anybody had any opinion on it. Mainly because I've seen a few friends noise cancel by holding the coil up in the air in front of them with it now vertical because it's just easier to do then trying to keep the coil horizontal and a foot or two off the ground.

I've always felt the extra effort should be made to keep the coil held horizontal like under normal hunting conditions and then noise cancelled that way so the EMI doesn't change between the horizontal or vertical aspects, and always made sure to do that with my Explorers. Never really saw the topic broached on any forums in the past, so I wanted to see what others had to say about it.

But in terms of my history on reading up/researching about EMI, I've done most of that in the past for reasons not even related to metal detectors. About 6 or 7 years ago, when I was intending to use cameras on RC electric planes I was building to transmit live video feeds down to a ground station, I found out this horizontal/vertical orientation of an antenna (which is pretty much what a coil is) is called polarization.

In some instances it's better to have the video transmitter's antenna vertical, and in others horizontal, and then the antenna on the video receiver on the ground is placed in the same orientation to better match the two. I would guess the same thing applies to a coil on a detector. Vertical it might pick up stronger EMI on certain frequencies than it will held horizontal.

But mostly I've read up on the subject of EMI years before that in other aspects not even related to metal detecting, being that electronics was always something I've tinkered with here and there. EMI doesn't just come from outside forces, but can be generated by components on the circuit board of a device as well (circuit noise).

The first time I had to research how chokes and capacitors could be used to tame internal generated EMI was a few deer trail cameras I was trying to build, back years ago when the prices of those things were through the roof, so I wanted to try to save some money and build a few myself.

I used a battery powered door chime motion censor, by cutting out the speaker and replacing it with a diode, to change the pulsing voltage to the former speaker which created the "chime", to a constant DC output that would properly energize a relay, which would then trigger a 555 IC timer circuit.

I had to build the timer circuit to then hold down a solenoid for the few seconds I needed to properly engage the camera shutter, since the voltage output from the chime wasn't long enough in duration to fire a relay/solenoid directly to properly push the shutter down in with enough time to finish the act.

So the motion censor's "chime" was just used to trigger the timer circuit into action. Problem was that the solenoid when energized produced EMI on the circuit board and sent the 555 IC timer into erratic behaviour or would even lock it up. That was the first time I had to read up on chokes and capacitors that might fix the problem.

More recently (about the last 6 or 7 years or so), I had to research/read up on EMI because early on with my attempts to fly RC planes with live video down feeds, I ran into issues with EMI in both aspects- external and internal.

The internal EMI (or circuit noise) due to the brushless motor generating EMI in the electronics, and also due to the pulse width modulation that an ESC uses to control the speed of the motor. Pulse width modulation controls the speed of the motor by adjusting how fast power is switched on/off in pulses to it.

Both of these things were causing bad static on the video feed, because I was powering the camera and it's video transmitter directly from the plane's battery instead of using a separate one to save weight. I had to use a linear regulator to drop the plane's battery voltage down to what the camera and transmitter needed, and found that circuit noise was traveling through the shared electrical connections for the power source and causing static. So once again I had to read up on and refresh my memory on how to use chokes and capacitors to cancel out circuit board noise.

The internal EMI problem was fixed, with no more static on the video feed, but then I still had problems with external EMI. The video transmitter on the plane was at times locking out the plane's receiver and causing the plane's controls to glitch out. Nothing scares you more than flying a plane and then all of a sudden realizing the controls are locked out , and I wrecked a number of planes I built until I worked that issue out.

Wasn't much I could due about the glitch out of the controls from the video feed, because it's the transmission of the video signal in the air that was sometimes locking out the receiver on the plane and I was no longer dealing with an internal EMI issue.

Short of changing the frequency of the plane's RX or the video transmitter to something different that hopefully wouldn't cross talk between the two as much, I fixed the problem by re-locating the video transmitter's antenna as far away from the plane's RX as possible, and also placing the video transmitter's antenna at the top of the plane while relocating the plane's RX antenna to the belly of the plane, so that the RX had more of a direct line of sight to the transmitter I use to control the plane from the ground.

All these things drove me nuts for a while, and I wrecked a bunch of planes because the controls locked out on me, or when they didn't I still wasn't able to record video on the ground due to the static. But eventually I was able to get all the issues figured out, and it was worth it, as this video of one of my early flights several years back shows...

http://www.youtube.com/watch?v=m0vjN-ilbM8

I've since found that I don't really use live video down feeds much, because I prefer to record the video directly on board the plane now, which makes for even better video quality than the loss of resolution that can happen with transmission. Even if I do transmit to a ground station so I can view what the plane views, I still prefer to have the actual video recorded directly on board the plane.

 

[Critterhunter]

Many have tested them.... but few find them effective. If they made a vast improvement i know a couple of the companies that have EMI issue would already have them on their machines. I believe they are also called torids ..... take a look: http://www.minelabmods.com/joomla/index.php?option=com_content&task=view&id=44&Itemid=42

Dew

So it looks like Minelabs already have them internally. Interesting read. Thanks!

Yep. Hard to say for sure with the picture below but sure looks like one to me. I drew an arrow to what I suspect is a choke on the GT's circuit board. Chokes can also take other shapes and forms. For instance, looking like small transformers, or even can be encased in metal cases looking much like a RF crystal to tune or select an RF channel on RC planes. Pic with some notation I drew on it below, along with a bit on voltage regulators, what they look like, and why lessor voltage of nimh rechargeables won't decrease a detector's performance...
[attachment 248693 IMG_6430.JPG]

 

[Rick in Pa]

Very interesting way to find a new detecting site. Looks like fun also.

 

[sovereignelite]

I like the coiling of the cable by itself and not around the shaft:never thought of that. On the sheilding in the GT: you might be on to something. Thanks for all the info. I haven't been on here much since my attempt to sell an XS2 Pro was deleted. Guess I haven't been a member long enough. Find this site to be really slow loading tooo. The other site I frequent is MUCH faster, but not nearly as interesting.

The primary source of EMI is it being picked up by the coil, because coils in effect are just giant antennas. So to reduce EMI coil selection is more important IMO. You can do that by using a small coil, or egg shaped coils appear to be less prone to EMI. I've always heard this, and I can say that indeed the 12x10 allows higher sensitivity settings around EMI than the 10" Tornado or the Ultimate, or at least it always panned out when I'd swap coils at the same site on the same day, the 12x10 usually allowed higher sensitivity settings. And this is without moving the coil, because you have to hold the coil still to see if chatter or nulling is due to EMI, where as when moving the coil on the ground those things might be being caused by ground mineralization.

If you do a search in the modifications forum, I think you'll find some discussions on the topic, as about a year or so ago I remember some talking about the subject.

As Tin Fin said, I'd be more worried about coiling the coil cable around the shaft, as that creates a inductive field, and inductors try to inhibit current flow. That's just one of the reasons why I run the coil straight up the shaft until behind the grip, mainly to get it away from the coil as fast as possible, but in reality It's still being coiled around my upper metal shaft behind the grip. I've read of people who coil the cable in a non-tight stand alone loop, and then hang that from the shaft via velcro, for this very reason.

Another approach is to shorten your coil cables. I plan to perhaps do that as one of my winter projects. I only want the coil cable long enough to reach the control box on the shaft without the meter in between, with just enough length to wrap it about 3 times around the shaft, so I've got extra slack to fix a short should I ever get one. Even though I always have a meter on my land shaft, I want enough coil cable length to insure ability to use it without a meter for re-sale purposes.

As for my Digisearch meter, it too has a ton of extra coil cable length, because it's made that way so if you are using it you can also still hip or chest mount the control box, because that's why the coil cables are so long on the Sovereigns in the first place- designed for land/water hunting. So not only do I have a ton of extra coil cable because the coil plugs into the meter and not the box, but I've also got a ton more from the meter to the box. Just way too much for comfort IMO.

The only coil I plan to keep at stock length is the 10" Tornado, because that stays on my water shaft and I need it long for chest mounting, or for in the future when I mount a waterproof box on a back shaft extension to throw the control box into when I'm water hunting. If I end up replacing the Tornado with the S-12 for water use, I also want to keep the Tornado at stock length because I plan to then trade it off as it has no use for me on land where I only use the 12x10, or my future 13" Ultimate or 8" Tornado sometimes.

From what I gather non of the stock or aftermarket coils for the Sovereign have shielding in the cable, due to the unique pre-amp on the RX winding in the coil which boosts the very weak received signal before sending it up the coil cable. This stronger signal makes it less prone to being washed out or contaminated by EMI noise, so I guess that's why they don't shield the cables on the Sovereign, while it's typical to do on all other detectors as they don't feature a pre-amp like this in the coil. I believe Ralph at Sun Ray did say early versions of the S-12 didn't have shielding in the cable, but the later versions (which have a different color cable) have shielding, but only because they needed those for making the Etrac/Explorer versions of the S-12, so I guess it just made more sense to order one type and use it on the Sovereign/Excal version coils as well. I think he noted that they never really saw any difference between the older non-shielded version and the newer one.

All that said, way I look at it never hurts to hedge your bets. By shortening the cable it should equal less EMI potential, less weight/mess on the shaft, and also gaurd against the induction issue of coiling the cable around the shaft.

Another area of concern for EMI is the circuit board in the control box it's self. There was a ran of ealier XS models I believe (not all of them), that didn't have shielding inside the control box. I remember running across posts where people were installing their own shielding. If anybody does that make sure it isn't going to touch anything and short out, and ground the shielding to the main negative trace ground coming from the battery. I noticed in my GT that the shielding only goes around the circuit board left to right from top to bottom, but the front and back ends are open, much like a "tube" of shielding around the control board. I would think EMI could easily enter from the front or back ends of the control box for that reason. I've been playing with the idea of installing some shielding to insure further against it. Next time I have my GT apart I might tackle that idea.

I remember when I first started investigating the Sovereign as a potential purchase, in my research I ran across a number of posts about EMI problems. I was concerned with that, but in truth I don't really find it any more prone to EMI than any other machine I've owned over the years, except of course my Explorers because you can dynamicly noise cancel them. I suspect many of the EMI issues I ran across posts on were either due to the non-shielding production run of an older Sovereign model (think it was the XS, and it wasn't every one, just some that weren't shielded), or perhaps was due to the older non-Tornado coils that perhaps were more prone to soaking up EMI than the newer Tornado versions. Even with the stock 10" Tornado I find the GT very well behaved around houses and such most of the time, but yes sometimes I have to lower the sensitivity a good bit if switching noise bands doesn't help. Not always though.