Standard DD Coil Question.

Okay,having watched Tom's DVD went out on a full days club dig yesterday.

I wanted to try out how keeping the coil as close to the ground as possible would work out (virtually scraping the soil), i have been keeping it off the ground a little in the past because of a noise issue.

I'll try to explain, many of the fields that i detect on are plowed and rolled,
this gets them reasonably flat but there are a lot of small earth and stubble mounds, large pebbles/stones etc that will break the surface.

For as long as i can remember (i have only been able to get out about 6 or 7 times in 18 months) when sweeping over and catching or knocking into any of these even slightly will produce a signal.

The signal is false of course but it does make you stop for a moment and recheck,when you lift the coil slightly to avoid bumping it no signal / noise apart from the normal ground chatter.

The soil was quite damp yesterday due to overnight rain and a steady light drizzle, this caused the coil to gradually gain weight due to the damp soil build up, because of this i would regularly give a the coil a clean just with my hand scraping the excess soil off.

When doing this i noticed that if i tapped the coil either on the main centre spine or on the outer edge this too would cause a loud clear signal just like any ground target, i hadn't noticed this before as it had allways been dry conditions previously.

Originally i put it down to having an extra sensitive machine and being new to it not knowing how to use it correctly,the above is what has caused me to raise the coil away from the ground slightly in an attempt to stop all the falsing, you can imagine how annoying this falsing could be on virtually every sweep.

I realise that lifting the coil can mean missing good targets, catch 22 comes to mind.

Is this coil noise as explained above normal?
Could some of you check yours out to see what you find.

I am beginning to wonder if i have a faulty coil.

Help much appreciated.

Take care, Mart.



Edited 1 time(s). Last edit at 04/12/2009 10:37AM by mart.

Matt,

What detector are you using? Are you in All Metal mode or Disc Mode? What do you have the sensitivity setting at? If the sensitivity setting is too high you will get falsing at the end of the swing, and bumping into weeds, sticks, clods of dirt, etc. Pull the coil cover off and clean it out. That will also cause falsing. What kind of soil are you detecting in? Mineralized? Sandy?, Clay? Gumbo? Good deep black soil?
Add a little bit more info for the guys here so that they can respond to a particular detector. The high sensitivity and the coil cleaning will work on almost every detector that I know off. But some other detectors may have some individual quirkiness that can be quickly answered to by someone who uses that machine. There are a lot of variables to consider.


For what it is worth, just me 2 cents,
Cuniagau

PS 6 or 7 times in 18 months does not give you a lot of field time to remember what works and what doesn't. Sometimes I can't remember what worked two weeks ago, let alone what worked 18 months ago.

“Never approach a bull from the front, a horse from the rear or a fool from any direction.”

Cuniagau thanks for your reply.

Sorry about not mentioning the machine i keep forgetting that Toms site is not just for Fisher detectors.
Any i am using the F75 with stock DD coil.
It happens with all settings, i usually use 2f,pf,disc 0 to 4 and sensitivity from 60 to 75.

Soil conditions are a combination of old crop that has been well plowed and turned with clay like qualities when you start digging.

I think the fact that when turning the machine upside down to clean away the build up of soil/mud etc and when tapping the coil center or outer ring removes ground conditions from the equation.

F75 owners does your machine sound off if you do this, does it give a signal just like when you pass over a good target because mine does hence why i am thinking the coil maybe faulty.

Take care, Mart.

Matt,

Also what does your GB set to? Another question is the FE meter on the right side of the screen, what kind of reading do you get on it? Highline wires near by? (looking for EMIs that might throw some instablity into the mix) Ok you F75ers,let's hear your opinions on this one. My first guess is Sen is to high and causing it to false on everything including the end of the swing. Does it repeat on the back swing? Or is it a one way signal?
Matt - also you might want to take the cover completly off the coil to clean. You might be surprise at how much silt and sand will collect and not come out by taping it.

Cuniagau

“Never approach a bull from the front, a horse from the rear or a fool from any direction.”

Cuniagau,

Well away from any power lines so not down to EMI'S.

It will happen when i am in the middle of a field virtually on my own, no other detectors or people nearby, no mobiles, power lines etc.

It does not happen when in the process of sweeping if i keep the coil sufficiently clear of the ground so as to not hit anything even with a fast sweep.

I did notice that if i held the detector a couple of feet off the ground and keeping my arm straight quickly wiggled the coil head from say 10 to to 10 past on an imaginary clock face it did give multiple signals.

You are right about the coil cover needing to be removed and cleaned and i will do that before my next dig but i think it's a bit more of a machine problem than just that.
Thanks again.
Take care, Mart.

....... and check one other thing. When the detector is set up..... and most prone to giving this false chatter..... lightly tap the coil wire..... about 1/2 the way down the stem. Maybe 12" - 18" above the coil. See if this causes the detector to act up.

Okay i still have the falsing as previously described with my F75.

I have cleaned the coil and coil cover, which is a good tip as dirt etc can get in there but it made no difference.

Tapping or gently pulling or moving the cable anywhere along its length does not produce any falsing.

Tapping or knocking the coil itself does produce a false good sound every time.

Could i please ask again if any of you F75 owners can check to see if your machine does this.

It is easy to do and would take a very short time but would assist me greatly in deciding to send my coil back to be checked out.

Thanks,
Take care Mart.



Edited 1 time(s). Last edit at 04/19/2009 08:56AM by mart.

Do a reset and post your exact settings after a ground balance. Record and post all your DATA.

I have two F75's....and a total of 4 of the 11" coils. Bumping the coil against anything (or even tapping it) WILL preduce a false...(every time).....so I think its SAFE to assume this is normal. My 75's have done this for the entire duration of ownership by me.(And I've experienced it on a few other detectors and certain coils) While I DO scrub my coil, I try to avoid actually hitting anything with it, due to the dependable false. It should be noted that this is more prevalant with higher gain settings. (or simply more noticeable). I dont think your coil is bad from what I've read in your posts. Streak!
PS: I wasnt going to respond to your post initially...........but your didnt seem to really get a straight answer from anyone about your problem, so here it is!!

Streak! Wrote:
-------------------------------------------------------
> I have two F75's....and a total of 4 of the 11"
> coils. Bumping the coil against anything (or even
> tapping it) WILL preduce a false...(every
> time).....so I think its SAFE to assume this is
> normal. My 75's have done this for the entire
> duration of ownership by me.(And I've experienced
> it on a few other detectors and certain coils)
> While I DO scrub my coil, I try to avoid actually
> hitting anything with it, due to the dependable
> false. It should be noted that this is more
> prevalant with higher gain settings. (or simply
> more noticeable). I dont think your coil is bad
> from what I've read in your posts. Streak!
> PS: I wasnt going to respond to your post
> initially...........but your didnt seem to really
> get a straight answer from anyone about your
> problem, so here it is!!

Streak you little Gem !!

You have indeed answerewd the question that i asked completely,i have seen you post on many Fisher Forums.

The straight answer is often the best reply.

I can now stop being bothered about a possible faulty coil.

I had started to adopt your approach concerning scubbing the coil while avoiding bumping things.

You are right about the higher gain settings definately more noticable on JE mode even with sensity down to the lower 50's.

Many thanks to you and the others in trying to help me out, much appreciated.

This problem has now been solved,(or STREAKED!!) case closed.

Take care, Mart.



Edited 1 time(s). Last edit at 04/20/2009 08:55PM by mart.