Now I understand

After reading Tom's post on choosing the best operating frequency for the F75 or F75 LTD and comparing it to the noise cancel feature of the Minelab Safari and SE I understand the principle better.
Thanks Tom for taking the time to experiment and post results here.

Markg were was that thread. i would like to read it again.
I can be ready when the snow melts thanks Mike

Gman, After seeing this post from Markg I had to go re-read that myself and it is very good information. There is a very long post called "Rcpt Ack of F75 LTD Prototype" just a few lines down. Look on page 4 for Tom's explanation on choosing the best frequency to aid in EMI. Randy.

You are welcome.

Yesterday (Sunday)......I had a strong reitteration of the importance of F1 - F7 freq selection whilst hunting a 3rd Seminole Indian War site. Private property.....bewtween two older houses......and minimal iron.

First target of interest: Eagle Button, Artillary 'A', 2-piece, Scovills Mfg, Circa 1841 (approx.) Coat (about the diameter of a nickel.....and the thickness/height of 3 stacked nickels).........just over 14" deep......with no iron nearby. (((F75 LTD, 'bp', Disc '1', Sens '99', 4-tone))). Before I took the shovel to the dirt......I experimented with control settings IRT freq selection. Only 3 of the freq's (F2, F3 & F6) would acquire this target. All other freq's were slightly more noisy.....making this specific target completely undetectable. Dropping Disc to '0'.........and ......... same thing. Only F2, F3 and F6 freq's would acquire this target....and with a bit louder/better resolution.......but, at the cost of a fairly large increase of GROUND (not EMI) feedback/noise. A Disc setting of '1' made the unit substantially less fatiguing by reducing ground noise.....for THIS particular site.

Second target of interest: A .69 Cal unfired musket ball at 17" deep.......no iron in close proximity. This is maximum/fringe depth for the F75 LTD. No air-gap forgiveness at this depth. Raising the coil 1/2" above the ground.......and this target would be completely undetectable....under any/all conditions. ONLY ONE freq (F6) would acquire this musket ball.

Third target of interest: A nearly uncirculated 1867 Shield nickel......just under 12" deep. (((Must have been from a passer-by hunter.......well after 3rd Seminole Indian War))). Only F3 and F6 freq's would detect this target. All other freqs were crippling.......with the worst offender being F7.........at THIS particular EMI-local-conditions site.

Tom

When detecting targets at this depth do you find the tone to be correct or off? Also how is the ID, jumpy or fairly consistent?

Tommy C.
(southernexplorer)
Deus - Etrac - GPX 5000

These are 'fringe depth' targets......and the ID.....in general.......is all over the board; YET, there is a 'averaging bias' in the direction .... as to the conductivity of the metal. If the object has a conductivity of....say '60' (like the .69-cal musketball).........it'll bounce all over the board......with the propensity of higher numbers (on average). If it's an item with a ID of ..... say...... '28' (like the 1867 Shield nickel)..........it'll bounce the entire spectrum........with a slight bias towards the bottom/middle end of the scale. My first question is: Is it ferrous.......or non-ferrous. My next question is: Is it large and deep .... like a coin or musketball..........................or small and shallow......like a percussion cap or air-rifle BB. The breadth (width) of the audio signal duration dictates this.....as long as the item is not partially masked. And.............in my inert dirt..............targets will 'better' resolve (better ID)....with a much faster coil sweep (coil whip)......ONCE I have determined that a target exists. I only perform this 'coil whip'.......in clean (nearly no targets) dirt. In these types of sites.........a larger coil is fully justified......and needed.

Tom checking the frquencies for the best one by your instructions do you turn the threshold up while in motion all metal or do you leave it at 0? I know you turn up the sensitivity to 99.





NASA-Tom Wrote:
-------------------------------------------------------
> You are welcome.
>
> Yesterday (Sunday)......I had a strong
> reitteration of the importance of F1 - F7 freq
> selection whilst hunting a 3rd Seminole Indian War
> site. Private property.....bewtween two older
> houses......and minimal iron.
>
> First target of interest: Eagle Button, Artillary
> 'A', 2-piece, Scovills Mfg, Circa 1841 (approx.)
> Coat (about the diameter of a nickel.....and the
> thickness/height of 3 stacked
> nickels).........just over 14" deep......with no
> iron nearby. (((F75 LTD, 'bp', Disc '1', Sens
> '99', 4-tone))). Before I took the shovel to the
> dirt......I experimented with control settings IRT
> freq selection. Only 3 of the freq's (F2, F3 & F6)
> would acquire this target. All other freq's were
> slightly more noisy.....making this specific
> target completely undetectable. Dropping Disc to
> '0'.........and ......... same thing. Only F2, F3
> and F6 freq's would acquire this target....and
> with a bit louder/better resolution.......but, at
> the cost of a fairly large increase of GROUND (not
> EMI) feedback/noise. A Disc setting of '1' made
> the unit substantially less fatiguing by reducing
> ground noise.....for THIS particular site.
>
> Second target of interest: A .69 Cal unfired
> musket ball at 17" deep.......no iron in close
> proximity. This is maximum/fringe depth for the
> F75 LTD. No air-gap forgiveness at this depth.
> Raising the coil 1/2" above the ground.......and
> this target would be completely
> undetectable....under any/all conditions. ONLY ONE
> freq (F6) would acquire this musket ball.
>
> Third target of interest: A nearly uncirculated
> 1867 Shield nickel......just under 12" deep.
> (((Must have been from a passer-by
> hunter.......well after 3rd Seminole Indian
> War))). Only F3 and F6 freq's would detect this
> target. All other freqs were crippling.......with
> the worst offender being F7.........at THIS
> particular EMI-local-conditions site.
>
> Tom

hey Tom were any test made in all metal using diff freq's. hmmm

On all 3 targets.............I did indeed test the all-metal mode...........and.......per expectations..... a very slight audio 'blip' was heard.......but NOT enough signal strength to drive the ID circuitry.......as long as the right freq(s) were selected. With the wrong freq(s) selected...... there were TOO much EMI noise.....completely washing out the very faint audio hit.

Yes, you can utilize all-metal mode to best select F1 - F7 freq. I (somewhat) prefer the ID mode......for selecting the best freq....although the all-metal mode is audibly easier understood. Use a threshold setting so as to JUST BARELY hear a 'slight' threshold. . . . with Sens on '99'. The game-plan is to MAKE as much EMI noise..........THEN start adjusting the F1 - F7 freqs.

And what ever you do to the freq's in the all-metal mode......it'll carry over into the ID mode.

to set the frequencies in the ID mode?

Thanks Tom! Once again this will aid me at my plantation site. Maybe next trip I'll pull that CSN Navy I'm looking for.

If the detector is going to "EMI false" on me anyway......selecting the freq whilst in ID mode allows me to know WHAT KIND of falsing will be presented. I prefer the audio falsing to ALL be iron tones. You will notice that some different F1 - F7 freqs.....give different 'chatter'. Some of these channels present multi-tone falsing.......and ....... maybe a particular channel presents ONLY iron tone falsing.....although it may be at the expense of greater EMI; yet, much more intelligible. User preference.

That is one SERIOUSLY helpful tip, regarding setting the frequency to a iron tone false.



Edited 1 time(s). Last edit at 01/18/2011 09:11PM by TerraDigger.

I do so many things autonomously.........that I had to ask myself this question.....WHILE I WAS IN THE MIDDLE of performing such task. Otherwise..... I would never be able to answer the 'why' question.

This is pretty stunning information to me...comes as a huge eyeopener. I've never played with the frequencies after setting it up once at a site (usually picking the most quiet one). Tom, do you think this would apply to beach conditions as well as inland, or maybe a better question would be have you experimented with the frequencies when testing the LTD on the beach? Thanks for the fascinating info and thread. BTW, is your LTD still stock, or 'customized'.

We cant thank Tom enough for all the good info he gives on here! Lots of others here too with good inputs!

Bart Davis,
[www.BigBoysHobbies.net]
Authorized Minelab, Garrett, Fisher and Teknetics Dealer

EMI is EMI.......regardless of location. And the mitigation there-of is paramount.......beach, dirt or otherwise. Usually......EMI on the beach is less....as you are further away from electrical sources.

My F75 is bone-stock (thus far).