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machine probe RX Gain

G

greenmeanie

Active member
How many of you guys/gals go by what the machine recommends when probing?
Mine always recommends around default RX Gain but it runs real stable.
I bumped it up to 10 and it still ran stable. Would it be smart to keep bumping it up or am I pushing my luck?
 
I'm wondering the same thing. The MXT is noted to be able to run at a higher gain than other machines because of the circuitry. I would suspect the V should be the same? My novice theory is that running it as high as you can with it remaining stable is a good thing to do.

I have a penny in my yard at 10". On recommended gain for my ground, the V barely picks it up. On higher gain, while still stable, it picks it up loud and clear.
 
My Spectra regularly reports (almost always) a suggested gain of 15. That said, I do find it a bit hot sometimes.

I think it had a lot to do with how well the particular coil was nulled... I also have a non-V super 12 coil which runs anywhere between 3 and 15 for suggested sensitivity.

John
 
As long as it runs stable, go for it. I can usually up it two notches above the ground probe suggestions.
 
I'll trade you dirt. :(

Monte
 
Monte said:
I'll trade you dirt. :(

Monte
Click to expand...

No kidding!!! As soon as I read the first thought I had was, "Where in the world is he that the soil is that light??". Wow!!!

Dave
 
I've been keeping mine at 15 and it's pretty stable. As jgedde stated it could be how well the coil was nulled. I hear a lot of folks saying to null the coil when you first turn it on...and I think maybe the manual says that, but I never do it that way....how do you know if you're over a target? I turn on the machine and flip the switch to get to the search screen then hold the pinpoint switch while checking for all metal in the ground under the coil...when I find a clear spot, THEN I null the coil. I believe that is logically what we should do (with any detector actually)...right? I you were to turn on the machine and null it right away and happen to be over a target I beleive that causes it not to really be nulled accurately. Correct me if I am wrong please!
 
What does "null the coil" mean? Is that the same as setting the ground balance? (I do just what you said for ground balance -- first go to pinpoint and make sure I'm not over any metal -- a feat in itself in some places -- then set the ground balance.)
 
We've got ground like that here on Long Island. Sandy composition, very low mineral content. The bad news is that it's not much of an advantage for old coins as they sink with time much faster in the sandy ground. Old stuff is DEEP.
 
It is not the same as ground balance.

Nulling the coil is an operation done by White's when the search coil is manufactured. Inside a typical (non-DD) search coil are two concentric coils. The inner coil is the receive coil, the outer coil is the transmit coil. Basically, the receive coil's output is summed with the output of a smaller pickup coil built into the transmit coil in such a way that the transmit coil doesn't interfere with the receive coil. Adjustments inside the coil are used for this. White's coils are more advanced than the simple example I mention, but the principle is the same.

Ideally, the best possible null results in the receive coil having no output when the coil is in free air. The deeper the null, the higher sensitivity can be run without overload or masking of the target's response by pickup from the transmit coil.
 
DavefromCt said:
I've been keeping mine at 15 and it's pretty stable. As jgedde stated it could be how well the coil was nulled. I hear a lot of folks saying to null the coil when you first turn it on...and I think maybe the manual says that, but I never do it that way....how do you know if you're over a target? I turn on the machine and flip the switch to get to the search screen then hold the pinpoint switch while checking for all metal in the ground under the coil...when I find a clear spot, THEN I null the coil. I believe that is logically what we should do (with any detector actually)...right? I you were to turn on the machine and null it right away and happen to be over a target I beleive that causes it not to really be nulled accurately. Correct me if I am wrong please!
Click to expand...

You're exactly correct, however the process you describe is ground balancing not nulling (which is done by the coil manufacturer). I agree 100% with using all metal to find a "quiet" spot before balancing.
 
So how do we know how well our coil is nulled? my probe very seldom recommends anything higher than 5 or 6. But, I do run it higher if stable and realized my probe reaction is most likely due to my ground.
 
Being a dyed-in-the-wool MXT'er, I live and die by the gain control. I live in a very highly mineralized area, yet will hunt the MXT in as high a gain setting as I can stabilize and stand...it takes practice.

I've had a lot of success in the deep silver program mode, and never felt confortable with the low gain settings that were necessary to stabilize the V in other modes...C/J, etc. Today, I decided to return to a soccer field from which I've pulled quite a lot of jewelry with the MXT.

Trimming the C/J mode, the suggested gain was 3. (I cranked the disc sensitivity down to 7:geek: The soil was dry as a bone and (of course) highly mineralized. I figured "what the heck", since most jewelry finds in this heavily used field are less than 2" anyway.

Imagine my suprise when the first target I hit was a +80. The analyze screen displayed the 2.5kHz signal as a perfectly smooth "high" curve and the other two freqs were much lower in amplitude and a bit "wavy". The pinpoint depth registered a little over six inches, so I decided to find out just how old this bottlecap really was. Nine inches later, I saw a 1940 silver quarter looking at the tip of my Lesche with dread in its eyes.

So...why am I posting this?

Simply because I finally have the confidence necessary to hunt with gain settings as low as 3. That's a hard pill to swallow for an MXT guy who thinks if it's not at least 2X, it's not deep enough.
 
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