F5 Complete Sensitivity Control

[ToddB64]

Hi Everyone !

I was reading my free copy of Dave Johnson's booklet GOLD Prospecting With A VLF Metal Detector and in the back on page 54, talking about the Fisher F5, it states that " Independent gain and threshold knobs provide complete control over sensitivity." .
Can this degree of control over sensitivity be achieved with other makes and models of metal detectors that have touch pad or knob type gain and threshold, or is it only obtainable with Fisher patented circuitry ?

Thanks for replies !

ToddB64

 

[tabman]

Your Tesoro Bandido uMax has a threshold and sensitivity knob. The Teknetics Omega has a single knob that controls both the sensitivity and threshold. When you turn down the sensitivity enough to stop EMI, you also lose those faint and hard to hear deep targets, because the threshold got turned down as well. Separate controls are much better. I read somewhere that the Omega is an upgrade from the F5.

tabman

 

[ToddB64]

Your Tesoro Bandido uMax has a threshold and sensitivity knob. The Teknetics Omega has a single knob that controls both the sensitivity and threshold. When you turn down the sensitivity enough to stop EMI, you also lose those faint and hard to hear deep targets, because the threshold got turned down as well. Separate controls are much better. I read somewhere that the Omega is an upgrade from the F5.

tabman

Thanks tabman !

So, do the Threshold and Sensitivity ("Sensitivity" being synonymous with "gain") control knobs on the B2 uMax provide the same complete control over sensitivity as claimed on page 54 of the DJ booklet I mentioned at the top of this thread......do you know ?

Also, am I correct that lowering a particular threshold "hum" has no affect on the sensitivity level set (read "dialed-in") on the B2 uMax, only the ability of the human ear to hear some of the low tones from small and/or deep targets ? Of course, the acuity of ones hearing and the quality of earphones used might overcome this problem to an extent.

ToddB64

 

[Mike Hillis]

Hi Todd,

Just to review....In Discrimination mode.....
The F5 has a Gain control that amplifies a target signal, thereby making the signal look bigger (20 settings)
The F5 has a Threshold control that does two things....1st, it changes the signal strength limit that a target signal needs to reach in order to be reported (-9 to 0) and, 2nd, at settings above 0 (0 to +9), it amplifies the audio response of the signal. So at a threshold setting of zero, the F5 is wide open to receive the smallest of signals, and at settings above zero, it amplifies the audio response of those smallest of signals. It is extremly versitile, allowing multiple setting combinations to achieve the same outcome as may be needed based upon site requirements.

There are others that do something simular.....such as the F70 which gain/threshold controls is almost identical to the F5, then you have the Coinstrike/Goldstrike that are somewhat simular, but lack the audio amplification of threshold settings above zero. Then there is the V3/V3i which offer a gain and discrimination control (it is a threshold control labeled "discrimination". don't ask me why )

The Omega doesn't fit into this category. On the Omega, settings from 1 to 70 control the gain, and settings of 71 and up invoke threshold changes. A setting of 70 is maxed out, and if you are in an environment that allows you to raise the gain to the max setting of 70 and maintain stability, then you may also be able to raise it higher and get some threshold pluses.

On units like Tesoro, we "supertune" by raising the threshold settings to amplify the audio response of signals. Unfortuantly at the cost of loosing the smallest signals through audio saturation as well as some discrimination ability.

So while the feature can be found on others, it is not as complete, or as easy to use as it is on the F5. Where the F5 really shines is the ability to run it very hot and sensitive to small low conductors at very low gain settings in conjunction with very high threshold setttings.

HH
Mike

 

[ToddB64]

Thanks Mike !

Todd

 

[Neita SC]

n/t

 

[mudpuppy]

Man! I learned something today..thanks!
Mud

 

[ToddB64]

I guess Monte V.B. took a look at this thread and decided nothing more was needed !

Todd

 

[MarkCZ]

The F5,
Coinstrike,
Whites 5900,
Whites XLT,
and those like them.

If you think of them in two parts it help to make sense of the sensitivity and the threshold and how they are different but effect one another.
You have an,
Audio circuit side, (that powers and sends a target report to the operator via the speaker or headphones)
Then you have the,
Detection circuit, (this powers the target detection circuit)

Now the two controls goes a bit like this,

Threshold, Pre-amp gain, signal balance adjust the audio's circuit trigger to an incoming signal from the detection circuit (if you think of the audio circuit like a motion detector then these controls adjust how sensitive it is to sounding the alarm). Some refer to it as setting the, Gate, or trigger of the audio amplifier.

Sensitivity, adjust the detection circuit sensitivity of what is being picked up buy the field of detection that it is powering.

Mark