Question about SENSITIVITY control

[Captain Kirk]

The following discussion relates to a set up of discrimination mode with tones set to "dp". The SENSITIVITY is the only function that will be varied.

The manual states that the SENSITIVITY is electronic gain control. That does not seem to be an accurate description. If it is a gain control function, then as the SENSITIVITY is turned up slowly the "chirps" from electronic noise would start faint and increase in loudness as the SENSITIVITY is increased. What appears to happen is that the detector is quite until some SENSITIVITY level is reached, then the the "chirps" first appear as maximum loudness. As the SENSITIVITY is increased further, then the "chirps" simple become more frequent with the same loudness.

It is my impression that SENSITIVITY actually sets some level of threshold such that no detection is indicated until the pickup signal is greater than that threshold. After the threshold is crossed, then a detection is indicated with a constant loudness as set by the volume control.

Am I missing something here.

Glenn

 

[Jackpine Savage]

this is not a sure find method to determine what the sensitivity control does (sets threshold level or preamp gain). I got the idea from reading a George Payne post. On one of his threhsold based designs with the sens set at min he stated and I'm paraphrasing, that you still get very good target response on coin sized targets. In the past the only detectors that I have had that got good air test along with very respectable in ground results with the sens set at minimum are the Fisher 1270 and the Troy X5. Are they thrshold based? I don't know for sure but a Fisher tech told me the sensitivity on the 1270 worked like a noise blanker which sounds kinda like a threshold control to me. I have not used any of Georges designs. It may not mean anything but what the heck try it and see.

Tom

 

[Jackpine Savage]

Glenn I am still curioous about this. Would you try something for me please? The next time you run into a situation where the T2 is noisy/chattery at higher sensitivity try turning down the volume control to see if that helps at all. With my Fisher 1270 I have run into areas where reducing the detector volume and readjusting the headphones to compensate smoothed things out without having to resort to lowering the sensitivity.

Tom

 

[Captain Kirk]

Tom,

In my hunting environment I can run with Sensitivity=80 with very little chatter. I can even increase Sensitivity to 90 and still run reasonably quite in most areas.

At this point my opinions on the T2 are:
* There is no threshold tone. When a target is detected, then a tone is generated. The loudness of the tone is essentially independent of the depth of the target. In the + settings there is a change in pitch as a function of the target depth/size.
* The volume control only effects the loudness of the tone. It does not effect sensitivity nor susceptibility to noise. If the noise is bothersome, then turning down the volume may be beneficial.

HH,
Glenn

 

[Dick from NC]

My experience is if I turn down sens. the volume seems to be reduced as though I'm turning down the volume. If I started getting chatter I'll reduce sens. to eliminate chatter. I run sens. and high as I can and it seems to pick up the deeper targets a little better. The T2 is a constant process of learning.
With my Explorer XS if I turn up the gain ( NOT SENS ) it will amplify the smaller deeper target but also amplify the bigger shallower targets so you cann't tell which ones a deep or shallow. The higher the gain the more unstable the detector. With the Explorer you can adjust sens. and gain independant of each other.

 

[Jackpine Savage]

I have some experience with the MXT and it sounds like perhaps the T2 is sort of a hybrid. The MXT's sensitivity control has steps of increased gain until you get to the + numbers where the audio target responses become less and less modulated. The MXT was easy to figure out and operated exactly as Dave said in the engineering report.

Tom