How does a manufacturer test a detector?

[Teleno]

The main sample and earth field pulse widths should be the same.

Wouldn't it be easier to use the EF pulse for cancelling the amplifier's offset and then integrating the clean signal alone? After all the EF is just a DC offset.

That way you don't need a differential integrator and can do away with accurate pulses and tight tolerance components.

[dbanner]

It's the integrator that does this task.

[Teleno]

It's the integrator that does this task.

That's my point. It does the task badly

[bklein]

If you turn the gain control down does the distance reduce ?

Not really. You hear the target starting from the same distance. It’s a whisper with gain all the way down which builds to a more solid tone as you advance the gain. Advancing after the default setting the tone gets distorted and modulated.

[Qiaozhi]

Wouldn't it be easier to use the EF pulse for cancelling the amplifier's offset and then integrating the clean signal alone? After all the EF is just a DC offset.

That way you don't need a differential integrator and can do away with accurate pulses and tight tolerance components.

I suspect your idea would only work if the signal created by moving the coil in the Earth's magnetic field was always the same. However, the signal will change depending on coil orientation with the magnetic compass. Also, the Earth field elimination process removes external EMI.

[Teleno]

I suspect your idea would only work if the signal created by moving the coil in the Earth's magnetic field was always the same. However, the signal will change depending on coil orientation with the magnetic compass. Also, the Earth field elimination process removes external EMI.

Usually a PI samples at 1000 KHz, the sweep speed being 1m/s. The displacement of the coil in 1ms is 1mm, negligible enough to consider the EF signal as a DC offset within that millisecond. The same applies to EMI at 50 Hz. I'm designing a MPP mod based on this principle.

[Qiaozhi]

Usually a PI samples at 1000 KHz, the sweep speed being 1m/s. The displacement of the coil in 1ms is 1mm, negligible enough to consider the EF signal as a DC offset within that millisecond. The same applies to EMI at 50 Hz. I'm designing a MPP mod based on this principle.

If you use a bipolar transmitter, you don't need the EF sample pulse at all.

[Koala]

Not really. You hear the target starting from the same distance. It?s a whisper with gain all the way down which builds to a more solid tone as you advance the gain. Advancing after the default setting the tone gets distorted and modulated.

Dam working as expected

if you Google surf dual field poor depth there's a few the same but can't see a solution.

one person had a click / notch at the lowest delay setting that wasn't mentioned in the manual. If they moved it clockwise slightly so it wasn't at the click position then it preforms. properly.

[Teleno]

If you use a bipolar transmitter, you don't need the EF sample pulse at all.

Sure, but that's far more complex than an offset canceller + simplified integrator. I suppose.

Also, in such a bipolar transmitter you'd need to subtract the signals in two consecutive Tx cycles, which implies assuming that the EF variation within two cycles is insignificant, which was also my assumption.

[bklein]

Dam working as expected

if you Google surf dual field poor depth there's a few the same but can't see a solution.

one person had a click / notch at the lowest delay setting that wasn't mentioned in the manual. If they moved it clockwise slightly so it wasn't at the click position then it preforms. properly.

I looked at the scope as I advanced the Delay : SW Off delay is same as just after the switch click.

[bklein]

Here is a TDI BH with similar depth. https://youtu.be/WREfs2SsjiY
Again this guy seems to be fine with the results.
So you are going to say pi’s don’t do well in air tests... but haven’t yet seen a video where you air test at 7” and then put the target in wet sand and sense it deeper... :-)
I’m really confused.

[Koala]

Here is a TDI BH with similar depth. https://youtu.be/WREfs2SsjiY
Again this guy seems to be fine with the results.
So you are going to say pi’s don’t do well in air tests... but haven’t yet seen a video where you air test at 7” and then put the target in wet sand and sense it deeper... :-)
I’m really confused.

but that 8-9" on a gold ring and your 4"

[bklein]

Well I’d expect it to be better on gold but way better than 9”. Right or no?

[Koala]

my Whites surf dual field as it is only picking up a gold ring at 4"

8-9" might be okay depending on the ring composition

Twice the original 4" what's changed

[bklein]

Just tried my surf pi 5? and pi pro 7-8? on the coins.
Next will try the two surf diy 1.2 boards.