damping resistor

[baum7154]

From my notes on open air testing vs testing over wet soil on a 1/2" square aluminum target .001" thick.

In open air best damping was at 1040 ohms.

Over wet grass and soil best damping was 980 ohms

Doing the math the in-circuit coil SRF in open dry air is 988 kHz …over wet soil/grass SRF is 931 kHz

Coil is 335uh.

If I did this right the effect of the wet soil was an additional 10pf of capacitance.

Note: This coil is shielded only by its unique winding geometry and has no separate Faraday shield layer.

Hope this helps,

Dan

[Wahyu]

Hi Dan,

Nice topic, thank for share, did you have measure current sink at open air and wet grass soil?

[baum7154]

Hi Wahyu,

Sorry, I did not measure the current change between free air and wet soil.

Dan

[kt315]

In open air best damping was at 1040 ohms.

for max sens you have to decrease dampres if you work with min delay and increase it if you work with big delay.
than more you take delay than a ringing leaves at left and you do not work in this area of range.
for example, DP has dampres 2k2 if you look on old first schematic. with delay 100-120us sens will be max.
in Surf Eric;s Foster mod - dampres was INCREASED from 220 to 390ohm, look the schematic.

[Wahyu]

Thank for reply Dan,

Hi kt315, it's posible to make auto damping for PI? becouse some soil make coil ringing, and silent detector, I do not know why some of this land makes coil ringing.
Did you have any information about this?

Wahyu.

[kt315]

do not think its possible easely. we do only simplest PI projects, no especial reason to complicate simplest to
microcontroller soft based DSP project. in my opinion you have to find gold optimal middle for the coil and stop.
and please more actively use SEARCH knob
http://www.geotech1.com/forums/searc...chid=378407&pp=

[kt315]

crosslinked to https://www.geotech1.com/forums/show...hat-went-wrong

[surfdetector]

This is it!!!

[ATTACH]28049[/ATTACH]

Free lunch awaiting!

I am curious for people's opinions regarding the start of sampling while still in saturation as suggested in this referenced post by Waikiki?

Thanks.

[Ferric Toes]

I am curious for people's opinions regarding the start of sampling while still in saturation as suggested in this referenced post by Waikiki?

Thanks.

I have used the underdamped mode successfully as in method 1. However, only with a low TX current and high repetition rate. This allows me to use a cermet trimmer as part of the damping circuit with a peak voltage of <200V. The optimum damping point is quite critical.

Eric.

[Orbit]

Hi Eric!
Have you ever to try to bfo detector do the balance of the earth geb ?

[Carl-NC]

I am curious for people's opinions regarding the start of sampling while still in saturation as suggested in this referenced post by Waikiki?

I'm doing that on a pinpointer design and it works just fine. But you either need very tightly controlled coil parametrics or hand-tweak everything. The pinpointer has a single-layer solenoidal coil so it is extremely repeatable.

[Ferric Toes]

Hi Eric!
Have you ever to try to bfo detector do the balance of the earth geb ?

My answer is no, but there was a detector in the 1970's that combined BFO with PI to give a measure of Fe/Non-Fe identification. You simply manually switched the mono coil between PI and BFO. I toyed with the idea of having a burst of sine waves in between TX and sample pulses but never did any experimentation.

One idea that comes to mind is to switch off the coil damping on each alternate pulse and do a BFO scheme on the resultant ringing. With a frequency to voltage converter somewhere in the circuit, it may be possible to subtract the result from the integrated PI signal to achieve GB. Perhaps someone will have the time to find out, but it is unlikely to be me. Too much else on the go .

Eric.

[Orbit]

My answer is no, but there was a detector in the 1970's that combined BFO with PI to give a measure of Fe/Non-Fe identification. You simply manually switched the mono coil between PI and BFO. I toyed with the idea of having a burst of sine waves in between TX and sample pulses but never did any experimentation.

One idea that comes to mind is to switch off the coil damping on each alternate pulse and do a BFO scheme on the resultant ringing. With a frequency to voltage converter somewhere in the circuit, it may be possible to subtract the result from the integrated PI signal to achieve GB. Perhaps someone will have the time to find out, but it is unlikely to be me. Too much else on the go .

Eric.

An interesting idea, right on I thought so between pulses to insert a sine signal I intend to try it,I'll let you know what I did! It came to my mind yes from frequency I get a converter dc voltage and that subtract from rx oscillator frequencies constant oscillator frequency of course before that and to convert that frequency into voltage means I have two reference oscillators one mix with rx ,and the other reference I would use for subtraction...
Thanks Eric!

[Ferric Toes]

An interesting idea, right on I thought so between pulses to insert a sine signal I intend to try it,I'll let you know what I did! It came to my mind yes from frequency I get a converter dc voltage and that subtract from rx oscillator frequencies constant oscillator frequency of course before that and to convert that frequency into voltage means I have two reference oscillators one mix with rx ,and the other reference I would use for subtraction...
Thanks Eric!

A phase locked loop may also have possibilities in such a circuit.

[Orbit]

A phase locked loop may also have possibilities in such a circuit.

Yes, and that's what I meant looks similar thoughts ,therefore I bought a few pieces 4046...