MONOCOIL SUCCESS

[mickstv]

I finally got the circuit built and it seems to function as mentioned except for one small problem, the frontend is a little deaf compared to a standard mono front end.


I end up taking the blocking fet circuit out and used a matched pair of 1k resistors and crobar diodes on the TX fet side then into a diff amp. My modified setup works fine, the TX is about 100us running about 400volts flyback and it's decay at the diff amp is about 6us.



Mick

[Midas]

I finally got the circuit built and it seems to function as mentioned except for one small problem, the frontend is a little deaf compared to a standard mono front end.


I end up taking the blocking fet circuit out and used a matched pair of 1k resistors and crobar diodes on the TX fet side then into a diff amp. My modified setup works fine, the TX is about 100us running about 400volts flyback and it's decay at the diff amp is about 6us.



Mick

Hi Mick, hope your Christmas went well. Thanks for the result. Sounds like it might be a no go... I wonder if the same is also true of the differential passive fet blocking scheme.

[6666]

.... here is another ( to be ) tested improvement ..... the differential head, damping and blocker circuit can be located in or very close to the search coil ... This will eliminate the flyback pulse having to travel up the coil cable to the control box ..

The blocker transistor Q2 should have a low "ON" impedance.

and again it is the most simple change ...

PS the TX switch device does not need a high voltage rating now ... the blocker handles the flyback volts

moodz

[ATTACH]17702[/ATTACH]

Moodz with your blocker invention
you say we dont need a high voltage fet switch
I have some logic level fets good for 30v and 55v
do you think they would work ?
thanks

[moodz]

Moodz with your blocker invention
you say we dont need a high voltage fet switch
I have some logic level fets good for 30v and 55v
do you think they would work ?
thanks

You can use a low voltage fet for the switch but your blockers must still be high voltage and able to carry the tx pulse current.
moodz

[nick_f]

Descrimination is available However it is via a two sample method which is not quite as "neat" as the single sample used on the differential coil.

However it is a vast improvement over conventional monocoil front ends.

moodz

Hey Moodz, it is called DISCRIMINATION, not Descrimination :P

[moodz]

Hey Moodz, it is called DISCRIMINATION, not Descrimination :P

Sorry I are an engineer.