TESORO GOLDEN SABRE

[dfbowers]

Just thinking with my fingers here but maybe putting the cap and also an impedance transforming circuit like a preamp or follower circuit in the search head will make it so the cable shielding is not so critical in picking up unintended noise. Much the same reason for using low impedance microphone's vs high impedance mic's on a sound system.

Jerry

You were reading my mind.. I have been thinking about the benefits of doing that for some time (Preamp in the search coil). I was trying to find a schematic but I think that one of the Minelabs had a rectifier in the search coil, and generated the power for the Rx pre-amp right off of the Tx signal.

As far as the cap in the search coil, I'm wondering if manufacturers do that just to ensure that the coil will tune the same on any detector.

[Jerry]

I think with parallel tank small currents flow from the driving source (not to be confused with the coil being part of the oscillator like the TGSL), but fairly large currents can slosh back and forth from the capacitor to the coil with a high-Q tank. That was the point about putting the cap in the coil head, to avoid all that current going up and down the cable.

-SB

Just thinking with my fingers here but maybe putting the cap and also an impedance transforming circuit like a preamp or follower circuit in the search head will make it so the cable shielding is not so critical in picking up unintended noise. Much the same reason for using low impedance microphone's vs high impedance mic's on a sound system.

Jerry

[simonbaker]

I did model this and the difference in loss was actaully very small.

I guess its because a parallel tuned ctt is a high impedance cct and only small currents flow.

If cap/coil were in series then there would be more currents flowing and more copper losses.
steve

I think with parallel tank small currents flow from the driving source (not to be confused with the coil being part of the oscillator like the TGSL), but fairly large currents can slosh back and forth from the capacitor to the coil with a high-Q tank. That was the point about putting the cap in the coil head, to avoid all that current going up and down the cable.

-SB

[golfnut]

You could try an LTSpice simulation to see if you could demonstrate a significant advantage to locating the cap near the coil.

Again I wonder if one advantage of putting the cap on the PCB is to filter out some cable noise.

There could be some advantage to putting a high-Q TX coil-cap tank in the search head to minimize the driving current in the cable -- that is, if you ever wanted to play with high-Q TX tanks, which may have some disadvantages such as ground sensitivity.

I did model this and the difference in loss was actaully very small.

I guess its because a parallel tuned ctt is a high impedance cct and only small currents flow.

If cap/coil were in series then there would be more currents flowing and more copper losses.
steve

[satdaveuk]

Thanks DON
All positive input is greatfully received, you have put alot into this project and its been noticed by all of us.
Dont know why maybe its the ground over here in the UK but still get better results by grounding the RX at the front end as per Tesro spec.

Im just starting round coil 12" coil 5.7/6.2mh, Let you all know how it goes


Regards

Dave

[golfnut]

great work right there

[Jerry]

Rats.. Sorry about the wasted disk space
I've only made that mistake three times this week so far..

Don,
It is most certainly not a waste of disk space.

Thanks again for all of the hard work you put in that will make the quest for building a metal detector a lot easier for a lot of people.

Jerry

[Qiaozhi]

Rats.. Sorry about the wasted disk space
I've only made that mistake three times this week so far..

Added latest versions here ->

http://www.geotech1.com/forums/showthread.php?p=95456#post95456

[der_fisherman]

Attached are the latest "TGSL 101" documents. It includes a revision date on the first page along with significant fixes. I also fixed some "bad English".

Don

They were damn good before!!!
Many thanks
andy

[dfbowers]

Thanks for your continuing hard work!

At risk of another revision, I'll mention that the revision date in the "part 1" document seems to have year 2011 instead of 2012.

Cheers ,

-SB

Rats.. Sorry about the wasted disk space
I've only made that mistake three times this week so far..

[simonbaker]

Attached are the latest "TGSL 101" documents. It includes a revision date on the first page along with significant fixes. I also fixed some "bad English".

Don

Thanks for your continuing hard work!

At risk of another revision, I'll mention that the revision date in the "part 1" document seems to have year 2011 instead of 2012.

Cheers ,

-SB

[dfbowers]

Latest TGSL documents

Attached are the latest "TGSL 101" documents. It includes a revision date on the first page along with significant fixes. I also fixed some "bad English".

Don

[bushra_kharif]

thanks 6666 for your comment on bf 245 and bf240 ,again can i use k118 to substitute bf 245?????
thanks

[6666]

MAX


would you still have the picture from your post #564 ?

that site has gone now
thanks
6666

[6666]

A BF240 is a NPN Radio Frequency Transistor

A BF245 is a N-CHANNEL JUNCTION FIELD EFFECT TRANSISTOR

they are not the same type of component