TESORO GOLDEN SABRE

[simonbaker]

Hi,I mean it's floating voltage... the battery drop is an issue (some battery less than other kind... e.g. nimh have about flat voltage till they drop very sharp, so big fluctuations are at initial and final drops, other batteries have much larger swing during discharge, e.g. old zinc-carbon)The fluctuations are also related to audio stage: when using internal speaker yor battery voltage have a ripple cause of current drained in that process: you can place a tank capacitor there to compensate more but it's always an issue... with headphones the problem is much reduced. Frequency is the audio frequency...some hundred Hz.It's right you have unregulated negative rail, but this affect just op amps: the tx stage uses +8v regulated there....only. If you change for battery rail... your tx supply voltage will follow the drop rate of battery: means huge instability at fast drops.Kind regards,Max

Ok, thanks.

I plan to experiment with 7 rechargeables = 7 * 1.2 = 8.4 volts, no regulation at all (leave out LM7808 ), just big capacitors and see how it works and any problems. I'm thinking original design was for alkaline and regulation was mainly for providing more hours of use as battery voltage dropped slowly from 12 v to about 10 v. As you say, rechargeables have flat discharge curve, maybe regulation no so important? I'll try it after build working MD, just slowly testing and building first.

[Max]

Mr.Max i only thinking about that.
You wrote your tx colil is around 5,7mH when i calculate with paralel 20n capacitor
result is 15,91khz.Im litle confuse..

Regards!
Thanks for your time.

Hi,
it's colpitts oscillator: capacitance at oscillator tank is by the 2 capacitors there... about 21.8nF not 20nF

This will give you calculated value of about 14.3Khz, but you know any meter has tolerance... so probably it's less than 5.7mH ... and capacitors could give (on mine PCB) something less than 21.8nF.

I can only say that you'll stay around 14.5Khz and few hundreds Hz variations are due to tolerances at coil and capacitors.

If you e.g. tighten not enough the wire at coils you'll get higher frequency than tightening very strong it... that's about coils... you'll difficault made 2 exactly the same using simple copper wires boundles... even with lot of care.

Now, I've used good quality components and lot of care at coil... so it's about accurate with say +-200Hz respect to indicated value when you try to replicate, cause of the above tolerances. Not big deal... select capacitors or add / subtract a few turns to get exact frequency if needed (usually isn't).

Kind regards,
Max

Mr.Max i only thinking about that.
You wrote your tx colil is around 5,7mH when i calculate with paralel 20n capacitor
result is 15,91khz.Im litle confuse..

Regards!
Thanks for your time.

[Max]

Max on new (30cm) TGS coil you got around 15,90khz?

Hi,
did you tight the wire with tape or something ?

You must get 14.6-14.7 Khz on tight wire.

Kind regards,
Max

Max on new (30cm) TGS coil you got around 15,90khz?

[Max]

I notice that the negative rail is unregulated anyway.

Can you tell what the nature of the fluctuations on the battery rail is? Does it have a frequency signature?

Hi,I mean it's floating voltage... the battery drop is an issue (some battery less than other kind... e.g. nimh have about flat voltage till they drop very sharp, so big fluctuations are at initial and final drops, other batteries have much larger swing during discharge, e.g. old zinc-carbon)The fluctuations are also related to audio stage: when using internal speaker yor battery voltage have a ripple cause of current drained in that process: you can place a tank capacitor there to compensate more but it's always an issue... with headphones the problem is much reduced. Frequency is the audio frequency...some hundred Hz.It's right you have unregulated negative rail, but this affect just op amps: the tx stage uses +8v regulated there....only. If you change for battery rail... your tx supply voltage will follow the drop rate of battery: means huge instability at fast drops.Kind regards,Max

[simonbaker]

Hi,
you could do that... but maybe is better changing also the zener there too...

In any case it's not so good cause there are little fluctuations on battery rail... and it's unregulated voltage.

I think will be good on e.g. power supply / bench... but could be a big mess on batteries.

Kind regards,
Max

I notice that the negative rail is unregulated anyway.

Can you tell what the nature of the fluctuations on the battery rail is? Does it have a frequency signature?

[Max]

I noticed in Compadre thread that a mod is to drive TX oscillation directly from battery voltage instead of regulated supply to get higher voltage, more depth.

Anyone try that for TGS?

Hi,
you could do that... but maybe is better changing also the zener there too...

In any case it's not so good cause there are little fluctuations on battery rail... and it's unregulated voltage.

I think will be good on e.g. power supply / bench... but could be a big mess on batteries.

Kind regards,
Max

[simonbaker]

Compadre mod for TGS?

I noticed in Compadre thread that a mod is to drive TX oscillation directly from battery voltage instead of regulated supply to get higher voltage, more depth.

Anyone try that for TGS?

[Max]

Max , I was told that after you finish building a vlf circuit , and it can be the Golden Sabre or Bandido or any Tesoro , that it is best to wind and make the smallest diameter search-coil possible 4 to 5 inch or less !! The smaller the TX field the better , and this will help to align , test or correct any circuit problems . And then this will eliminate Chatter when the gain or sensitivity is at maximum with a full size search-coil . We all have our personal alignment or test proceedures . But maybe when we slap on a big Search coil right away , that is a big mistake ???? Smallest search coil first , then we calibrate or test with maximum gain at minimum noise , then we increase the coil size and re-check the gain , noise , and Tx waveform . I wonder what size search-coil Tesoro does on its initial tests at the factory ?? Maybe they use a Tiny 2 inch I.B. dummy coil and do a sweep analysis right before the audio IC ???........... Take Care........Eugene

Hi,I think they use the 5'' as reference during tests... but maybe smaller ? Don't know.... just remember they have the 5'' around... used for trashy sites... probably they prefer using it at the end.The larger the coil the more the noise... right: this is expecially about 50 or 60 Hz noise entering the big RX... much more easy than on smaller ones, I know.But I'm lucky with the 30cm DD cause it gets just a little more than 10''DD , standard coil for homemade TGS.If you rise gain to max in my big TGS you can spot some chatters from time to time... with monostable ON you notice that.But there's a silly trick: rotating the notch pot (even when notch is disabled) you can reduce and about totally null that effect.

Kind regards,
Max

[amtech2005]

TESORO GOLDEN SABRE

Max , I was told that after you finish building a vlf circuit , and it can be the Golden Sabre or Bandido or any Tesoro , that it is best to wind and make the smallest diameter search-coil possible 4 to 5 inch or less !! The smaller the TX field the better , and this will help to align , test or correct any circuit problems . And then this will eliminate Chatter when the gain or sensitivity is at maximum with a full size search-coil . We all have our personal alignment or test proceedures . But maybe when we slap on a big Search coil right away , that is a big mistake ???? Smallest search coil first , then we calibrate or test with maximum gain at minimum noise , then we increase the coil size and re-check the gain , noise , and Tx waveform . I wonder what size search-coil Tesoro does on its initial tests at the factory ?? Maybe they use a Tiny 2 inch I.B. dummy coil and do a sweep analysis right before the audio IC ???........... Take Care........Eugene

[Max]

Hi! MAX

Many thanks for explanations.

Today I tested my TGS with omega coil on beach.
In ALL METAL MODE ...sensibility almost fully clockwise produce ocasional falses and detect a coin at 23 cm+_ on dry sand.
On wet sand...no conditions...many falses.

In DISCRIM. MODE sens. almost at end detect a coin at 23 cm too.(on dry sand)
On wet sand (near water) 1/3 sensibility half discrim. adj. with some falses detect a coin at 12cm+_.
Our beaches has lots of black sands and pull tabs

Regards

DIRCEU

Hi,
for beach hunting is maybe better using PI, unless you use TGS only on dry sand... which is still very good.

A simple PI could solve many problems at wet sand... but, of course, no disc.

Kind regards,
Max

[Max]

Max what you use on your 30cm DD coil,foil or graphite?


Regards!

Hi,
in first I've made used mylar. In this you see in the picture had just foil... so used foil.

Performance is similar.

Kind regards,
Max

[DIRCEU]

Hi! MAX

Many thanks for explanations.

Today I tested my TGS with omega coil on beach.
In ALL METAL MODE ...sensibility almost fully clockwise produce ocasional falses and detect a coin at 23 cm+_ on dry sand.
On wet sand...no conditions...many falses.

In DISCRIM. MODE sens. almost at end detect a coin at 23 cm too.(on dry sand)
On wet sand (near water) 1/3 sensibility half discrim. adj. with some falses detect a coin at 12cm+_.
Our beaches has lots of black sands and pull tabs

Regards

DIRCEU

Max what you use on your 30cm DD coil,foil or graphite?


Regards!