TF-900_TM800

[ivconic]

hello , pics of C-SCOPE TF9000 HPX , same board but mine is populated and yours not, why ?

[ATTACH]57485[/ATTACH][ATTACH]57486[/ATTACH][ATTACH]57487[/ATTACH]

Mine too, now, photo is taken when I started to solder components.
So!?
Sinclairuser is absolutelly right!
Same machine: Discovery TF900, White's TM-800 and Cscope 9000 HPX !??
The heck Yes!
Who copied from whom? $1Mil question!

[nickel_n]

here is the link to the US patent.
you may all ready know it
https://patents.google.com/patent/US4348639A/en

[Carl-NC]

Who copied from whom? $1Mil question!

I've posted this somewhere before...
Jim Karbowski originally came up with this design and sold it under his own company, "3D Electronics" in Corvallis, Oregon. This is a 40 minute drive from Sweet Home. He then sold or licensed the design to Discovery Electronics (Sweet Home) who built the TF900. White's first model was the TM600 followed by the TM800 which were the same design and built by Discovery. Discovery also contract-built the Cscope 9000. White's later produced their own design, the TM808, based on the 6000di circuit.

[Jose]

I built this detector a few years ago with the schematic published in this forum, I used ferrite toroids that I found at hand, even the TX and RX are different. I make the coils as indicated in the diagram, the RX tuning was done by adding capacitors in parallel.
The final frequency was 12.8 kc and it is necessary that the aluminum antenna is inside the toroid and short-circuited, otherwise the frequency is very different, the size of the antenna also influences the frequency
The selector key was replaced by separate reversing keys.
Mechanical rigidity is important and so are the contacts where the aluminum antenna closes.
Do not delve into the theoretical knowledge of this detector, only some tests were done, but it seems to work well.

[Jose]

[Skippy]

Here's Magnetics Inc page of ferrite material datasheets, design guides etc. worth a look.

https://www.mag-inc.com/Design/Techn...Core-Documents

I notice there is a toroid close to 25mm diameter in their range, the '42507' size.

[ivconic]

I built this detector a few years ago with the schematic published in this forum, I used ferrite toroids that I found at hand, even the TX and RX are different. I make the coils as indicated in the diagram, the RX tuning was done by adding capacitors in parallel.
The final frequency was 12.8 kc and it is necessary that the aluminum antenna is inside the toroid and short-circuited, otherwise the frequency is very different, the size of the antenna also influences the frequency
The selector key was replaced by separate reversing keys.
Mechanical rigidity is important and so are the contacts where the aluminum antenna closes.
Do not delve into the theoretical knowledge of this detector, only some tests were done, but it seems to work well.

[ivconic]

Here's Magnetics Inc page of ferrite material datasheets, design guides etc. worth a look.

https://www.mag-inc.com/Design/Techn...Core-Documents

I notice there is a toroid close to 25mm diameter in their range, the '42507' size.

You probably won't believe me, but until a few months ago I had a large metal bucket in the attic, full of ferrites,
toroids, various chokes ... but most of these torus rings.
A lot has been collected in over 30 years of work.
I was sorry to throw up.
And then all of a sudden, I don't know what the hell was wrong with me; I decided in vain to clean the ceiling and I
could hardly take that bucket to the dump because it weighed over 70kg!
And now that I remember that ... I would kill myself!
Now I start again from the beginning, I collect pieces of electronics from waste, in search of such toroids ...

[Skippy]

It's a good idea to seperate them by 'category' when salvaging them, or even individually label them, if you can be bothered. That help identify their future re-use. For example one from a known 50 kHz SMPSU circuit will be different to one from a radio-frequency power amplifier ( balun ), and interference-suppression types are different again. Be wary of those used in common-mode interference filters, often green painted. They are weird things, usually very-high u ferrite, that is lossy, even at a few kHz. They give unexpected results when swept over a detector.
Apparently one way to distinguish powdered-iron cores is : scrape them hard with a sturdy knife, they will start to scratch up, and small bits can be removed. Whereas ferrite is too rock hard, and you will just get a blunt knife blade.
The method I mentioned previously, where any u over 500 means it is ferrite is also true. Most powdered iron / permalloy etc blends have u below 200.

[Davor]

Hello world

[Davor]

About mH inductances at connection, this core provides impedance transformation. It follows a square law of the turn ratio, and the loop going through a core acts as ~half turn or a bit more. So if there are 78 turns in a primary /.5 turn secondary, squared, times .7uH single turn loop, times .8 coupling factor, you get ~13mH inductance.
I first came across this kind of coupling when assembling a Harris MW AM transmitter with modules contributing a central rod via toroid transformers, acting as direct DA modulator of thermometer type. The modules not contributing (either as a binary zero or if faulty) must be shorted. Big advantage of the concept is that modules may use the same PSU, and there are no floating supplies.
But...
Although I liked the concept, and thought it was a very good idea for a metal detector, I evolved. Q factor of a coil depends upon a loop conductance. Aluminium is not famous for good joints, and specific conductance is not optimal. So, I'd go with a simple multi-turn coil instead.

[Davor]

As for a core material, it should provide a self-inductance of a primary a few times higher than the transformed loop inductance. So if a resulting inductance is 13uH, then self-inductance of a primary on a core should be >40mH, and the only concern may be core saturation on Tx side.

[Jose]

"So, I'd go with a simple multi-turn coil instead."


Perhaps the advantage of the aluminum antenna, in this case, is that it does not need shielding and is connected directly to GND.

[ivconic]

About mH inductances at connection, this core provides impedance transformation. It follows a square law of the turn ratio, and the loop going through a core acts as ~half turn or a bit more. So if there are 78 turns in a primary /.5 turn secondary, squared, times .7uH single turn loop, times .8 coupling factor, you get ~13mH inductance.
I first came across this kind of coupling when assembling a Harris MW AM transmitter with modules contributing a central rod via toroid transformers, acting as direct DA modulator of thermometer type. The modules not contributing (either as a binary zero or if faulty) must be shorted. Big advantage of the concept is that modules may use the same PSU, and there are no floating supplies.
But...
Although I liked the concept, and thought it was a very good idea for a metal detector, I evolved. Q factor of a coil depends upon a loop conductance. Aluminium is not famous for good joints, and specific conductance is not optimal. So, I'd go with a simple multi-turn coil instead.

Welcome back!
Splendid explanation!

[Davor]

"So, I'd go with a simple multi-turn coil instead."


Perhaps the advantage of the aluminum antenna, in this case, is that it does not need shielding and is connected directly to GND.

So does a centre-tapped bifilar coil. Or a shielded one. In both cases you'd get a better Q.