TF-900_TM800

[ivconic]

"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.

His objection makes a lot of sense and I fully understand what he is talking about. I once had a TM-808 (and in the meantime a few in service) ... and one single flaw that that detector has; is both the biggest and the worst it can have!
And that is the choice of how the coils will connect to the main pcb.
Although it looks really cool, fancy ... it's actually an unseen failure!
Because the weight of the construction, the choice of materials, vibrations during movement and manipulation, assembly, disassembly, transport; all this leads to accelerated oxidation and deformation of the metal.
And those "banana" jacks that are hidden in the tube; they slowly loosen and lose contact.
And slowly it is affecting more and more, first the stability of the detector and how the problem is progressing; in downtime or in malfunction.
Almost everyone I have had on the service so far has the same problem.
The solution is simple, the "banana" jacks are removed and the TX and RX pcb are connected with a good coaxial cable with 2 middle leads and
a good copper braid that is around those two leads.
The pipes are drilled and the cable is pulled out. And on the detector box, 3-pole connectors are installed on the front and back.
As well as the corresponding connectors on both cables.

[Carl-NC]

Hello world

Hi, welcome back!

[ivconic]

A small group of people interested in this topic ... but SELECTED!
I couldn't have wished for better!
Okay ... Skippy ... I owe you the most that I got serious for a while and started looking at things the right way.
Instead of me blabbering on like this ... pictures will say more than words:

[Skippy]

Hmmm .. that nicely shows the problem with salvaged cores. Based on my experience, the yellow/white cores are powdered iron, likely u = 75 -> 125, good for SMPSU up to 100 kHz, for example, with lots of energy storage capability. Green cores are from common-mode suppression filters, ferrite with u = 5000 -> 20000, but designed to soak up AC energy , not store it efficiently, so they have limited uses.

If you want to get experimental, at low cost, buy some type '43' ferrite cores, they are the most commonly seen medium-u types, I see some FT114-43 for sale at less than 4 Euro each. You will need +90% more turns than the original, to compensate for the u = 850, rather than u = 3000 that you ideally need. They will need some thicker wire on the TX, to keep Q-factor the same, about +40% diameter, roughly.

-----

And regarding the aluminium loops : making a good electrical connection at the joint needs care. Abrade the surfaces with clean aluminium-oxide abrasive paper, just before joining. This will remove the Al oxide layer, without contaminating it with anything else.

[ivconic]

Hmmm .. that nicely shows the problem with salvaged cores. Based on my experience, the yellow/white cores are powdered iron, likely u = 75 -> 125, good for SMPSU up to 100 kHz, for example, with lots of energy storage capability. Green cores are from common-mode suppression filters, ferrite with u = 5000 -> 20000, but designed to soak up AC energy , not store it efficiently, so they have limited uses.

If you want to get experimental, at low cost, buy some type '43' ferrite cores, they are the most commonly seen medium-u types, I see some FT114-43 for sale at less than 4 Euro each. You will need +90% more turns than the original, to compensate for the u = 850, rather than u = 3000 that you ideally need. They will need some thicker wire on the TX, to keep Q-factor the same, about +40% diameter, roughly.

-----

And regarding the aluminium loops : making a good electrical connection at the joint needs care. Abrade the surfaces with clean aluminium-oxide abrasive paper, just before joining. This will remove the Al oxide layer, without contaminating it with anything else.

Skippy, it seems like your "job" here is to constantly worry and upset me ... but in a productive and helpful way, so thank you so much for that!
Not only will this help me fix this detector; I will also learn something new.
See; the "antenna" rod that goes through the "shaft" is 9.5-10mm in diameter, I'm not sure, my caliper is not accurate.
Or is it a difference in metric systems, my caliper measures in mm and shows something between 9.5 and 10mm.
No matter, let's assume it's 10mm.
And that's a limiting factor too.
I can't wind too many turns on the torus, because then the rod won't be able to get through the center of the torus.
The original "red" torus is 22x6mm and the "hole" is 14mm. So the cross section is 6x4mm.
So if the rod is 10mm and the "hole" is 14mm, I have 4mm left in total, or 2mm around the rod, free space for windings.
At the same time, subtract at least 0.5 mm, so that the rod can be easily passed without damaging the wire on the windings.
That subtraction of 0.5mm around the rod will totally mean 1mm less.
In that case I no longer have a total of 4mm but 3mm; or 1.5mm around the rod space to the surface of the torus.
The coil must fit in those 1.5mm. In the case of RX this will not be a problem with this current number of windings.
Well even in the case of TX this will not be a problem with the current number of windings and current wire thicknesses.
Any change in the thickness of the wire to more, as well as an increase in the number of windings; leads to a situation where
it is impossible to pass the rod through the torus.
Problem, problem!

[ivconic]

All this problem would be minor or would not even exist; if we only knew the exact type of the original torus. Its "number" and properties.
But there are so many standards, manufacturers and their internal labels in the world ...
For example, here in local store, I have an offer like this (you have to click on a certain torus, in order to open a new page that says what type it is).

http://www.proelectronic.rs/Feriti/F...gra%20okrugla/

[Qiaozhi]

All this problem would be minor or would not even exist; if we only knew the exact type of the original torus. Its "number" and properties.
But there are so many standards, manufacturers and their internal labels in the world ...
For example, here in local store, I have an offer like this (you have to click on a certain torus, in order to open a new page that says what type it is).

http://www.proelectronic.rs/Feriti/F...gra%20okrugla/

Earlier this year I did some work on a power electronics application that required the use of toroidal cores, and had a similar problem.
The simplest way to characterize an existing core is to determine its value.
This can be calculated using the following equation:



The value of is one of the parameters supplied by the manufacturer.
However, if you have an existing core without a datasheet, you can easily find the value by winding 20 turns on the core and measuring the inductance. It doesn't have to be 20 turns, but this a recommended minimum to get an accurate reading.

In your particular case the core already has a winding of 75 turns and a measured inductance of 13mH, which gives:



is normally listed as nH/turn-squared, so in this case a datasheet would state that was equal to 2311.
The value of 2311 tells me that this core is made of ferrite. Iron powder cores have much lower values in the 10s and 100s.
One other important point in power applications to avoid core saturation, which I think will be unlikely in this instance.

If you have a number of similar sized cores available, the next step is to determine their value. As I said before, you only need 20 turns before measuring the inductance.
If you can find a core with an close to the original, then you will need to calculate the number of turns required to achieve the same inductance.
For example, let's say you have found a core with an of 2000, the number of turns required to achieve 13mH will be:



This result implies that you should attempt to find a core with an value below (but close to) 2311, otherwise there may be too many windings to fit inside the core or there may not enough room for the aluminium rod.

If you cannot find a suitable ferrite core in your junk box, then it should be a reasonably simple matter to search for a core online that has the correct physical dimensions and value.

[Skippy]

Good to see the true dimensions. It is a type FT87, also known as '42206'. 0.87" OD , 0.55" ID , 0.25" thick.
You are wanting an A_L value of about 2000 mH / 1000T ( = 2000 nH / T² )
This would suggest a ferrite of type F or T would be correct. u = 3000

There is also the possibility of using a thicker version, the FT87-A, but then the cross-sectional area is double, and a lower u ferrite is needed etc etc

[ivconic]

Earlier this year I did some work on a power electronics application that required the use of toroidal cores, and had a similar problem.
The simplest way to characterize an existing core is to determine its value.
This can be calculated using the following equation:



The value of is one of the parameters supplied by the manufacturer.
However, if you have an existing core without a datasheet, you can easily find the value by winding 20 turns on the core and measuring the inductance. It doesn't have to be 20 turns, but this a recommended minimum to get an accurate reading.

In your particular case the core already has a winding of 75 turns and a measured inductance of 13mH, which gives:



is normally listed as nH/turn-squared, so in this case a datasheet would state that was equal to 2311.
The value of 2311 tells me that this core is made of ferrite. Iron powder cores have much lower values in the 10s and 100s.
One other important point in power applications to avoid core saturation, which I think will be unlikely in this instance.

If you have a number of similar sized cores available, the next step is to determine their value. As I said before, you only need 20 turns before measuring the inductance.
If you can find a core with an close to the original, then you will need to calculate the number of turns required to achieve the same inductance.
For example, let's say you have found a core with an of 2000, the number of turns required to achieve 13mH will be:



This result implies that you should attempt to find a core with an value below (but close to) 2311, otherwise there may be too many windings to fit inside the core or there may not enough room for the aluminium rod.

If you cannot find a suitable ferrite core in your junk box, then it should be a reasonably simple matter to search for a core online that has the correct physical dimensions and value.

I've been trying for years to distract Davor from trash-talking ... now I see that I have to persuade you to stop doing it too ...
Joke aside, this time I fully understand your "trash-talk" and that post of yours will serve as a reference and reminder for me. I will copy it to a txt file, to have it on hand.
Everything you wrote to me is 100% clear and understandable. Thanks for that!
But there is another problem, Skippy has started to regularly scare me with extra conditions around the core!
"This color is storing the energy, that color is eating it all ..."
All that remains is to "agree" on it and clarify it.
In my post you quoted, you have a link from a local vendor, when you click on one of the torus; a new page opens and somewhere below in the text it says something like:


FERITNO JEZGRO OKRUGLO (RING FERRITE CORE on Serbian)
R12.5, 1020nH
DIMENZIJE(DIMENSIONS): 12.50mm (O.D.) x 7.50mm (I.D.) x 5.00mm (L)
MATERIJAL(MATERIAL): N27
INICIJALNA PROPUSTLJIVOST(Initial permeability on Serbian): 2.000


Is the AL=1020nH here?
And "U" from Skippy's posts is 2000 in this case?
Ok, and how to know is the core storing energy or sucking it? (Skippy's fault if this sounds funny!!!)

[ivconic]

Good to see the true dimensions. It is a type FT87, also known as '42206'. 0.87" OD , 0.55" ID , 0.25" thick.
You are wanting an A_L value of about 2000 mH / 1000T ( = 2000 nH / T² )
This would suggest a ferrite of type F or T would be correct. u = 3000

There is also the possibility of using a thicker version, the FT87-A, but then the cross-sectional area is double, and a lower u ferrite is needed etc etc

FT87, searhing on Aliexpress and i got this:

https://www.aliexpress.com/item/32848336509.html

[Skippy]

That's the correct size, just not a correct ferrite mix. Type 43 is medium-u, 850.

This is Amidon's version:
https://www.amidoncorp.com/ft-87-fc/

Type 'F' ferrite, u = 3000, giving the toroid an A_L = 1800 mH / 1000T

[ivconic]

That's the correct size, just not a correct ferrite mix. Type 43 is medium-u, 850.

Tell me exactly the correct "name" so I to look up for it.

[Qiaozhi]

I've been trying for years to distract Davor from trash-talking ... now I see that I have to persuade you to stop doing it too ...
Joke aside, this time I fully understand your "trash-talk" and that post of yours will serve as a reference and reminder for me. I will copy it to a txt file, to have it on hand.
Everything you wrote to me is 100% clear and understandable. Thanks for that!
But there is another problem, Skippy has started to regularly scare me with extra conditions around the core!
"This color is storing the energy, that color is eating it all ..."
All that remains is to "agree" on it and clarify it.
In my post you quoted, you have a link from a local vendor, when you click on one of the torus; a new page opens and somewhere below in the text it says something like:


FERITNO JEZGRO OKRUGLO (RING FERRITE CORE on Serbian)
R12.5, 1020nH
DIMENZIJE(DIMENSIONS): 12.50mm (O.D.) x 7.50mm (I.D.) x 5.00mm (L)
MATERIJAL(MATERIAL): N27
INICIJALNA PROPUSTLJIVOST(Initial permeability on Serbian): 2.000


Is the AL=1020nH here?
And "U" from Skippy's posts is 2000 in this case?
Ok, and how to know is the core storing energy or sucking it? (Skippy's fault if this sounds funny!!!)

Yes, 1020nH is no doubt the value. This means 1020nH/turns-squared.

The number of windings required to achieve an inductance of 13mH would then be:



which I assume would be too many to fit within the space.

[ivconic]

I stumbled on this and it might be usefull:
https://coil32.net/rf-toroid.html
Downloaded it and now trying to see some details.

[ivconic]

That's the correct size, just not a correct ferrite mix. Type 43 is medium-u, 850.

This is Amidon's version:
https://www.amidoncorp.com/ft-87-fc/

Type 'F' ferrite, u = 3000, giving the toroid an A_L = 1800 mH / 1000T

I'm sorry, I missed the link! Afterwards you wonder why I ask stupid questions!
Fellas, do not take me for evil; my tiny brain is not able to understand everything at once, I need time.
I have never dealt with ferrite rings before, this is all new to me.
Thanks for the link!