Found this picture of a RF? choke on the coil cable of a metal detector, wondering ...

[Carl-NC]

Apparently enough. Usually these things are added while the unit is being tested at the compliance lab. They play around with adding ferrite beads & chokes until they can get it to pass EMI, then production units have to include the same solution.

[Polymer]

Thank you all for your insights and links.

I was praying that someone might whisper the secret recipe for the ferrite which only lets the gold signals pass through!

I am playing around with beads and toroids on my surf pi, putting them on coil wires & component leads to see what happens,
as I do have an emi issue and am hoping to at least cut some of it down.

Have read a lot about this in the meantime and for me this seems more complex & quirky than the capacitor stuff appears to me.

Back to playing around ...

[sinclairuser]

Thank you all for your insights and links.

I was praying that someone might whisper the secret recipe for the ferrite which only lets the gold signals pass through!

I am playing around with beads and toroids on my surf pi, putting them on coil wires & component leads to see what happens,
as I do have an emi issue and am hoping to at least cut some of it down.

Have read a lot about this in the meantime and for me this seems more complex & quirky than the capacitor stuff appears to me.

Back to playing around ...

get yourself one of those nice big snap on ones, about an inch long and 3/4 of an inch thick, put it as close to the plug at the control box end that you can, dont put one at the coil end.
and try it see if it makes a difference for you, i put one on the first barracuda i built as it was sensitive to noise, it did seem to help, but made no difference to the second one i built, rebuilding that one with top quality components and full shielding (box,cable and coil) cured it completely.
i use chokes on my radios and associated equipment, since computers entered the shack noise was a problem, but can be cured with time and patience, chokes are just one tool used with others to get rid of noise and its harmonics, so i gave it a try on the barra, now shielding is a better option but if the noise is minimal a quick choke fix might kill it, its worth a try for the sake of a quid.
give it a bash let us know what happens.

[Polymer]

get yourself one of those nice big snap on ones, about an inch long and 3/4 of an inch thick, put it as close to the plug at the control box end that you can, dont put one at the coil end.
and try it see if it makes a difference for you, i put one on the first barracuda i built as it was sensitive to noise, it did seem to help, but made no difference to the second one i built, rebuilding that one with top quality components and full shielding (box,cable and coil) cured it completely.
i use chokes on my radios and associated equipment, since computers entered the shack noise was a problem, but can be cured with time and patience, chokes are just one tool used with others to get rid of noise and its harmonics, so i gave it a try on the barra, now shielding is a better option but if the noise is minimal a quick choke fix might kill it, its worth a try for the sake of a quid.
give it a bash let us know what happens.

Much appreciated, I'll definitely give it a bash.

What do you exactly mean with high quality components?
for example, like sourcing from real distributers or getting cerdip chips and also resistors & caps from known good manufacturers?
I have been looking into this topic, because it looks like there are so many iffy parts on the market.
The only ic I have not been able to find in cerdip is the 5534. Have you been able to find any, would it be beneficial?

The main noise problem I have on the surf & bara appears to be spikes at a frequency of 2 to 3 Hz.
This looked like a DC Wobble at first with the timebase of 2-20us on the oscilloscope which I use typically for measuring PI stuff.
Yes, I'm learning to use my oscilloscope ...

I'm dodging the shielding part for now ... I might come back crying

Have a nice weekend, cheerio

[ionut_mtb]

Much appreciated, I'll definitely give it a bash.

What do you exactly mean with high quality components?
for example, like sourcing from real distributers or getting cerdip chips and also resistors & caps from known good manufacturers?
I have been looking into this topic, because it looks like there are so many iffy parts on the market.
The only ic I have not been able to find in cerdip is the 5534. Have you been able to find any, would it be beneficial?

The main noise problem I have on the surf & bara appears to be spikes at a frequency of 2 to 3 Hz.
This looked like a DC Wobble at first with the timebase of 2-20us on the oscilloscope which I use typically for measuring PI stuff.
Yes, I'm learning to use my oscilloscope ...

I'm dodging the shielding part for now ... I might come back crying

Have a nice weekend, cheerio

Shield of the coil and detector is very important, even when doing tests. You will see clear waveform after that. Quality of the components will give you, again, clear waveform, less noise. meaning 1% tolerance, metal film resistors, tantalum/silver mica/polypropylene capacitors, low dielectric constant materials for building the coil, low noise preamp/opamp and so on. This is my opinion,.

[sinclairuser]

Much appreciated, I'll definitely give it a bash.

What do you exactly mean with high quality components?
for example, like sourcing from real distributers or getting cerdip chips and also resistors & caps from known good manufacturers?
I have been looking into this topic, because it looks like there are so many iffy parts on the market.
The only ic I have not been able to find in cerdip is the 5534. Have you been able to find any, would it be beneficial?

The main noise problem I have on the surf & bara appears to be spikes at a frequency of 2 to 3 Hz.
This looked like a DC Wobble at first with the timebase of 2-20us on the oscilloscope which I use typically for measuring PI stuff.
Yes, I'm learning to use my oscilloscope ...

I'm dodging the shielding part for now ... I might come back crying

Have a nice weekend, cheerio

what I mean by quality components its, new old stock ceramic chips or even metal packages if you can find them, top quality 1% resistors, wima caps and nichicon electrolitics, simple stuff really.
I double check components and match transistors, all stuff we should do already but quite a lot of us buy a kit and slap it together, which i'm guilty of myself I have done that in the past and it bit me in the arse.
look on ebay and other sites for suppliers of components to radio enthusiasts they can be a good source for quality stuff new old stock, job lots can be good too, my advice is to avoid the sites that sell a thousand resistors or caps for 10 pounds, basically you get what you pay for.
and search direct for metal or ceramic, good luck.

[Polymer]

what I mean by quality components its, new old stock ceramic chips or even metal packages if you can find them, top quality 1% resistors, wima caps and nichicon electrolitics, simple stuff really.
I double check components and match transistors, all stuff we should do already but quite a lot of us buy a kit and slap it together, which i'm guilty of myself I have done that in the past and it bit me in the arse.
look on ebay and other sites for suppliers of components to radio enthusiasts they can be a good source for quality stuff new old stock, job lots can be good too, my advice is to avoid the sites that sell a thousand resistors or caps for 10 pounds, basically you get what you pay for.
and search direct for metal or ceramic, good luck.

Thank You for your input, ideas & confirmation!

Just stumbled across some bogus ceramic 4093 and 40106 ic's whilst searching ... grrrrr
I did manage to get genuine old stock consumer ic's from the 80's & 90's for the baracuda & surf PI a while ago.

I mainly do have WIMA PP capacitors, but find there is often not enough space on the boards to fit them (they are more squarisch or fatter),
so I sometimes had to resort to the skinny PE Capacitors. How did you get around that problem?

I did find a nice resistor set on ebay, way more expensive than the typical el crappo offers. They are advertised as "YAGEO" or "ROYALOHM",
dependent on availability. This appears tricky to me as I do not really trust in the latter, which have steel leads and I don't know that brand.
Do you happen to have any experience with resistors from that company?

Most of my electrolytics are from a little known manufacturer called "Frolyt". I have known them for around 20 years and
you'll be surprised, they are manufactured in Germany. Thought that might be of interest.
https://www.frolyt.de/en/

[sinclairuser]

yes mate have used and still have some yageo stuff, http://www.yageo.com/portal/product/product.jsp
is a direct link, have a look they sell allsorts, I like to buy direct if I can, royalohm are one of those brands that you have probably been buying already, I understand element 14 and digikey get stuff from them so if they are genuine they should be fine, if you want current quality chips another good tip is to join microchip and texas instruments, get a few samples and set up your profile so you can order.
texas instruments will let you buy smaller orders, so you can order 10 of this and 10 of that, 25 transistors etc, so ordering 50 items is really easy its a good way of stocking up your parts draws, and you don't have to worry about fakes and stuff like that.
wima caps can be quite beefy in some tolerances, but that is a fault of the supplier not wima, wima makes smaller form factor caps but suppliers often supplant them with other brands due to cost, but for our purposes I think its better to pay more for the right part, we a making 1-3 devices at most so we can choose the best, a manufacturer only does this at prototype stage, by the time they go to production and the "bean counters" have costed the design cheap generic components will replace the good stuff, we don't need to do that.
I have heard Frolyt mentioned on the tapeheads forum, they seem to be good for replacing caps in high end tape machines.

[ionut_mtb]

facebook picture off minelab explorer

[Polymer]

yes mate have used and still have some yageo stuff, http://www.yageo.com/portal/product/product.jsp
is a direct link, have a look they sell allsorts, I like to buy direct if I can, royalohm are one of those brands that you have probably been buying already, I understand element 14 and digikey get stuff from them so if they are genuine they should be fine, if you want current quality chips another good tip is to join microchip and texas instruments, get a few samples and set up your profile so you can order.
texas instruments will let you buy smaller orders, so you can order 10 of this and 10 of that, 25 transistors etc, so ordering 50 items is really easy its a good way of stocking up your parts draws, and you don't have to worry about fakes and stuff like that.
wima caps can be quite beefy in some tolerances, but that is a fault of the supplier not wima, wima makes smaller form factor caps but suppliers often supplant them with other brands due to cost, but for our purposes I think its better to pay more for the right part, we a making 1-3 devices at most so we can choose the best, a manufacturer only does this at prototype stage, by the time they go to production and the "bean counters" have costed the design cheap generic components will replace the good stuff, we don't need to do that.
I have heard Frolyt mentioned on the tapeheads forum, they seem to be good for replacing caps in high end tape machines.

Hello Sinclairuser, I finally got a collection of WIMA Foil capacitors, all in the smallest dimension available. Yippee .....

I think I am starting to understand the matching business of JFETS as you mentioned. This picture sort of said it all for me.
Someone was so nice as to put the test results on the net:

[Polymer]

[ATTACH]41514[/ATTACH]

facebook picture off minelab explorer

Thanks Ionut_mtb! I have returned from travelling and brought a box of assorted, defined ferrite stuff with me for playing around.

[Sean_Goddard]

Well, I added one to my Eagle Spectrum and it definatley does something. I can now work a lot nearer to electric fences (before was 60yds or so, now it's more like 25yds)


With a VLF it will flter out fast spikes with a PI it will filter out fast spikes and stuff your detector as the fast edge is needed. So many non technos on other forums who swear blind that, as per the audio crew, gold capacitors or unobtainium resistors make the amplifer sound SOoooooo much brighter and alive . Emperors new clothes syndrome if you ask me (a bit like LRL's.....Shhhh Rant mode suppressed)!

[Polymer]

Well, I added one to my Eagle Spectrum and it definatley does something. I can now work a lot nearer to electric fences (before was 60yds or so, now it's more like 25yds)


With a VLF it will flter out fast spikes with a PI it will filter out fast spikes and stuff your detector as the fast edge is needed. So many non technos on other forums who swear blind that, as per the audio crew, gold capacitors or unobtainium resistors make the amplifer sound SOoooooo much brighter and alive . Emperors new clothes syndrome if you ask me (a bit like LRL's.....Shhhh Rant mode suppressed)!

Hi Sean,
Thank you for your reply! I have an XLT spectrum myself and will try this. Did you put the ferrite just short of the plug to the box, or somehow
inside the xlt?

I got your point with ferrites being not good for letting fast transients pass thru for PI purposes.

There is a rumour of aurelium ferrites being used to let only GOLD signals pass through to a PI detector.
It a military thing apparently, but you can get the secret composition of aurelium from www.got*scammed*again.BS 😈
It's nearly free too!
Just couldn't resist writing this ....