TESORO GOLDEN SABRE

[bushra_kharif]

Hi ALL I am new member of your forum , now i am building tgsl but i didnt find bf 245 i only find bf 240 ...can i use it as substitute for bf 245???
thanks
bushra_kharif

[simonbaker]

All I say,

In order to maintain the least losses - or to keep the maximum efficiency and gain/sensitivity.


You should strive to minimise loss in a circuit.


Rx tuned circuits are a little like a pendulum. magnetic energy picked up by the coil generates a voltage across the coil - which charges the cap.

The energy is passed from L to C and back again using the complimentary electrical properties of Ls and Cs.

In an ideal world this would be a lossless system.



The coil and cap should be co located to incur least loss of picked up signal energy for every 'oscillation of picked up signal energy'


Steve

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.

-SB

[der_fisherman]

All I say,

In order to maintain the least losses - or to keep the maximum efficiency and gain/sensitivity.
You should strive to minimise loss in a circuit.
Rx tuned circuits are a little like a pendulum. magnetic energy picked up by the coil generates a voltage across the coil - which charges the cap.
The energy is passed from L to C and back again using the complimentary electrical properties of Ls and Cs.
In an ideal world this would be a lossless system.
The coil and cap should be co located to incur least loss of picked up signal energy for every 'oscillation of picked up signal energy'
Steve

Dear Golfnut,
do not be upset but for me that is simply not an electronic answer......it may be basically correct, but I would like to have a proper factual answer please. 100% correct.

I am certainly not an analog or a radio electronics person, the last time I worked on such circuits they were in a gun turret on an RN warship in the 60's. I am a digital person for many years now.

I can still understand a correct explanation from someone who works a lot with analog electronics though, perhaps someone else here can help us both further as to what to watch for.....

Have a great new year and
Regards from
Andy

[golfnut]

All I say,

In order to maintain the least losses - or to keep the maximum efficiency and gain/sensitivity.


You should strive to minimise loss in a circuit.


Rx tuned circuits are a little like a pendulum. magnetic energy picked up by the coil generates a voltage across the coil - which charges the cap.

The energy is passed from L to C and back again using the complimentary electrical properties of Ls and Cs.

In an ideal world this would be a lossless system.



The coil and cap should be co located to incur least loss of picked up signal energy for every 'oscillation of picked up signal energy'


Steve

[der_fisherman]

Hi Satdave I mentioned this, but I have not tried,

There may be some improvement having the cap in the coil head.

The cable is just carrying signal voltages then , and not oscillating currents from coil to remotely located cap via the cable.


Steve

Very interesting concept, but am certainly no expert in this area, but as the cap is basically a "tuning" cap, how could that be true that having it in the head stops some signals? The Rx circuit is still carrying an AC receive signal to the electronics, it has been "tuned" thats all.......
I must admit that I have NOT actually 'scoped such a circuit myself in this area to see what differences there are before and after the cap, maybe next year if you cannot help me more.
Can you point me to any websites that cover this subject in fine detail so that I can learn more about this?
Can you also elaborate your own thoughts on this subject please?
My thoughts that the combination of L & C will give a frequency at which the circuit is most sensitive or "tuned", the length of the cables do two things, they add some more resistance and a small amount of inductance.
But when the cap is on the PCB, you have a better chance of being able to change or modify it than when its in the search head......
thanks in advance.
Andy

[golfnut]

Hi Satdave I mentioned this, but I have not tried,

There may be some improvement having the cap in the coil head.

The cable is just carrying signal voltages then , and not oscillating currents from coil to remotely located cap via the cable.


Steve

[simonbaker]

Good points Simon just come out of my workshop and have spent the last 4 hours plus playing about with these emi filters and there is very small amount of difference if any in the workshop conditions but of course we dont metal detect in the workshop do we.
The best advise I can give is what I said in the past go buy some of that USB3 cable the cable is labled nasa shuttle cable 80 degrees 30v, it has 6 cores incl violet for those who want to stick to Tesro colour codeing, two of the pairs have there own screening then on top of that second mylar independent screening insulated independent of the main heavy screening plus a second over all screening of mylar around the body plus its reinforced with two lots of rope running through the entire lenth, so its also very robust.
I use the two pairs that have there own screening for TX and RX then solder all screens together both front and back end wired as per Tesro
And can honestly say I dont get any instabilty problems at all in real use unless ive done a error with the coil nulling, im now down to 6.3mh for RX using .39 gauge and 6.91mh for TX using .25 gauge and im getting my 30cm for £1 coin air test with a nice clean signal in the workshop and 28cm in the test bed which is full of old iron nails etc.
I cant get any where near those setting with the cheap usb2 cable and once you compare the construction you can see why, Ive proved this no end by swapping cables.
Firstly we all know and you yourself have proved that spikes been picked up from the TX bleeds through the RX,so what does that tell us... isolate the two best as we can.
You will always get noise pick up from the search heads and if you try and filter that out you will filter out are finds.
the cable is the answer and what im using is better results than the cable supplied with the factory coil, infact im thinking of changing the cable on the 8" coil i but dont know the best way round it.
If you have trouble obtaining the cable give me a shout and next time im doing my orders will by a few 5m lenths and send one over to you, I just hope the price is the same as last time.
Hope this helps
All the best
Dave

Good cable info, thanks.

If it turns out that the RX coil picks up the dominent noise, then the cable may be secondary anyway. However, if you can demonstrate that a certain cable really makes a difference over another one, certainly worth investigating. Of course, there can be a number of reasons the cable has an effect.

Regards,

-SSB

[satdaveuk]

I haven't tried it yet, but trying to think how it might work. I'm guessing it chokes off any "common-mode" signal coming up the cable -- of course we don't want it to block the 14.5 kHz differential signal. Maybe it will be more important with the "grounded RX" coil configuration than the "ungrounded" RX coil configuration, because the ungrounded configuration has better common mode rejection???

One question I have is how a shielded cable responds to such a choke, and if that is different to a side-by-side pair such as a power cord. I think they work the same, but just wondering.

I still suspect that the worst noise is picked up by the RX coil and looks like the normal differential target signal, so the choke wouldn't stop it. The only way I can think to reduce it (so far) is dual RX coils which cancel the noise but don't fully cancel the target signal. But it makes a very awkward search head. I've started experiments on that.

-SB

Good points Simon just come out of my workshop and have spent the last 4 hours plus playing about with these emi filters and there is very small amount of difference if any in the workshop conditions but of course we dont metal detect in the workshop do we.
The best advise I can give is what I said in the past go buy some of that USB3 cable the cable is labled nasa shuttle cable 80 degrees 30v, it has 6 cores incl violet for those who want to stick to Tesro colour codeing, two of the pairs have there own screening then on top of that second mylar independent screening insulated independent of the main heavy screening plus a second over all screening of mylar around the body plus its reinforced with two lots of rope running through the entire lenth, so its also very robust.
I use the two pairs that have there own screening for TX and RX then solder all screens together both front and back end wired as per Tesro
And can honestly say I dont get any instabilty problems at all in real use unless ive done a error with the coil nulling, im now down to 6.3mh for RX using .39 gauge and 6.91mh for TX using .25 gauge and im getting my 30cm for £1 coin air test with a nice clean signal in the workshop and 28cm in the test bed which is full of old iron nails etc.
I cant get any where near those setting with the cheap usb2 cable and once you compare the construction you can see why, Ive proved this no end by swapping cables.
Firstly we all know and you yourself have proved that spikes been picked up from the TX bleeds through the RX,so what does that tell us... isolate the two best as we can.
You will always get noise pick up from the search heads and if you try and filter that out you will filter out are finds.
the cable is the answer and what im using is better results than the cable supplied with the factory coil, infact im thinking of changing the cable on the 8" coil i but dont know the best way round it.
If you have trouble obtaining the cable give me a shout and next time im doing my orders will by a few 5m lenths and send one over to you, I just hope the price is the same as last time.
Hope this helps
All the best
Dave

[homefire]

There out there. I tried one here on a Garrett detector because of a local Radar and it helped.

http://parts.digikey.com/1/parts/672270-ferrite-h-f-emi-clamp-9-09mm-hfa163090-0a2.html

[golfnut]

They reduce signals running up the braid.



If a device sources a lot of emi noise, these ferrites serve to reduce noise on the way out.

Same the other way round.


I would fit it at the box end, rather than the coil end.

if you are in a noisey environment and 'one' helps-- 2 should be better and so on.

Schaffner make a good one.

[simonbaker]

Sorry for the bad link. Here it is again:

http://metaldetectorsnow.co.uk/4-99-clip-on-inline-emi-rfi-ferrite-filter-minelab-whites-tesoro-garrett-etc-2/

I have been doing some additional reading on ferrite beads and metal detectors and there seems to be some contoversy on thier effectiveness. Maybe others on this forum have investigated the usefulness of the idea before? I guess they have their place.. Just wondering if it might be here..

I haven't tried it yet, but trying to think how it might work. I'm guessing it chokes off any "common-mode" signal coming up the cable -- of course we don't want it to block the 14.5 kHz differential signal. Maybe it will be more important with the "grounded RX" coil configuration than the "ungrounded" RX coil configuration, because the ungrounded configuration has better common mode rejection???

One question I have is how a shielded cable responds to such a choke, and if that is different to a side-by-side pair such as a power cord. I think they work the same, but just wondering.

I still suspect that the worst noise is picked up by the RX coil and looks like the normal differential target signal, so the choke wouldn't stop it. The only way I can think to reduce it (so far) is dual RX coils which cancel the noise but don't fully cancel the target signal. But it makes a very awkward search head. I've started experiments on that.

-SB

[Jerry]

That figures. I just removed one a VGA cable I was going to try on my next coil. Oh Well.

It does sound like it is worth trying though.

Thanks for posting it.

Jerry

[der_fisherman]

Sorry for the bad link. Here it is again:

http://metaldetectorsnow.co.uk/4-99-clip-on-inline-emi-rfi-ferrite-filter-minelab-whites-tesoro-garrett-etc-2/

I have been doing some additional reading on ferrite beads and metal detectors and there seems to be some contoversy on thier effectiveness. Maybe others on this forum have investigated the usefulness of the idea before? I guess they have their place.. Just wondering if it might be here..

Very interesting.

The clip on ones should allow exact testing while running as you can put them on and take them off really easily. I really like the idea.

It should also be checked as to how the Tx and Rx signal are affected, just to see if there is any marked loss loss of voltage....

Regards

Andy

[satdaveuk]

Hi Don
There fitted on alot of the more exspensive 20m HDMI leads ive sold in the past to customers but to date ive never experienced any difference.
Ive only ever read negative feedback on these for metal detectors until your post but after saying that if you have seen a difference then maybe they work for these, I have a permanent one on a lead ill try and cut it out for experiments.

Regards

[dfbowers]

Don,,, is this somehow different than those ferrite slugs sold on ebay for MD's or the same??
Ebay item #160686129804 and several more? This particular item number search
on ebay will explain what this supposedly does for detecting sensitivity etc.
I wasn't able to follow the link you provided so cannot read what it said.
PM

Sorry for the bad link. Here it is again:

http://metaldetectorsnow.co.uk/4-99-clip-on-inline-emi-rfi-ferrite-filter-minelab-whites-tesoro-garrett-etc-2/

I have been doing some additional reading on ferrite beads and metal detectors and there seems to be some contoversy on thier effectiveness. Maybe others on this forum have investigated the usefulness of the idea before? I guess they have their place.. Just wondering if it might be here..