IDX-PRO+VDI

[hoadlies]

HI ,,DON,,KOALA, STEVE,& ALL ..
THANKS so much for the Advice given SO,SO helpfull ,I try not to ask too many Questions as I have learned so much from reading this thread many times now !!!
But Some areas are confusing to me [My old brain & memory is not as used to be] HA.Haar..

OK,,,, DON thanks for the video link & I see your Geb pot @ approx 12 oclock + ,Mine is full clockwise to just reject ferrite so I will play with the RX caps I have a 22n+10n at present ..
My TX seems happy with a 1uf MPK cap frequency measured at TX is 6,58 khz seems OK????
Don what did you switch-on,, towards the ending on the video,,, PP??????

KOALA,, Yes I saw your post in the thread that you added 10k ??? to geb pot I can try that Thanks..

STEVE ,,, Thanks Mate for the numerous replies very helpfull ..

OK ,,TX cap in coil housing that confirmed ,I will put RX cap in control box .

I will get back to you later with some air test figures , ..as you describe..

I hace potted the TX coil 100% & the RX coil 50% allowing to adjust RX more accuratly !!

For your interst I have used a 10.5'' coil wear-plate for a base I used 1x layer of Fibre-glass mesh to stiffen-up the flimsy Skid-plate seems OK,I need to fashion some ears etc for the wand handle..

DON's shells are great But Postage is so high from the states ..,,,,GEORGY may be another option ,But first to get this first build up & running ..
AS ''Mine-lab''-factory- is in Sth Australia ,I went to ADELAIDE [capital of Sth AUST ,200ks south of my home] ..i struck a friendly fellow there but they will not sell Coil Shells ,''BUGGA''.. incidently ''COIL-TECH'' are also in a suburb of Adelaide but I never got time to go & ask there ..i dought also if they would sell shells.. they do not like us DIY people !!!!

MUCH Appreciated,,,,,,,,,,,CHEERS from a still BL*&@#y Hot ''OZ'' BARRY..

[dfbowers]

Hey Barry. I found out that the tolerance of my caps was enough to throw off phasing, especially the 1uF tx capacitor.
I just went through my box until one worked just right. I built 4 coils for my IDX. 9" and 10" DD plus an 8" and 10" concentric.
The 10" DD air test at almost 50" for coins. The concentrics behave better in actual use but the ground up here isn't too bad.
As for the video, I started in all metal mode, balanced to a ferrite loop stick and then switched to disc mode.
BTW.. it's been nothing but snow and freezing rain in the eastern US : ( cold and windy.. and the power just went out... send some heat this way please!
Don..

[hoadlies]

HI,DON,,,, YES you are welcome to some of our ''HEAT'' as long as you give -up some of your ''COLD'' weather ..WE very rarely see any snow here in the MID-Nth,a bit at times on some nearby tall hills but only every few years or so..

OK on the tolerance ,Thats interesting ,I have been measuring the caps [multi-meter only,but seems accurate enough ] ..
Today I have had about an hour only to do more testing ,but tonight I will do more [Cooler in my shed at night this weather!!.] [ie] MY shed W/shop is a 30x40Ft x 10 ft high all steel construction & we have had 2x weeks of 39-44 c heat & 25 at night WHEW..& continuing into next week..

I secured the TX & RX terminations in coil ,,,to cable perminently,,,so as I have more acurate testing..

I had a double beep ,So reversed the TX wires & yes single beep ..[STEVE Question] I can detect my wedding ring @8-10'', Reject small -iron not bad ..coin 20c piece similar to ring..
But cannot attain 180DEG scope trace !! But still working on that ..
I will post A pic of the 2x seperate traces tomorrow [I only have a single ch scope But STEVE taught me how to use the exturnal set-up & it works great ]..
question Don ALL,METAL SWITCH ,,???? THE PP switch ??? or other ????..
ITS a very interesting project to keep the old Grey-matter alive,,HAHaar I like it..

I will answer Steve later with my findings ..

WELL,,DON ,Keep Warm mate some heat is on the way over Hahaar.. BARRY..

[dfbowers]

Barry.. all metal and PP are the same.
Also, forgot to ask. Are you using lm324s or lf347s in your project? For some reason (I do not know why) the lf347s make a significant difference.
Also, if you have not already discoved this, the threashold setting in PP mode has much influence on the disc mode.
Don..

[golfnut]

Hi, make sure you have NO metal near your coil when doing your testing / nulling / phasing.

Well done eradicating the double beep

[golfnut]

All of these effects are linked together



" I can detect my wedding ring @8-10''

This sounds a bit lean, try reducing Rx cap by 2n and retest for extra air range - this brings Rx tank closer to Tx operating freq.

If you have Tx and Rx tuned TOO CLOSE together it will air test real well but will be too twichy on soil - like Dons, DD.

You can visualise how close the Rx tank is wrt Tx freq - put scope on preamp out , note pkto pk level - add 2n2 and Level should REDUCE -as Rx Tank now peaks lower freq - air test will be worse.

If you reduce RX cap by 2n the level should get bigger. So has more sens and will air test a bit better.

Both of above true if Rx is tuned BELOW Tx

(I made a cap switch box using an 8way DIP switch and 1,2n2,3n3,4n7,5n6,10,22,33 caps - this lets you tack this in to set up. Remove and measure - then add appropriate cap an confirm with retest.)

When you tweak - must retest all alloys, have similar mass targets of ferrite, iron, gold, bronze, nickel, lead, silver

Check - reject ferrite using GEB reject iron using Disc - while set to reject iron and ferrite - check for ACCEPT of gold br ni le Si


It is wet grey windy flooding cold. S




Reject small -iron not bad ..coin 20c piece similar to ring..
But cannot attain 180DEG scope trace !! But still working on that .."

[TANCE]

Please provide modified complete circuit diagram

Thank you

[Koala]

All of these effects are linked together


If you have Tx and Rx tuned TOO CLOSE together it will air test real well but will be too twichy on soil - like Dons, DD.

But cannot attain 180DEG scope trace !! But still working on that .."

I made a DD that air tests 16" for a 2P coin iron clad or copper. Very twitchy on real ground. Does work exceptionally well on very dry sand apart from that its useless. Learnt the hard way large air test is not the be all end all. i will have to make a new one soon as its too heavy as well.

[golfnut]

Hi Koala, you may be able to tweak yours too. If you added say 1n,2n,3n to existing Rx cap to pull it down a little - the sens will reduce and be less twitchy.

You would have to check you can still reject ferrite, iron, and accept all target alloys.



If no joy, you could drop the Tx frequency a little - adding say 22n to Tx - you could do this in the box.

This on its own would make it worse, what you may do then is reduce the Rx cap quite a bit - this would put the Rx freq above Tx - you may have to reverse the Rx coil connections as well?


you can get most coils to work on these, be prepared to muck about with them a little away from absolutes in the write ups.

S

[golfnut]

pcb variants

Recently I asked Silverdog for the current pcb on the store plus an earlier one which had a short.

Ive studied them side by side and I cant see any circuitry deltas between them. S

[hoadlies]

HI , Firstly DON YES my kit came with the LF347!!& I was unaware of the threshhold interacting with the disc-mode ,I am yet to come to terms with the controls proper but getting there with those ..thanks mate..

STEVE,,Thank's yet again my desk is all wood but coil is close within 12'' or so ,, to my various things like solder station scope etc etc so I moved the coil to a plastic upside down tall basket about 3-4 ft away from all things ,I notice the cable affecting the unit touching & moving it about causes beeps ?????
Also If I disconnect & reconnect the shield wires to cable shield it alters the null ???I maybe have not wired them correctly the coil -Shield's & cable shield,,, all go to the ground around the board 1st pin on board left top..

I used your wet grass connections ?? ,I think Don uses a 4-core all seperate shielded cable ..I thought to maybe use some audio 2x core [microphone cable] would need 2x cables ,But as I read most are using this USB-2 cable with no problems So I should be able to succeed with it Too!![If it ain't broke why alter it ] HA,Haar..
Last night I was testing & moved the Coil as mentioned & I have Fluro lighting in my shed & wondered if that affected the coil ??? ,will see today without need for lights..

I have altered the rx caps up & down but maybe need to persevere more with that following your advice ..

YES I see some news on you bad weather in the UK very bad washing rail way tracks into the SEA !! Wow thats severe ..
Keep safe inside Mate..

KOALA ,, ARE you australian ???? going on your site name!!!! I live in the Mid-North of SA 200ks Nth of adelaide small town only 130 people ..

This is my first Coil & DIY M/D ,But as you I am keen to Build a second coil [concentric as Dons instructions] after I get this one as close as poss..

I recieved my 2x rolls of that 0.2 wire that's got a thin insulating coating on it ,,Have you used that Wire??? for RX only..

THANK's A LOT FELLA"S ,,BARRY..

[hoadlies]

a quicky question please

HI STEVE,DON & ALL
WHAT value of cap have you in C1 position on board my board is 220n???? 0.22uf I think the board layout vary,from early to late boards ?????because this cap goes across RX coil leads ????
I maybe wrong ????

CHEERS BARRY..

[hoadlies]

HI STEVE,DON & ALL
WHAT value of cap have you in C1 position on board my board is 220n???? 0.22uf I think the board layout vary,from early to late boards ?????because this cap goes across RX coil leads ????
I maybe wrong ????

CHEERS BARRY..

HI,, YES I was wrong so disreguard the above''sorry'' ,After I found I was looking at a Pic of an earlia board with cap placements in different order ..

Ther seems not to be an official Schematic for this latest board..
I know STEVE has looked into that ..

NO WORRIES ,,,,,,,,,,,,,,,BARRY..

[golfnut]

The kit uses labelled parts to go in where the silkscreen says. So if you all build to the silk screen I know they work without errors.

As for a schematic, the one I put on here a while ago is very close. ( I did put optional trimmer on the Disc RC timing - you should really disregard my options and try usual build first, if you feel the need for flexibility in Disc timing , try a trimmer plus small series resistor. )

I don't have quite so much spare time currently but I will help tidy it all up in near future.


Barry , it sounds as though you dont have a RX cap fitted. This will make the build harder.

The Rx cap is (depending on how you made your coil ) tack a 30nF across the pins where you soldred the Rx wires on. try up to 5n either way to help range and phase, ferrite reject etc

DONT POT ANYTHING yet - !!!


The 220n is part of a filter pole to give zero gain at DC, there is no holes for Rx cap - I guess there should be in a better layout.

As for cable I have used Belden 2x twin core screened and also 2coaxes with no drama

S

[hoadlies]

HI STEVE ,, I see now I have confused you with this post above ,,I have fitted RX cap to RX coil windings 22n ,+ 10n= 32n ,, higher & lower values etc..
I will continyou to do your method of switching caps to try to get improvements Thanks for the help given in your posts in above messages..

Incedently I have not added any mods!,, I built the kit as per silk-screen & it definately works as should .. I am sure no worries with the build I feel its my coil construction letting me down ,So I may build a second coil to start over fresh ,now that I have a little more knowledge on the coil build proccess!!..

I will post again after I do that with hopefully better results ..

I appreciate all the help I have been Given ..,,,,,,,
CHEERS TO ALL ,,BARRY..