IDX-PRO+VDI

[golfnut]

Oh I see, Id imagine your coils are fine. Its now how shielding, screening, cabling, location in shell/phasing is done,

Im sure you will make something that will be ok.

Don't be tempted to pot too early.. S

[ossamaussama]

what is the idea for phase shift without any cap in rx i should hear one beep for copper metal target is that indication of initial good phase shift?

when i put capacitors in parallel with rx coil i reach max voltage at 27 nf
in this way it is resonance frequency match between rx and tx

now reducing capacitor to 18 nf i get all needed reject frite iron every thing is ok



if i try to go above 27nf i hear double beep :
and when i sweep rx coil i get very good sensitivity but without ability to reject frite

TX frequency is adjusted to 6.5k hertz using computer sound car scop software

how can explain?

[golfnut]

what is the idea for phase shift without any cap in rx


I don't have any info for No Cap on Rx..




i should hear one beep for copper metal target is that indication of initial good phase shift?


I set up correctly all targets are single beep....



when i put capacitors in parallel with rx coil i reach max voltage at 27 nf
in this way it is resonance frequency match between rx and tx


Yes - I believe it is.... you cant use machine like this TOO Twichy




now reducing capacitor to 18 nf i get all needed reject frite iron every thing is ok


This puts your Rx coil cap freq Above the Tx freq... Good initial phase!!




if i try to go above 27nf i hear double beep :


With the large cap you are below the Tx freq - as per design - but initial phase is 180 out...


You can use it like this, you just need to reverse Rx coil connections and should be good to go...



and when i sweep rx coil i get very good sensitivity but without ability to reject frite

This should improve when you do larger cap and RX coil reverse...


You sound V close.. S

[ossamaussama]

thanks golfnut for reply

[ossamaussama]

what is the idea for phase shift without any cap in rx


I don't have any info for No Cap on Rx..




i should hear one beep for copper metal target is that indication of initial good phase shift?


I set up correctly all targets are single beep....



when i put capacitors in parallel with rx coil i reach max voltage at 27 nf
in this way it is resonance frequency match between rx and tx


Yes - I believe it is.... you cant use machine like this TOO Twichy




now reducing capacitor to 18 nf i get all needed reject frite iron every thing is ok


This puts your Rx coil cap freq Above the Tx freq... Good initial phase!!




if i try to go above 27nf i hear double beep :


With the large cap you are below the Tx freq - as per design - but initial phase is 180 out...


You can use it like this, you just need to reverse Rx coil connections and should be good to go...



and when i sweep rx coil i get very good sensitivity but without ability to reject frite

This should improve when you do larger cap and RX coil reverse...


You sound V close.. S

try to tune rx below tx frequency without any success cannot reject frite rod
but with 18 nf ( Rx frequency is above tx) i get 25-30 for coin air test

[golfnut]

If you go for the big cap - so below Tx.... Do you get double beep. ... if Yes - then reverse Rx coil connections and retest.


If you get single beep, and Rx is below Txas per design,. If you cant reject ferrite in this state then you would need to ...


Re locate the Rx OR Tx coil in shell a lttle or try a cap value tweak of Tx or Rx..


Really you would have done this work before potting your coil... ( Assuming you made it! )

S

[golfnut]

"cannot reject frite rod" How long is this..... 100mm???? You only require a length 20mm long.


Do not pass it closer than 25mm. Use it like a coin at 3" - 4" ( ~10cm )

S

[ossamaussama]

it is 10 m long and 12 cm far

and yes it is home made dd coil


i will stop on 18nf on rx coil

it is just questions

thanks man


i use zlecop which is sound card pc scope to set tx to 6.5khz
dont know if it accurate software

[golfnut]

If you got scope ... Put L CH on TX and R CH on peamp out/..

When you get Rx sig phase like this it will work

good luck S

[hoadlies]

WIRE GUAGE ????? RX COIL

HI ALL ,, A question if I may,,IDX COIL ..

Concerning RX wire GUAGE ,Steve helped me earlier on the subject ..But I had ordered some tinned,thin PVC coated wire [CHEAP from CHINA] the actual wire is 0.2 mm BUT I found that is was no good for the Job I could not get anywhere near the 34 Mh & the bundle was very large ..with 270 T ..ITS IN THE BIN..

I tried also some .34 & a similar outcome ..way oversize bundle..
OK Now I have some 0.25mm enameled wire from some solinoids [easy to unwind etc & its free HaHaaar..]plenty of supply also..

I wound a RX coil with that & easilly produced 35mh ,,BUT the resistance is much lower than specs!!!!,,,, I see in the threads ..I see 90 ohms quoted Mine is only approx 60 odd ohms.

[My 1st coil using 0.23 mm was around 76ohms ???..]

''However I saw a post'' [But cannot now find it ,,,,where some one suggested to add a series,resistor to get a reading of 111ohms on the RX COIL??????? does this make any sense ???????Does the Preamp need to see the correct load ????..

MY existing Coil[1st built coil] after many cap changes is now showing promiss ,But I want to build another for a better match to the IDX ..

SORRY to see the WET weather in the UK & the COLD in the US ,We here are having Fires as to the extreme Heat ..ADELAIDE STH AUST has now an all-time record of over 40c in a row WHEW,,

CHEERS TO ALL ,,,BARRY..

[golfnut]

Hi Barry, the differences in coil resistance is not a concern here. 30/40/50/60/70 its no drama.

The Rx coil and cap when parallel resonant is fairly high impedance in the k ohms so a small series R only affects the bandwidth of the Rx tank a little. Or you could say the Q of the tank.


The Q of the Rx tank is approx. 2 PI Freq L/R (assumes cap is lossless )

If the R was 60ohm the Q is 23
If the R was 90ohm the Q is 16


I dont see any real problem. Give it a go... Don't POT until shielded, phased, Nulled, tacked, Cable fitted and cut to length.. So no changes after you got it going!!!


If you added a series 33R to your coil this would be the same as the one in the text you mentioned. Same electrical properties and performance

Good luck S

[hoadlies]

HI STEVE ,THANKYOU for clearing that up for me .That very nice to know ..

INcedently my original 1st-built coil is still not fully potted ie the TX is fully potted ,But the RX is only 50% potted allowing movement of the strait section of the D,!! But ''ITS very- very'' touchy to the Lightest movement & I can reject the Ferrite with 50% geb travel [pot] ...,Thats Better..

I am to try to make a FIBRE-GLASS Coil housing [hopefully as light as possible] resin is very heavy!!!..

HOPE you area is coping with the heavy Rain MATE ,,,,,,,,,BARRY..

[golfnut]

Hi, that sounds good....


For Weight I put lots of small closed cell board cut up and superglued in all over the big areas.

You can get microballons - tiny hollow glass spheres and mix in the resin too - boat/canoe guys use it..



Very wet ground local river is well up. No local floods fortunately..

Steve

[hoadlies]

Thanks Steve ,, Good you are not flooded ,,We here are into the hottest period I have known & i am 74!! ..
We are OK as for fires at BOOBOROWIE STH AUST.. BUT theres a big one only 40 odd ks Nth of us in scrub & forrest area ,been burning for 4 weeks now in inaccesible rugged hilly country ,,,,,we here only have the tree's grown by land owners etc..
Tomorrow we are to get a cool change & next day Rain ,I will believe it if it gets here HA.Haar..

Great tips on filling vacant area's with styrene foam pieces , I have plenty resin & glass mat ,but I need to keep resin to minimum [wieght]
Today to put board & pots in a housing ,Nylon with shield tape inside & YES I am aware to not ground the speaker socket etc ,at least there is much info on this great site to warn of dangers..
After I get it running OK ,I may try some of your Mods later-on..

GREAT HELP,, STEVE ,,TAKE it Easy mate ,,,,,,,,,,,,,BARRY..

[golfnut]

No worries, for completeness Barry - - the filler board I used was not styrene -- as this disolves on contact with polyester resin #!!!

It was pvc board / core material like this.....

http://www.ecfibreglasssupplies.co.u...-foam-5mm.aspx

S