[x] Welcome at THunting.com!

A fun place to talk about Metal Detecting, Treasure Hunting & Prospecting. Here you can share finds and experience with thousands of members from all over the world

Join us and Register Now - Its FREE & EASY

THunting.com
Treasure Hunting & Metal Detecting Community
   
Advanced Search
*
Welcome, Guest! Please login or register HERE - It is FREE and easy.
Only registered users can post and view images on our message boards.
Did you miss your activation email?

Login with email, password and session length
Or Login Using Social Network Account
2
News:
Pages:  1 2 3 4 5   Go Down
Print
Share this topic on FacebookShare this topic on Del.icio.usShare this topic on DiggShare this topic on RedditShare this topic on Twitter
Tags:
0 Members and 1 Guest are viewing this topic.
Offline Homefire
Global Moderator
Platin Member
*****

Join Date: Jan, 2009
Thank you634

Activity
1%
Male
United States
Posts: 15906
Referrals: 0

52355.00 Gold
View Inventory
Windows NT 10.0
Windows NT 10.0
Firefox 62.0
Firefox 62.0

Awards
« Reply #20 on: September 11, 2018, 06:27:07 am »
Go Up Go Down

   Yes 2N2907 should work quit well.    Ref 50-70Khz, yes it's a proven Hot Frequency on gold in a VLF machine.  Not going to make much difference in your BFO I do not think.   Most BFO machines I've messed with run way higher then 1K.  I can't think of any reasons not to try.   

Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,58074.msg325359.html#msg325359




Logged
Offline giuhalftrack
Copper Member
*

Join Date: Aug, 2013
Thank you3

Activity
0%

Italy
Posts: 61
Referrals: 0

355.00 Gold
View Inventory
Mac OS X
Mac OS X
Safari
Safari

WWW Awards

Tesoro silver uMax, NAUTILUS DMC II / DMC IIa, IGSL-TGSL
« Reply #21 on: September 12, 2018, 12:41:18 am »
Go Up Go Down

Quote:Posted by Homefire
So basically your saying  there are Little or No National Rules or Laws regarding Metal Detecting ?  All is handled locally ?  What are the Basic National Laws regarding Metal Detector Use ? 


There isnt a nationl law on metal detecting. The only mention is in the law For archeological search that states that the only entity allowed to do research are university and state entities and metal detecting by common People is stritly proibited in know archeological areas. The problem arises when you are on a search of one of this area and you dont know that.. In fact these area are not published to avoid depredation. But i think this is enought For this topic.. Let Return to BFO its more fun t'han law 

Posted on: September 12, 2018, 12:32:15 am
Talking about frequency low frequency will be a must to have a Little ground respinse but maybe if we use a BFO to locating Black sande this is a drawback Huh? Hope some member with more Knowledge will clarify this general rule.

Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,58074.msg325366.html#msg325366




Logged
Offline Homefire
Global Moderator
Platin Member
*****

Join Date: Jan, 2009
Thank you634

Activity
1%
Male
United States
Posts: 15906
Referrals: 0

52355.00 Gold
View Inventory
Windows NT 10.0
Windows NT 10.0
Firefox 62.0
Firefox 62.0

Awards
« Reply #22 on: September 12, 2018, 10:06:32 pm »
Go Up Go Down

Any and All BFO's I've ever used were running up into the 100Khz - 300Khz range.  One running at 1Khz is going to have a hell of a bundle of wire on the coil I would think ? 

Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,58074.msg325377.html#msg325377




Logged
Offline giuhalftrack
Copper Member
*

Join Date: Aug, 2013
Thank you3

Activity
0%

Italy
Posts: 61
Referrals: 0

355.00 Gold
View Inventory
Windows NT 6.3
Windows NT 6.3
Firefox 62.0
Firefox 62.0

WWW Awards

Tesoro silver uMax, NAUTILUS DMC II / DMC IIa, IGSL-TGSL
« Reply #23 on: September 27, 2018, 01:57:12 am »
Go Up Go Down

Ok now that i'm back from holidays i'm on the project again.

I have assembled a first prototipe with "junk" components so do not criticize aesthetics  Cheesy

I have used multiple capacitor or resistors to obtain the "strnage" values present in the schematic (subsequently i recalcualte values for use the standard series and silicon transistor).
I have used germanium transistor similar to the ones in the schematic (the transistor listed in the schematics are available on ebay).

The "infamous" L2 inductor is made... 200 turns of 0.47mm wire on the toroid core (similar in dimensions) have an inductance not as aspected... (need more testing).

The TX PCB produce a sligtly distorted sinewave but for now is working... i have used a 100uH inductor to simulate the search coil.

A picture just for fun  Wink

Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,58074.msg325547.html#msg325547



There are 1 attachment(s) in this post which you can not view or download

Please register for viewing them.

WP_20180927_001_russian_BFO.jpg


« Last Edit: September 27, 2018, 02:01:21 am by giuhalftrack »
Logged
Offline Homefire
Global Moderator
Platin Member
*****

Join Date: Jan, 2009
Thank you634

Activity
1%
Male
United States
Posts: 15906
Referrals: 0

52355.00 Gold
View Inventory
Windows NT 10.0
Windows NT 10.0
Firefox 62.0
Firefox 62.0

Awards
« Reply #24 on: September 28, 2018, 09:56:00 am »
Go Up Go Down

    First we need to get something behind us !   ""I have assembled a first prototipe with "junk" components so do not criticize aesthetics  Cheesy""

I prefer the term Trash Recovered Repurposed Technology!   Or as you please Aka Scrounging !  LOL

Sir no one going to laugh at your work !  Anyone who can SCROUNGE Parts with a goal in mind creating a functional project of them has my Respect !!!!   Many people could only wish they had those SKILLS !

I'm Impressed Sir !   Shocked

To this day I shudder thinking about winding a toroid  by hand.  Every time I've ever attempted the feat I ended in failure.  Always resorted to SCROUNGING a suitable substitute !!!    Embarrassed

So can you get it Putt Putting ?  Low Roar maybe ?  Getting the two oscillators close enough to hear the Heterodyning process is not so easy some times.  I've never achieve it without some tweaking the first few goes . 

Ok, waiting !  Would be most interested to hear a Audio File if you could manage something like that ?

Cool Beans !   

Germanium Transistor are like ancient technology as Transistors  go.  Funny thing is it's hard to beat them even today for the sensitivity they can achieve. 


 



Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,58074.msg325559.html#msg325559




Logged
Offline giuhalftrack
Copper Member
*

Join Date: Aug, 2013
Thank you3

Activity
0%

Italy
Posts: 61
Referrals: 0

355.00 Gold
View Inventory
Mac OS X 10.13.3
Mac OS X 10.13.3
Safari 11.0.3
Safari 11.0.3

WWW Awards

Tesoro silver uMax, NAUTILUS DMC II / DMC IIa, IGSL-TGSL
« Reply #25 on: September 29, 2018, 11:42:41 am »
Go Up Go Down

Quote:Posted by Homefire
 ....I prefer the term Trash Recovered Repurposed Technology!   Or as you please Aka Scrounging !  LOL...

...To this day I shudder thinking about winding a toroid  by hand.  Every time I've ever attempted the feat I ended in failure.  Always resorted to SCROUNGING a suitable substitute !!!    Embarrassed ...

....So can you get it Putt Putting ?  Low Roar maybe ?  Getting the two oscillators close enough to hear the Heterodyning process is not so easy some times.  I've never achieve it without some tweaking the first few goes .... 



Seem that I'm improving my language skills here Wink love the sound of the word SCROUNGING ...  Cheesy

... for the TRRT (trash recovered repurposed technology) i think explain perfectly the sense of the process !!!

For toroid winding see the attached picture... i use a sort of "spool" build with cardboard.. you need to use this tool to go inside and out of the toroid without making a mess... I remember
 my uncle using a similar tool to repair fishnets (se other image).

I'm finishing the connections on the detector and as soon as possible i make a video of the machine working.

Thank you for your compliments



Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,58074.msg325569.html#msg325569



There are 2 attachment(s) in this post which you can not view or download

Please register for viewing them.

136.jpg
WP_20180929_004.jpg


Logged
Offline Homefire
Global Moderator
Platin Member
*****

Join Date: Jan, 2009
Thank you634

Activity
1%
Male
United States
Posts: 15906
Referrals: 0

52355.00 Gold
View Inventory
Windows NT 10.0
Windows NT 10.0
Firefox 62.0
Firefox 62.0

Awards
« Reply #26 on: September 29, 2018, 04:42:30 pm »
Go Up Go Down

   Yes, I knew about the Shuttle Trick but never was so proficient with the processes.  Always Drop the thing and end up with a Wire Birds Nest at my feet.   

Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,58074.msg325573.html#msg325573




Logged
Offline giuhalftrack
Copper Member
*

Join Date: Aug, 2013
Thank you3

Activity
0%

Italy
Posts: 61
Referrals: 0

355.00 Gold
View Inventory
Mac OS X 10.13.3
Mac OS X 10.13.3
Safari 11.0.3
Safari 11.0.3

WWW Awards

Tesoro silver uMax, NAUTILUS DMC II / DMC IIa, IGSL-TGSL
« Reply #27 on: September 30, 2018, 02:01:20 am »
Go Up Go Down

this morning i tune the reference oscillator and now i'm ready to build a coil so the search oscillator could be tested.

I attach to pictures:

the one with the blue track is from the reference oscillator (approx 509KHz)

the one with the yellow track is from the search oscillator, it runs at 545KHz, i think is a bit too high but consider that i'm using a 100uh SMT inductor to simulate a coil.

If I have understand the design of this machine the filter/mixer constituted by T2, L2, C6 is tuned to the difference of frequency of the search and reference oscillator (1KHz)
so producing as output a voltage of 0,5V necessary to shut down the audio circuit (schmidt trigger), as a metal approach the search coil the search osc. freq. changes so the difference of the frequency at
the mixer is not 1KHz anymore.. and because the resonant frequency of the mixer is 1KHz any input difference frequency results in a drop of the voltage at mixer output.

I think this design is interesting because instead of human ears distinguishing the tone change (need skills and good exercise) there is a circuit distinguishing the tone change...
one question is in my mind from the first reading of this project...
If we use a circuit to sense the frequency differences why not make a BFO in the VLF range ??  Tongue

Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,58074.msg325577.html#msg325577



There are 2 attachment(s) in this post which you can not view or download

Please register for viewing them.

WP_20180930_001.jpg
WP_20180930_002.jpg


Logged
Offline Homefire
Global Moderator
Platin Member
*****

Join Date: Jan, 2009
Thank you634

Activity
1%
Male
United States
Posts: 15906
Referrals: 0

52355.00 Gold
View Inventory
Windows NT 10.0
Windows NT 10.0
Firefox 62.0
Firefox 62.0

Awards
« Reply #28 on: September 30, 2018, 09:12:09 am »
Go Up Go Down

Yes,  Like a I said above .  It's not so easy to align both oscillators to the point they motor boat sound.  Everything has to be all but Identical in values.   Even using 1% components can throw you off enough to fail.        I have a somewhat basic BFO circuit here some place that uses Gates to compare the frequencies.  It's like super simple and yet in my few attempts to make one work, I couldn't get the coils right.  LOL  

""the one with the blue track is from the reference oscillator (approx 509KHz)the one with the yellow track is from the search oscillator, it runs at 545KHz, i think is a bit too high but consider that i'm using a 100uh SMT inductor to simulate a coil.""

Yep, that's a 36KHz difference and your never going to get the audible.   Replace one of the caps with a Variable Trim Cap if you can.  Or  Parallel  with a smaller cap maybe ?   Once you get it rolling measure the pair of caps and try to find something fixed close enough in value.  

I have one of those Chinesium Do All transistor checkers that works for that stuff.




Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,58074.msg325579.html#msg325579



There are 1 attachment(s) in this post which you can not view or download

Please register for viewing them.

1a.jpg


« Last Edit: September 30, 2018, 09:14:02 am by Homefire »
Logged
Offline giuhalftrack
Copper Member
*

Join Date: Aug, 2013
Thank you3

Activity
0%

Italy
Posts: 61
Referrals: 0

355.00 Gold
View Inventory
Mac OS X 10.13.3
Mac OS X 10.13.3
Safari 11.0.3
Safari 11.0.3

WWW Awards

Tesoro silver uMax, NAUTILUS DMC II / DMC IIa, IGSL-TGSL
« Reply #29 on: September 30, 2018, 03:23:13 pm »
Go Up Go Down

Quote:Posted by Homefire

...Yep, that's a 36KHz difference and your never going to get the audible.   Replace one of the caps with a Variable Trim Cap if you can.  Or  Parallel  with a smaller cap maybe ?   Once you get it rolling measure the pair of caps and try to find something fixed close enough in value....  

I have one of those Chinesium Do All transistor checkers that works for that stuff.



oh yes !! i'll make large use of trim-caps ... in the document there are more than one component to be tuned (resistors and caps) but the original instructions (that i found in internet and translate from russian with google... Cool) are oriented to substitute components of different values.. (no way). For the measurement I have a brand new unit-603 cap and inductance meter... good instrument for home purposes.

I think at the end i'll share a "new" schematics with trimmers and tuning instruction for those who want to try this machine...

p.s. i'm reading the book "inside metal detector Overton Moreland"  Wink where the BFO principle and some variants are clearly explained.

Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,58074.msg325581.html#msg325581




« Last Edit: September 30, 2018, 03:28:41 pm by giuhalftrack »
Logged
Print
Pages:  1 2 3 4 5   Go Up
Jump to:  

Powered by SMF 1.1.19 | SMF © 2005, Simple Machines | Sitemap
Copyright THunting.com