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Offline dbannerTopic starter
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« on: October 29, 2014, 02:09:17 pm »
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check out this vintage russian bfo. germanium pnp transistor and a hard to source ferrite toroid for L2.there is a video on you tube. just search "Металлоискателю 40 лет". incredible depth on coins.

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« Reply #1 on: September 05, 2018, 10:49:23 am »
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I'm building now Smiley for the L2 toroid i think it is 100mH inductor, i said because the website in russian states that the mixer with L2 must oscillate at 1Khz and because we know the capacitor value that forms with L2 the tank circuit I have calculated to be... 100mH

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« Reply #2 on: September 05, 2018, 04:13:57 pm »
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  Cool Beans.  What are you going to use for a Core ?

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Offline giuhalftrack
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« Reply #3 on: September 06, 2018, 02:13:42 am »
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I was using a core of different dimension from the one listed in the project....

but... this is my odyssey

1) I try to calculate the right inductance and wind the core by hand.. but i made wrong calculations and made an inductor of 100uH  Clapp
2) I cut the core in half and wind the two parts then gluing them together... a very bad work  Thumbs Down
3) every time i measure things (inductance) with oscilloscope measuring the frequency of the tank circuit... because my homemade inductance meter do not measure over 10mH  Funny

so...
I have ordered a non toroidal inductor of 100mH and a capacitance and inductance meter.. when i return from holidays i assemble all to make it work.. i hope

I think they want a toroid to mitigate interference...

for those who want to know original data for the inductor:
The mixer coil (L2) is wound on a ring core made of ferrite of M2000NMA grade K38 X 24 X 7 mm.
The coil has 200 turns of PEV-2 wire with a diameter of 0.47 mm.
The 100mH value is calculated by me (not tested) because we have a tank circuit with C = 0.250 uF and a frequency of 1KHz.


I'm a BFO enthusiast  Hello




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« Last Edit: September 06, 2018, 02:29:26 am by giuhalftrack »
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« Reply #4 on: September 06, 2018, 07:37:44 am »
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   I like BFO too.  They Work most well to track the Black Sands paths for panning Gold. 

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« Reply #5 on: September 06, 2018, 09:37:09 am »
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Quote:Posted by Homefire
   I like BFO too.  They Work most well to track the Black Sands paths for panning Gold. 


yes i give it a try in the Ticino river... very fine gold (flakes of 3mm max) but there is a lot in certain areas....

little OT:
I have read somewhere that BFO could find  voids in the soil... is this correct ?

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« Reply #6 on: September 06, 2018, 02:24:25 pm »
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  I guess they would be noticeable if you knew what your hearing ?  Not heard of any thing like that.  When your chasing the Black Sands your looking for  the Swing to the Mineral side.  NOT the Metallic Side.   I use flags like this to get a visual of how the Black Sands were being Deposited.  Pan the locations with the most concentrations. 

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https://www.uline.com/Product/Detail/S-16061FO/Flagging-and-Marking/Stake-Flags-2-1-2-x-3-1-2-Fluorescent-Orange?pricode=WB2055&gadtype=pla&id=S-16061FO&gclid=CjwKCAjwoMPcBRAWEiwAiAqZh_HBcX5nXLMDv6254qlD4ogSukIis2ie0oeO_rG9ykA2gZ0BtMubcxoCChUQAvD_BwE&gclsrc=aw.ds


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Offline giuhalftrack
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« Reply #7 on: September 07, 2018, 02:54:02 am »
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Quote:Posted by Homefire
  I guess they would be noticeable if you knew what your hearing ?  Not heard of any thing like that.  When your chasing the Black Sands your looking for  the Swing to the Mineral side.  NOT the Metallic Side.   I use flags like this to get a visual of how the Black Sands were being Deposited.  Pan the locations with the most concentrations. 

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the black sand chasing is interesting !!  I'll try maybe this winter... the river it's at low level in winter...  Cheesy

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« Reply #8 on: September 07, 2018, 07:24:04 am »
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 You know the Insides of the Bends is the best, right ? 

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Offline giuhalftrack
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« Reply #9 on: September 07, 2018, 08:23:15 am »
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yes I know i have a little knowledge of placer mining, I'm a mining technician and geologist but never land a similar job  Cry so my culture is only theoric.

I know the basic of placer gold mining I've read many sources of this mining techniques mostly u.s. resources, they are very "skilled" because they run this kinds of operations from many years ago.
In my area Romans perform a sort of "drift-mining/water mining technique" there are their tails in the forest they move mountains for gold in the moraine of the north Italy lakes

I know this is OT but... is difficult stop talking about GOLD !!!  Kiss


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