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australian electronic gold prospecting forum.com  |  Recent Posts
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 11 
 on: Yesterday at 22:03 
Started by Aziz - Last post by Aziz
  
What is considered too high a value of capacitance for the cable, I retested a 1200MM twisted pair with PE insulation striped from a cat5 cable and its 56PF. (DE-5000)

If the twisted pair was put into heat shrink wrap, or 3MM  PE cable spiral wrap and then put inside the outer braid from some coax for a shield ,
whats wrong with that ?,

the twisted pair also adds about 20uH to the total inductance

I only need 1000MM for my testing so the  capacitance would be even lower at that length.

Muntari and IBgold great ideas on your projects

Hi 6666,

making a simple low capacitance shielded coax cable isn't that difficult. I will show this how to do it soon.
The only drawback is, that the cable may not be bendt too much. And it is quite thick (up to 8-10 mm diameter).
Aziz

 12 
 on: Yesterday at 22:00 
Started by Aziz - Last post by WM6
  


If the twisted pair was put into heat shrink wrap, or 3MM  PE cable spiral wrap and then put inside the outer braid from some coax for a shield ,
whats wrong with that ?,


Probably it is a little complicated way.

Then it is better to use two shielded parallel cable and get way lower inter-wire capacitance.

 13 
 on: Yesterday at 21:51 
Started by Aziz - Last post by 6666
What is considered too high a value of capacitance for the cable, I retested a 1200MM twisted pair with PE insulation striped from a cat5 cable and its 56PF. (DE-5000)

If the twisted pair was put into heat shrink wrap, or 3MM  PE cable spiral wrap and then put inside the outer braid from some coax for a shield ,
whats wrong with that ?,

the twisted pair also adds about 20uH to the total inductance

I only need 1000MM for my testing so the  capacitance would be even lower at that length.

Muntari and IBgold great ideas on your projects

 14 
 on: Yesterday at 20:35 
Started by Aziz - Last post by Aziz
Hi all,

I have analysed my sound card impedance meter further.
Most measurement errors come from the inbalance of the left/right input channels. And there is a phase offset error at high test frequencies.

So I have to implement a calibration function into my measurement software before I can make any measurements with it.

Cheers,
Aziz

 15 
 on: Yesterday at 19:29 
Started by Aziz - Last post by Aziz
  
Great work guys and thanks for the effort your putting in. Regards to the coax .Would a twisted pair feed line not be as good as a coax and why . thanks

Hi Alex,

a twisted pair cable would have more capacitance. And has no shielding.

Cheers,
Aziz

 16 
 on: Yesterday at 19:28 
Started by Aziz - Last post by Aziz
  
Hi Muntari,

I used a brown paper backed white paper almost like wall paper from IKEA and glued it on, self adhesive would be a better option the bad news I did the self resonance tests today using a piece of coax I had hanging around the coax measures 113.7 pf and the self resonance of the coils with shielding and coax are 361 KHz and 353 KHz so too low I think.

Regards, Ian. happy face

Hi Ian,

throw that coax cable out of the window.  smile

My relative thin oscilloscope cable (4 mm diameter, 2.07 m length) has even 73 pF for the whole lenght and connectors.
Please take a look at high impedance coax cables. Don't use 50 / 75 Ohm coax cables.
As deemon proposed, a cheap oscilloscope cable could also be used for this purpose.

Cheers,
Aziz

 17 
 on: Yesterday at 19:11 
Started by Aziz - Last post by Alex
Great work guys and thanks for the effort your putting in. Regards to the coax .Would a twisted pair feed line not be as good as a coax and why . thanks

 18 
 on: Yesterday at 16:36 
Started by Doug - Last post by Doug
Report on the mining districts of the NT:1912
  
doug smile

 19 
 on: Yesterday at 15:57 
Started by Doug - Last post by Doug
GUIDE TO THE PALMER RIVER AND NORMANBY GOLD FIELDS,NORTH QUEENSLAND, 1875
  
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 20 
 on: Yesterday at 15:46 
Started by Doug - Last post by Doug
Ballarat field :Bradford
Includes  a section on the Ballarat indicator beds.
  
doug smile

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