Author Topic: Help! I need to make a galvanic isolation on my trunk line.  (Read 284 times)

Offline dsk

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Help! I need to make a galvanic isolation on my trunk line.
« on: March 07, 2018, 01:48:35 PM »
My trunk are noisy, when it put in a galvanic separation to the CO everything is fine, for the moment the separation is a set of wireless jacks next to each other. Do you have any more practical solutions for me, a sketch or schematic.  This line uses DTMF. 


Thank you!


dsk

I have even got a regular New York number :-) 646 570 1796

Online Haf

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Re: Help! I need to make a galvanic isolation on my trunk line.
« Reply #1 on: March 07, 2018, 01:54:48 PM »
dsk,

I guess it's not a matter of poorly shieled wires, right? Maybe the signals from your CO (assuming that it is no POTS line any longer) are too strong. I had something similar once, was one of the hubs nearby sending wrong signals. After contacting the provider they fixed it.

Haf
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Offline dsk

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Re: Help! I need to make a galvanic isolation on my trunk line.
« Reply #2 on: March 07, 2018, 02:35:36 PM »
The line comes from an ATA FXO port, and the line is from my PAX designed about 1920 built about 1946. I use a SMART-1 for tone to pulse converting.


dsk

I have even got a regular New York number :-) 646 570 1796

Offline kb3pxr

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Re: Help! I need to make a galvanic isolation on my trunk line.
« Reply #3 on: March 07, 2018, 03:41:30 PM »
The line comes from an ATA FXO port, and the line is from my PAX designed about 1920 built about 1946. I use a SMART-1 for tone to pulse converting.


dsk

Most ATAs don't have a polarized plug and use a switching power supply. It is possible that noise is passing through the RFI suppression capacitor or other potential sources of noise with the AC line or the power supply. Since these power supplies don't have a polarized plug, unplug the supply from the AC line, turn the plug over (reverse the polarity) and try again.

What this will do is reverse the polarization of the AC side of the supply and may place the neutral side in a more preferable place.

Offline dsk

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Re: Help! I need to make a galvanic isolation on my trunk line.
« Reply #4 on: March 07, 2018, 04:01:53 PM »
That is another issue, The Norwegian power supply, we have a 230V Delta with floating ground, no neutral at all.  We can measure about 133V to ground from any live conductor (until first ground fault in the system).

dsk


I have even got a regular New York number :-) 646 570 1796

Offline kb3pxr

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Re: Help! I need to make a galvanic isolation on my trunk line.
« Reply #5 on: March 07, 2018, 05:11:08 PM »
Ungrounded delta makes sense for this problem. This capacitor I mentioned provides a high impedance (at mains frequency) path between the primary (mains) and secondary (ATA) side. If the PAX line is referenced to earth, you are providing a path between mains and earth.

Online twocvbloke

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Re: Help! I need to make a galvanic isolation on my trunk line.
« Reply #6 on: March 08, 2018, 05:05:29 AM »
You should be able to use an isolating transformer, these are just a 1-to-1 ratio transformer that takes the dodgy mains in and outputs a separated supply that is isolated from the problematic side of things... :)

Offline dsk

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Re: Help! I need to make a galvanic isolation on my trunk line.
« Reply #7 on: March 12, 2018, 03:43:30 PM »
Ended up with this one, and it is working  :) 


(I use this line for incoming calls only)


dsk


I have even got a regular New York number :-) 646 570 1796