Elastix 2: Openvox A400P FXS Line Noise

alex_rhys-hurn

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#1
Hello Folks,

Well, this is my first post in these forums, as I am newly migrated over to Elastix from Trixbox.

I have Elastix 2.0.1 with Openvox A400P with two FXO and two FXS modules on it.

Everything is working properly.

But when I use the FXS handsets I notice my Local Medium Wave radio station on the line.

I can hear the radio station quite clearly but faintly.

I dont have any form of echo (the MG2 echo canceller is in use) and apart from the interference from the radio station the call is clear and works well.

With the FXS handset I get this interference regardless of what extension or outside line I call.

I have looked at all the documentation about line noise on TDM400P which is normally related to IRQ issues, but I definitely dont have that problem here.

The FXS card is connected with a 1.5 meter RJ11 CAT 3 cable to the CAT5 Patch Panel, which then goes through approx 15 meter length of CAT5E cable to the RJ45 Wall socket where I have a 3 Meter RJ11 CAT 3 Patch cord.

Can anyone help me with this?

Alex
 

tbooth

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#2
This is common when when you are close to a radio station. I have had to put filter on handset cords to correct it. I got mine at www.mikesandman.com
 

alex_rhys-hurn

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#3
Dear tbooth,

Thank you for your reply.

There are medium wave radio stations within 3 kilometers from me.

But why did this not happen with Trixbox? All the hardware is the same, the only thing new is Elastix, and its admittedly more recent drivers.

Regards,

Alex
 

dicko

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#4
It can happen, and is just good old fashioned physics (nothing to do with Elastix or even TrickyBox, don't even bother going there) really old people remember something called a crystal set or "cat's whisker" receiver, all that took was long bit of wire, the antenna, add a bit of inductance (often overly long and coiled cable) and capacitance (the self capacitance between the twisted pair counts, insert a semi conductor , the detector, which extracts the AM signal and we have a tuned circuit that could listen to radio stations, The most critical bit was the semi-conductor, copper oxide is such a beast, so apart from rearranging the wiring which will often change the natural resonance of the circuit which might either change the station or make it go away, it is usually best to first check your punch-downs and RJ connectors for corrosion, because that is a common place for oxides to build up, just pull them and re-punch them. Sometimes it is necessary to add a "wave-trap" (series capacitor and inductance, sometimes called a "slug") at the MPOE "minimal Point of entry", where you first get hold of the pair that goes to the telco, a good butt set on high impedance will normally let you hear such intrusions


Low pass filters and the ability to provide dynamically proper impedances (to provide adequate "sealing current" which both reduces oxidation and provide proper low echo line termination) are usually used on the FXO interface to reduce such effects, many interfaces have them (for example Digium, Rhino, Sangoma and Xorcom) and dahdi provides some hints as to what needs tuning (at least to the mainstream hardware) , you will have to check with Openvox as to how well they integrate with the dahdi driver you use (some believe they aren't quite as rigorous . . .)

dicko
 

alex_rhys-hurn

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#5
Wow!

Thank you for taking the time to provide some background, which has helped me understand the problem.

Many thanks again!

Alex
 

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