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Asterisk PBX has a lot of echo

Posted on 2004-11-19
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Last Modified: 2012-08-14
Has anyone experienced echo when setting up an Asterisk PBX?   We have a couple of them setup and one that is fed by analog lines gets awaful echo.   We have tried modifying the echo and receive /transmit parameters, but have been unable to come up with the right combination.  
In addition the phone lines were experiencing interference from a local radio station and we had to put filters on the stop the noise.  The side affect is that some tones are not captured properly when customers attempt to dial an extension.

 Any suggestions would be greatly appreciated.
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Question by:DanRaposo
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Expert Comment

by:Joel_Sisko
ID: 12631316
First, I think the best place for this question would be in the VoIP section under Networking, should ask admin to delete this and put the question over there (more telephony savy folk over there such as myself).

In reagrds to the the echo issue is it internal to internal? Internal to external? What cards are you using? What type of phones? How are you connecting to the CO, T1/PRI or analog?

In regards to the RFI issue, are you picking up AM or FM? I have had the same thing happen to several clients over the years. If you are using Loop start lines (assuming you are since you have RFI) sometimes going to Ground Start lines can help. Also going to  digital T1/PRI will cure the problem on the CO connection.

Also RFI is picked up thru the handset coil cord, which filters did you use? You can try to go to the following site for a few other types:

http://www.sandman.com/rf.html

I can address more of your issues over in the VoIP section in Networking of EE.

Kindest regards


Joel_Sisko

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by:turn123
ID: 12639584
Hi DanRaposo :-),
Since we haven't heard from you for a couple of days could you please give us an update on the status of this question?
See:  http://www.experts-exchange.com/help.jsp#hi51 Thank you, turn123's friendly update request script.
Offtopic comments about this script to http://www.experts-exchange.com/Applications/Q_21188389.html please :-).
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Author Comment

by:DanRaposo
ID: 12644081
Hi,  I am goign to try and get the switched the the VoIP section. and I will add more details to tthe problem there.

Thanks
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Author Comment

by:DanRaposo
ID: 12644199
Can you please move this quetion to the VoIP section in Networking of EE?   If this is not the right procedure please advise.  

If I need to repost I will, but I would also like to retain the comments provided by the other experts.



Thanks

dan
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Expert Comment

by:turn123
ID: 12644358
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by:DanRaposo
ID: 12644674
Turn 123 ... thanks for the help in posting this question to the proper site.  All further comments will be handled here.

Joel

Internal to internal calls do not receive any echo.  It is only when we go through the PBX to the outside world.  We are using Digium Wildcat T1 board in a Dell Server.  The T1 goes through a Carrier Access ADIT 600 for FXO and FXS connections.   The carrier is SNET.   The CO connection is 3 analog lines.   The RFI is indeed AM.  We pick up a local station on the 1230 band.  It is configured for loop start.  There is no digital service available in the area although we may switch to cable digital telpehone when available.

The filters we applied were a SNIX on the first line in the trunk and a couple of cheap ones from Radio Shack on the additional lines.

When we applied the filters we did reduce the RFI, but we made it a lot more difficult for the phone system to pick up DTMF signals along the 3-6-9 band.  In regards to the RFI through the hand coil, can that be reduced with better hand coils?

Here is a link to the SNIX  http://www.sncmfg.com/telecom/noise_protection/snix.html   It is the square one.
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by:Joel_Sisko
ID: 12649831
In regards to the RFI, you need to isolate where it is coming in from: (follow my order in the testing)

Pick up station phone --> Dial another station phone, do you hear the radio? If yes then put phone into speaker mode, hang up the handset (both phones). Do you still hear the radio, if not, then caol cord coul dbe the culprit. To answer your question, yes the better the qulaity the better the signal, but the shorter the coil cord the better. Sometimes using a 4 foot verses a 6 foot does the trick. The coil cord acts as an attena.

Lets say you dial internally and no RFI, then dial to the outside world. Dial out using each CO line, see if its on all of them. Then go to the PBX, disconnect the station cable from the phone you used to test internal and used to dial to the outside. Connect phone directly to PBX, still hear the RFI, if no then it might be the cabling inside your office. If this is the case, sometimes apllying an electrical drain to the unused cable pairs does the trick. If you still hear the noise at the PBX, then disconnect the CO line from the PBX, in your case before the ADTRAN, connect directly to the CO line with same phone if possible or buttset. If you do not hear the RFI, then the PBX might be causing the probolem. Two things to do, have a metal shield built to cover the PBX and then apply an electrical drain to connect to the shield. Also make sure that you have a true Isolated ground for the PBX eletrical supply outlet.

Lets say you still hear the RFI before the PBX, go to the CO demarcation point (MPE), disconenct your side from theirs, use phone to dial out on CO side of demarc, if you still have RFI, call the Phone company, they are legally responsible to fix the problem. If you connect to the demarc and no RFI, then start working agian your way forward to the desk phone to find it.

Also I would recommend using the stuff at the site I sent you, Mikes products do the trick each and every time. Once you isolate where the RFI is coming from we can devise a way to fix it.

This should help get you going. I will address the echo on the VoIP channel (trying to hit number 1 )
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Author Comment

by:DanRaposo
ID: 12655287
It is my understanding that all comments in a pointer question should be in the orignal question (this one)  so I am pasting the insightful coments from Joel here and will follow up with a response to both sets of comments and have all other respones go here.   If I am wrong please advise.



FROM JOEL

First, if the filters to combat the RFI were placed on the analog lines in front of the PBX, the dB level of the voice signal might have been reduced to low or the filters might be filtering part of the DTMF signal.

Also, you need to check to see that you do not have high loop current of your incoming lines from the CO, they are resposible to provide from 18mA to 110mA, but systems burn out at 35mA, weird stuff happens above 27mA. Check this first, if the loop current is between 18mA and 27mA then we can rule this out as a problem. Lets say you do have high loop current, go to http://www.sandman.com, they have devices to bring it down ot 25mA and they do not effect the dB level of the voice signal.

Assuming loop current is goode, need to try to isolate where the echo is being intorduced, the Adtran could be the problem also, you might want to swap the ADTRAN and see if problem is still there, if so then we can focus on the PBX side of things.

Let me know on the loop current and we can move on from there.

Kindest regards
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Author Comment

by:DanRaposo
ID: 12655402
Joel,

You are correct about the DTMF signal being blcoked by the filters, but I, thus far, have been unable to improve it much.

We jsut got a Halcyon 704 Universal Data Test set, but we don't know how to use it yet.  I assume that will be able to tell us the loop current.  I will check that and get back to you on it, but I am not sure how long it will take me to learn how to use it.

We originally had an ADTRAN installed and tried a couple others.  We also changed the entire PBX and no change.   We then did some research and found the Carrier Access to be superior in regards to echo cancellation and it improved it some but not enough.   I will check the loop current and try your other suggestions as well.
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Joel_Sisko earned 2000 total points
ID: 12657512
Based upon your response, you changed the entire PBX and no change in  what? The echo was still present? or the RFI?

Great test set you bought, but might not might really need it if the problem is on the analog side. Do you have a quality voltmeter that handles DC voltage and milliamperes?

Also do you have a butt set or even an analog phone?

If you need a butt set for every now and then I would recommend the following:

http://www.test-um.com/testum/product_detail.asp?itemno=LB255

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Expert Comment

by:Joel_Sisko
ID: 12657541
Also another question? Did the RFI and the echo problems happen around the same time frame?
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by:DanRaposo
ID: 12658173
The RFI and Echo have both been there from day 1.   I believe the RFI only comes across the first line in the trunk but I may be mistaken.  The problem for me is that the system is in Connecticut and I am in RI so I need to get to it for this testing.
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Expert Comment

by:Joel_Sisko
ID: 12658727
Have you ever tested the analog circuit with a butt set or analog phone prior to the CSU's and PBX for echo?
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Author Comment

by:DanRaposo
ID: 12658765
NO We have not, but we had another phone sytem on there (BizPhone) which had no echo problems.


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Expert Comment

by:Joel_Sisko
ID: 12658865
What about the RFI with the BiZPhone? Alsocheck for RFI on the lines also? Also do you know if the radio station boosted their wattage output at all or changed equipment or towers? Also has DSL service just been recently added to the area?
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Author Comment

by:DanRaposo
ID: 12659279
There was no radio with the BizPhone.  I do not know if theradio station boosted their signal or not.  DSL is not available in the area.
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Expert Comment

by:Joel_Sisko
ID: 12660039
Okay, check the RFI and Loop current at the demarc if levels are good then move inward.

Any reason that you are not using  Digiums TDM04B bundle? Why are you using the T1 card?

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Expert Comment

by:turn123
ID: 12680417
Hi DanRaposo :-),
Since we haven't heard from you for a couple of days could you please give us an update on the status of this question?
See:  http://www.experts-exchange.com/help.jsp#hi51 Thank you, turn123's friendly update request script.
Offtopic comments about this script to http://www.experts-exchange.com/Applications/Q_21188389.html please :-).

~~~Turn123
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Author Comment

by:DanRaposo
ID: 12699389
I am still interestedin this answer, but I am the only person in the IT department and I support 130 users in 4 states ... and their phones ... top that off with our file server has been goign belly up since Wednesday and I have been unable to respond.   I willnot likely getto work on this for about a week.
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Author Comment

by:DanRaposo
ID: 12820342
We are going to attempt to test the suggestions provided by Joel on Thursday.   Unfortunately I am on vaction the week after so I may not post again until after holidays.
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Expert Comment

by:Joel_Sisko
ID: 12831971
Have a safe and merry time!!!!!
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Author Comment

by:DanRaposo
ID: 12976961
Please do not close this question ... we are having problems getting all the cables needed to test the lines by Joel's recommendations.  As I stated earlier, I am very busy handling many tasks and cannot always dedicate the time needed to one particular issue.   We consider this important and Joel and everyones help vital.  I do not want to violate any agreements with experts exchange.  It is a valuable resource.


Thanks

Dan
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by:turn123
ID: 13001944
Ok skipping this one for now.  Please note that questions come up on my list to be cleaned 21 days after the last comment.
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