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Which Analog Telephone Adapter has the best power supply on the analog ports?

timnet
timnet used Ask the Experts™
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I have installed tweny or so Linksys PAP2T-NA ATA's.
One of them is connected to a legacy half mile long twisted pair.
The PAP in this position has failed twice, it gets very hot.
I need a 2 FXS port ATA with a power supply which can handle this.
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Dave BaldwinFixer of Problems
Most Valuable Expert 2014

Commented:
What do you have connected to that line?  The length of the line by itself doesn't affect the power supply loading.  But something is loading it if that connection causes the power supply to get hot.

Author

Commented:
It is an unusual connection. The lines go to a radio shack where they are connected to a piece of equipment which allows two phone lines to be connected to an emergency radio system.
This equipment was previously served by a TelRad PBX.
I won't be able to replace this equipment, I need to duplicate the power the TelRad had.
Have you tried a Patton Smartlink 4022?

Author

Commented:
It does'nt seem that they make that, or maybe not any longer. There is the 4112 with 2FXO?
Fixer of Problems
Most Valuable Expert 2014
Commented:
Any chance that this is a problem of RF feeding back down the lines and causing the overheating?  Older equipment with transformer outputs was not sensitive to RF on the lines but newer equipment with solid state outputs often has been.  I'd be surprised if the Cisco engineers ever thought that unit would be used like you're using it.

Author

Commented:
Yes there might be that chance. Is there a filter I could place on the lines?
The Telrad was installed in the late nineties, is it probable that it has 'transformer outputs'?
The PAP gets very hot after it fails, but just warm until that.

I found RFI filters which might be the ticket if the telephone cable around the radio shack is picking up from the large antenna. Would this be what I need, if the frequencies match up?

Description: Reduce radio interference on both lines. Radio Shack's 2-Line Telephone Line Filter eliminates most broadcast, CB and amateur radio interference by reducing RF current on telephone wiring before it reaches your equipment. Convenient modular (RJ-11 type) connections allow use at your phone or wall jack. Can also be used for single line telephone. 25dB Rejection from 3-30MHz range. Insertion Loss from 300Hz to 3KHz: <1dB. Open Circuit DC Impedance: >5M Ohms.
Catalog #: 279-151
Dave BaldwinFixer of Problems
Most Valuable Expert 2014

Commented:
That's what I was thinking of.  Try it at the Linksys end of the line.

The Linksys/Cisco unit is 'office equipment'.  If the Telrad was a regular PBX, they could have had inductive outputs or simply have been designed to handle long lines and RFI.  I know we had to design audio equipment for radio stations to deal with those problems plus nearby lighting strikes.
Dave BaldwinFixer of Problems
Most Valuable Expert 2014

Commented:
Another thing you could try is putting a 100 ohm / 2W resistor in each lead.  They will lower the signal level a little bit but they will also raise the line resistance and lower the off-hook power consumption.

Author

Commented:
These comments have been extremely helpful. I am going to find the radio transmitter frequency and install filters as soon as possible.

It was my first thought that power consumtion was involved but the notion of interference disrupting the PAP components seems to fit the scenario better. The extra heat seems to be there only after failure.

I am going to hold off on adding the resistors. It seems you are saying they would also reduce the level of the DTMF tones on the line. (I have had considered raising the power level from the PAP to get the DTMF signals working consistantly, but luckily found a different solution.) The filters may affect the DTMF, I'll find out.

Giving it a try, thanks.

Dave BaldwinFixer of Problems
Most Valuable Expert 2014

Commented:
You're welcome.  Let me know how it works out.

Author

Commented:
Will any low pass telephone line filter block 450-490Mhz?

Author

Commented:
How about a dsl filter?
Dave BaldwinFixer of Problems
Most Valuable Expert 2014

Commented:
Most phone line filters including a DSL filter will provide some attenuation for 450-490MHz.  Sometimes a knot in the cable will.  The Linksys unit is almost certainly a plastic case so that's no help.

Is it possible to measure the DC line resistance?  Regular phone lines On-hook are expected to be 5 Megohms.  Anything above 10k On-hook would be Ok.

Author

Commented:
Most everyone I've spoken to goes with the overheating solution.

For overheating:
  It is a common failure mode
  The room is not actively cooled
  The room does get to 80 degrees on occasion

For RF microheating:
  The adjacent PAP has not failed
  The phone lines in the area of the transmitter are not very twisted
  The failures have not been associated with off hook power consumption
  The lines are almost never used, being our on premises 911 #

I have renewed my plea to the building managment to insall a larger room fan.
I have ordered a spot fan for the PAP.
I will be onsite in a few days and plan to measure the line resistance.
I have been unable to find a telephone filter for 450-490Mhz.
Should I tie knots in the wire, cool the PAP and daisy chain a few 30Mhz filters?
The failures of the previous PAPs took about three weeks so it would be a long time to discover if this solution worked. I do not yet have access to an osciliscope which could discover this high frequency.(I am still looking)
Dave BaldwinFixer of Problems
Most Valuable Expert 2014

Commented:
Don't bother with the oscilloscope.  In such an uncontrolled environment, you will pick up every radio in sight including aircraft radios and you won't be able to tell which one is your problem.  Radio Shack has 4 snap together RFI filters listed on their web site.  Your local store may have one or more of them in stock.

Do you have lightning in the area?

Author

Commented:
Yes we do have lightning, I think you asked earlier and I didn't want to touch the question then; lightning is the major causal factor for the revamping of the phone system. We would disconnect all the phone lines at the Telrad PBX whenever lightning threatened, otherwise we would have blown ports. We have twenty one buildings spread over a couple hundred acres and shallowly buried copper lines. The two pair of lines we have been talking about are the only ones I am planning to use in the new system, all else has gone to wireless and fiber ethernet. The radio shack is in a very tough place to get wireless and expensive to move.

I have just contacted one of our volunteers, we are not-for-profit, who has radio and electronics experience. He is going to visit the site with me Saturday, 50 miles into the mountains from Fort Collins CO. He has suggested toroid chokes(I think), which is where you may be going with the Radio Shack filters, but he wants to look the situation over and make sure the antenna connections are still good etc. He agrees that we need to get as clear a diagnosis as possible so that the solution is relatively permanent.

So I will cool the PAP and clear the copper.

Your help was invaluable, too bad I can't fly you out for some cool mounatin air. I'll keep this thread alive at least until Saturday so I can let you know what we find on-site.
Dave BaldwinFixer of Problems
Most Valuable Expert 2014

Commented:
I've been there.  You get more than a little bit of lightning.  I was standing on the balcony of an apartment in Fort Collins one June afternoon (a long time ago) and counted over 100 lighting bolts that I could actually see in about 20 or 30 minutes.  Lovely afternoon thunder showers.

I would probably go ahead and make the other test but you need some serious lightning protection.

Author

Commented:
I'm not sure what is at the radio shack but there hasn't been any damage there over the years.

In the phone room I have a pair of MLP-270M from this web page http://www.sandman.com/surge.html this is as heavy duty as I could find. I was looking for some kind of optical isolation but found nothing in the telephone market.

If this were to fail...
Dave BaldwinFixer of Problems
Most Valuable Expert 2014

Commented:
The MLP-270M sounds good.  That page has very good info on it too.  So much info on lightning protection schemes is garbage, it's nice to see someone who understands the problem.

You may want to check the MLP-270M and make sure it's still good and not loading the phone lines itself.  It's hard to get a good ground up on the rocks but something is better than nothing.

Author

Commented:
I have waited nearly two weeks after placing ferrite chokes on the phone wires in order to see if there was another failure. There wasn't. Thank you, Dave Baldwin, I have no idea how long it would have taken for the radio interference idea to pop up without your help, I pretty sure I would still be struggling with it.

I did find a local RF engineer, Marv Ross, who was able to visit the site and offer advice. He suggested ferrite chokes at both ends of the lines and suggested that most of the energy was getting on the lines right in the radio shack.

 From Amidoncorp.com I ordered:
  4 FT-37-61 - 2.4
  4 FB-61-5111-2.5 - 3.0
  4 FT-50-61 - 3.0
  4 FB-61-5111-3 - 3.0

I shortened all the wires in the radio shack
I added two ferrite chokes to each line as close as possible to the exit at the radio shack
I added two ferrite chokes to each line as close as possible to the entrance at the phone room
I did put a fan on the PAP

I noticed right away that the phone call to the radio shack equipment had lost a hiss sound, this I had mistankenly attributed to radio noise beyond this connection. So that was the first good sign and the PAP is still working after 12 days with a lot of radio activity.

Excellent and thanks again
Dave BaldwinFixer of Problems
Most Valuable Expert 2014

Commented:
Glad to help.