[Asterisk-Users] Qs about FXO/FXS cards

[Jim Van Meggelen]

Truman Beal wrote:
> One thing to look at is the proximedy to the powersupply of
> your audio
> devices.  Some mobos have their chipset integrated in very closely to
> their power supply pins.  With an unclean power source the fluxuations
> would be enough to add some of the white noise which would
> give you the
> whine.  Excellent examples of that are on the really small
> all in ones.
> Sometimes power source it self may be in quesiton, and a
> cheap ups with
> nothing else on it would probably solve that one quickly. 

I have to warn people about cheap UPS units. They have to be a
*POWER-CONDITIONED* UPS to gain the power quality benefits. Many
*cheap*UPS*units*do*not*clean*up*the*power!* Some even make it worse. If
it doesn't say "power conditioned", it isn't; it's nothing more than a
battery back up (you will not like what these cheap UPS units do to your
input power when running on batteries).

For eample, APC Smart-UPS models provide power conditioning. ABC
Back-UPS do NOT. Run a Back-UPS on battery only and check out the
harmonics on the output - ouch! It's AC, but it is NOT a sine wave -
it's a square (some of them deliver a "stepped square" or
"pseudo-sinusoidal" waveform). Not clean at all. 

Just remember that power conditioners and UPSs are not the same thing.
You can buy stand-alone power conditioners (PowerVar and OneAC make
these), stand-alone UPSs (many cheaper UPS units are this type), or UPSs
with built in power conditioners (PowerVar, OneAC, and APC).

Know what kind of UPS you are buying. 

If you see them trying to tell you something about any kind of
"protection", without actually saying the magic words "power
conditioned", you cannot be sure that your UPS is giving you clean
power.

> Addionally,
> you may want to see if your power supply offers any sort of shielding.
> Mylar can offer a small amount of shielding, but some power supplys
> won't cool effectively, and the results of that are similar to
> fireworks- (see tom's hardware guide to power supplies)-

Spend the extra money and get PC Power & Cooling (no, they don't pay me,
they are simply the best - no contest).

> Alternatively, you find some cases offer no shielding to the outside
> with their plastic constructs.  A good quality case may be in
> order, and
> if you are racked, you may want to make sure one of the other machines
> in the rack may not be grounding out onto the rack, thus causing
> additional headaches.

Noise could be getting in from all over, eh?

> For my setup, I'm not using the onboard stuff in favor of an old sb
> live.  

What's the SB live for? Console?

> I't moved of to a slot farily away from the digium board , and
> too close for my comfort to the networking cards.  I gain fairly good
> quality, and not enough white noise for me to really pick it
> up.  In my
> house, there are a few spots where power isn't the cleanest, so I'm
> certain that I'm getting at least some noise, despite every
> machine is
> fed from their own ups :)

[here he goes again . . .] Are they power-conditioned UPSs?



> Hope that helps-
> T
>
> Jim Van Meggelen wrote:
>
>> Dorn Hetzel wrote:
>>
>>
>>> On Sat, Jan 01, 2005 at 07:23:58PM -0500, Jim Van Meggelen wrote:
>>>
>>>
>>>> [...]
>>>> What if, for example, the TDM400 issues were a cumulative thing? If
>>>> you had over 6dB of attenuation on the PSTN loop, coupled with
>>>> greater than 5V potential on the neutral-ground of your elecrical
>>>> receptacle, compounded by a cheap power supply, exascerbated by a
>>>> Via-chipset, would you not be virtually guaranteed some strange
>>>> behaviour? But if your PSTN was -3dB, your electrical feed derived
>>>> from a power conditioner, your power supply manufactured by PC
>>>> Power & Cooling, and a ServerWorks chipset-based MoBo, would your
>>>> system always be faultless?
>>>>
>>>>
>>>>
>>> Can you recommend any favorite motherboards?
>>>
>>>
>>
>> That is the million dollar question. Chipsets and MoBos seem to
>> change so fast that I've lost confidence in my ability to make sense
>> of it all. The Intel and ServerWorks chipsets are generally well
>> regarded; Via chipsets are almost universally avoided for audio
>> work. The linux-audio-dev folks seem willing to give nVidia's nForce
>> chipsets a chance. In general, I would avoid PC-class motherboards,
>> and go with server-class motherboards. That being said, the ultimate
>> goal would be to find a way to build a reliable Asterisk system on
>> *any* half-decent motherboard.
>>
>> Personally, I'm of the mind that power (the power supply, the AC
>> being supplied to the system, and grounding) plays as much of a role
>> as the motherboard does, but that is a working theory only. I wonder
>> if clean power on a lousy MoBo might serve as well as dirty power on
>> a quality MoBo. If one reads about power quality issues, the
>> symptoms of dirty power sound suspiciously similar to the kinds of
>> problems people are having with their analog Asterisk cards.
>>
>> I'm also wondering about the TDM400s ability to handle PSTN loops at
>> the extreme limits. Since those TDM cards were probably developed
>> largely in a lab environment, the telco lines would have been
>> simulated with a channel bank or C.O. simulator. What happens when
>> the lines fall out of certain limits? Annenuation, loop current, and
>> longitudinal imbalance are all factors that proprietary PBXs are
>> able to correct within fairly wide limits - but they do have limits
>> (a Norstar, for example, tends to have trouble pulling dial tone
>> when attenuation exceeds 7dB). Has the TDM400/FXO been similarly
>> optimized? It must have limits; what are they?
>>
>> I think what we are all looking for is some empirical evidence of
>> what conditions cause the biggest problems. Is it the TDM400 that is
>> to blame (either hardware or drivers)? Or is it Linux? PC Hardware?
>> Telco Lines? Electrical? Grounding? A combination of some or all of
>> those factors? No one seems to know for certain.
>>
>> Where much frustration comes from is the fact that a typical PBX
>> simply does not suffer from these troubles. We've come to expect
>> that our telecom equipment handles these little noises for us (so
>> much so that we're suprised to find that these are genuine
>> engineering issues). With Asterisk, some of the responsibility for
>> correcting those problems falls to us, the system designers.
>> Unfortunately, a comprehensive engineering methodology for analog
>> devices on Asterisk does not yet exist. It's all kind of
>> hit-and-miss.
>>
>> Cheers,
>>
>> Jim.

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