AC voltages on analog lines 1

[derid]

Can someone tell me if there are AC voltages present on an analog line(PSTN) in idle mode in the USA ?
for example (FSK modulations, carriers, tones etc...)
What is the maximum allowed noise amplitude on such a line ?

 

[Deweyhumbolt]

All Telco is DC.



"Adversity is Opportunity

 

[strmwalker]

yes ac voltage can be present on a PSTN line it should
less then 3.5 volts but i have seen it as high as 6 volts
then higher the voltage the louder the ac hum.i just
had this issue with a local telco in south carolina and
it turned out to be someones hot water heater in a house
that the heating element was bad and it feed ac voltage back
thru the phoneline the cut the the grounding from that drop
and the ac voltage was gone .with that being said dont ever
believe telco is only dc a PHONELINE RINGS AT ABOUT 109
VOLTS AC and it will KNOCK YOU ON YOUR A$%.

no problems only solutions

strmwalker

 

[donb01]

Ring voltage is 90V AC though, isn't it?

I know he asked about idle mode, but I wondered about 'all'....

 

[Deweyhumbolt]

My apologies for All. I've been down on one knee more than once, in wet grass, across a protector, with incoming ring voltage. You'd think I'd a had a better answer.

"Adversity is Opportunity

 

[derid]

Thank you for your answers.

Of course there can be ringing voltage and there can be losses too.
The question was in normal conditions and idle mode are there some other AC voltages like :
- FSK or DTMF modulation for CLIP
- carrier frequencies to get 2 channels on one twisted pair
- signaling tones
etc ...

 

[strmwalker]

deweyhumbolt that a great one i have done the same here is your star

no problems only solutions

strmwalker

 

[hawks]

Ok you got me curious:

On Hook 0.00 – 0.05
Off Hook with Dial Tone 0.15 – 3.15
Off Hook with No Dial Tone 0.05 – 0.15
Off Hook While Dialing Digits 0.05 – 3.05
Ringing 88 - 99


The Analog lines I have come off a channel bank though, so I would be interested to see what someone gets from straight copper lines.

 

[jknichols]

If you have DSL, the that would be considered a high frequency AC that is there all the time.

Caller ID is present only between rings, so I wouldn't really consider that on an "Idle" line.

 

[SYQUEST]

The types of voice band audio or data on a loop or ckt would depend on its use, if you are talking about "AC signals" other than harmonic content or induction noise.

Just what are you looking for?

....JIM....

 

[jerryreeve]

If you want to see what there is get an o'scope and put it on your phone line. you will see all of the AC from the DSL, Ring, noise, Dial tone, and most important of all the Voice signal that rides on the talk battery.

----------------------------
Hill?? What hill??
I didn't see any $%@#(*$ Hill!!
----------------------------
JerryReeve
Communication Systems Int'l
com-sys.com

 

[derid]

I do have an oscilloscope but the cable of my probe is unfortunately a little bit too short : I'm living in Europe !!!

I am a telecom designer.
A few weeks ago I sent a doorphone interface to the States. That interface can make a doorcall to a local phone or to a remote phone through a trunk line.
The doorlock can be activated by mean of a DTMF digit on the phone.

The communication between telephone and doorphone is OK as long as the trunk line is not connected.
Once the trunk is plugged into the interface he can't even open the door anymore (trough DTMF signal).
In idle mode, only a capacitor connects the trunk to the interface, so only an AC signal can trouble the DTMF signals

I suspect him to have put it on a digital line instead of an analog line, but I wanted to be sure that any other AC signal could't be present.

If somebody can send me an AC screen shot of a Telco in idle I would be very happy.

Thanks for the help.

Bernard

 

[allisland]

As STRMWALKER replied before there "shouldn't be any AC on phone lines, if there is it will cause a hum, and if you can test AC on line it's a valid trouble to give to local Telco to repair(good luck)

Now question, is your doorphone powered? how is it supposed to be wired? dial tone in/station out?
Are they trying to install it using a POTS line or going thru a PBX??

 

[derid]

It is powered bij 12Vac or 13.8Vdc and can be installed either on a POTS line or a PBX

The circuit is isolated from the trunk by means of a 600 Ohm transformer

More info on :

http://www.electronic-design.be/en/htm/body/parlofonie/tpi+/TPI+GB.pdf

 

[allisland]

How is the line wired , if it's across a winding of a 600 Ohm transformer it's going to cause the line to go out of service (short cicuit)

 

[derid]

The schematic diagram is on :

http://www.electronic-design.be/downloads/data/trunk.pdf

When on hook, K1 is off and the ringing voltage goes trough R13/C9.
The ac voltage at "AUDIO" is detected by the ADC of the microprocessor as a call.

It looks like there is always a signal at "AUDIO" once the trunk is connected.

They have probably connected the trunk to a digital line, but the customer says that this is not true.

 

[allisland]

Ask your customer what happens to his telephone line when connected to your doorphone , is he still able to use it make calls etc?, ask him if he has additional lines to try it on.
Also is your power supply compatable to our 120v 60Hz?

 

[SYQUEST]

After reviewing the PDF files my comments are:
1. the documentation is very poor! No specifications!
2. what system standards it is designed to operate?
3. in the USA it requires FCC part 68 approval to be connected to the PSTN.
4. the schematic is incomplete! Where is the rest of the circuit?
5. the device or its control unit would need a ring generator in order to ring any tel instrument connected to it.

With negatives like these, you might want to get something else. The production values seem to be very low!

....JIM....