EMF radiation from inverter?

[SunEagle]

Most of you guys missed out on the fun when it came to what some of my college friends could do in the 70's with Ma Bell.

They were known as Phone Phreaks and built blue boxes to get free long distance phone calls. One of them actually went on to working for the telephone company.in research and design.

[wblanford]

I also spent some time maintaining the college step by step phone exchange and telephone system that was used for all the dorms in the early '70's. Lots of time spent in the basement.

[DanKegel]

My primary job was to design all digital toll switching, so I know little about the step by step, number 4 crossbar, and
other mechanical systems that we replaced

Cool!

I helped maintain my dorm's electromechanical phone exchange back in the early '80's. It had 60 lines, and it was cool to watch the switches step as people dialled. Alas, one day it burned up. We then built a hybrid digital/analong replacement using 4x4 CMOS analong crossbar chips, controlled by a 6502. (The analog part was designed by a seriously good analog EE, who later went tp HP back when it was still HP. The digital part was designed by a guy who put himself through college by selling a spreadsheet written for the IBM5110 in machine language. I built a lot of it and wrestled the software into behaving... including cobbling together a 6502 assembler and linker for the PC.) That ran for eight or so years until it got flooded in an epic water fight, after I graduated.

Good times

[inetdog]

My primary job was to design all digital toll switching, so I know little about the step by step, number 4 crossbar, and
other mechanical systems that we replaced. But I did have some occasion to reverse engineer some analog lines.
Don't know what Originating Sleeve Control is.

The double speed rotary dial I believe was standard for operators, guess all the office equipment could handle it.
Bruce Roe

Oh, that fancy electronic stuff.

I don't think that ordinary subscriber lines could handle 20pps dialing. But for operators who needed it to make the most money for the company or for subscribers who were willing to pay it was available. It put additional restrictions on line impedance, etc. and so was not supported by default.

One note from the paper that Dereck linked, which he may find interesting:

During the ring the CO may or may not remove the loop feed DC voltage.
If Caller ID service is provided, the CO can send caller ID information between the ring pulses or prior to the ringing using FSK (Frequency Shift Keying) or DTMF signaling in the VF band. The European EN 300 659-1,2,3 standards describe the subscriber line protocol used for caller ID and other services.

So for systems that detected the AC impedance loading down the ring generator through the SLIC for off hook detection (maybe not common in the US) the 48V might actually go away.
And the DTMF or FSK Caller ID signalling might also hit the line before the first ring.

[bcroe]

Maybe down in Panama you can. Up here in the states, at least in Caliphonia, you have to pay extra to get the CO configured to detect pulse dialing on your line. Default is TouchTone only for new lines.

Back in the 60s I knew a guy who was a commodities broker. He had a special phone configured to double the dial pulse speed, with CO equipment to match. It allowed him the tiny but important edge to dial phone numbers faster.

PS: My test to see whether someone really understands old school TELCO technology and step-by-step COs is to ask them to explain Originating Sleeve Control.

My primary job was to design all digital toll switching, so I know little about the step by step, number 4 crossbar, and
other mechanical systems that we replaced. But I did have some occasion to reverse engineer some analog lines.
Don't know what Originating Sleeve Control is.

The double speed rotary dial I believe was standard for operators, guess all the office equipment could handle it.
Bruce Roe

[Sunking]

You guys are just guessing; when you have made real measurements, let me know. My analog work (no guessing)
was before Caller ID, things may have changed a lot. Bruce Roe

Guessing? You are full of it. Doing professionally for 40 years designing and operating the equipment. If you would have clicked the Link you would see Dave and I know exactly what we are talking about. Anyone with half a brain could easily look it up on the internet. POTS line have not changed in 125 years.

Try looking up Suscriber Line Interface circuits. In the biz we call them SLIC's. What you are seeing is old dilapidated copper wire circuits with leakage.

[bcroe]

There may be a small transient voltage at the moment when the ringing machine is switched into series with the circuit, before it gets to the time interval where the ringing voltage is present. And if you were listening carefully on a butt set you might hear a click. But certainly not any kind of voltage change that lasts a second.
As you note, if the 48V were taken away there would be no way to determine when the phone was answered.
Also, I suppose that in a modern exchange the CallerID data might be transmitted before the first ring in addition to between rings. That might also be detectable.

You guys are just guessing; when you have made real measurements, let me know. My analog work (no guessing)
was before Caller ID, things may have changed a lot. Bruce Roe

[Sunking]

Maybe down in Panama you can. Up here in the states, at least in Caliphonia, you have to pay extra to get the CO configured to detect pulse dialing on your line. Default is TouchTone only for new lines.

Called marketing. In your local PSTN Switch at the Telco your number has a DN table of features your phone company can turn on/off. DTMF use to be extra for them to turn on. Today most default so you can use either. However all Land Line Telcos are going bankrupt and trying to find anyway to make a buck. So in the land of Fruits and Nuts, they charge extra to set the Rorary Dial Feature Bit in your DN to ON

The Telcos really screwed up in the 80's. They failed to see the threat of Cellular and CATV putting a coax in everyone's home. By the time they realized the mistake in the late 90's was too late. There was over 1 billion miles of fiber installed in the 90's and early 20's buy WorldCom and other LD phone companies that sat dark for a decade . Just sittingg there running all around cities. Now Google is buying it up for pennies on a dollar and putting fiber in homes. ATT is trying, but local Telcos are too broke to try and catch up. Google in certain cities offer Giggabit Fiber to homes. Kansas City , Austin, Provo, and Gainesville FL are some of oogles market. Apple is rumored to be doing the same.

[inetdog]

There are all kinds of tricks and test you can do on your phone line. If you have really fast finger and can count, you can dial a number by pushing the on-hook button. The easiest number to dial is the Operator. Just punch the On-Hook button 10 times as fast as you can. Remember Rotary Dialers? That is exactly how they worked before DTMF.

Maybe down in Panama you can. Up here in the states, at least in Caliphonia, you have to pay extra to get the CO configured to detect pulse dialing on your line. Default is TouchTone only for new lines.

Back in the 60s I knew a guy who was a commodities broker. He had a special phone configured to double the dial pulse speed, with CO equipment to match. It allowed him the tiny but important edge to dial phone numbers faster.

PS: My test to see whether someone really understands old school TELCO technology and step-by-step COs is to ask them to explain Originating Sleeve Control.

[Sunking]

Interesting!

There are all kinds of tricks and test you can do on your phone line. If you have really fast finger and can count, you can dial a number by pushing the on-hook button. The easiest number to dial is the Operator. Just punch the On-Hook button 10 times as fast as you can. Remember Rotary Dialers? That is exactly how they worked before DTMF.

There are even numbers you can dial to test your phone, find out what the number is, Ring Back, Silent Termination, milli-watt tone and so on.

[icebox]

Any DC current is detected as off-hook. The 48 volt battery is not a Voltage source, it is a current source being pushed by a 48 volt battery. You POTS line interface card at the CO or Repeater is a 12 ma current source, with a 60 ma limiter in the event of a CO line short to prevent burning wiring and equipment up.

But yeah Ma Bell frowns supplying you power from their battery. They even have a way to prevent it. Take your phone off hook and walk away. Initially you wil here the alarm tone alerting you of the off-hook condition. That will time out and disconnect your line. Then once every minute connects battery. If current flows, you stay disconnected. Only after you hang up will they reconnect your line.

To test if you have Talk Battery, blow or talk in the mic, you will hear your self. Any telephone guy knows that trick when they use with a Butt Set. Ever pick up the phone with no Dial Tone, but you have talk battery? It means th eTelco is over loaded and no more network connections to send you dial tone.

Interesting!

[Sunking]

Actually electronic phones and other customer devices may put a strictly limited DC load on the line at all times. TELCO does not like this but they have to accept it. If the customer adds up too much such load through multiple devices his phone stops working properly. Just as the AC impedance which loads down the ringing machine is limited.
The goal is to get off hook detection and ringing to work properly both at a phone right next to the central office and at a phone which is at the end of the maximum allowed cable distance.

Any DC current is detected as off-hook. The 48 volt battery is not a Voltage source, it is a current source being pushed by a 48 volt battery. You POTS line interface card at the CO or Repeater is a 12 ma current source, with a 60 ma limiter in the event of a CO line short to prevent burning wiring and equipment up.

But yeah Ma Bell frowns supplying you power from their battery. They even have a way to prevent it. Take your phone off hook and walk away. Initially you wil here the alarm tone alerting you of the off-hook condition. That will time out and disconnect your line. Then once every minute connects battery. If current flows, you stay disconnected. Only after you hang up will they reconnect your line.

To test if you have Talk Battery, blow or talk in the mic, you will hear your self. Any telephone guy knows that trick when they use with a Butt Set. Ever pick up the phone with no Dial Tone, but you have talk battery? It means th eTelco is over loaded and no more network connections to send you dial tone.

[inetdog]

The only load is YOUR PHONE. When on hook no current flows and you will have full open circuit battery voltage at your house 24 x 7.

Actually electronic phones and other customer devices may put a strictly limited DC load on the line at all times. TELCO does not like this but they have to accept it. If the customer adds up too much such load through multiple devices his phone stops working properly. Just as the AC impedance which loads down the ringing machine is limited.
The goal is to get off hook detection and ringing to work properly both at a phone right next to the central office and at a phone which is at the end of the maximum allowed cable distance.

[Sunking]

Also, I suppose that in a modern exchange the CallerID data might be transmitted before the first ring in addition to between rings. That might also be detectable.

Bellcore standard 202 modem modulation. It is a analog AC signal between the first and second ring. Like your frequency selective ringer is picked off the line with a capacitor high pass filter. Try it sometimes. Pick your phone up during the first ring. You will not have Caller ID becuase you picked up before it was transmitted.

None of this applies to VOIP. Well sort of. Your modem will mimic the Telephone line with one exception. Due to the short loop length can use 12 volt supply current sources. PBX uses either 24 or 48 volts depending on size.

[Sunking]

Its not a hard regulated 48V; the station end (not the office battery) varies with the load situation. Maybe you ought to put
a scope on it like I did. And I'm older than you. Bruce Roe

Bruce you have no clue what you are talking about. Office battery is a solid extremely well regulated 52 volts battery of roughly 10,000 to 100,000 AH battery. The only load is YOUR PHONE. When on hook no current flows and you will have full open circuit battery voltage at your house 24 x 7. When you lift the receiver you complete a current loop of 12 ma depending on how far away you are in cable feet of the CO. The voltage will drop to 4 to 15 volts at your house when off-hook to form a Current Supply. Your microphone in the TX varies the resistance in your phone to modulate the DC voltage.

Educate yourself before you spout off about how something works. Start Here as it is the basis for all Telephone circuits. It is the exact same principle Alexander Graham Bell came up with 140 years ago, and how every PTSN switch works today no matter what country you live in.

For Pete sake the Ringer is AC voltage. DC has nothing to do with a ringing phone on a land line.