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 Rotary Phones and the NBN
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 Return to top of page · Post #: 1 · Written at 7:04:14 PM on 28 February 2012.
Elijah B's Gravatar
 Location: Melbourne, VIC
 Member since 28 February 2012
 Member #: 1098
 Postcount: 8

As far as I know no rotary phones will work on the optic fibre of the Australian NBN. This is sad for me as I want to create a traditional office and I don't much fancy the appearance of minimalist modern phones but would be much happier with a traditional Bakelite phone.

I have seen a few tone converters available for overseas phones, but none for Australia. Is there any way to make a rotary phone compatible with the fibre network? I'd even be happy with a new phone in a reproduction style, so long as it would work in Australia.


 
 Return to top of page · Post #: 2 · Written at 2:24:55 PM on 17 March 2012.
6A8G's Gravatar
 Location: Wellington, NZ
 Member since 24 July 2009
 Member #: 517
 Postcount: 61

I've found such a device which works for New Zealand dials on Trade Me. The seller recommends http://www.dialgizmo.com/index.html for other countries - maybe give this a go?


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6A8G.

 
 Return to top of page · Post #: 3 · Written at 8:50:15 PM on 17 March 2012.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
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There's a few Pulse-DTMF converters out there though people need to be aware that anything used on Australia's phone network needs to display the A-Tick logo and an ACA approval number.

I've been looking into this matter too and would be keen to acquire such a device though I wouldn't risk the $11,000 fine over a non-compliance issue.


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A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 4 · Written at 5:00:55 PM on 1 May 2012.
Relayautomatic's avatar
 Location: Canberra, ACT
 Member since 24 April 2012
 Member #: 1136
 Postcount: 122

The question of using old phones on the NBN has come up in another forum and I have been doing a bit of research on the matter. Currently all Telstra exchanges I or other collectors that I know, can access still support decadic/loop-disconnect/’pulse’ dialling although DTMF signalling/dialling is now the 'standard'. Besides the odd rotary dial phone, there is still a lot of non-phone equipment in use such as fax machines, alarm systems and data collection devices that use ‘dial-up’ connections and decadic dialling.

The old Step-by-Step (SxS) exchanges used an L&K relay set to detect a phone 'off-hook' and an 'A' relay in the First Selector to feed current to the line and to detect each pulse as a digit was dialled. As a dial pulse was received it was passed to an electromagnet in the Selector which stepped up one level for each pulse. It was critical that the dial was set to run at 10 pulses per second and would allow enough time between each digit dialled for each selector to find and connect to the next idle selector. With Crossbar switches the function of the relay sets was the same but the pulses were sent to a register. The register then controlled the actual switching so in theory the dial pulse rate was not so important. The new electronic exchanges have a module known as a Subscriber Line Interface (SLIC) that replaces the function of the L&K and the A relays plus it can detect DTMF tones. The SLIC does a lot of other functions that were not possible with the old electromechanical switches. On the NBN there will be a unit (Network Termination Device plus Power Supply Unit) installed at each house that will be the interface between the fibre-optic cable and the phone/data cabling in the house. It will have two phone ports (UNI-V, 2-wire interface) and four data ports. The Network Termination Device will perform the function of a SLIC.

To have an old phone work on the NBN there are four considerations:

- line voltage and current available to the phone
- the Network Termination Device must recognise a phone 'off-hook'
- the Network Termination Device must recognise decadic signals/pulses
- the Network Termination Device must be able to drive the bell motor in the phone

From reading the NBN tech specs (http://www.nbnco.com.au/assets/documents/nfas-product-technical-specification-v3.pdf) each UNI-V port will supply a line voltage of 42 – 56 V DC with at least 18mA on Cat 3 cable. That will be more than sufficient for a phone and it may be necessary to pad the line with a resistor to limit the current as anything over 32mA can ‘fry’ the carbon transmitter/microphone.

The specs state that they meet the Australian Standard AS/CA S002:2010 which sets a line current of 9mA as indicating a phone is ‘off-hook’ so there should be no problem with the Network Termination Device recognising when you lift the handset. However there may be a problem with old phones that have a leaky capacitor not releasing the line when the handset is put back onto the cradle.

Whether or not the Network Termination Device will recognise decadic signals/pulses is not clear. The NBN doco refers only to DTMF but Australian Standard AS/CA S002:2010 specifies both decadic and DTMF signalling. It is possible that the Network Termination Device may recognise decadic pulses but not be able to encode the digit as it does with a DTMF tone. If it can only cope with DTMF then a unit like the DialGizmo may be required to solve this problem.

The last requirement may be the real 'show stopper'. The bell motor in a typical 300 Series or 400 Series phone works on 75 – 90V at 17 – 30Hz and requires more power than an electronic ringer in modern phone. Typically an electronic ringer in modern phone has an REN of 1 or less. The NBN tech specs state that each UNI-V port will supply a ring voltage of 50V at 25Hz into a load of REN 3. (Australian Standard AS/CA S002:2010 specifies 90V RMS 25Hz.) This is only 66% of the minimum voltage so the bell motor may not work or possibly just buzz.

I have a tried a DialGizmo on both a POTS line and a digital PABX and it certainly worked as advertised. Therefore I think that it would work on with Network Termination Device.

As for the ACA certification as noted by Brad, the DialGizmo site does not mention it having certification. In any case it would be of little importance because any old phone that you use it with would not have certification either. An old phone with a dial would not pass certification because components with exposed metal parts are not permitted. (In days past I was involved in preparing phone gear for type testing for AUSTEL approval and out of curiosity I tested the insulation on a No.10 dial; it failed at less than 300V DC. The interesting thing was that the then standard Telecom phone, supposedly compliant, would also fail the insulation test as it would flash over from the 4T receiver to a moist conductor, such as an ear, held against the receiver cap.) The main concern of certification is/was for electrical safety with mains powered devices not failing in such a way as to put 230V AC down the phone line. Having recently examined a few failed but approved switch mode power supplies, I think that the average ACA certification number must come off the back of a cornflake box these days. In any event with the NBN there will be perfect insulation between the phone and the exchange in the form of a non-conducting glass fibre cable. ;)

The other issue may be, can you afford to afford to use the NBN for your phone calls? I was at a seminar a couple of years ago which had Senator Kate Lundy as one of the speakers. At the time she was the minister responsible for the NBN and went on at some length about the great benefits it would bring such as being able to download movies from the USA so much faster. However she was very coy about what it would cost the subscriber. During a break a few of the attendees posed the question of cost again. After explaining that the NBN Co would not bill the subscriber directly but rather charge the selected ISP who would build this cost into their pricing, she said that the projected average monthly cost would be $200 per month per subscriber. She said that she thought that this was 'very reasonable' for 'the benefits the NBN would deliver to the household'. It may well be for an 'elected representative of the people' but those present begged to differ on this point. I assume that this figure would include an allowance for data downloads but I for one will not be signing up for that package. So far I have not been able to get any Telco or ISP to quote a figure for telephony only. I have a mobile phone and I’m not afraid to use it!

Andrew


 
 Return to top of page · Post #: 5 · Written at 9:02:14 PM on 1 May 2012.
Brad's avatar
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 Location: Greenwich, NSW
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I think the issues raised in your last paragraph warrant further discussion, given that one or two providers, including Telstra have signalled an intention to do things their own way instead of conforming, which is what the purpose of one public network is supposed to achieve.

Telstra said at the end of last year that when they start moving their punters to fibre, it will only be for Internet. Telstra phone subscribers will remain on the copper network until the Commonwealth forces Telstra to start shutting the copper network down.

Surely it would be better for Telstra to do the right thing and move all services over at the one time. Then again, in Telstra's eyes, something that is less expensive, easier, more efficient and less wasteful is off the agenda because it would be too sensible.

One other thing is the amount of choice we'll get. There's supposed to be three bandwidth speeds available, namely 25, 50 and 100MBit. Why isn't the Commonwealth Government saying, "okay, we have this fancy new $40bn network - let's realise the potential and justify the expense and stop ISPs from offering anything less than 100MBit."

After all, since the equipment capable of transporting data at 100MBit is already in place, with the future possibility of a firmware upgrade to allow 1000Mbit, there is no greater expense to ISPs for allowing 100Mbit to everyone on the network. The lower speeds available will be one method used to inflate prices needlessly.

Still, most of us will have some time before we have to worry about it. Where I live the glass is still more than two years away.


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A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 6 · Written at 10:05:00 PM on 1 May 2012.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5997

.Relayautomatic: The bell motor in a typical 300 Series or 400 Series phone works on 75 – 90V at 17 – 30Hz and requires more power than an electronic ringer in modern phone.

The Dialgizmo site says: "If you connect your old rotary phone to a VoIP line, it will ring with an incoming call, and you will be able to pick up the phone and take the call, but you won't be able to make a call because the pulse dialing is not understood." -- hence the need for a Dialgizmo.

So, in light of the bit I have bolded, does that imply that existing VOIP phone interfaces are providing a ringing voltage of something like 90 RMS at 25Hz?


 
 Return to top of page · Post #: 7 · Written at 1:06:34 PM on 2 May 2012.
Relayautomatic's avatar
 Location: Canberra, ACT
 Member since 24 April 2012
 Member #: 1136
 Postcount: 122

In answer to the question posed by GTC, it seems to depend on the equipment maker. In a previous 'life' I worked in IT and Comms and had access to a number of systems. My then employers did not encourage me to do any 'hacking' (in the original 'play with the hardware' meaning) but on the couple of occasions that I did, the ring signal was in the range 80 – 90V at 20 – 25Hz. However on a few other digital PABX units that I have been able to 'examine', the frequency was 50Hz (mains supply frequency in Australia). I don't have access to a VoIP system now but two blokes I know, both phone collectors, have built their own VoIP switches running Asterisk software and connected to an ADSL line. The hardware used is all commercially available kit and the SLIC puts out 90V at 20Hz. (See http://www.asterisk.org/ and http://en.wikipedia.org/wiki/Asterisk_(PBX) )

During my investigation on this question, I made e-mail contact with the bloke who sells the DialGizmo, Justin, and asked if the device generates or modifies the ring signal in any way. His answer was, "The DialGizmo will pass the Ring voltage to the phone. The DialGizmo will handle up to 2REN passed when a ring signal is sent through it." This means that the DialGizmo has no part in the ringing function so whatever the switch/SLIC puts out is what goes to the bell motor.

My comment on the performance of the bell motor in the 300 Series and 400 Series (also the original 200 Series) phones was intentionally simplistic to reduce the size of the post. In fact it is possible to 'tune' a bell motor to work on 50Hz by carefully adjusting the distance between the armature and the coils and also the travel between the clapper and the bells. However being a mechanical function it will go out of adjustment over time. (Allow about an hour and a lot of patience per bell motor.)

The 'battery eliminator' (mains power supply) installed with the cordless PMBX by the Australian PMG in the 1950s and '60s had a ring supply of 75V at 50Hz. However the bells tended to buzz loudly rather than ring. (Childhood memories from 1959 and 1963 plus more recent tests on old gear in my collection.) I doubt that the installation techs would have spent the time necessary to adjust the bells in every extension phone. Many of the power supplies used on small PAX installations supplied by the likes of Telephone Rentals also had a ring supply of 75V at 50Hz but the phones connected usually had a buzzer or a DC style bell with only one gong. (I have a couple of these PAX power supplies but they are in poor condition so it would be unsafe to connect them to the 230V mains to run tests.)

The bell motor in the 801AT would tinkle/buzz at 50Hz but the later 802AT (STC design as I recall) had a better armature arrangement that would ring effectively at 50Hz. The bell motor in the later versions of the British Tele 706 and in the Tele 746 was a different design that worked well at 50Hz. I have tried adjusting the bell motor used on a Bellset No.1 for 50Hz but could not get it to do more than just buzz. Given the much longer magnetic path I doubt that it could resonate effectively at any frequency over 30Hz.

The significant thing is that all these ring power supplies old and new, put out at least 75V regardless of frequency but the ring voltage on the NBN Network Interface Unit will be just 50V. Obviously this will be adequate for an electronic ringer but I doubt that it will be enough for an electromechanical bell motor. At present nobody I know is connected to the NBN so I cannot make a visit with one of my old 'friends'.

Andrew


 
 Return to top of page · Post #: 8 · Written at 8:32:23 PM on 2 May 2012.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5997

Once again, many thanks for a detailed and informative post.

In a former life, many moons ago, I did telephony as a subject with the PMG publication "Telephony II" being the text. I have forgotten just about all of it but reading your posts is removing some of the rust.

I wish I hadn't thrown Telephony II away, but I also wish I hadn't stripped the 2+4 PMBX that I bought from a mate for the princely sum of 1 cigarette (when he was desperate), but I guess you can't carry the accumulated junk of a lifetime from house to house.

I suppose those bell motors were designed originally for magneto operation. What did the typical magneto output? It gave a hell of a belt so I seem to recall it was up around the 100 volts mark. And I guess typical cranking speed would have generated about 25 cps?

As for compatibility with the NBN and whatever that will look like, I suppose somebody will design a box to convert the ring voltage to the required voltage and frequency to tinkle the old beauties, but I guess that will need to be mains powered.


 
 Return to top of page · Post #: 9 · Written at 9:29:04 PM on 2 May 2012.
Brad's avatar
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 Location: Greenwich, NSW
 Member since 15 November 2005
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 Postcount: 6334

Just about everything connected to glass will require a powerpoint. The modem, with it's two phone and four ethernet sockets will need one and so will a switch if you want to hard-wire any devices, which will also need mains power. I am sure the phone will work from power supplied by the modem though as it does from the copper network at the moment.

See more here on pages four and five.

Of course the power supply unit contains a small backup battery though gasbags will have trouble making this last during a blackout.

Serious subscribers will end up using a sinewave UPS with a larger backup battery but most will assume a UPS chews power (which they do) and avoid them on the premise that their electricity costs will go up.


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A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 10 · Written at 9:37:01 PM on 2 May 2012.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
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 Postcount: 5997

Can't say I'm looking forward to all of that junk on a wall in the house; it would be a different proposition if building a new dwelling.

And I wonder how they are going to "cable" apartments and the like, with risers and MDFs, etc?


 
 Return to top of page · Post #: 11 · Written at 10:05:48 PM on 2 May 2012.
Brad's avatar
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I live in a flat and it's not all bad. The copper wire will get used as a draw wire to bring in the fibre through existing conduits between the MDF and each flat. In fact, on a per customer basis, retrofitting blocks of flats is probably easier and quicker than for freestanding dwellings.

When I shifted in here I had to get a second phone service installed here so I could have the two Internet connections required to run my web server. Whilst it is possible to host a website with one, for technical reasons, it is definitely much better to have two.

The Telstra serviceman was here for about ten minutes. He used the existing spare pair in the phone cable (red and black), connected a socket in the flat and then patched it in on the MDF in the meter room down stairs. He then left and an hour later they enabled the connection at the exchange.

Changing to fibre won't be that quick but it shouldn't be much slower. Equipment-wise though, there is a lot of stuffing around and 10 watts is by no means measley when one allows for the fact that the equipment is permanently on. My 54 inch plasma telly chews 4.7 watts on standby and most people complain about similar consumptions on any equipment on standby.

Like Elijah, I use a bakelite phone on each connection here. I don't use any services that require me to press one to be on hold, press two to be stuffed around, press three to pay an extortionate bill, etc so I don't miss that side of using a pushbutton phone. When I ring up Pizza Hut their robot requires yes and no answers rather that button pressing so that gets me around that one.


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A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 12 · Written at 11:20:15 PM on 2 May 2012.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5997

10 watts is by no means measley when one allows for the fact that the equipment is permanently on

I guess we'll see people switching off their NTD gear and letting the battery run down, too. Methinks the the Mumbai "support" centres are going to be busy.


 
 Return to top of page · Post #: 13 · Written at 11:09:33 AM on 3 May 2012.
Brad's avatar
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 Location: Greenwich, NSW
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I am wondering how pensioners will handle things. I remember that both my grandmothers never had card accounts with the banks because people of that generation didn't comprehend doing business with a machine. They kept their passbooks and always visited a branch.

Because ISPs aren't exactly renowned for customer service there will be problems there too. Seniors won't understand what all the blinking lights mean regardless of whether or not they are told by the installer and when things go wrong they will ring their ISP only to be put on hold for ages only to be connected to someone who cannot speak fluent English. (Ever noticed that sales staff answer the phone, smile, speak clearly and seem interested in our business but helpdesk staff are dumbed down with standard boring answers to sensible questions and you celebrate three birthdays whilst waiting for them to answer the phone?)

One other thing too, the battery's plastic shell may well have a five year guarantee but what about the battery itself? This particular battery is common in fire alarm panels and I look after seven or eight such panels where I work. We are lucky to get two years out of them.

For what it is worth, I support the new fibre rollout and actually wish that more people would be getting connected to it instead of being forced onto wireless technologies. There is a lot to think about between now and the completion of the rollout though.


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A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 14 · Written at 4:12:26 PM on 3 May 2012.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5997

This particular battery is common in fire alarm panels and I look after seven or eight such panels where I work. We are lucky to get two years out of them.

Similar batteries keep appearing at HRSA auctions with 12 months use on them. They are from emergency exit lights and are brought along by a maintenance contractor. As I understand it (from him) those exit light batteries have to be changed every 12 months.


 
 Return to top of page · Post #: 15 · Written at 4:54:04 PM on 3 May 2012.
Brad's avatar
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Strange that. I am the chief fire warden where I work and I know of no such regulation, nor would I be happy if it did become compulsory as there's hundreds of exit lights and spitfires to maintain.

There is a recently introduced compulsion to replace batteries in fire alarm panels, hydrant pumps and sprinkler pumps every two years though. That's not so bad because there's far fewer of those to look after and the time limit is more reasonable.

Exit and emergency lights are rapidly moving to LED illumination and the batteries can be a lot smaller and most are just two AA-size rechargables and these can go for ten years at a time whilst still performing to the 90 minute rule in a drain test.

Lead-acid batteries are still common in emergency lighting of the type with two 10 watt floodlights though these fittings are subject to the same BCA regulations as other types of emergency lighting.


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A valve a day keeps the transistor away...

 
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