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Old 14th Nov 2018, 12:55 pm   #1
Tractionist
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Default Does Virgin Media support pulse dialling?

Hi Guys,

I've recently recovered and also inherited a couple of nice Ercofon's - which I'd like to use occasionally. They are both rotary dial K14 seven contact 'International' Swedish built units that were converted some time ago for U.K. use [with BT flex and wall jacks etc.].

These units certainly worked on a BT system up until around the mid 2000's - but don't seem to facilitate dialling-out via my current Virgin Media [fibre] arrangements.

Googled enquiries re. Virgin Media support of pulse dialling seems to have generated several seemingly 'evasive' responses from VM on various forums and threads - so my query is "what actually is the truth?"

Another query is: What is the REN number for these particular units? And: can this be lowered by up-rating a resistance/by how much/which one?

Thanks all ...... in anticipation!
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Old 14th Nov 2018, 2:10 pm   #2
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Default Re: Does Virgin Media support pulse dialling?

Pulse dialling from my 746 certainly works on Virgin here, but I can't help wondering if it depends on how old the exchange equipment is?
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Old 14th Nov 2018, 3:50 pm   #3
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Default Re: Does Virgin Media support pulse dialling?

I don't have a pulse dialling phone to hand at the moment but pulse dialling worked OK here last time I tried it a few months ago.
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Old 14th Nov 2018, 5:02 pm   #4
Dave Moll
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Default Re: Does Virgin Media support pulse dialling?

I have no personal experience of this, but has oft been said here that even where loop-disconnect dialling is supported by modern exchange equipment, the frequency and mark/space ratio may need to be within quite tight limits.
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Old 14th Nov 2018, 5:07 pm   #5
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Default Re: Does Virgin Media support pulse dialling?

We are on Virgin Media and used a converted Trimphone for a few years in the sitting room.

I hope this helps.
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Old 14th Nov 2018, 5:50 pm   #6
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Default Re: Does Virgin Media support pulse dialling?

Our two 706s work fine on Virgin Media via their coax/fibre system.
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Old 14th Nov 2018, 9:14 pm   #7
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Default Re: Does Virgin Media support pulse dialling?

Lowering REN by inserting resistance is a myth. Bell motors are largely inductive and adding series resistance does little.
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Old 14th Nov 2018, 9:37 pm   #8
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Default Re: Does Virgin Media support pulse dialling?

My understanding is that because Virgin as an amalgamation of former small local companies it depends on the equipment those former companies installed. LD certainly works fine in the former Yorkshire Cable area. I had heard that it didn't work in the North-East but OldTechFan96's post seems to dis-prove that.

I expect Dave to be right in that the equipment does work but has a much lower fault tolerance than in the days when dials were the norm.
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Old 14th Nov 2018, 9:50 pm   #9
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Default Re: Does Virgin Media support pulse dialling?

Hi, Pulse dialling does work (to a point) on Virgin Media POTS lines, however as has already been mentioned it does depend on the legacy switch (exchange) that a particular area uses.

Here on Teesside VM use a Nortel DMS100 switch which can be somewhat unforgiving of incorrect dial speeds.
I believe this is due to that fact that the DMS100 is of an American design and expects a different make/break ratio of dial pulses compared to a Switch such as System X or System Y, which I guess have better tolerance of differences in dial speeds.

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Old 16th Nov 2018, 4:11 pm   #10
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Default Re: Does Virgin Media support pulse dialling?

Quote:
Originally Posted by winston_1 View Post
Bell motors are largely inductive and adding series resistance does little.
Actually a bell-movement is nearly as resistive as it is reactive, typically 1776 + j2085. This gives an impedance of 2729 Ohms Z. The capacitor tunes out some of the inductance and, on a single line, results in an impedance presented to the ringing circuit of (typically) 1776 - j1451 and a capacitive impedance of 2293 Ohms Z, resulting in an increase of current through the bell movement.

The telephone bell that has served us for long has been extremely well designed. It is robust and simple and almost indestructable. It can be overloaded without damage. Fifty, sixty, seventy and eighty-year-old movements will still work as well as on the day they were manufactured. I don’t know about the design specifications, but I do know that an electromagnet will dissipate most power when the resistance is the same as the inductive reactance, i.e: the phase angle is 45 and the modulus is at its maximum.

But yes... Adding a resistor just causes even less current to flow, causing nearly half the ringing voltage to be dropped across it. I tend to leave them out. I believe REN is referenced to a more modern 59D 4000 Ohm d.c. bell, typically 7186 + j8275.

To quote from the European Telecom Standard ETS 300 001: 'Instead, these parameters are defined in terms of the concept of the "ringer
equivalent number" or REN of the TE; this is a measure of the numbers of items of equipment that can be connected in parallel, the reference for a REN = 1 being a simulated ringing detector circuit consisting of an inductor of 55 H in series with a resistor of 7 kohms.'


Which fits in nicely with the spec of the 59D bell-movement.
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Old 16th Nov 2018, 5:09 pm   #11
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Default Re: Does Virgin Media support pulse dialling?

This won't be as eloquent as Russell's post, but I'm sure many of us have found when a mechanical bell appears to be taking more of its share of the available current, the cure is to put a resistor in series with the offending bell and empirically adjust its value for the highest resistance that is consistent with the bell ringing reliably.

Maybe a plumbing analogy is called for?

How about balancing central heating radiators using the lockshied valves?

(Sorry no j notation).
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Old 16th Nov 2018, 5:41 pm   #12
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Default Re: Does Virgin Media support pulse dialling?

Quote:
Originally Posted by rambo1152 View Post
...and empirically adjust its value for the highest resistance that is consistent with the bell ringing reliably.
Which can actually be as low as 12mA sinusoidal! Of course, I did my experiments upon which I derived my figures on the bench with negligible resistance between generator and load. Line-length and impedance characteristics will have an effect too.



Quote:
Originally Posted by rambo1152 View Post

(Sorry no j notation).
What? Outrageous!
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Old 16th Nov 2018, 6:53 pm   #13
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Default Re: Does Virgin Media support pulse dialling?

Thanks chaps ..... I knew you'd have the answers! I've just serviced one unit .... and it performs perfectly - but doesn't seem to like being on an extension ......
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