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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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26th Aug 2022, 10:20 am | #1 |
Pentode
Join Date: Feb 2008
Location: Leicestershire
Posts: 204
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Break/ Make Ratio (Telephone dial)
We have a project on the go to produce a low-cost dial testing device and that has led us into some poking around with dial testing and specs. It is a lot more interesting than it sounds!
Anyway, I have plenty of existing 'old school' test kit: 3x Labline Telephone Landline Simulators and 3x Dial Digit Analysers. I have a fully services no.12 dial in a 332 which I have set up using the Dial Digit Analyser which indicates it is pretty exactly to GPO spec. Each of the three devices agree with their colleagues, but the Lablines do not agree with the Dialled Digit Analysers regarding Bk/Mk ratio. Now for clarity, the Dial Digit Analyser is displaying timings in ms, but since the dial is very close to 10pps they are pretty much equivalent. I am rejecting the idea that they are old and uncalibrated so just out of spec since they agree with each other and all of a similar vintage. So has anyone any idea what’s going on here??
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Last edited by Radio Wrangler; 26th Aug 2022 at 11:36 am. Reason: Making title a bit more meaningful |
26th Aug 2022, 1:24 pm | #2 |
Heptode
Join Date: Feb 2022
Location: Leicestershire, UK.
Posts: 690
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Re: Break/ Make Ratio (Telephone dial)
Probably of no help to your good self BB but we often had to adjust the mark / space ratio on tape driven alarm 999 autodiallers whilst out in the field. This was achieved by connecting a ohm reading multimeter across the phone line output, trigger the autodialler & then adjust a preset on the pcb to give a known deflection. Very crude but it did work.
Rog |
26th Aug 2022, 3:46 pm | #3 |
Diode
Join Date: Aug 2022
Location: London, UK.
Posts: 7
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Re: Break/ Make Ratio (Telephone dial)
For those of us unfamiliar with some/all of your test kit, could you add some photos of it?
Have you tried the same test using Audacity? |
26th Aug 2022, 4:42 pm | #4 |
Heptode
Join Date: Jan 2008
Location: Hakadal, Norway
Posts: 643
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Re: Break/ Make Ratio (Telephone dial)
It is a lot info here: http://www.classicrotaryphones.com/f...8786#msg218786
It would really be nice to get something that was easy to use, and possible to just plug in to a modern pc. Last edited by dagskarlsen; 26th Aug 2022 at 4:47 pm. |
26th Aug 2022, 5:54 pm | #5 |
Heptode
Join Date: Jan 2008
Location: Hakadal, Norway
Posts: 643
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Re: Break/ Make Ratio (Telephone dial)
What use to be the problems with old totary dials?
1: Speed Most exchanges tolerates 8-12 pps, some ATA's does acsept rotary dials but only at a more correct speed, not sure how accurat but quite extreme. (I use to try to tune in to 10-11 pps) 2: Slowing down at the end of the return. Some of the pulses wil then be to slow. 3: Break make ratio Usually not a problem, pretty much of the equipment accepts a 50/50 rate. UK Standard has 2/3 =66.66667% break Many other countires has 60% break, I use to tune in to something between, and it has always been OK, so my goal will be 63.5% but everything between those 2 standards seems to work well. 4. Some dials has pretty short breakes, and the last break is long, those were made for the very first 7A echanges, and will usually not workwithout modifications. The ideal tool lets me dial 0 ten times, and then give me the avarage speed, max, speed and minimum speed. The same about makes and breaks. In addition we could wish a drawing with time scale and 10 lines where the breaks ar visible and starts at the first break start. On the other hand The german tool mentioned in the thred I linked too is doing the job good enough, I just need to connect my RS232 adapter to the PC. |
29th Aug 2022, 1:43 am | #6 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,297
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Re: Break/ Make Ratio (Telephone dial)
Are the two different test system types using the same method to detect the line breaks? If they are measuring current or voltage in the line they might be set to a different trigger point. What line voltage are they providing and is it resistive only or using the BT “A” relays?
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30th Aug 2022, 9:44 am | #7 |
Heptode
Join Date: Jan 2008
Location: Hakadal, Norway
Posts: 643
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Re: Break/ Make Ratio (Telephone dial)
Audacity just use the recording of the sound going off and on, the more traditional systems use 24-60V DC and a relay. The readings of a complete telephone may differ pretty much depending on the ringer/capacitor connected depending on the tool used. If we measure the dial only, the readings are quite similar. The Old Siemens writer, and the Audacity solution is pretty accurate, but you have to do the calculations. The German software are more sensitive to other components in the circuit, so that may be of importance to know, usually it is good enough. In 90% of the cases, dial speed is the only thing needed to adjust.
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16th Sep 2022, 9:21 pm | #8 |
Nonode
Join Date: Oct 2014
Location: West Midlands, UK.
Posts: 2,181
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Re: Break/ Make Ratio (Telephone dial)
Interesting bit on Wiki
https://en.wikipedia.org/wiki/Pulse_dialing. Strange how things stick in your head. My recollection from nearly 60 years ago on test desk was 10 pulses per second and 66% break ratio. ( if that is any help) |
31st Oct 2022, 7:54 am | #9 |
Heptode
Join Date: Jan 2008
Location: Hakadal, Norway
Posts: 643
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Re: Break/ Make Ratio (Telephone dial)
Yesterday my old Automatic Electric wall telephone bacam so bad (slowing down in the end of the return) that I had to clean and oil the dial (no oil on the speed regulator) Then it was working good enough again. Since my equipment accepts it I did not tune anything.
Here is the result of the dial test after cleaning: |