I've recently been playing with telephone dials again, and discovered that a handheld dial tester existed which would save faffing around with an oscilloscope. I managed to pick one up on eBay for slightly more than I would have liked to have paid, but it is in perfect condition so I can't complain too much.
Naturally I didn't read the manual and immediately started playing with it, but it turns out it doesn't function quite like how I'd anticipated. Still, I'll probably get some use out of it.
Digit Analyser and Tele 290 test set
Usage
The analyser takes 4x 1.5v AA batteries or there's a 9v DC input on the side. There's also a switch to select 50v or 25v volt operation for a standard phoneline or lower voltage PBX respectively.
With the analyser plugged into the line with the telephone on the hook in parallel, the LCD display will show the word "CLEAR" to indicate the phone is on the hook.
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Display showing CLEAR
Once the phone goes off hook it'll display "SEIZE" to indicate the line has been seized.
Display showing SEIZED
The behaviour then differs slightly depending on if you're using a Loop Disconnect (Pulse) or DTMF telephone.
Loop Disconnect
The dialled digits will be displayed on the screen along with the Break and Make periods measured in milliseconds (See oddity #2)
Display showing dialled digits and Break / Make period
Pressing and holding the "Display Pages" button then displays the Break and Make periods in milliseconds again, but also displays the dial speed in PPS.
Display showing PPS, Break and Make periods
If you've dialled multiple digits, the screen will show the range for PPS / Break / Make, which might be useful when troubleshooting a dial that slows down at the end of its rotation.
Display showing range for PPS, Break and Make periods
The more observant of you might notice that the PPS is somewhat fast and out of spec for a standard "BT line". As the telephone I'm using is electronic rather than electromechanical it seems unlikely it would have drifted out of spec, so perhaps the analyser isn't accurate? I'll have to do some further testing at some point.
DTMF
When manually dialling with DTMF, the display will just show the digits as they are dialled.
Display showing dialled digits
You can then clear down the call and press "Display Pages" to see more information. Depending on the phone you might see the message "Analysis Invalid Manual Dialling?" - This probably means the tones are being generated with each button press, and the gaps between them vary too much to calculate the additional information.
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Display showing error
If you're testing something like a cordless DECT phone or a PBX that collects the digits, then dials them all at once, you might not see this. Or if you're telephone has a last number re-dial, you can press it to dial the digits sequentially. If everything's gone well, pressing "Display Pages" should display the TONE ON and TONE OFF periods, and cycle to another page showing the Digits Per
Display showing Tone On and Tone Off periods
Display showing Tone on and Digits Per Second
Oddities
Oddity #1
I assumed you'd be able to connect a telephone directly into the BT 431 socket on the tester and test the dial. Unfortunately it doesn't work like that, it needs to be connected to a telephone line with the phone in parallel. I can't really fathom why this is a requirement as the unit contains batteries and it could just power the phone locally to perform the test, but ho-hum.
Even more bizarrely, the analyser only has a single socket, so you have to use your own splitter. It would have been nice if they included two in the unit itself.
Even more bizarrely, the analyser only has a single socket, so you have to use your own splitter. It would have been nice if they included two in the unit itself.
Oddity #2
When measuring a dial, you're usually interested in 2 things, the Pulses Per Second (PPS) and the Break/Make ratio, expressed as a percentage. The analyser handles PPS fine, but it displays the break and make periods in milliseconds. It's trivial to convert it into a percentage, but it would be much more useful if it displayed both the milliseconds and the ratio.
User Manual
I wasn't able to find a decent copy of the manual anywhere online prior to buying the analyser, but fortunately it came with one which I've since scanned. Here's a copy of the Fern Developments Dialled Digit Analyser 1A Operating Instructions / User Manual.
Digit Analyser 1A Operating Instructions (Click to expand)
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