More phone stuff

Been trying to do more with the ghost phone, as previously mentioned on day 7 of the kitchen remodel.

Prognosis: Not going well

So, I had incoming calls working with a 30Hz ringer, and it was pretty robust. But I wanted to get pulse dialing working as well, so I decided to get a used Grandstream HT502 (which supposedly supports pulse dialing, although isn’t documented about it). Unfortunately it doesn’t allow setting the ringer frequency arbitrarily; it only has a few country-specific settings, and all of them are (as far as I can tell) either 20Hz or 25Hz.

A bit of history: back in the day, not every house had its own phone line; instead a bunch of houses would be connected on a single “party line” loop. Lots of people know about this. However, here’s the bit I didn’t know: For this setup (and a few other niche circumstances), some telephone networks actually provided different ringer frequencies for different members of the loop; this was called “selective ring.” So, you could have some incoming calls ring at 20Hz, some at 30Hz, some at 50Hz, and so on. So that’s why different phones could be configured with different ringers. My AE90 was probably configured with 30Hz for this reason1.

The reason for these different ring frequencies is down to the way that mechanical ringers in phones worked; the telephone line would have a DC bias voltage (typically around 48V), and then when ringing was to happen, there’d be an additional AC voltage applied on top of this, which the mechanical ringer was tuned to resonate at. And the physical bell also causes the clapper to bounce off of it, contributing to the mechanical resonance.

However, by having frequencies at certain harmonics – 20Hz vs. 30Hz, for example – the clapper will be going one way while the signal is trying to push it the other way, causing the motion to cancel out rather than resonating, and so while the clapper vibrates a bit it never makes it all the way to the bell.

Back when I had this phone connected to a regular landline (which rings at 20Hz) I was able to get a very faint ring by moving the bells right up against the clapper – so that tiny vibration would be enough to (quietly) ring. So, my theory was that a 25Hz signal would have enough resonance with the 30Hz of the ringer that maybe the vibration would be far enough that I could get a reasonably-loud ring out of it anyway2.

So, the HT502 arrived today, and I installed it, and I set it up to ring at 25Hz by setting the SLIC to UK, and… nothing. There was a single “ding” and then the call went to voicemail. All calls after that went to voicemail immediately.

I checked the device status and it showed the line as being “off hook.”

What’s more, this happened when going back to the OBi200.

After a lot of experimentation I determined that my phone line still has a 4V 25mA connection to the CenturyLink NTI. So, I tried a bunch of stuff, and tried going back to the previous OBi 200, and… same issue. Well, sometimes. It would sometimes say it was “on hook,” and sometimes “off hook.” The actual reported current and voltage seemed to vary without much rhyme or reason.

I tried rewiring my jacks so that I’d be on line 2, since I didn’t find any current or voltage on the jack where the phone itself is to be plugged in, but apparently the jack in my office does have two lines connected to it, and they’re not directly connected to each other. The wiring in them is of completely different types anyway; the kitchen jack (where the AE90 goes) has modern UTP coloration while the office jack is the old Bell quad color code. (Even more bafflingly, there’s a stray set of wires within the jack box in the office, which is also Bell quad-color.)

Gah, the wiring in this place is so… weird.

I thought maybe I’d have better luck disconnecting from the NTI; a few years ago I looked at it and found it baffling, but maybe I’d understand it better now. So I went down to the NTI in the garage (having to move a whole bunch of stuff out of the way, because someone’s decided to use the space in front of the telco room as their personal dumping ground) and here’s what I saw:


I actually did find a separate NTI that was just for my unit, oddly enough, and it was the modern kind with internal modular plugs. But I unplugged those and it made no difference to my unit. I know the previous owners were using CenturyLink DSL instead of the building’s Comcast (for some reason) so maybe that was to accommodate the DSL connection somehow. I don’t know. Maybe I’ve disconnected someone else’s landline. I should probably plug them back in or something.

Anyway, my guess is that the OBi 200 has a higher threshold for off-hook detection, and tonight it’s just been a little marginal because it’s raining and who knows what that does to the ancient, bodged-together wiring in this building. I did notice deep in its settings that the detection threshold is also configurable. So maybe I should stick with the OBi and just raise the threshold a bit more to give a bit more leeway. Or maybe I could call CenturyLink and see if they’d be willing to disconnect my unit from the NTI and do whatever’s necessary to ensure both of my wiring runs are bridged together. I’d expect that to only make things worse, though, and I’d expect CenturyLink to also charge a ridiculous amount for the service call. (Of course I can’t find any information about NTI/TNI servicing on CenturyLink’s website. Maybe someone else will have better luck.)

Or maybe I could get an actual phone line instead of doing this VoIP thing. But then suddenly we’re looking at $25/month instead of $0.85/month, all for a silly experiment. And apparently CenturyLink doesn’t support pulse dialing anymore (although that’s information that came from folks who might not actually be on CenturyLink; people get really confused with modern VoIP-based services).

Of course for this silliness I care way more about incoming calls than outgoing, anyway, so maybe I should just stick with the OBi.

Or spend even more on a Grandstream HT812, which both officially supports pulse dialing and has way more configurability on its physical interface…

Oh, or maybe I could find a WiFi-enabled SIP adapter and hook it up to the telephone outlet upstairs, which is in the same loop as the kitchen outlet, and then disconnect the kitchen from the rest of the loop. Or maybe the outlet in my bedroom is on that same loop and I can connect the HT502 to the Ethernet port on my bedroom AirPort Express. Yeah I have options.

EDIT: Turns out that the USB port on the OBi200 is there to add a WiFi adapter to it. So yeah this is seeming like the way to go.

  1. I had previously (erroneously?) believed that the 30Hz ringer was due to different ringer standards being available in the US in the 1960s, and the 20Hz standard not being established until much later. It’s possible this is still true, but it’s seeming pretty unlikely, especially given the timeframe. 

  2. Incidentally, I was unable to find any simple online resonance simulation that I could use to verify this. Aside from some ancient, no-longer-working ones written in Flash, anyway. Well, then there was the one written in Java. Maybe I’ll eventually build a little web toy for this because it’d be fun to play with. 


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