spa112 ring strangeness

[cacodem0n]

I'm troubleshooting a non-working caller-id between spa112 and telos hx6 (this is google'able). while checking whatever possible, I tapped into the phone line and got the attached graph (a lot more of actual data available upon request, the whole session sampled at 200khz). what surprised me was the 48v DC part for half a second, right after the ring and before caller-id.

anyone knows what it is, and is it disable'able?

[Dan Lukes]

It look like polarity reversal.

You didn't disclosed neither what caller id method you configured on SPA112 nor what method you configured on HX6. But in short - method configured on both devices must match or HX6 will not understand signal generated by SPA112.

[cacodem0n]

hx6: fsk after ring
spa112: bellcore (n.america, china), fsk method: bell202

[Dan Lukes]

It looks good.

The spurious polarity reversal should not harm - analog line have no strict polarity defined and device must work with whatever polarity. Some methods of caller id are exception - change of polarity is considered "signal". HX6 either know polarity reversal to be "start signal" or doesn't use polarity (in such case polarity doesn't harm).

But in short - you can't tune details of selected caller id method on SPA112. Even if the PR in question cause your troubles, you can select another caller id method only. On both devices, of course.

[cacodem0n]

will come back after capturing what the real polarity reversal  looks like. I seem to remember having tried it, and it didn't look this exact way. at least, it wasn't 0.5s DC. I'm not sure that I'm barking in the right direction, but, the session that worked (not spa112) didn't have that DC part. it makes me think - maybe, it's some call feature that I don't know of and it can be disabled?

[Dan Lukes]

You can select another caller id format only. You can't modify parameters of particular format selected.

But are you sure the LR is the only difference ? Even if both devices are using same start signal and same modulation, the content of data transmitted can be in either MDMF format or SDMF format. SPA112 use MDMF (not configurable). If HX6 supports SDMF only, it will not understand MDMF message ...

Just guessing, of course ...