LINE Port LoopCurrent question
Mango:
Obihai's support responded quickly; unfortunately their advice was not to use the OBi with this POTS line :(
drgeoff:
The OBi can only measure the loop current that is passing through itself. There are only three things that can give a high reading for LINE port off-hook current.
1. Faulty measuring circuit in the OBi.
2. Faulty OBi LINE port.
3. Too high a voltage being applied to the OBi's LINE port. This ought to manifest itself as a too high TipRingVoltage for LINE port on-hook. Normal for this would be say 49 +/- 4.
If this is a POTS line (metallic pair all the way back to the Telco CO) then there is very little possibility for any equipment the telco is responsible for to cause an abnormally high loop current. (Abnormally low is a different matter.)
If possible try the following. Get a line splitter or doubler or whatever they are called in the US. It just puts two phones in parallel on the same line. Use that to connect both an ordinary phone and the OBi110's LINE port to the telco line. Plug a second phone into the OBi's PHONE port.
Make or receive a call with the OBi's phone using the telco line. If the audio is distorted leave the OBi phone off-hook and take the other phone off-hook and listen to the quality in its earpiece. Then put the OBi phone on-hook and listen again on the other phone.
Report what you hear.
Mango:
Thank you very much for responding. I checked TipRingVoltage. It has been fluctuating between -51V and -53V.
This is a POTS line and is fed out of a CO.
I performed your test:
1) OBi phone off hook - audio severely distorted.
2) Phone directly connected to POTS line off hook - audio mostly normal, with slight buzz. OBi phone slightly less distorted.
3) Other phone back on hook - OBi phone was severely distorted again.
4) OBi phone on hook and other phone off hook - audio completely normal.
I tested another OBi110. The audio sounded different, but was still distorted.
drgeoff:
That's puzzling. Symptoms point the finger of suspicion at the 110 but two of them being faulty is less likely.
When you test with the second 110 are you also using a second PSU?
Having two 110s allows you to do another experiment. You can connect the PHONE port of one 110 to the LINE port of the other 110. The PHONE port of the first will act as a telco line in terms of providing CO battery voltage to the second 110. See if the off-hook LINE current still fluctuates. You can also compare the first OBi's PHONE port current measurement with the second OBi's LINE port current measurement. They should be the same nominally.
You can also swap the two 110s over. All observations should be the same as before. If they are markedly different, something is wrong and probably exonerates the POTS line.
Mango:
I redid tests with three OBi110 devices, and assigned some arbitrary numbers to them so that it is more clear about what is happening.
OBi110 #1, HardwareVersion 3.4: LINE Port LoopCurrent 62 mA, severe audio distortion.
OBi110 #2, HardwareVersion 3.4: LINE Port LoopCurrent 9 mA, very very quiet audio.
OBi110 #3, HardwareVersion 2.8: LINE Port LoopCurrent 62 mA, normal audio.
#3 has a damaged FXS port, so only works properly if the call is routed by IP to some other device.
Yes, I have tried multiple AC adapters. I also checked them with a multimeter just now, and measured slightly over 12V.
I will try your other experiment later.
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