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Hybrids matched to "fake" phone lines

G

gunterm

I have an older Gentner Digital Hybrid II unit, works great and matches well to normal phone lines.

When tried with my Packet8 phone box at the house, I was unable to match it. After reading the manual throughly I discovered a jumper inside the box to turn off the DC coupling check for phones without "battery", which the Packet8 doesn't have.

After changing the jumper I was able to null with the same reading on the multimeter, however the same problem exists as always has, the calling party on the other end hears themselves echoing back.

So since this is incompatible with IP lines should I just ditch this hybrid and purchase something else designed to be connected to phone handsets? Do you have some device recommendations? It's possible the hybrid is too old for fake lines and a Telos One or newer device would like it.
 
A Telos One wouldn't be any better, nor would any of the other hybrids. IP lines are an animal unto themselves, and as such, don't belong anywhere near being on the air at a professional radio station. ISDN is inherently 4-wire, and provides perfect separation. Lines coming off a channel bank on a T1 will look like a central office line with the added advantage that the effective line length is always the same, regardless of whether the caller is next door or across the country. The DH-II is still a good digital hybrid, but wants to see something that looks like a CO.
 
A Telos One wouldn't be any better, nor would any of the other hybrids. IP lines are an animal unto themselves, and as such, don't belong anywhere near being on the air at a professional radio station. ISDN is inherently 4-wire, and provides perfect separation. Lines coming off a channel bank on a T1 will look like a central office line with the added advantage that the effective line length is always the same, regardless of whether the caller is next door or across the country. The DH-II is still a good digital hybrid, but wants to see something that looks like a CO.
 
It could be a problem with your VOIP box. Sometimes the echo cancellations settings are not right. It can happen on a per-call basis. VOIP is a very dark art sometimes.
 
I would think that the Packet8 adapter would have to provide some sort of "talk battery" voltage, otherwise folks would not be able to connect standard telephones to it and have them work properly.

The DC check jumper in that hybrid is probably there for use in a 2-wire dry pair setup where a station would have a leased line to some location where frequent remotes occur (sports venue, etc.), or to deal with some PBX systems that don't provide DC on the talk path. I've never dealt with a 2-wire dry pair configuration, although a college station I helped at used 4-wire dry pair setups between the studio and the on-campus sports venues. (2-pairs, one for the program audio and one for talkback from studio to remote location)
 
I agree with techie2, it has to have battery voltage. But if you can't null the hybrid without that jumper setting, then your probably need to leave it that way.

I'm suspicious that caller audio is getting in to your "SEND" feed. IP phone has significant delay, and any caller audio that gets into your send feed will result in echo. You don't, by chance, have your monitor speakers up loud enough for the caller to hear himself, do you? Or headphones too loud?

Try this: Disconnect your SEND feed and see if the "echo" goes away.
 
greg.hahn said:
I agree with techie2, it has to have battery voltage. But if you can't null the hybrid without that jumper setting, then your probably need to leave it that way.

I'm suspicious that caller audio is getting in to your "SEND" feed. IP phone has significant delay, and any caller audio that gets into your send feed will result in echo. You don't, by chance, have your monitor speakers up loud enough for the caller to hear himself, do you? Or headphones too loud?

Try this: Disconnect your SEND feed and see if the "echo" goes away.
Click to expand...

It nulls up the exact way a real phone line does when the jumper is set inside to disable support for battery voltage on the line, without it the reading is way off and there is heavy leakage.

I don't know how the audio is leaking back to the caller, I assume its just a function of the IP phone, because I use headphones when testing this to eliminate the chance of any leakage.
 
greg.hahn said:
I'm suspicious that caller audio is getting in to your "SEND" feed. IP phone has significant delay, and any caller audio that gets into your send feed will result in echo. You don't, by chance, have your monitor speakers up loud enough for the caller to hear himself, do you? Or headphones too loud?

Try this: Disconnect your SEND feed and see if the "echo" goes away.
Click to expand...

Great point...if the caller is getting into the send audio it could be caused by an improper mix-minus situation.

I could understand seeing lots of send audio on the Gentner caller output if it was getting a poor null. There's always some sort of leakage there. If callers are hearing an echo of themselves even with a proper mix-minus arrangement, then it could be the VoIP adapter or service. The VoIP adapter probably has a pretty cheap hybrid circuit for its POTS line emulation, so it could be that, or something up with the echo cancellation.

Is your test caller calling in from a regular POTS line, another VoIP line, or a cell phone? I've occasionally noticed weird echo issues with my cell phone, so I'd discount any test results that involve a cell caller.
 
The other end is either a cellular phone or another VOIP line, same network too. I haven't tried a POTS line yet since I don't have access to one.
 
It's been a long time since I've played with a DHII, but I seem to remember a capacitor across the line that could be changed to compensate for either very long or very short lines. I would suspect you have a very short line. Check the manual.
 
As alluded to earlier, your DHII isn't making any attempt to null out caller send audio. It's only responsible for what comes out of the caller out port. Either you're not using mix-minus, or your VOIP adapter is doing a poor echo cancellation job. But you can't blame the hybrid.

Tom Hartnett
Tech Director
Comrex
 
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