I need to connect PC Modem to wireless analog telephone :(

[flower1]

so I need to establish wirelles connection beetwen pc modem and telephone line using analog wireless telephone. I tried to connect mic and headphone from wirelles telephone to line of modem, modems start recognizing, but can't establishing connection . I think problem is mic and headphone from wirellesphone is in same circuit and come like microphonia efect. So can someone help me how to do this.
This is circuit which I used. Please I need realy help for this...

 

[Lewish]

I can't be much help, but one thing you are overlooking is the fact that a modem looks for the voltage on the phone-line. If that voltage is about 48V, then the modem knows the line is not in use. If the voltage is around 7V, and the modem isn't in a connect condition, then the modem knows the line is in use.
I hope this helps a little.

 

[flower1]

Lewish Thank you but I know this , voltage of line is 52V ,
and thats what you said is matter for waiting dial tone or maybe not while i senfd to modem phone line sound and modem start dialing.
Second! i established connection but with 1200 bps
on one other forum one user told me that modems 24000 bps and higher don't use just frekvency modulation , but also phase of sound changing, and this is problem.PHone can't work with this type of sound
So i need now how to work with this phase change of sound signal. Something must be possibile to make to resolve this problem , What to do with phse changing before send signal to phone?.
And Lewish one thing I established connection without ampliefer, did you know whats voltage out from phone?-very small and modem recognize it and work.
Maybe Im in wrong, than tell me whats however.
Please can anybody help me?

 

[buzz41]

What you are attempting should be possible, but not at 56k speeds, not even in theory. In fact, due to distortion and noise, it will likely be much lower.

One thing your ckt probably needs is a hybrid connection between your send/receive ckts and the modem line. The modem already HAS a hybrid internally to separate its send/receive. The hybrid allows the two connections to a single bi-directional line while isolating the two from each other. Without a hybrid it is difficult to avoid oscillation.

The BEST solution would be to find the hybrid coil on the modem and bypass it, connecting each path separately to the modem in/out circuits from your mic/spkr ckts.

 

[flower1]

Thank you buzz41 for Your response, but it will be dificult to fond on modem where is in/out signal before entering to hybrid.However I need connection for 28000 bps.Thank You.Can you a litle bit more explane abouit this what you said me about hybrid and connection to modem?

 

[flower1]

And what you think which speed can be working?

 

[Lewish]

Well, just as a point of reference, the maximum data-rate for cellular modem is 19.6Kbaud. BUZZ makes a good point that you probably need a hybrid connection. You can probably build your own.
I seriously doubt, however, that you are going to get to 28Kbaud. If you do, publish it, others will want to know how.

 

[buzz41]

Here is a link on telephone interfacing. From what I have looked at, there is a lot there at the right level to help you.

http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html

Just below the middle of that long page, are some op amp interface circuits that might be of interest.

Your wireless link COULD have a wider audio bandwidth than the telephone system, and the clever modems might use it to help compensate for any extra noise and distortion if the app is a stand alone modem-to-modem arangement. But, if the link will connect to the telephone lines, that advantage will be lost and the wireless link noise will just add to the existing noise.

So, getting 28K or even better might be possible with just the wireless link, probably a tough target, though, if used in combination with a telco connection. Go for it.

 

[flower1]

Buzz41 thank You so much, but one thing I dont know, what's
"telco"

 

[buzz41]

re: telco
Sorry, just meant the telephone company - jargon.

If the modem path is through the wireless link, then through the telephone system to a remotely located modem, both systems will add noise, distortion and bandwidth limitation of their own. The sum of these will determine what the modem sees and limit connection speed.

So, as a thought, breaking that path into two separate links could, in theory, give a higher throughput. ( device modem to wireless link to local modem - back-to-back modem data connection - second modem to the telephone line )

 

[flower1]

Buzz41 can you help me to find where is hybrid coil on modem in/out where to find el.circuit of modem?
I have US Robotics Sportster Voice 33.6K

 

[modem]

Can you explain Buzz41 did I must have 2 modems to connect to third?