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[?] Would like to decode and display V22bis data (2400baud)

Hi, I have some high-quality DAT recordings of a V22bis (2400 baud) data exchange between a modem and a computer, which were made by recording across the telephone line via a suitable interface.

I'd like to be able to decode, display and analyse the data in these recordings, preferably using hardware circuitry to drive a suitable serial interface program (such as Tera Term or similar). I realise that my recordings are of a two-way data exchange, so any decoded information will need some 'untangling' to separate the go and return paths, however, since I'm only interested in observing and understanding the actual handshaking procedures, I'd be happy to accept results that are not entirely perfect.

Can anyone recommend a simple and effective way to do this? I was wondering if any of the dedicated data modem ICs that were all the rage when modem speeds were much slower than today, are still available. If so, can anyone recommend one that could translate the actual V22bis tones into suitable logic levels?

I'm sure that the experts in this NG will have already realised that data is NOT my speciality subject so, if I'm asking for something silly or unreasonable, please feel free to tell me (but gently) the error of my ways. ;-)

TIA - Dave

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David C.Chapman - (dcchapman@minda.co.uk)
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Reply to
David Chapman
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V22bis (like other low-speed protocols) uses separate frequency ranges for each direction so disentangling the data shouldn't be a problem. In principle, you could feed the signal back into a commercial modem and get it to demodulate it and spill the data to the controlling PC where you could capture it (e.g. with HyperTerminal).

The trick would be to get the modem to think it was connected which might require a lot of trial and error with initialisation settings, etc. It'll be easier if you can establish the connection via a real phone line (e.g. a PBX extension) as the modem may not cooperate if the line voltage and current aren't right. The older (and dumber) the modem, the more likely it is to work.

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Steve Hayes, South Wales, UK - remove colours from address
Reply to
Steve Hayes

Are you trying to get yourself or us int jail?? If so, no thank you...

Reply to
Sjouke Burry

first stop is to get a nice old modem that you can locate the AT command set for.

You can force old modems into believing there is a connect with the correct commands. This will all depend on the modem. This assumes you want the data itself. I fail to believe you're after handshake data, as that's so easy to replicate with two modems.

I'd grab my external MultiTech or Microcom 2400 baud modems for a task like this.

Reply to
Cydrome Leader

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That is more of a maybe. Though two modems (to two ports) may do it well. V.22bis is QAM not FSK. Higher speeds can get really ugly for using recordings.

Reply to
JosephKK
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I've recently been told about this product which seems to be ideally suited to the job:-

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Many thanks to all those in this NG who offered other interesting suggestions.

- Dave

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David C.Chapman - (dcchapman@minda.co.uk)
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Reply to
David Chapman

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