[GreenKeys] Bell 103 demodulator?

[W2HX]

Thanks, Jack. Actually, on this EMU (see previous email from me) to get the tones to emanate from the rear speaker, you have to select "Acoustic Coupler" I suspect if I were to open up this unit, I might find that IC chip you mention below. 

73 Eugene W2HX


-----Original Message-----
From: GreenKeys [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Jack Hart
Sent: Saturday, September 13, 2014 12:31 PM
To: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Bell 103 demodulator?

ZCZC

The Bell 103 is rated up to 300 Baud, the code doesn't matter; it's a simple AFSK type of modem.
Ma Bell used a lot of them with Model 28's in the day...
the tones are 2225/2025 and 1270/1070...200 HZ shift.
These are "Answer" and "Originate" tones for full-duplex operation on a 2-wire connection. The 101-type modem in the Model 33 TWX uses the same tones. I used to copy 170 shift ASCII with a 33 (optioned for 4-wire to separate the tones).
The 103 standard was used in acoustic couplers and there's even a single IC chip that can provide the 103 tone sets.

Jack K0TTY

NNNN


-----Original Message-----
From: GreenKeys [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of epvgk at limpoc.com
Sent: Saturday, September 13, 2014 10:42 AM
To: Dave G4UGM
Cc: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Bell 103 demodulator?

On Sat, Sep 13, 2014 at 09:54:48AM +0100, Dave G4UGM wrote:
> Well those tones about sound right for Bell 103, as I see from
> 
> http://en.wikipedia.org/wiki/Bell_103_modem
> 
> "The answering station used a mark tone of 2,225 Hz and a space tone 
> of
> 2,025 Hz."
> 
> So is 266.6 baud the right number? Might be worth looking in something 
> like spectrum lab but I can't get a decent waterfall display and I am 
> not really used to the tool.
> 
> Dave.

yeah, and also, should the encoded data be expected to be ascii? 7 or 8 bits? 
parity? and even if so, does it contain something that would even look like text? 

> 
> -----Original Message-----
> From: GreenKeys [mailto:greenkeys-bounces at mailman.qth.net] On Behalf 
> Of epvgk at limpoc.com
> Sent: 13 September 2014 09:42
> To: W2HX
> Cc: greenkeys at mailman.qth.net
> Subject: Re: [GreenKeys] Bell 103 demodulator?
> 
> On Fri, Sep 12, 2014 at 08:36:00PM -0700, W2HX wrote:
> > Hello folks,
> > 
> > I have an audio file (wav) that I have been told represents data in 
> > the following audio format:  Bell 103 data, 266.6 baud, 850 shift,
> 1300/2100 tones Does anyone know what software can be used to decode 
> this? I am posting it here in case it helps figure this out.  Thank 
> you
all.
> > 
> > http://www.w2hx.com/x/PRC-319/
> > 
> > 
> > 73 Eugene W2HX
> 
> I fiddled around with it a little but no luck. The tones appear to be
> 220 Hz
> 
> apart, not 850, if the file's WAV header is correct and it's sampled at
> 16khz.            
> The tones seem to be 2228 and 2008 Hz, with the higher one as mark.
> 
> Even so, I couldn't get minimodem or fldigi to decode it to anything 
> human
> 
> readable either as ascii or baudot with any of the permutations of 
> options I
> 
> could think of... :(            
> 
> 
> eric
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