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'[EE:] Bell 103 protocol over CDMA phone possible?'
2006\02\01@195309 by Jay Shroff

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Hi All,

I am hoping that someone on piclist has experience with this

I would like to try sending data over the traffic channel  (voice channel)
on a CDMA phone.  Since CDMA has a variable rate voice coder I am assuming that any high speed modulation schemes would be foiled by the vocoder.

My data requirements are pretty small so  I am guessing that even with the vocoders I should be able to do AFSK modulation (Bell 103) scheme and the vocoders would allow  that to pass thru?

I am planning on trying this out on my Verizon phone but if someone has already tried this it would save me some time :-)

Thanks
Jay




2006\02\01@200358 by David VanHorn

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>
>
> My data requirements are pretty small so  I am guessing that even with the
> vocoders I should be able to do AFSK modulation (Bell 103) scheme and the
> vocoders would allow  that to pass thru?



you were right to worry about phase problems, but there's an even more
insidious problem.. Silences.  When the packets don't make it, the phone
fakes it with silence.
Transparent to the ear, but the modem will not be happy.  If it works, it's
cause you got lucky.

Sorry.

2006\02\01@215824 by Jay Shroff

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Ahh, you are correct I forgot about that.  know of an encoding scheme that might work for low data rates over a lossy channel such as CDMA.

I could compensate for the drop outs by implementing a TCP/IP type protocol on top of the encoding layer.

If only I had a way of turning off the vocoders :-)

I could live with data rates of 150 - 300 Bps


{Original Message removed}

2006\02\01@222758 by David VanHorn

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On 2/1/06, Jay Shroff <spam_OUTjshroffTakeThisOuTspammyrealbox.com> wrote:
>
>
> Ahh, you are correct I forgot about that.  know of an encoding scheme that
> might work for low data rates over a lossy channel such as CDMA.


All depends on the rate and size of the dropouts.
I've seen ones that dtmf woudn't work through..

2006\02\02@100045 by Robert Ammerman
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From: "Jay Shroff" <.....jshroffKILLspamspam@spam@myrealbox.com>
> Ahh, you are correct I forgot about that.  know of an encoding scheme that
> might work for low data rates over a lossy channel such as CDMA.
> I could compensate for the drop outs by implementing a TCP/IP type
> protocol on top of the encoding layer.
> If only I had a way of turning off the vocoders :-)
> I could live with data rates of 150 - 300 Bps
>

DTMF could probably give you about 20 symbols per second at four bits per
symbol = 80 bits per second. The vocoders have to be tuned to let DTMF
through for obvious reasons.

You might even be able to push the symbol rate a bit.

Bob Ammerman

2006\02\02@122121 by Peter

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> If only I had a way of turning off the vocoders :-)
>
> I could live with data rates of 150 - 300 Bps

DTMF is sort of guaranteed to pass. You could slow down in case of
trouble.

Peter

2006\02\02@122156 by Peter

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On Wed, 1 Feb 2006, David VanHorn wrote:

> On 2/1/06, Jay Shroff <jshroffspamKILLspammyrealbox.com> wrote:
>>
>>
>> Ahh, you are correct I forgot about that.  know of an encoding scheme that
>> might work for low data rates over a lossy channel such as CDMA.
>
>
> All depends on the rate and size of the dropouts.
> I've seen ones that dtmf woudn't work through..

Uhh, could you tell if there was a human at the other end ?

Peter

2006\02\02@133704 by David VanHorn

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>
>
> DTMF could probably give you about 20 symbols per second at four bits per
> symbol = 80 bits per second. The vocoders have to be tuned to let DTMF
> through for obvious reasons.


Classic timing is 50mS on / 50mS off. so 10 symbols/sec.
I have pushed it to 17-ish using a routine that shrinks the off-time between
non-identical digits.

Unfortunately the audio dropouts will torpedo DTMF as well.
What cell phones and cordless phones do apparently, is to generate tones for
you while passing the data as data by some other method.

2006\02\02@133900 by David VanHorn

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>
> DTMF is sort of guaranteed to pass. You could slow down in case of
> trouble.


You could, but if the silences are punching holes in your tones, it may not
matter how long you keep them on.. You need 50mS of good tone to meet spec,
and usually about 45mS actual minimum for the detector.  Get a silence, and
you have to start aaaaalll over, as a film loader!

(bonus points to anyone who can name that movie)

2006\02\02@134118 by Jay Shroff

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Thanks Bob & Peter. I guess I will have to go with DTMF. I was hoping that I could do something better. I was told there was a company out there that offered a modulation scheme that could do 800bps over CDMA, but looks like that must be a "marketing spec"

-----Original Message-----
From: Peter <.....plpKILLspamspam.....actcom.co.il>
To: "Microcontroller discussion list - Public." <EraseMEpiclistspam_OUTspamTakeThisOuTmit.edu>
Date: Thu, 2 Feb 2006 19:21:19 +0200 (IST)
Subject: Re: Re: [EE:] Bell 103 protocol over CDMA phone possible?



> If only I had a way of turning off the vocoders :-)
>
> I could live with data rates of 150 - 300 Bps

DTMF is sort of guaranteed to pass. You could slow down in case of
trouble.

Peter

2006\02\06@233632 by Martin K

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face
Ironically I am looking to do the same thing over CB radio for very
limited use (unencrypted and all that jazz)
I found this website that you might be interested in. I'm thinking
something could be done very similarly with a few opamps and PLLs. The
XR2206 and 2211 chips don't seem to be easy to find and/or cheap. I
think something like 1200/2200 FSK should be reliable, though I have to
admit I don't know the intricacies of expecting cell phones to work
worth a crap for analog transmission.
I know I do a lot of "what.. What.. WHAT?" on my cell phone.
--
Martin Klingensmith


Jay Shroff wrote:

{Quote hidden}

2006\02\06@235026 by David VanHorn

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On 2/6/06, Martin K <martin-distlistsspamspam_OUTnnytech.net> wrote:
>
> Ironically I am looking to do the same thing over CB radio for very
> limited use (unencrypted and all that jazz)


Legalities aside.. Ever hear of a ham radio TNC?
It's been done.

KPC-3, TNC-2, and several PIC and AVR based versions.

2006\02\07@070318 by Mark Jordan

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On 6 Feb 2006 at 23:50, David VanHorn wrote:

> On 2/6/06, Martin K <@spam@martin-distlistsKILLspamspamnnytech.net> wrote:
> >
> > Ironically I am looking to do the same thing over CB radio for very
> > limited use (unencrypted and all that jazz)
>
>
> Legalities aside.. Ever hear of a ham radio TNC?
> It's been done.
>
> KPC-3, TNC-2, and several PIC and AVR based versions.
> --


       Just look for "Baycom modem".

       MJ

2006\02\07@174708 by Martin Klingensmith

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face
David VanHorn wrote:

>On 2/6/06, Martin K <KILLspammartin-distlistsKILLspamspamnnytech.net> wrote:
>  
>
>>Ironically I am looking to do the same thing over CB radio for very
>>limited use (unencrypted and all that jazz)
>>    
>>
>
>
>Legalities aside.. Ever hear of a ham radio TNC?
>It's been done.
>
>KPC-3, TNC-2, and several PIC and AVR based versions.
>  
>
Yes I know what it is. This would just be for one day use for something
like a soap-box derby on steroids. (start/stop signal transmission)
I'm not sure a PIC would be the easiest plan for the analog section, but
for the digital part of course.

Other than that, I suppose I am wondering if I could get a modern modem
to emulate Bell 103 mode?
--
Martin K


--
Martin Klingensmith
http://wwia.org/
http://nnytech.net/

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