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From: Vladimir Vassilevsky on 21 Dec 2009 14:49


steveu wrote:

>>
>>Jadran wrote:
>>
>>
>>>Hello,
>>>
>>>I m implementing fax/modem detection.
>>
>>You are implementing fax/modem detection to do what?
>>

>>Fax/modem signal = wideband noise-like signal with high energy. It is
>>very distinctive from anything else.


>
> Its only wideband once the image modem starts. I assume he is trying to
> detect if its a FAX near the beginning of a call for some selection reason.

It's the answer side that starts fax/modem negotiation. Utter evil
things like automatic telemarketing come to mind. He'd better do
something peaceful, like missile guidance system.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
From: steveu on 21 Dec 2009 20:44
>
>
>steveu wrote:
>
>>>
>>>Jadran wrote:
>>>
>>>
>>>>Hello,
>>>>
>>>>I m implementing fax/modem detection.
>>>
>>>You are implementing fax/modem detection to do what?
>>>
>
>>>Fax/modem signal = wideband noise-like signal with high energy. It is
>>>very distinctive from anything else.
>
>
>>
>> Its only wideband once the image modem starts. I assume he is trying
to
>> detect if its a FAX near the beginning of a call for some selection
reason.
>
>It's the answer side that starts fax/modem negotiation. Utter evil
>things like automatic telemarketing come to mind. He'd better do
>something peaceful, like missile guidance system.

For things like unified messaging people want to answer the phone, see if
a FAX machine is calling, and either handle the call as a voice mail or a
FAX. For T.38 FAX over IP people want to detect either FAX tone (CED or
CNG) to see if the call should be renegotiated as a T.38 FAX call. There
are several perfectly innocent reasons to want to do FAX detection.

On the other hand, I hope all telemarketers have severe long term problems
in the toilet.

Regards,
Steve

From: Jadran on 22 Dec 2009 09:19


Hello,

do you have idea how reliable is tone matching alone as fax detection,
there are sone cases when none of tones is transmitted?

>Demodulating the FSK, and looking for the initial flags of the HDLC data
>is a fairly simple thing to do.

Anyway, this seems as simple way to ensure fax is actually detected.
Please can you suggest which of FSK demodulator/decoder design shemes seems
most suitable only for this purpose, having in mind low computational
complexity. Short scheme description would be helpfull.

Dont worry you are not helping someone in telemarketing bussness, I m not
bothering people for living :).

Thanks for support

Jadran
From: Randy Yates on 22 Dec 2009 10:24
"Jadran" <jsirotko(a)yahoo.com> writes:

> Hello,
>
> do you have idea how reliable is tone matching alone as fax detection,
> there are sone cases when none of tones is transmitted?
>
>>Demodulating the FSK, and looking for the initial flags of the HDLC data
>>is a fairly simple thing to do.
>
> Anyway, this seems as simple way to ensure fax is actually detected.
> Please can you suggest which of FSK demodulator/decoder design shemes seems
> most suitable only for this purpose, having in mind low computational
> complexity. Short scheme description would be helpfull.
>
> Dont worry you are not helping someone in telemarketing bussness, I m not
> bothering people for living :).
>
> Thanks for support
>
> Jadran

Jadran,

There's a new technology out called the Internet, and a company called
Google makes this wonderful search tool for ti. Why don't you try
utilizing this tool to answer your questions?
--
Randy Yates % "And all you had to say
Digital Signal Labs % was that you were
mailto://yates(a)ieee.org % gonna stay."
http://www.digitalsignallabs.com % Getting To The Point', *Balance of Power*, ELO
From: Jadran on 22 Dec 2009 14:46
>"Jadran" <jsirotko(a)yahoo.com> writes:
>
>> Hello,
>>
>> do you have idea how reliable is tone matching alone as fax detection,
>> there are sone cases when none of tones is transmitted?
>>
>>>Demodulating the FSK, and looking for the initial flags of the HDLC
data
>>>is a fairly simple thing to do.
>>
>> Anyway, this seems as simple way to ensure fax is actually detected.
>> Please can you suggest which of FSK demodulator/decoder design shemes
seems
>> most suitable only for this purpose, having in mind low computational
>> complexity. Short scheme description would be helpfull.
>>
>> Dont worry you are not helping someone in telemarketing bussness, I m
not
>> bothering people for living :).
>>
>> Thanks for support
>>
>> Jadran
>
>Jadran,
>
>There's a new technology out called the Internet, and a company called
>Google makes this wonderful search tool for ti. Why don't you try
>utilizing this tool to answer your questions?
>--
>Randy Yates % "And all you had to say
>Digital Signal Labs % was that you were
>mailto://yates(a)ieee.org % gonna stay."
>http://www.digitalsignallabs.com % Getting To The Point', *Balance of
Power*, ELO
>

Randy,

well I already did that, problem is there are too many alternative
solutions, so I m here asking help of experienced proffesional to
recommend me good starting point, or in concrete case recommend most
propriete FSK demodulation approach for my not so common problem.

So I m trying to discuss posibilities and pick optimal, that's what you
have to do when wonderful search tool Google returns too many results and
you dont have experiance in field. Maybe your wonderful Google does it for
you, unfortunately mine is not working like that...

Anyway, I realy dont understand why you have such hostile attitude toward
normal question and want to flame.

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