Busy Tone Frequency & Pattern?

Hi,

I have found in the web that following information about busy tone of my country:

Tone: Busy Freq: 480 + 620 Amp: -13 Cadence: 0.5 seconds on, 0.5 seconds off,REPEATED

What is the meaning of "Freq: 480 + 620"? Is it a dual tone frequency?

If yes, could I calculate its existence by just a timer?

I can get rectangular waves in the telephone line using call progress filter.

Reply to
eeh
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If they mix together, how can I analyse the Call Progress signal by MCU in time domain? I used MT8880 which has a call progress filter.

Reply to
eeh

There are two basic types of tones used: Precise and non-precise. The former is being replaced, over time, by the latter.

The two tones you listed in your original post are "precise tones." They are simply combined and sent as two tones (not mixed in a non-linear device).

FYI, often the non-precise tones are used in pairs and one IS modulated by the other.

Single tone signals predate the precise and non-precise tone usage.

Don

Reply to
Don Bowey

You may want to look at this site:

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Alan

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Reply to
Alan

You need to select a DTMF transceiver that can handle the call progress tones of your country. The MT8880 datasheet says that the CP accept passband is 320 - 510 Hz, and the reject limits are 290 Hz and 540 Hz. The high tone of the CP tone pair you are trying to detect is outside the accept band, and will not be passed to the MCU. Therefore, the MT8880 is of no value to you. You might think about building separate BP filters for the CP tones if you need to process them.

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Dave M
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Reply to
DaveM

Oh I see. Thanks!

But I now change to another method which is to detect the interval of the tone on/off period to recognize the tone type. It is OK now to recognize busy tone and ringback tone.

However, I think it is too long to determine whether connection is estalish if the ring tone period is 3 seconds (0.4+0.2+0.4+2=3 seconds). Anyone know if there exists a faster method?

Specification found in internet for my city: Tone: Audible Ringback Freq: 440 + 480 Amp: -13 Cadence: 0.4 seconds on, 0.2 seconds off, 0.4 seconds on, 2.0 seconds off,REPEATED Detected by CPA or SPC: Yes

Besides, what is CPA or SPC?

Reply to
eeh

There are some tone detector IC's CML micri circuits.

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Reply to
Joe G (Home)

PS

-13 is -13dBm in to 600R

480 and 620 are 2 tone frequncies mixed together.

Joe

Reply to
Joe G (Home)

Besides, if the remote side person accepts the call and says "hello", I find that with this method in most time the busy tone is recognized incorrectly. So I should think another approach to achieve this.

Reply to
eeh

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