How to Set the DTMF to Achieve a Private Call

Many customers talking about the DTMF, they say that the DTMF is used in analog radio and can be used to mank calls, so what is the DTMF?

What is DTMF?

In short, DTMF is an abbreviation for dual-tone multi-frequency signaling, it consists of a high-frequency group and a low-frequency group.

A high-frequency signal and a low-frequency signal are superimposed to form a combined signal which represents a number.

DTMF has 16 codes, the DTMF signaling can be used to call the corresponding radio.

And it can be used to simulate voice channel transmission signaling, it also has a wide range of applications in communication.

There are many types and applications of DTMF signaling. If you really want to know, it is a huge problem.

So today we will focus on how to use RT87 to implement the selective call and code squelch DTMF signaling function.

The Usage of DTMF Selective Call

Need two analog radio RT87 radio and one programming cable, connect the RT87 with the computer, choose the right port, and read from the radio A or B.

Set the same frequency:435.52000, same CTCSS:250.3, push the PTT button, A can make a call with B.

a. Radio A opens the selective call as shown below, set the Key Assignment: Choose Key function-1 is Optional Signal code, B remains unchanged.

Push the PTT button of A, the two radio cannot connect;

b. Radio B opens the selective call as shown below, push the PTT button of A or B, the two also cannot connect;

c.Press the side of the key 1 of radio A, you can see “DTMF CALL?” On Screen, enter the DTMF Num such as “0” I set, press PTT of A or B, A can call B.

But B cannot call A at this time unless B make an optional call to A.

The Usage of DTMF Code Squelch

Set the same frequency:435.52000, same CTCSS:250.3, push the PTT button, A can make a call with B.

a. Radio B opens the code squelch, radio A keeps unchanged, push the PPT button of A or B, the two radio cannot connect;

b. Radio A opens the selective call, put the PTT button of A, the two cannot connect.

Press the side of the key 1 of radio A,  enter the DTMF Num such as “0” I set, press PTT of A, A cannot talk to B because B has open the code squelch.

c. Radio B press the side of the key 1,  enter the DTMF Num such as “0” I set, press PTT, B can talk to A, but A also can not connect to B, it is one-way.

Conclusion

a. The selective call is similar to turning on CTCSS, you must know the ID code, intermediate code, and group code of the other radio to call, and it is one-way.

You can select to talk to it, but it cannot call you unless making a selective call.

b. Code squelch is equivalent to turning on the squelch in the selective call, a radio select to call you, you cannot receive because you open the code squelch.

But you can make a selective call to it if it does not open the code squelch.

c.DTMF is used in analog radio.

d.RT 87 can open the selective call and code squelch.

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