The transistor is used to turn off the transmitter.

 

Where did you get that cct from ? Does it work ?

The transistor there appears to be used as a switching transistor as mik3 mentioned. It would be used to turn on the TX on and off.

However, I dont think the transistor is used properly.

If pin 4 of your controller is 0V, then the transistor is off. If pin 4 is 5V, you have 5V at the base of the transistor. However, bipolar junction transistors are current devices, not voltage devices. I'm unsure that that circuit would work as intended.

I would instead, have the 4.7K resistor going out of pin 4 to the base of the transistor rather than from +5V. This way, it would work.

Or alternatively, you can replace the bipolar junction transistor with a mosfet since mosfets are voltage devices, and with 5V at the Gate, it would turn on.

 

Is the first page of this thread missing?

 

This does appear to be thread that has been inadvertantly disconnected from its original thread. Perhaps mik3 can provide us with the pertinent thread. Once the original thread has been identified this thread can be remerged with it.

hgmjr

 

I was trying to answer to another threat.

I don't know how I created a new threat!!!!

Mistakes happen.