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Introduce the principle of small radio transmitters

2016-04-08 12:32  
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This article is a small radio transmitter introduce the principle. The principle of combining text comprehension is a good suggestion. The circuit is only mono, accepting an audio input from a microphone or other source. Input impedance is a Maugham. Input sensitivity is 5 mv and Max input signal is 10 mv. Transmitted signal can be uncovered an FM radio. The principle is simple but effective. 

Then solder in all the parts. Here is the parts list:

D1 Varicap diode (eg. BB119)
D2 1N4148
R1 100K
R2 220K
R3 22R
R4 1K trimmer
R5 1K
R6 56K
R7 1M
R8 1K2
C1 5pF ceramic
C2 6pF ceramic
C3 15pF ceramic
C4 trimmer cap
C5 15pF ceramic
C6 1nF ceramic
C7 100uF electrolytic
C8 4.7uF electrolytic
C9 100pF ceramic
T1 BF244A or BF245A FET
T2 2N3819 FET
T3 BC307/8/9 or BC557/8/9 PNP

Bear in mind that in addition to the components, there is a jumper wire which needs to be fitted (marked with a dashed line in  PCBPLAN .GIF).The power supply to use is 9-14 V DC, one of the little rectangular 9V batteries is fine. Connect this to the and – points on the PCB. The sound input goes to the points marked “MIKE”. The antenna should be connected to the point marked “ANT”. The emitter’s output impedance is 50 ohms.


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