CMOS
Advanced Member level 3
RF Transistor Selection
Hi,
I am constructing FM transmitter to work in radius of 100 feet. For the frequency multiplier section I used BF494 with voltage divider bias (R1=15k, R2 = 4.7k). The colector has LC tank circuit with 4.7pF capaitor between collector and emitter. Varactor diode is used for frequecy modulation which is coupled to the tank circuit using 22pF trimmmer. The value of emitter resistor Re=68R. A 75 cm antenna is coupled to collecter of BF494 using 2.2pF capacitor. Frequency = 100MHz. Vcc = 9V.
My problem is that I am hardly getting 40 feet range using above configuration.
I tried replacing BF494 with 2N3904 but there is not significant improvement in the range. How do I increase the output power? Which transistor should I use.
Hi,
I am constructing FM transmitter to work in radius of 100 feet. For the frequency multiplier section I used BF494 with voltage divider bias (R1=15k, R2 = 4.7k). The colector has LC tank circuit with 4.7pF capaitor between collector and emitter. Varactor diode is used for frequecy modulation which is coupled to the tank circuit using 22pF trimmmer. The value of emitter resistor Re=68R. A 75 cm antenna is coupled to collecter of BF494 using 2.2pF capacitor. Frequency = 100MHz. Vcc = 9V.
My problem is that I am hardly getting 40 feet range using above configuration.
I tried replacing BF494 with 2N3904 but there is not significant improvement in the range. How do I increase the output power? Which transistor should I use.