Which other transistors can I use

[Abdul Ahad]

The transistor which this scheme requires is S9018, I cant find it here.I have 2N3904 transistors.Can I use them ?

 

[dorke]

The general answer is No.
The 9018 has a min fT of 700MHz while the 2N3904 has 300MHz.

You can try BF959 or 2N5179 etc.

 

[Audioguru]

The circuit is a 100MHz FM transmitter so of course a 300MHz 2N3904 transistor will work. My FM transmitter works fine with 2N3904 transistors.
But the circuit is so simple that it will have problems:
1) The antenna is connected directly to the tuned LC circuit so the radio frequency will change when something moves towards or away from the antenna and changes the capacitance. My circuit has an RF amplifier to isolate the tuned circuit in the oscillator from the antenna.
2) The radio frequency will change as the battery voltage runs down. My circuit uses a small low dropout voltage regulator.
3) The received sounds from an electret microphone will be weak. My circuit has an audio preamp.
4) The received sounds from an electret microphone will be muffled with reduced high audio frequencies. My circuit has pre-emphasis like all FM radio stations have and it sounds perfect.
Here is my circuit:

 

[73's de Edd]

To me . . . .Looks like it's just displayed and being all solved for you.

Just stick with the specified low drop out regulator instead of a MORE common 7805, so that you will thereby be able to drain down that 9 V battery to its lowest level while still retaining a regulated output.

Also confirm if that QUITE DESIRABLE - - - MECHANICALLY STABLE, heavy gauge enamelled coil winding is seeming to be ~ 18gauge (or 1 mm to you ).

And, it is being wound on a 1/8 in (or 4 mm to you ) winding form for 10 turns AND should be no closer to each other than is being shown or else, have one coil mounted at a right angle to the other.

? for Audio Guru . . . . is that electret element . . . being a pull from some German equipment, as it doesn't resemble all of the far east counterparts that I have seen.?

73's de Edd

 

[Audioguru]

The microphone on my FM transmitter is the small electret one in my daughter's first cell phone about 20 years ago. It still has its rubber boot. Today it is in the VU meter in my family room.

 

[Terry01]

[QUOTE="Audioguru, post: 1748333, member: 45691Today it is in the VU meter in my family room.[/QUOTE]

VU meter??

 

[Audioguru]

VU meter??

I have a VU meter project that I posted almost 12 years ago at www.electronics-lab.com . It uses a logarithmic LM3915 bar graph IC with a peak detector and AGC that I designed to increase is range to 50dB. Its microphone is very sensitive and it has a rechargeable 9V battery so it can be portable but it is almost always trickle-charging.

 

[Terry01]

Ah cool. I have never heard of a VU meter before.

 

[AnalogKid]

Ah cool. I have never heard of a VU meter before.

Tsk tsk TSK - kids these days ...

https://en.wikipedia.org/wiki/VU_meter

ak

 

[Audioguru]

An old VU meter showed average signal levels and let clipping and its severe distortion to occur. My circuit uses a very fast responding peak detector instead.