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[SOLVED] Building a Voyager MKII (FM Radio Transmitter)

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SeriousTyro

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I was looking into building a FM Radio Transmitter.
I found this schematic:
Voyager MkII Page 1

I was wondering for the BC547 transistors, could I use 2N3904 transistors?

I was also wondering, will I be able to get most of these parts from my local electronics store? Specifically the Air trimmer, axial ceramic capacitor, microphone?
I'll be using through-hole resistors instead of surface mount one.

Is the only difference between an axial ceramic cap and a regular ceramic cap the shape?

Thanks,
Will
 

In this application the 2N3904 shouldn’t give you more hard time than the BC547 and ceramic caps are ceramic caps, doesn’t matter whether they are axial or radial ..

IanP
:wink:
 
@Ian Thanks, that's good to know.

When would I have to worry about switching the transistors? i.e, What specifications should I be looking at between the transistors?
 

In those low-power, low-voltage applications almost any small signal transistor can be used, the only thing is that as this is RF device the said transistor should have [Ft] at least 2-3 times higher than the frequency it is going to work at ..

IanP
:wink:
 

Hi there,

For your caps see if you can get NP0 ceramics, NP0 do not change much with temperature, for your trimmer caps you might well have to use plastic die-electric ones.
I have just been working on an fm transmitter for testing and listening to my old time valve radios, I have used 2n3904's and bc547's, they both work well.
You should be able to use a radial cap instead of an axial one, just bend the leads to make it axial (it might be done for a stability reason keeping the 2 connections apart).
The 10pf accros the collector emiiter on the osc transistor wants to be very close to the tranny, if you can solder it to the legs of the device on the top side of the board.

If you want a really good circuit that is very stable frequency wise have a look at this one, I just built it and it works well.

Crystal Locked FM Bug

Edit: word of warning with the trannys, the 2n3904's have the same pinout as the pn2222's on the schematic, bc547's on the other hand have a diffo pinout, you need to solder them in 180 degrees rotated (the end 2 pins are reversed).
 
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