I know theres a lot of schematics for fm transmitters on this forums already, but i wanted the opinions of the people who made them. I'm looking for something with short range, but high quality. Just need it for a transmitter inside my car. I would like it with as few components as possible so its real low consumption.

 

What frequency are trying to transmitt at?

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fm between the 88 Mhz and 108 Mhz

 

I just added this, so it may not show up on geocities server until tommorrow.

http://www.geocities.com/hamfiles/FMTrans.htm

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I saw something like that last night when i was browsing for some schematics. Have you built that yet? I havn't tryed to use that type of diode yet.

 

Well it depends what you mean buy good quality. Any quality of
a transmitter can be good or bad depending on point of view.
(modulation, frequency, output power, power consumption, size,
stability, mono or stereo, signal quality, sexy looks...).

I've built tons of FM transmitters of all shapes and sizes but most
of them ware simple ones using 2 transistors. All of them have
really crystal crisp sound. Just make one, and then you'll know for fact.
How hard it is to put few components together and with no crossing
of signals? When I'm in bad mood, I make one in 10-15 minutes on
piece of cardboard. It's really that simple. Just do it...
Here is one that is really simple using only few components.
Don't expect too much from it though, but it sure does work...

Attached Images

xmitter2.gif (34.6 KB, 1995 views)

 

 

I'll give one of those a try, just want a transmitter for my cd player and mp3 player since the tape adaptor sucks. How do you put those together so fast, i've built a few and spent hours trying to get them to work with no results. I put them on breadboards but i kept all the leds short and it was all soldered good. Never any luck though

 

Yes, I built this one when I was going to school. It's a direct FM transmitter, "funny" diode is a varactor diode, kind of like a diode and capacitor combined. As I remember, it worked very well at 87-90 MHz, but you could not tune the full FM band too well. It was crystal clear at 87 Mhz. I used a regular small 9 volt battery.

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That's the problem, they won't work on breadboard. Capacitance
between rails is too big for project that runs on so high frequency.
Choose for oscillator transistor with high frequency. For 88-18MHz
you will need trasistor that can oscillate at 300MHz.
How do I make it so fast? Well, it doesn't have to be pretty.
Just get something with holes (sometimes I would scrape away traces
of some old PCB and use just board with holes). Place components
close to each other in a same arangement as on schematic and
make sure pins stick through holes. Bend the pins to secure
components fom falling out. Make sure to join proper ends with
a small bob of solder and that's it for the quick and dirty.
Most of the components are not critical so reasonably similar values
are ok. When missing feedback capacitor (the one that goes accross
collector and emiter of RF transistor, value 3-7pF) I make one by twisting
wires and cutting the length to ca 12-15mm. Some guys
use this type of "capacitor" in parallel with the coil as well to adjust
frequency (cutting the "braid" shorter reduces capacitance and in this
case increases frequency).
Take a look at my last post. It is a link to 3V transmitter with only few
components. It doesn't get much simpler than this. See the PCB for it?
What do you think how long it takes to do it on a piece of ANY board
(even without copper clad, just by using Frankenstein method
I've mentioned)? To do it in SMT, and without microphone, whole thing
could fit in a 3.5mm (1/8") phone jack including two wristwatch batteries.
Wouldn't that be what you are looking for?

 

http://www1.jaycar.com.au/productVie...Max=&SUBCATID=

This website has a very good transmitter, and it was designed by a high profile magazine publisher "Silicon Chip"

Apparently the main engine of the transmitter is a BH1417f device. Look it up in google for specs.

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I built a similiar transmitter a while back. Little 2 transistor model, worked great. I used it to tell my kids to turn their stereo down. (me yelling through an already loud stereo proved rather effective).

 

lol, yeah something small and simple is what i'm looking for. IT must not have been a breadboard, just one of those boards with a bunch of holes drilled in it. vero board or something similar. I've just had bad luck, built about 3 or 4 and some have barely worked others didn't at all.

 

While we're on this subject, I built this transmitter, and it will only transmit about 30 feet or so. I used a transistor that had an hfe of about 13 I think it was. hfe means gain, right?? How high of a gain should it have?

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As long as it works at all it's high enough, if it's too low it won't oscillate.

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