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4W FM Transmitter


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Hello folks.

I'm trying to build the 4w transmitter and since I am a newbie when it comes to electronics and rf I would to ask a couple of questions:

1) For C3 it says "4,7 mF/16V" can someone elaborate on what this value is ? is it 4.7 uF or nF ?

2) for L2 it is to be 1MW .. I have Awg-18 copper wire, and would 8 turns spaced 5mm do ? or can I just plug off the shelf inductor ? if so what value ?

Thank you kindly.

Project Link: http://www.electronics-lab.com/projects/rf/021/index.html

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Sorry for that folks.

The original text was in Greek and it did made sence back then. The text in the above web-link was translated to English using a PC translation utility which doesn't understand electronics terms such as Ohm and Farad. :P
As a result the reading and understanding of the text is rather difficult.

Anyway, mF = uF and MW = MOhm.
As for L2, take a 1MOhm/0.25W resistor, and wrap a few turns of 0.5mm (or so) wire on it.
Play with the values if you are not satisfied with the results.

After all these projects are there for you, to experiment and learn.


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  • 1 year later...

Hi Sasi,
The author says to keep Q2 in a refrigerator, and doesn't have a pic showing his huge high-velocity fan.
He says it draws 400mA at 16V which is only 6.4W.

I searched two heatsink manufacturers but they don't have heatsinks for that old 2N2219 anymore. Maybe you can steal a clip-on heatsink from an amplifier that was made in about 1968.

Q2 is operating in class-C so it is not on all the time, and maybe it is 70% or more efficient.
Sure, with a refrigerator and fan this project can produce 4W.  ;D


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Now I wouldn't normally say this but this is a really crappy circuit - many people here have posted  circuits better than this, I just don't get it, why aren't these added to the vast archive of projects here?

And they should ammend or even  remove crappy circuits like this.

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Hi Alun,
We use these crappy circuits for entertainment. He, he. We also have a DC motor speed controller that is nothing but a variable frequency oscillator, and a 12VDC to 120VAC inverter that doesn't work and it blows-up its capacitors! Lots of fun.

We can't delete them because people have actually built them and talk (complain) about them.
I fix the ones I am interested in, and they usually end up being posted by me as a new project because I improve them while fixing them (Plants Watering Watcher, Electronic Stroboscope, etc).
There is a transistor tester that uses a flip-flop IC but its clock pin is grounded by mistake.
There is a 0-30V, 0.02-3A power supply that doesn't provide more than about 25V, and burns-up at full load.
There is an 8W amplifier that produces about 2W.
I should make a complete list and post it somewhere.  ;D

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Hay, I have a few of those transistors, and the heat sinks that clip on to them (recycled).  So they are that old 1968, maybe I can sell them on eBay as antiques ;D ;D.

Yes that would be good audioguru, a list of projects that will work and a list of one's that will give (you) a headache.

And the (you) means just that, everyone will be wanting you to fix the ones that don't work ;D ;D.

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Why not just modify the ones that don't work properly?

I've also noticed a lack of circuits in the project section that people here have designed.

I have designed numerious circuits and I'm sure audioguru  has far more that could be added to the projects section.

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Not as bad as I first thought, all this needs is pre-emphasis, just ask audioguru.

What's the bandwidth, approximately what renge of frequencies does this oircuit broadcast on simultaniously?

Does it cover the whole FM band or just a small part of the dial?

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Hi Sasi,
I don't know what is a "J-pole" antenna, and I am sorry I can't calculate range. This much RF power is very illegal.

Many years ago I installed doctors' radio-paging systems in hospitals. Before installing "leaky cables" on lower floors and reducing the RF power, I needed an RF power output of 25W to have not very good coverage of a whole hospital and its grounds. Its RF power was also illegal.
I got a complaint from another hospital about 60km away in another country. My radio paging system was activating their doctors' receivers! Whenever we had a "code blue on the 4th floor", their doctors would rush to their 4th floor. ;D

I think Alun is asking about whether your transmitter is covering the whole FM band because his radio is overloading and causing it. My Walkman radio does, but its local-dx attenuator eliminates it.

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He, he. Your refrigerator was too small!
[move] ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D  ;D ;D ;D [/move] 

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Hi Radiopirate,
On the 1st page of this thread, I posted the spec sheet for the 2N2219 transistor. It shows that it is not possible for it to dissipate more than only a couple of Watts with any heatsink. If it is not tuned properly in this circuit, it will try to dissipate many Watts. :o

Use thermal grease between the transistor and its clip-on heatsink. Use a fan to help dissipate the heat. Reduce the supply voltage to reduce its power dissipation until you tune it. If the trimcaps cannot be adjusted for a peak in the output power, adjust the coils by stretching or compressing them.
Aren't you tuning and operating the transmitter with a proper antenna connected? ???
Do you have an RF field strength meter? ???
With it tuned properly, turn up its supply voltage slowly and stop when it becomes hot.  ;D

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hey all readers  (yes you)

im building the 4w fm transmitter and need a bit of help

1st l1 it says it is 4turns 7mm diameter
but 4 turns of what

and the t1,t2
is a 2n2219 but i cant find that at my local electronic shop is there a simalar sort i could use in stead


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Hi Spleblem,
Most answers to your questions are explained in the other recent post anout this 4W FM transmitter project here: http://www.electronics-lab.com/forum/index.php?topic=338.0

You are going to need a refrigerator for T2 or a clip-on heatsink and a big high-velocity fan. The circuit must have a proper antenna and be tuned to it or T2 will burn-up.  ;D

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