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Is transistor faulty or something else amiss

Audioguru

Sep 24, 2016
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A simple FM transmitter sounds awful without producing low and high audio frequencies. Also its radio frequency wanders all over the place.

My FM transmitter uses the oscillator trimmer capacitor to select a vacant radio frequency and the trimmer capacitor on the RF amplifier is broadly peaked for maximum output power. My coils made with thick enamelled wire are like this:
 

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Devnode

Jul 13, 2015
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A simple FM transmitter sounds awful without producing low and high audio frequencies. Also its radio frequency wanders all over the place.

My FM transmitter uses the oscillator trimmer capacitor to select a vacant radio frequency and the trimmer capacitor on the RF amplifier is broadly peaked for maximum output power. My coils made with thick enamelled wire are like this:
Thank you so much. Now i just need to get some components and i'm at work.
I will let you know as soon as i am done. Wish me luck.
 

Audioguru

Sep 24, 2016
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The law says you must not transmit a radio signal without a licence. The RF cops will catch you if you cause interference to somebody receiving a real radio station. The FM transmitters used for transmitting your MP3's to your car radio have a range of only 1m.
Good luck.
 

Devnode

Jul 13, 2015
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The law says you must not transmit a radio signal without a licence. The RF cops will catch you if you cause interference to somebody receiving a real radio station. The FM transmitters used for transmitting your MP3's to your car radio have a range of only 1m.
Good luck.
Hi, Audioguru. I take note of that. However the transmitter i first tried out was, like you told me, very bad. I exchanged the polyester caps with ceramics and it worked but very unsatisfyingly. So im going to try yours now. Im just waiting for my components then ill be onto it. I learned very valuablevlessons from that transmitter though and from your advice on this forum. Im very gratefull for that. Thanks untill i post a pic of my Audioguru tx on the forum. Be blessed.
 

Audioguru

Sep 24, 2016
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The transistor has nothing to do with the unsatisfying results of the horrible extremely simple circuit that worked but performed and sounded bad.
 

majoco

Nov 10, 2019
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I've made a few of these VHF FM transmitters for various purposes and they usually worked pretty well. My usual problem was finding the frequency - it doesn't need much to send the frequency out of the VHF FM band! There isn't enough power to make a frequency counter work - in the end I used a spectrum analyser at work! You'll need an analogue receiver with AFC - the transmitted frequency is not stable enough for a digital tuner.
Give us a photo of the track side of your vero board - double check that you've cut the holes where required. I'll find one of my old ones and check the coil turns and diameter.
 
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Audioguru

Sep 24, 2016
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In my first post in this thread I said all the problems of this extremely simple circuit and how I fixed them.
 

Devnode

Jul 13, 2015
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I've made a few of these VHF FM transmitters for various purposes and they usually worked pretty well. My usual problem was finding the frequency - it doesn't need much to send the frequency out of the VHF FM band! There isn't enough power to make a frequency counter work - in the end I used a spectrum analyser at work! You'll need an analogue receiver with AFC - the transmitted frequency is not stable enough for a digital tuner.
Give us a photo of the track side of your vero board - double check that you've cut the holes where required. I'll find one of my old ones and check the coil turns and diameter.
Hi, Majoco.
I'm so sorry to respond only now. Reason is i've been working out of town lately and i don't have enough time to tinker for now at least. I hope to be back home by December. I will have some time for my hobby again and upload the photo for you to see.
Thanks anyway for your kindness.
Have a good day.
 
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