Guest Aliyu Umar Posted February 8, 2011 Report Share Posted February 8, 2011 Hi allI built the below audioguru FM transmitter circuit but the circuit does not provide the said output and Q3 is getting hot. I am getting 3.2v and 1.3v across R6 and R7 respectively instead of 2.03v and 2.25v. but when i removed C5 from the circuit I got required voltage, pls your help is highly welcome. Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 8, 2011 Report Share Posted February 8, 2011 It won't work if you build it on a breadboard or with its parts spread too far apart. It must be made on a compact pcb or stripboard layout like I did.C5 allows Q2 to be a common-base amplifier so it can oscillate. Without C5 then Q3 will get hot without having a signal.But adding C5 to your circuit seems to stop its oscillation which is odd. Quote Link to comment Share on other sites More sharing options...
Guest Aliyu Umar Posted February 9, 2011 Report Share Posted February 9, 2011 Hi AudioguruI used strip board and the parts are not spread too far, please have you design PCB for it?I will be grateful if i can have it from you.Thank you. Quote Link to comment Share on other sites More sharing options...
Hero999 Posted February 9, 2011 Report Share Posted February 9, 2011 It's subjective - can you please post a photograph?You also need to shorten the excess strips.No, he doesn't have a PCB for it and neither do I. If you design one and post it, I would be grateful. Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 10, 2011 Report Share Posted February 10, 2011 I have two pcb designs made by people for my Mod4 FM transmitter.I haven't tried them and nobody said they work.Here is the most detailed one:FM_Tx__mod4._Bottom.pdfFM_Tx__mod4._SS_Top.pdf Quote Link to comment Share on other sites More sharing options...
Hero999 Posted February 10, 2011 Report Share Posted February 10, 2011 Thanks audioguru, looks like I was wrong. Some people have been busy since this subject last came up. Quote Link to comment Share on other sites More sharing options...
Guest Aliyu Umar Posted February 14, 2011 Report Share Posted February 14, 2011 Hi Audioguru,I greatly appreciate for the pcb design and at the same time sorry for not replying quick because i was away. I will go ahead with the construction.Thank you.Hero999Below is the attached photograph of the transmitter, the dimension is 8cm by 5.5cm. Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 14, 2011 Report Share Posted February 14, 2011 Hi Nguroje,Your stripboard layout is similar to mine but is missing the very important 1000pF high frequency supply bypass capacitors. The electrolytic bypass capacitors are good for audio frequencies but are useless at 100MHz. Quote Link to comment Share on other sites More sharing options...
Guest Aliyu Umar Posted February 14, 2011 Report Share Posted February 14, 2011 The capacitor is at the back of the transmitter. Quote Link to comment Share on other sites More sharing options...
Hero999 Posted February 14, 2011 Report Share Posted February 14, 2011 Where's he microphone?Have you checked the pin out of the transistors? Quote Link to comment Share on other sites More sharing options...
Guest Aliyu Umar Posted February 15, 2011 Report Share Posted February 15, 2011 Hi Hero999 as it failed to produce the required output, i feel discourage to test the transmitter with a microphone.They are ok, I checked my connections also several times there is nothing wrong. Quote Link to comment Share on other sites More sharing options...
Hero999 Posted February 15, 2011 Report Share Posted February 15, 2011 How did you measure the output?What transistors did you use? Those don't look like the 2N3904 as it has a metal package but a newer version is available in plastic. Quote Link to comment Share on other sites More sharing options...
Guest Aliyu Umar Posted February 16, 2011 Report Share Posted February 16, 2011 what i mean is that the range am getting from the transmitter is nothing compare to what i read from this forum. They are 2N3904 plastic transistors. Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 16, 2011 Report Share Posted February 16, 2011 Measure the battery voltage and measure how much current the transmitter is using. My transmitter used a brand new 9V alkaline battery that measured 9.2V when new and 8.0V after one hour. The current was 53ma when the battery was new.I measured the range across a huge river valley with nothing in between.I used a transmitting antenna 80cm long and hanging vertically out a window in my home. The home stereo antenna and car radio antennas are also vertical.My FM dial is full of stations so I used the same frequency as a low power foreign language radio station on the other side of my city. Its interference reduced my range.I measured the range to be more than 2km to my very sensitive home stereo and very sensitive car radio, about 400m to my cheap Sony Walkman portable radio and across the street (about 80m) to a cheap "radio" from The Dollar Store.Did you measure the range with nothing in between?With a new 9V alkaline battery? About 53mA of current?With 80cm long vertical antennas?To a very sensitive radio? Quote Link to comment Share on other sites More sharing options...
Hero999 Posted February 16, 2011 Report Share Posted February 16, 2011 what i mean is that the range am getting from the transmitter is nothing compare to what i read from this forum. Are you measuring it by tuning your radio until you hear static which is silenced when the transmitter is turned on or are you using a power meter or oscilloscope?They are 2N3904 plastic transistors. Sorry, I forgot that the 2N3904 does normally come in a plastic package, I confused it with the 2N2222A.Yes you're right, from your photograph the transistors do seem to be connected correctly. Quote Link to comment Share on other sites More sharing options...
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