Milli Vanilli Watts

[Mongo82]

Bought one of those car transmitters for fun, 5v choose frequency, led stuck on a board with 5 buttons etc. Quite impressed by something so small how effective. Checked the tiny sa, noise seemed pretty similar to most just a little lower. Anyway I decided to add a wire antenna soldered to board. Checked my tiny sa again and deviated either side considerably, and it wiped the scanning function on my fm/dab radio and some stations. My thought was its a cheap DAB £20 jobby I was right up close to Chinese sprogger. Then thought occurred if like most antennas, could it be because its not to freq. Would it solve that issue? I made a flowerpot antenna again night before, and managed to get it bang on. Not digressing, but could you make a flower pot but thin version using 2bits of 1mm ground wire to make an ultra thin version but with similiar dimensions? Because the wire is so thin I wonder if you might get some gain and ofcourse better results? Probably a dopey question but I'm not too proud to ask...

[radionortheast]

I don’t think its possible to get the bandwidth of an antenna narrow enough for it work as a filter.
I have one without a display, the numbers on the chip are scrubbed off I suspect it is an 8027, the sound quality is very good on it, you’ve got stereo the right pre emp, nothing to mess about with, its a shame the rf signal is very noisy on it, knocks out other fm stations compleatly, there are two duplicates less strong that the main 12mhz either side of the main.

I played about with one of the small lcd ones only yesterday afternoon, someone said reducing the voltage down would get rid of the noise, at 2v there was a nice clean carrier, but it wouldn’t lock onto a frequency, I guess the advice here and else were about dropping the voltage down ending up with some useable dosen’t make sense. I didn't think these 8027 things were useable, I found this from Albert, maybe they'd found some way to config it with their own board, these things are so tiny theres noway you'd be able to solder the chip, sounds like they are set up to produce perfect stereo from the get go with no messing.

I was really surprised by the output spectrum from the QN8027. I expected it to be like the Rohm chips - noisy! They're surprisingly monotonic, with the 19 kHz pilot at exactly 9% of maximum deviation. There's little or no carrier noise when run at 3.3V, but the noise floor rises as the voltage goes up towards the upper limit of 4.2V. We found that there was more noise from the Atmel chip we were using to programme it! We had serious problems getting the digital crud from the logic out of the 8027 carrier. The solution turned out to be a combination if physical separation (we put the SM ICs on opposite sides of the board) and two ground planes - an RF one and a logic one.

I guess the only way to get the stereo would be to pick it up from a radio send it into a mono transmitter, seems like a lot to do, I guess the radio will be filtering out the stereo pilot, as I don't think there is an mpx output on the 8027.

[Mongo82]

radionortheast wrote

I played about with one of the small lcd ones only yesterday afternoon, someone said reducing the voltage down would get rid of the noise, at 2v there was a nice clean carrier, but it wouldn’t lock onto a frequency, I guess the advice here and else were about dropping the voltage down ending up with some useable dosen’t make sense. I didn't think these 8027 things were useable, I found this from Albert, maybe they'd found some way to config it with their own board, these things are so tiny theres noway you'd be able to solder the chip, sounds like they are set up to produce perfect stereo from the get go with no messing.
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I know people moan about Dazaro on youtube on his oscilator manipulation stuff and its not crystal controlled but he does have value eductionally. Anyway he added an rf amp to one of those lcd transmitters but did insist in adding a low pass filter. So would perhaps bring voltage down on transmitter, then into an rf amp which i think gave him 3 watts at 15vs but instead keep the voltage around 9v with the low pass filter? Would that work and be a lot cleaner?