Blue one that EFR checked out as well, seems he measures a bit less harmonic and nothing below carrier.



VCO PLL - seems to be terrible according to him - 6 months old -45db or so in aircraft band



And this follow up of same one :



The reality of these is just cause they sent him a best case scenario review one what they might send to others remains completely unknowable so something you might get will have a strong second harmonic, they may just have doctored the one they sent for a review.

If they can get the second harmonic down to - 40 or so why cannot the fools who make this stuff add a low pass filter that would cost them $4 with minimal power losses 4 coil/4cap.

I don’t know if it was these but I liked it were he showed the difference between mono and stereo, it was a bh number chip, (a slinky number ) it was like a hedgehog when stereo was activated in mono it seemed alright, with a bh chip you could connect your own encoder, thats why they ended up with an mpx input.

i think they made an error trying to power it on 13.5v, i think they were maybe thinking, they would get extra watts, likely putting high voltage into the chip. (maybe it could end in a chip pan fire ) i was waiting for them to switch the scanner to nmb mode, they would hear the carrier drifting off frequency it was abit disappointing, they didn't show that.
testing something to see if it gets warm is a good test, specially of an rf output device, it takes a while for power supply to get warm, your best off looking at the voltage seeing if it drops, know if the power supply can handle it. if its been run to the max their might be different loading conditions so it might blow anyway, relax with the max lol

A bh puts out small spurs close to the aerial, likely hear it in ajoining rooms on other frequencies, likely with an aerial indoors, the qn puts out noise which covers the fm band which goes out further, with 5-7w with a loft or outdoor aerial it would be unlikely for your neightbours to hear anything on fm. The best option is if you wanted something to go to pcs buy something that isn’t a chip, stereo encoders will have a filtered output, which the bh chips don’t have, I suppose then you can hear shania without bothering anyway.

Theres not a tx that dosen’t have a filter, i think what people are meaning when their adding an extra, the amplifier isn’t good quailty so will spur without a match, its kind of stab in the dark that it works for them, without changing values of c. If you make a filter you connect to the back of any transmitter, changing the values of c get the perfect match, none of the signal will lost, get rid of spurs the amp maybe creating from having an imperfect match, it won’t take away the other stuff that the chip is creating, if it is one, which it doesn't have to be.

I think it was EFR who tried out one of these or a simliar one, i’m guessing it might of been a bh chip, with them been able to pick up other stations.

Please stop wasting everyone's time with these worthless noise generators. NONE of the "transmitter" ICs are capable of truly clean operation (at ANY supply voltage).

These ICs were developed for just one purpose - to allow cordless connection of a portable CD or MP3 player to a car radio from inside the car's cabin. They were NOT designed to be amplified: they would just generate a couple of milliwatts of RF - possibly with a crude switching stereo coder as part of the deal - and that's it. Spectral purity wasn't an issue, because the signal strength was so low that it wouldn't get far outside the car. A PLL was included in later ICs, to keep the things on frequency, since most modern car radios also have PLLs for frequency stability.

The very first time I saw one of these things, it was in a little metal box, with a car aerial socket in it and a coaxial lead with a car aerial plug on the far end. There was also a +12V lead to power the thing. It was designed to be plugged directly into the car radio, and the car aerial was to be plugged into this little metal box, and there were a stereo pair of coaxial leads with stereo 3.5mm plug on the end coming out of the box, to plug into a CD or MP3 or cassette player. As I recall, it was a "Yamaha"-branded effort, and it could be tuned over part of Band II by means of a screwdriver adjustment. It didn't have a PLL, and it drifted!

If you want a cheap rig, learn how to build a proper one yourself. There are kits around for beginners, and they're not difficult to construct if you know how to solder neatly. If carefully constructed, you'll find that the output will be clean (many million times cleaner than one of those "audio sender" ICs), and sensible choice of operating frequency will avoid interference to other services. Forget these Chinese sprog-boxes!