Studio1 said:
Kage Michaels said:
... to decouple any RF from the BA1404 chip. Not doing that makes the chip squeal on air for some reason.
I seriously hope you are not using a BA1404 device for on-air work.
LOL for part 15 work yes which it is well suited for.
Besides as much crap flinging as people throw at the BA1404 and other similar FM transmitter chips it's actually not a bad chip for its stereo generator itself for low power transmitters. The problem is with how it's incorporated into cheap kit transmitters.
The problem comes in when using its built in VHF oscillator which is prone to harmonics and spurs because of the oversimplified cruddy oscillator being designed into the same chip.
When using just the built in BA1404 stereo multiplex generator and running its composite output to a well shielded separate PLL oscillator and RF buffer it's quite possible to design a stable clean transmitter with quality stereo separation of well over 50db and little distortion.
Also taking into consideration the removal of any pre-emphasis in the transmitter itself and leaving that to be done by the audio processing chain like that of my original suggestion.
Of course it's impossible to achieve this with a cheap kit like those sold by Ramsey without major modifications which one may as well just yank the chip and rebuild the whole thing from scratch, but keep in mind that some of the more high end all in one box exciters used for LPFM licensed service *that are FCC approved* are built exactly this way incorporating very similar chips to do its time switched DSB-SC ultrasonic L-R channel, L+R baseband channel, pilot generation and so on all in the same device.
Now outside of that long winded comment I must say there is no reason not to use a quality processor with even a cheap FM transmitter kit.
People here forget that Part 15 FM can serve a small community legally, and AM even greater coverage (up to 1/4 mile).
May be flea power but it can still be educational and fun.
Also with the addition of proper audio processing you decrease the spectral content (limiting deviation) of your FM flea power signal thus increasing its range theoretically, and reduce adjacent channel interference which is ALWAYS a good thing.
Using pre-emphasis before the transmitter when placed properly in the audio chain or done directly in the 8100a will also greatly protect over-modulating on high frequency audio content in the transmitter which once again will increase your range without resorting to using higher (illegal) power levels that could interfere with licensed services.
Pirates and part 15 operators always worry about spectral content when it comes to their RF output (hopefully) and that is good to keep in mind and protect so not to cause interference, but it's also greatly important to get your audio spectrum clean so that your stereo pilot stays lit, you don't cause aliasing between audio channels, you reduce useless bandwidth sucking your listener range away from you, and the #1 is sounding good!
