Hello,
I need information about transmission antenna tuners. Are they illegal to use
with a part 15 transmitter such as a capacitor/inductor configuration. I was
Hello,
I need information about transmission antenna tuners. Are they illegal to use
with a part 15 transmitter such as a capacitor/inductor configuration. I was
wondering cause the problem is that the 200 in One lab kit transmitter is creating harmonics like on upper parts of the AM band. How do I supress
AM transmission harmonics? I don't want to use this transmitter kit circuit cause of the woefully poor audio quality and also it creates harmonics in
the upper parts of the AM band. Would an antenna tuner help get rid of
harmonics? Also how do you get good range with the transmitter and not
get harmonics?
Adam E.
Experimenter Part 15 Operator/ DJ
Well,dont expect much from these types of transmitters,they are more educational than useful. Now that you are ready to get serious,seek out a quality transmitter which has all the proper filtering and modulator stages needed for good results. I have to say,the SS Tran is a great transmitter at a reasonable price,I'm sure there are others. Search this site for all the reviews... Regards,Lee
If the audio going in is too high level (very easy to do if the circuit originally was supposed to hook up to a little mic or a speaker used as a mic, and you've hooked a CD player to it or something) that can cause an AM transmitter to sound pretty bad. And it can "spatter", putting out all kinds of unpleasant harmonics.
That'd be my best guess considering you're getting both bad sounding audio and apparent harmincs.
But if you reduce the volume of your source player until it's definitely not sounding distorted and you're *still* getting the harmonics then I'd wonder how far your receiver is from the transmitter circuit. If it's too close, even a tiny transmitter can saturate the receiver's front end and result in you hearing what seems to be your signal all over the band. Put 20 or even 10 ft between the lab kit transmitter and the receiver and if it clears it up then that was part of your problem.
A couple questions about the circuit if I may. How many transistors are in it? What are you using for an antenna?
The overmodulation and saturation problems I mentioned could happen with even a fairly good AM transmitter circuit. But the lab kit is probably not going to be something you're going to want to use for on the air. Often those little project kits are just one or maybe 2 transistors and the oscillator is being modulated directly from the sound source, which tends to be pretty unstable and the signal can be as much FM as AM. Not good if you're looking at making a nice antenna to hook it up to and trying for range.
You can still learn a lot tinkering with such things. No reason why you couldn't tinker with some tuning circuits and see what they do for it.
I'd suggest maybe you take a look at Bill Bowden's circuit and note the little pi tuning network right before the antenna that's made up of the 300 pf fixed capacitor, the 140 uH coil he gives instructions for winding and the 30-300 pf variable capacitor. Personally I'd just swipe the variable tuning capacitor out of something like an old transistor radio instead of going out and buying a 30-300 new for the project. You could probably find all the parts you'd need to make it in any old junked radio and it wouldn't take all that long to wind the coil, so why not? Then you can play with it and your little lab circuit and see if a tuner makes a difference. Even look up other types of tuning networks like a T or L type and try those too, if you want to get real educational. They all have their advantages and disadvantages.
I don't know the kit or the exact circuit, but you'll probably want something better for actually being on the air much with. But no reason not to tinker with what you have onhand and learn what stuff does in the meantime.
You *will* hear a lot about Phil's SStran kit. There's a good reason for that. If you went to buy just a box (or a few boxes) of ready-made commercial gear that do what even just the audio section he designed into it does, you could easilly spend more than what he sells the whole kit for. It's a lot of "bang for the buck" circuit-wise, from what I can tell, and enough people here have worked with it that it has quite a following with some folks here. It can seem sometimes like no matter what you ask somebody will tell you to buy the SStran kit (at least if you were talking about building the transmitter), but just bear in mind that it's what they found to be good and they know that you could end up spending as much trying to get a circuit that maybe isn't well designed to sound as good as you'll want. So it's real advice based on their own experience.
But if you don't have the cash onhand for it and you do have the 200 in 1 lab, may as well experiment and see what you can get it to do and what you can learn. Just don't expect great results out of it. But adding a tuning section could be done with just a few parts, the caps being common and the coil being fairly easy to make. So why not?
A word of advice though.. Don't get tempted to up the power on your project lab circuit to try and get more range, since the ones I've seen are usually a one or two transistor circuit where the oscillator is being modulated directly by the audio, and that tends to not be a real clean output. Higher chance of causing interference and getting reported, and if the FCC dropped by and it is also over legal power?.. You could definitely be in serious trouble.
Daniel