Total posts : 45366
Don’t apologize for your “barrage” of posts. That’s how you will learn and that is why this board and we posters are here, and here is a learning opportunity for you:
If you think your transmitter is clipping a simple way to verify this is to reduce the audio amplitude into the transmitter. At very low input volume do you still hear the distortion? Things are complicated apparently since the transmitter has some AVC built in which may function to keep the audio at an unacceptably high level regardless of the feed volume.
Now for some unpleasant information which many don’t like to hear yet it is what it is and it can keep you out of trouble. According to the specifications from the manufacturer and your reported range test results your transmitter is illegal with respect to part 15 rules. Since you are new to this I am offering the following information, but keep in mind that FM hobby transmitter operation can be legal and if you read on, you will gain information about this.
First, it is not legal to sell in the US an assembled transmitter which is not FCC certified and your unit is apparently not. This is between the seller and the FCC and shouldn’t be a problem for you except when you are caught operating it outside the limits of the rules.
Kit transmitters such as the Ramsey line are legal to sell without this certification yet keep clearly in mind that the use of such devices outside the FCC rules places the burden on the user and not the kit provider. There are others such as the Belkin and CCrane lines which are assembled and certified and should be no problem to put on the air.
The FCC rules do not specify the power output of an FM transmitter; they specify the field strength at a distance and this has nothing legally to do with power. A transmitter which provides 500 mW of power will certainly produce a field strength which exceeds the limits and will be illegal to use with almost any antenna. In fact, it is commonly known that a power of around 11 nanowatts (500 mW is about 45 million times this power) using a 30 inch antenna will produce the maximum legal field strength. A legal field strength with a typical receiver will produce a range of just a few hundred feet as opposed to what you have reported with your transmitter.
You may choose to continue but you should know what consequences you may have if you are caught and cited by the FCC.
Now for some encouraging information. Many of us use and enjoy our part 15 FM transmitters and stay out of trouble. There are two ways to do this. Purchase a FCC part 15 certified transmitter and use it as instructed or build one from a kit and set the range to about 200 feet or so and enjoy your on the air time. Using a “500 mW” transmitter is just inviting trouble, especially since your signal is apparently not clean. I advise returning this to the manufacturer and getting a refund and then doing some research, such as asking questions here, about how to do this legally.
Any questions from you or others regarding this are welcomed and I will do my best to help.