2 Pieces Digital FM Transmitter Module Stereo FM Transmitter DSP PLL 76.0-108.0MHz Stereo Frequency Modulation with LCD Display Line/USB/Mic Input, DC 3.0V – 5.0V

The two units came in anti-static bags. The only documentation is on this listing page.They work right out of the bag with micro USB power connected and no antenna. Adding an antenna is necessary for better range (reception over longer distances).There are volume and frequency up/down buttons as well as a mute (“pause”) button. For the frequency buttons: If you long press, they will go up/down in 1 MHz units steadily (i.e., release button when you reach the value). Short presses increment/decrement in 0.1 MHz steps.USB to FM: Plugged into my Macbook Pro, it appears as a USB audio output device, and can broadcast system audio to the displayed FM frequency. This is handy, considering newer Mac’s lack headphone outs. The device’s microphone is not available as a sound input device via USB.Mic to FM: If I plugged the unit into a power supply, (either USB without a data connection, or the solder points) the microphone became active. The mic signal is actually excellent, with a clear and full response.Line Input to FM: With an external media player plugged into the line input, the mic is disabled. The line input’s sound quality is also excellent. It has full frequency range, and the dynamic range is as good as can be expected from FM. A couple of times, I experienced some unexpected background noise, but I suspect it was unrelated to the transmitter.There’s an option to connect a single-wire antenna with a thru-hole solder connection. The instructions recommend a 75 cm telescoping antenna. However, as my use is just around the house, and I wanted to keep the unit more portable, I just soldered a 12-inch length of 18 AWG solid copper wire. I can go around my house (away from the transmitter) and the signal strength is quite good.There are also two thru-holes for power, which are clearly labeled. It says 3.0-5.0v. I soldered a 3-AAA battery holder to those points and it works perfectly, even with rechargeables. The seller recommends disconnecting the external power source when connecting to USB (so it is not receiving power from both at the same time).I’m SUPER pleased with this purchase. Getting a two-pack makes this an unbelievably good deal. It’s a truly excellent product at a great price. I bought another 2 pack.Though this transmitter does offer “campus” bands (additional frequencies below the standard range), I’ve never needed these, as I’ve always found some available frequency.UPDATE SEP 2024: Units are still going strong. Another review mentioned that USB did not work with their more recently purchased units. I also had purchased again more recently and find that the USB works as before, even with a recent Mac.I’ve been using one of these transmitters with a 12″ wire antenna, along with a small MP3/FM player, for my in-ear monitoring system. When I arrive at the venue, I find a quiet, unused FM frequency on the MP3/FM player. Then I set the transmitter to that frequency. I feed my monitor signal into the FM transmitter. After setting correct levels, it just works. I’ve used it on 20 gigs and never had an issue. Sounds fantastic.