UCEC XY-MK-5V / XY-FST 315Mhz Rf Transmitter and Receiver Module Link Kit for Arduino/Arm/McU/Raspberry pi/Wireless DIY(6-Pack)

These work pretty good once you have the antennas soldered correctly, cut to the right length, and receiver tuned.For 315 MHz, 1/4-wavelength is 23.8 cm, or about a 9.4" long antenna. But the transmitter and receiver have small loading coils on them (I'm assuming this is so the antennas don't have to be as long). Based on my rough estimate, the tx antenna length should be about 6.5", and the rx antenna length should be about 8.25".The antennas should be soldered so that they are connected to the transmitting end of the loading coils on the boards. For the receiver this point is fairly obvious, but the tx has the "ANT" print in the wrong location. The hole that is connected to the coil is on the side of the board, NOT the top (where one might expect it to be based on the print. I suspect this is the reason why some are having range problems.Once you get the antennas soldered and cut to the right lengths, you still have to tune the rx. For this purpose I used the Radiohead library and a sample sketch (I used an arduino board) which sends "Hello World" over and over again via the tx. Running the rx sketch on another arduino across the room, I turned the tuning knob until I saw "Hello World" on the serial monitor.Once I got the tx and rx tuned, I went outside, and was able to get about 250 feet line-of-sight before I lost comm. I might be able to get more distance if I tune the antenna lengths better (I just based mine on rough estimates), but I don't have the equipment (and patience) to do that. I wasn't too sure how the loading coils affected antenna length.

I tested two and they worked well. I sent a message from the transmitter about 50 feet (using 5v from Arduino) to the receiver. Then I taught a class using them and not all of them worked that way. The class was a disaster so I guess there is some pairing technique I didn't know about. They have the potential to be awesome with better documentation and tutorials.

The transmitters included in the kit came with two different part numbers marked on the resonators, 3 each "R315" and "R315a". The R315 resonators measured between 314.925Mhz and 314.98Mhz on my frequency counter. This is within spec. However, the transmitters with R315a resonators measured out at 315.10Mhz, 315.14Mhz, and 315.18Mhz. This is well outside of acceptable limits on the datasheet, which specifies a maximum frequency of 315.075Mhz. They're so far out of spec that I wonder if the R315a resonators were manufacturer QA rejects that ended up sourced at a discount and built into these transmitter boards. Being that far off frequency causes poor reception quality. As such three of the transmitters are likely not usable.The receivers I also had poor luck with. I could not get any receiver to work at a distance of more than about a foot from any transmitter. I did try aligning one of the receivers as suggested in reviews here, but I only gave it a limited amount of effort, and failed to improve performance. If your intent is to receive these signals on a raspberry pi, then using an RTL-SDR dongle as a receiver will be far superior to using one of these receivers. If your intent is to receive with something that has less compute capability, such as an arduino, then I'm not sure what you should do -- maybe put some real effort into alignment and you can get better performance than I did.I did attach antennas to the receivers and transmitters as suggested in reviews here.So why did I give it three starts instead of one star? What I was really interested in were the transmitters, three of them were usable, and the price was pretty good even if half the transmitters were not usable. I'd have probably given it 2.5 stars had that been a possibility. If you buy these, I suggest you be prepared to individually evaluate the transmitters and accept the possibility you might have some duds in the mix.

Really frustrating. Some did not work at all and had solder smears on the back. Using just the 5V usb, the range was about one inch line of sight. With antennas soldered on, that doubled ( I used Ryan H's review for this info- thanks). I finally hooked them up to a 12 volt power supple and am getting the range I need. At least on two pairs so far.

These work OK. Unable to get more than 2 feet away from transmitter - maybe antenna issues. These are cited as 315 mHz; most are 433 mHz. That will affect antenna length. Be good to know in advance the recommended antenna length. Good for learning about RF control. Simple and easy to use. They all seem to work.

I can't believe how good and consistent these work. I soldered on an antenna and they work without fail with an Arduino Nano and a small battery pack for hours and days on end. Used a little library called Radiohead Library, which is pretty straight forward and makes these boards work really well.

40% of the transmitters did not work out of the box. I've not checked all the receivers but the two I used worked.

the ranges were abysmal. I'm still working on trying to increase them , non of the antennas I've put on them has helped.