These modules worked very reliably when sitting only close to each other on a table. When separated by about 20 feet with ordinary office furniture, and a 13 cm wire attached to each (in the middle of the 10 to 15 cm suggested), they were able to communicate, but approximately 20% of messages were corrupted.
Perhaps using better antennas could help, but each board has a loading coil that appears to be designed for relatively short antennas, and no other documentation seems to exist regarding best antennas.
These modules can work well for low performance, non-critical applications. For more demanding applications, more sophisticated (and more expensive) RF modules should be considered.
When using an external antenna a 1/4 wavelength is recommended. Ideally use 50 impedance ohm single-core wire, the length of the antenna 433M is about 17cm (1/4 wavelength). When locating the receiver antenna keep it as far away as possible from shielded areas, high voltages, and any other possible interfering frequencies.
1. Tune your antenna to the proper length. You can use this site to calculate a suitable length depending on frequency. (http://www.csgnetwork.com/freqwavelengthcalc.html). Full wave is most optimal, but ½ or ¼ is next best. You can experiment by adding/trimming length to the antennas. This will reduce your SWR. (http://en.wikipedia.org/wiki/Standing_wave_ratio)
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原文：http://www.cnblogs.com/turtlegood/p/4758363.html