Radio Interference Test Third-order Intermodulation

Test station: W2710C digital radio, a total of three frequencies: namely 225.1250/232.1250MHz, 226.5000/233.5375MHz, 224.0375/231.0000MHz。
Test platform: three with "serial testing assistant" computer。
Requirements: three radio transmitting random data to observe the three stations could receive interference data.
Here are three stations by changing the frequency of cross-communication test results:

What is the third-order intermodulation interference
We know that any linear system there is a non-linear coefficient. Third-order intermodulation is when two signals A linear system, due to presence of a non-linear factors of the second harmonic signal with another signal of the fundamental beat generation (mixing) after the parasitic signal. Such as second harmonic of F1 is 2F1, he produced a spurious signal and F2 2F1-F2. As a second harmonic signal (second signal), another signal is the fundamental signal (first-order signal), the synthesis of the two of them third-order signal 2F1-F2 = F3 (F3 will receive the radio frequency interference ), 2F1-F2 is called third-order intermodulation signal, which is generated in the modulation process. And because the interaction of these two signals generated beat signal modulation, this new generation of signal as the third-order intermodulation distortion signal. Generate this signal is called the third-order intermodulation distortion. As the F2, F1 signal is generally closer to, but also caused 2F1-F2, 2F2-F1 will interfere with the original baseband signal F1, F2. This is the third-order intermodulation interference. Since there will be third order, of course, there are higher order intermodulation, these signals would interfere with the original baseband signal. Because the order of intermodulation generated by the higher signal strength, the weaker, so the major third-order intermodulation interference, to consider more. Through the above test results prove the existing three groups of third-order intermodulation frequencies will not produce interference, the scene of the problem may be caused by external signals.