I have about 200+ 900 Mhz XR900 radios installed in vehicles for network access. These same vehicles have 2 way radio's operating at the 400Mhz range. We have confirmed that when a user holds the mic down for about 2 seconds, the 400Mhz radio will completely overpower and/or temporarily block the 900 Mhz signal and the client loses connection to the 900Mhz AP, until the users stops talking on the 400Mhz radio.

In discussion with the 2 way radio tech, he believes this is caused by Harmonics, and suggested we try to find a way to filter our radio's so they are not affected by this. He contacted the manufacturer of the 2 way radio and they indicated that don't have filters to fix this from the 400Mhz side of the equation.

有人遇到这个问题?有这样一个费尔吗ter that would protect the 900mhz client from this supposed harmonic convergence?

Usually the first move would be to physically move each antenna as far apart as possible but as this is vehicle(s) and what type, your options maybe limited, you could try a cavity filter on the output of 2 way radio to supress harmonics, another possibility is RF from 2 way radio coming into the 900Mhz DC power supply lines, the use of RF ferrite beads might help or try a second battery for a quick test, with the number of vehicles I suggest hiring in RF test equipment so any modifications can be evaluated quickly.

It can't be harmonics unless the UHF Two way radio frequency is exactly one half of the frequency of the 900MHz signal. More likely is 'blocking'. In which case there are two solutions, distance and filtering.
Distance, make the two antennae, coax cables boxes and DC power leads for the two systems as far apart as possible. Also makes sure that the 900MHz system is earthed well and shielded well.
Filtering. Adding a filter to the UHF Two way radio will not make any difference if it is blocking, so you add a band pass filter to the 900MHz antenna system.