Kento wrote in post #15181550
Really? Explain to me how Electromagnetic Interference, specifically Radio Frequency Interference or RFI doesn't have an effect on the S/N ratio (signal to noise) of the digital components inside the transmitter and receiver of a wireless system...
The reason is RF in of itself will not increase the noise floor which would contribute to lowering the signal to noise ratio (S/N), you see in order for RF to cause that type of interference three things must happen, first the RF level needs to be high enough to enter the circuit, second it must be picked up by a component of the circuit that is to say a wire lead or printed circuit (PC) board land which acts as an antenna and third the RF must be demodulated to a frequency or frequencies within the audio spectrum. What is pictured above is a Harris 5Kw (5000) watts output AM transmitter (and remember what I stated about AM) and just to the left of the transmitter is the “audio” rack which holds the studio to transmitter link receiver, an audio processor known as an Optimod and some remote control equipment, then note the temp'ed in audio cables run between the rack and the transmitter and add to that this transmitter hut is located within the antenna farm in a concrete building without a Faraday shield, which in other words is a relatively hot RF area and yet there is no interference induced into the audio chain. Need more? What you see above is the rear of a 15Kw output UHF TV transmitter which is installed at the base of the tower supporting gain UHF antenna array giving the station an effective radiated power (ERP) of around 45Kw, note the audio cabling from the rack to the transmitter, yet nary a bit of RF interference, and as if that wasn’t enough RF, consider this, there are three other high power UHF transmitters within the same building also feeding gain arrays, can you say RF city. Wayne
Now with an amplitude modulated signal where the signal strength varies with the level of modulation that demodulation process can be a relatively easy process as any non-linear junction (diode transistor etc.) will do the demodulation, but with a frequency modulated signal the RF level remains constant and is not subject to being so easily demodulated down to the audio level.
That stated we have the following factors which make it tough for the RF of a body pack wireless transmitter to raise havoc with itself, to begin with the internal transmitter only puts out 100 to 200 milliwatts of power which is a very low power level and the modulation for the majority of the transmitters on the market is FM, as such two of the needed components to cause interference with an audio signal are already not present, then add to that the fact almost all modern body pack transmitters utilize surface mount components and extremely short lands which do not provide long enough conductive lengths to become an effective antenna to induce any stray RF into the circuit.
Why does length matter well for example lets take a “D” block transmitter which has a center frequency of 660mHz which has a wavelength of .454 meters or 17.87 inches, now at unity gain which would be a quarter wave that works out to be about 4.46 inches which is longer than the longest dimension of a typical body pack transmitter nor less the tenths of an inch lands on the PC board.
Now should you have any doubts about the inability of 100 to 200 milliwatts of power to cause RF interference consider this.