CCMC30 Common Mode Noise Filter

Noise filters are nothing new and are often used for transmitting purposes. They are used to prevent unwanted radiation via the coax shielding. It is less known that they can also suppress unwanted radiation when receiving signals, especially when an active antenna is used. However, in this case, the situation is reversed: en route to the antenna, unwanted interferences from electric home appliances can be effectively eliminated.

NTi’s Coaxial Common Mode Noise Filter (CCMC30) has been especially optimized for maximum common mode noise rejection of >30dB wide band in the frequency range of 150kHz – 30MHz. With slight limitations a much wider frequency range is covered. In the medium wave range for example a noise suppression of up to 45 dB can be achieved.

This is possible by using a cascaded system of ferrite cores with various frequency dependent material properties, combined with high quality coaxial cable. For outdoor use, the system is housed in a water-proof enclosure. We recommend to connect the CCMC30 as closely as possible to the receiver.

With regard to efficient noise suppression, the CCMC 30 is not very much different from the galvanic isolator GI1000. However, the CCMC30 performes down to lowest frequencies including DC voltage, in contrast to the GI1000, which blocks DC voltages and very low frequencies. The CCMC30 can thus be connected directly to the coax cable which passes the supply voltage or the control signals to the active antenna. Even a cascaded use of the GI1000 directly at the receiver input and the CCMC30 following it directly after the coaxial power inserter can in some cases lead to an increased efficiency. Especially in the lower frequency range, surprising improvements can occur: