Broadcast Devices LPF-100 Composite Low Pass Filter

The LPF-100 Composite Low Pass Filter is a modern approach to filtering FM composite base band stereo audio. The LPF-100 offers at least 15 dB of noise reduction at 67 KHz and more than 30 dB of attenuation at 100 KHz. Distortion generated by aggressive processing techniques, noisy STLs and stereo generator birdies can now be suppressed effectively without materially impairing stereo performance. The LPF-100 is a tenth order, linear phase filter approach that is designed to work with any stereo generator output. The unit accepts 3.5 VPP base band audio and provides three level controlled, isolated 3.5 VPP nominal filtered outputs.

The LPF-100 FM Stereo base band low pass filter is a 10th order, linear phase electronic filter that is designed to reduce base band noise levels while not materially affecting stereo performance or modulation depth. The LPF-100 can be used when noise from studio to transmitter links, processing equipment or stereo generator anomalies interfere with SCA performance or where noise levels are high enough to induce multi path like effects in received signals. The experts will tell you that the best low pass filter is a linear phase filter that offers good step response, low ripple in the pass band and little non linear group delay in the pass band. These are essential characteristics of an FM stereo path for good stereo performance. Poor phase response results in poor stereo separation due pilot phase error. Poor amplitude balance causes cross talk between main and sub channels resulting in poor stereo separation. The LPF-100 offers minimal group delay error and good pass band amplitude response. Phase and amplitude errors are within the correction range of most modern stereo generators. Because the LPF-100 has low overshoot, it doesn't rob your station of modulation. What you get in return is reduced base band noise resulting in better SCA performance and low cross talk.

Minimizing noise in the stereo base band has another important benefit in today's digital broadcasting environment.Less transmitted noise from your analog transmitter means better mask performance when adding in band on channel digital broadcast carriers to an existing system. Less interaction between analog and digital signals is a plus for better digital performance.