ComPol, Inc. is the technology leader in SCA. The reason is our unique approach to the reception of SCA. In the mid 1980's it became clear that the traditional methods were inadequate. When a signal is received, it contains not only the subcarrier(s), but the main channel, the stereo, the RBDS, and a lot of noise. Before the signal can be recovered it must filtered from all the other contents of the station's transmission. This requires a filter that is wide enough to include all the components of the SCA signal and and narrow enough to rejects everything else. The only practical method of making filters at subcarrier frequencies is with coils, capacitors and resistors. The complexity and expense of an ideal filter would make the receiver too expensive. There are, however, inexpensive filters made of ceramics that are nearly ideal, but their frequencies are too high.
The solution was to use a process call heterodyning. This process allows two frequencies to be added or subtracted to achieve a new frequency. Thus if the subcarrier is 67 kHz and the inexpensive filter is 455 kHz, a third frequency of 522 kHz will cause the 67 kHz subcarrier to become a 455 kHz signal that can easily be filtered. (522 - 67 = 455)
The result is a simple and inexpensive replacement for the coils, capacitors and resistors. Because the filter is almost perfect, the signal has excellent frequency response, low distortion, and low noise. Furthermore, alignment is simple and will not drift over time, temperature and vibration. This approach makes mass production of quality SCA receivers a reality.
ComPol has acquired US Patent No. 5,023,933 for this technology.
The quality of the ComPol receiver is also a result of careful design. The problems encountered by the users of SCA receivers can be traced to specific causes and then rectified. We have sought out and rectified those problems and the result is a nearly ideal receiver. On our Products Specs page, we show typical performance characteristics. In reality, these values are almost worthless. There is no standard method of measuring SCA performance, and laboratory tests do not accurately simulate real-world conditions. We can only recommend a real-world evaluation.