during a period of transition from broadcasting analog tv signals to broadcasting digital tv signals , digital tv reception is susceptible to disruption owing to co - channel interference by analog tv signals . during this same transition period usually a digital tv receiver will incorporate an auxiliary analog tv receiver . this auxiliary analog tv receiver is advantageously used during digital tv signal reception for determining the amount of co - channel interference by analog tv signals , so that comb filtering can be selectively applied to symbol coding recovered from the digital tv signal , for suppressing artifacts of co - channel interfering analog tv signal when they are large enough to have substantial adverse on symbol decoding . the amount of co - channel interference is estimated from synchronously detected analog tv signal .