Will FM SCAs (67 & 91 kHz) be protected with the addition of the HD Radio carrier? Will it be possible to continue the SCA signal when the analog carrier is eliminated?
Both the 67 kHz and 92 kHz FM SCAs are protected and can continue to operate when the system is operating in the primary carrier mode (digital carriers start at about +/- 129kHz). There is a slight (2 dB) degradation in the signal to noise ratio of the 92 kHz subcarrier. However, this has proven not to be a problem and several stations running 92 kHz subcarriers and IBOC have not had interference problems with their 67 or 92 kHz SCA channels. It will not be possible to transmit the analog subcarriers in all- digital mode. When HD Radio goes all digital, the functionality of the SCAs will have also been converted to all digital, by that time.
