AMband.org

The National Radio Systems Committee has issued two revised AM standards and deleted the NRSC-3 receiver specifications standard as obsolete on September 26. The revised standards are NRSC-1-A and NRSC-2-A. NRSC-1-A specifies the preemphasis and deemphasis curves and bandwidth limitations for AM transmission, while NRSC-2-A sets the standards for RF emissions from AM stations. The NRSC intends to publish the revised standards as soon as a procedural review is completed, in about four weeks.

The NRSC also adopted a guideline for recommended bandwidth for AM transmission. NRSC-G100 provides guidance for operators who would like to decrease first adjacent channel interference by operating with bandwidth narrower than the 10 kHz limit. Using the full 10 kHz bandwidth is lost on most receivers, as nearly all receiver IF filters limit audio response to much less than 10 kHz. Benefits from this technique are limited to cases where the licensees mutually agree to bandwidth reduction of stations that interfere with each other.

The National Radio Systems Committee has released a study on the effects of reducing the bandwidth of AM transmissions from the present standard of 10 kHz.  The study used representative receivers to present transmissions of speech, sports, music and commercials with bandwidths of  5 kHz, 7 kHz and 10 kHz.  The study assumes that both the desired and undesired stations operate using the same standard.

The results showed that mutually reducing transmission bandwidth down to 5 kHz  is a big plus for speech.  There was either a benefit, or no change from the 10 kHz results when reducing the transmitted bandwidth to 7 kHz irrespective of format or first adjacent channel interference level. (more…)