Most hams want to do the right thing when it comes to operating on our very limited frequencies. That means keeping our signals as narrow as we possibly can to reduce interference to others. The FCC rules state that we should operate with good amateur practices and have also said that voice bandwidth using communication quality audio is appropriate. I have never heard any interpretation of the rules by FCC spokespersons that indicated that any width was acceptable. That is why wide bandwidth modes, such as "narrowband" FM are prohibited below 28 MHz.
The only reason we tolerate the use of the extremely wide band AM mode is due to "grandfathering" the mode due to the historical background. Also, it is a mode that can be homebrewed much easier than SSB and most importantly it is rarely used. You may find a couple of nets on a given band but that is about it. If a large percentage of hams operated wide AM, or even wide ESSB, there would be a strong call to completely eliminate those modes. If several hams wanted to run full audio DRM at around 10 or 12 kHz, it would not take long for us to petition the FCC to prevent further use of such inappropriate HF modes. As it is, the upper 10 kHz of 75 meters is rendered nearly useless in the evenings due a SWBC DRM station here in the midwest U.S. It causes a drastic increase in the noise floor of that part of the band. While we can not do much about it coming from a commercial SW station, we sure would not tolerate it for long if many (any?) radio amateurs started this kind of operation on HF. 73, Rick, KV9U expeditionradio wrote: > > Hi Rick, > > In USA, there is currently no bandwidth limit for a digital voice > signal on HF. > >
