Re: Improved 1 kHz DSP Audio in New CC Skywave SSB Model


Guy Atkins
 

Hi Gary,

The recordings from the Skywave SSB sound very nice in 1 kHz bandwidth, something I've noticed in my Skywave SSB also.

Do you feel the adjacent channel rejection is as good with the SSB model using its 1 kHz filtering? Or, I wonder if it is spec'd at plus/minus 1 kHz rather than 1 kHz total width? It just sounds to me like there's more audio recovered than I would expect from a 1 kHz narrow filter.

These inexpensive radios with DSP filtering do not have the processor power to get anywhere close to the proverbial "brick wall" shape factor of SDR radios (and I wouldn't expect them to). With that in mind we could just be hearing more audio frequencies as a result of a modest slope to the filter edges. I recall seeing some measured filter plots of one of these SiLabs-powered DSP radios that a hobbyist posted (possibly from an Eton Satellit) and three of the voice bandwidth filters were actually quite close to one another in actual measured width, and the filter slopes were pedestrian.

On the other hand, I wouldn't expect the Skywave SSB model to have a poorer performing 1 kHz filter (letting in more frequencies at the filter edges); maybe the audio gain stages and AGC are simply better in the SSB radio?

I hope someone with more insight into these little DSP marvels than myself can step in to provide more information.

I'm not complaining, as the result certainly does sound great from a signal intelligibility standpoint, Gary! My main question would be--does rejection of nearby domestic channels seem as good as with the non-SSB model?

73,

Guy Atkins
Puyallup, WA

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