On 5/23/2018 12:54 AM, Richard Lamont wrote:
Jim - in this context, are you using the definition of "occupied bandwidth" as in ITU RR 1.153, i.e. 99% mean power? If so, how do you do that with the P3 SVGA?
For CW, I transmit a long series of dits, put the P3 in peak mode, and accumulate peaks. When the display stops changing, I freeze it, use the cursor to manually log enough points to define the curve on both sides of the carrier, starting at -20dB carrier and every 5 dB until the data falls off screen. I then save the screen to a file.
I've done essentially the same thing with RTTY and PSK. For SSB, my test signal is bandwidth limited Pink Noise. Pink Noise is widely used as an audio test signal because both spectral balance and dynamics are a good first approximation of speech. Pink Noise is defined as equal power per percentage bandwidth, whereas white noise is equal voltage per Hz. Pink noise can be though of as white noise with a 3dB per octave rolloff. That's not easy to generate -- an RC rolloff is 6 dB/octave.
And this important comment. NC0B uses White Noise as a source. This is VERY BAD practice, because it puts nearly all of the modulation above the voice spectrum, and greatly de-emphasizes speech. I've corrected him on this three times, first as long as five years ago, yet he continues to do it wrong. The importance of this is that GOOD audio processing is designed for the spectrum and dynamics of speech, so any audio test signal should approximate speech as closely as possible. Rob is a great engineer and does ham radio a great service with his testing, but he fails to even attempt to understand the difference between RF and audio.
As to my credentials to say this -- I spent 40 years in pro audio, with much of my work directed to sound systems for both speech intelligibility and music. For 20 years, I've been a member of the AES Standards Committee, and of Working Groups on Speech Intellibility. About ten years ago, I was elected a Fellow of the AES.
73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
