Re: uBitx Modulation only lows no highs in frequency response
Hi Jerry,toggle quoted messageShow quoted text
That is a pretty good description. I have my BFO set so that the incoming signals start rolling off at 300 Hz just as you have described. A few decades ago when we were looking at "compandered" SSB we were shown that the human voice has three main 'bands' of audio spectrum that are required for intelligibility. The lowest band is at 300 Hz. there is a mid band (I don't recall the frequency range) and high band around 1500 to 1800 Hz. Compandering used some Rube Goldberg approaches to squeeze those bands all together (with multiple filters and mixers) so as to reduce the RF bandwidth used to transmit it. There was also some kind of pilot tone to help sort it back out at the receiver. Did I mention Rube Goldberg? It kind of worked in the lab. But not in the wild.
So our SSB filter would like to bridge all of those bands without mashing or bending them. Even with the narrower passband of the stock filters in the uBitx we can get all of that fitted in if the BFO presents that lowest frequency band at about 300 Hz (as you have described). The high end will be close to 19 or 20 kHz. Mine is right around 1900 Hz. "Narrow SSB filters are designed and installed with a 1.8 kHz bandwidth. So the uBitx filters are at the narrow side of SSB. They may sound a little better for armchair chatting at 2400 to 3000 Hz. The bottom end still wants to be rolling off stuff starting around 300 Hz and the wider passband used to to increase the high end of the audio spectrum.
That will probably be very good for digital operation too. I am a CW guy and it does nothing to hurt CW either. I have several times outlined how to set the BFO this way by using the noise shadow displayed on all of the digi-mode screens and the audio frequencies shown on the scale below it. If yours is working well for you just go take a look - without changing the BFO. The noise starts to drop off about 300 Hz on one end (or wherever your is actually set) and the other end it starts dropping off well above 1800 Hz. With CW (or other narrow) filters that noise band is obviously much narrower and the width of that 'noise shadow' is much less - as expected.
On 07/22/2018 10:29 AM, Jerry Gaffke via Groups.Io wrote:
You got it right.
bark less - wag more