Hi all... I have heard a few of these 'rack audio' SSB stations... and beleive it or not some make SSB almost sound good... (almost) they tend to have a high bass level... high end is cropped... but with a stable receiver they do sound... errrr OK... very 'smooth' response... all things considered that is...
For what ever that's worth ehhh??? 73 Vince ka1iic -.--. On Fri, 26 Jul 2002, Donald Chester wrote: > > > > >From: "Jeff Edmonson" <[EMAIL PROTECTED]> > > > >...the 'rack audio' SSB guys who are adding pre-emphasis, tone-tailored > >audio > >into their SSB rig, AFTER the Balanced modulator... > > Jeff, > > I'm not exactly sure what you mean. You put the audio INTO the balanced > modualtor and rf (in the form of a DSB signal) comes out. Immediately > following the balanced modulator is a bandpass filter to suppress one of the > sidebands. No matter how wide the response of the audio fed into the > balance modulator, the filter will limit the bandwidth of the SSB signal, > except for distortion products generated in the amplifiers that follow. > Maybe the "hi-fi SSB" ops are replacing their bandpass filters with wider > ones to achieve a wider audio frequency response in the SSB signal. The > problem with that is that the skirt slope of a wider filter is not as > steep, so at lower audio frequencies, they lose sideband suppression. > However, I have seen some phasing type SSB circuits using digital techniques > in the audio phase shift nework, that can result in real hi-fi SSB with good > sideband suppression down to 50 cps or so. > > We need to make a distinction between "wide" signals resulting from wide > audio frequency response, versus spurious sideband products resulting from > distortion. Whether AM or SSB, most "broad" signals result from distortion > products (splatter), not the frequency response of the audio itself. I > doubt if a clean hi-fi AM or SSB signal would get much attention from Riley. > It's the guys who don't know what they are doing, and generate garbage way > beyond the normal passband of the signal that are causing the problem. > > At the Dayton FCC forum, this topic came up, and both Riley and Bill Cross > seemed to indicate that the FCC was not contemplating specific bandwidth > limits, because that would hamper experimentation. They said the rules are > intentionally vague in order to allow the maximum flexibility for > experimentation. But the rules do call for "good engineering practice" and > they could use that to go after someone who repeatedly causes harmful > interference with splatter from a distorted signal. > > If activity on a band is light, for example during the daytime on 75 or 160, > or on 10m when there is no skip propagation, I see no reason why a ham > shouldn't run hi-fi double-sideband AM with audio response 20-20,000 cps if > he so wishes. But it wouldn't be good amateur practice to run the same > signal when the band is heavily occupied. It's a matter of common sense and > consideration, not more restrictive FCC regulations. > > On my signal, with the 3400 cps cutoff, the pre-emphasis curve with the > rising response compensates for the loss of highs. Normally, with flat > response, if the highs are cut off at 4000 cps or less, you need to cut the > bass somewhere around 200 cps, or else the audio will sound bassy. There > has to be a balance in frequency response. I have found that with the > pre-emphasis, many report my signal as "broadcast quality", completely > unaware that I am cutting off the treble at such a low frequency. The upper > midrange boost balances out the flat low frequency response. > > With a "bassy" signal, there is a difference between too much bass and not > enough highs. "Tinny" audio is usually the rusult of not enough bass, not > too much treble. Many times I have heard ham signals that lacked any high > frequency response above 2000 cps, and they would get "bassy audio" reports, > so what they would do was cut the bass by reducing the values of some > coupling capacitors, and the rusult was extremely restricted audio, perhaps > 600-2000 cps, and it sounded weak, unintelligible, like a tin-can telephone. > The secret is to strike a balance between the highs and lows. For good > intelligibility, the lows need to be flat down to 200 cps or below, and the > highs up to at least 3000 cps, with a proper response curve to strike a > tonal balance. > > A SSB signal should be approximately 1/2 the bandwidth of an AM signal with > the same audio. The pro-SSB advocates who claim a SSB signal is 1/3 the > bandwidth of AM need to review their arithmetic: one sideband is, by > definition, one-half as wide as two sidebands. The "1/3 bandwidth" signals > can be achieved only by pinching the frequncy response of the SSB audio to > the point of compromising intelligibility. You hear plenty of SSB signals > like that. Next time, listen closely, and try to note how much of the audio > you actually hear, and how much is missing while your brain subconsciously > fills in what is left out. Of course, most ham QSO's are trivial enough > that it isn't hard to do, and in the case of DX contacts "you're 59 in ..." > the vocabulary of conversation is so limited that it is easy to guess the > missing parts, especially if phonetics are used. > > We are not aware of how much information we miss even in normal > conversation. When I lived in France many years ago, I knew a girl who was > a real George Harrison fan. She had a record of one of his songs, and had > difficulty understanding the words. She asked me to write them down in > English for her. I thought it would be easy, since I had heard that song > many times and thought I understood every word. So I listened to the record > and tried to write out the lyrics word by word. I was amazed at how often > I hadn't a clue exactly what the word was, due to slurred speech or the > loudness of the instruments in the background. Casually listening to the > song, my brain subconsciously filled in the holes in the text, and left me > with the impression that I understood perfectly. We all do that every time > we listen to anyone speak. Just try to transcribe word for word what is > said in a recorded conversation or speech. > > That's the only reason anyone can understand so-called "communications > quality" voice restricted to 600-2700 cps or so with a 2.1 kc/s SSB filter. > > Don K4KYV > > _________________________________________________________________ > Send and receive Hotmail on your mobile device: http://mobile.msn.com > > _______________________________________________ > AMRadio mailing list > [email protected] > http://mailman.qth.net/mailman/listinfo/amradio >
