Re: [AMRadio] Audio response and Long distant QSO's (was: Suggestions Please)
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... e 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
Re: [AMRadio] Suggestions Please
From: "Jeff Edmonson" <[EMAIL PROTECTED]> ...but, running a rig, with an audio response of 50hZ to 5kHz? Where does the "excessive" line stop? When band conditions (congestion) don't permit it. When the band is crowded, I find receiving bandwidth greater than 6 kc/s unuseable. Under congested condx, audio beyond 3.5 kc/s will probably not be heard anyway, so argument can be made that it should not be transmitted, since it only wastes spectrum space. But under less crowded condx, if you can reasonably expect to be able to open your rx bandwidth to 8-10 kc/s, the extra audio can make a difference, and there is prenty of room in the band for other stations to operate besides 2-3 kc/s away from at AM carrier. That's why I have the choice of two low-pass audio filters in my rig. On 10m. I often run with no filter. On the low end, the human voice goes down to about 100 cps or below. The voice sounds more natural when these frequencies are present, but it can be counterproductive to boost them to generate "jukebox" sound. Just keep the transmitter response flat and use a good microphone. If bass frequencies are transmitted, they must be balanced by the highs, or else the signal will sound bassy and will be unintelligible under noisy/QRM condx. I balance my bass by using a pre-emphasis curve beginning at 800 cps and reaching about 10 dB at 2000 cps and above. I then sharply cut off the highs above 3400 cps, or gradually cut them off above 5000 cps, selecting the appropriate passive L-C filter. Don K4KYV _ MSN Photos is the easiest way to share and print your photos: http://photos.msn.com/support/worldwide.aspx
Re: [AMRadio] Audio response and Long distant QSO's (was: Suggestions Please)
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.
Re: [AMRadio] UTC S-21 specification
Thanks, 73, W4AWM
