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SSB Carrier Supression

Discussion in 'General Electronics Chat' started by Space Varmint, Dec 3, 2008.

  1. Space Varmint

    Space Varmint New Member

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    Hey all!

    Before I start posting any schematics I'm gonna do a little research first and ask this panel of experts.

    Here's my question. I'm listening to these ham operators, and I know allot of them got more money in their equipment then I can afford, but still, I am envious of the beautiful signal they put out. I just love how even when they speak there is no carrier heterodyne, just raw speech.

    So I'm looking over some schematics on the internet and of course they want you to buy allot of them which is taboo for my wallet at this time. What I did see was after a guy had filtered the signal, then up converted it just as I am doing, he used an attenuator. Is this the key? Because I looked at some descriptions of high dollar transmitters and it was mentioned that VOX switching was used in some of the linear amplifiers. I'm thinking in the really nice ones they probably use both.

    Anybody know?
     
  2. Boncuk

    Boncuk New Member

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    Google for balance modulator.

    The carrier wave is nulled by an exact opposite phase signal produced by the balance modulator.
     
  3. Papabravo

    Papabravo Well-Known Member

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    It is generally a good practice to ensure that a linear amplifier stays linear. The fastest way to make an amplifier go nonlinear is to overdrive it. The key is to take power output up to the limit but not over it.

    I'll let you in on another secret. You get far more bang for the buck out of your antenna than out of your amplifier. Compare a 100 W transmitter to a 1500 Watt Transmitter/Amplifier combo
    Code (text):

    10 * log (1500/100) = 11.76 dB
     
    A good yagi-uda or log periodic antenna might give you 24 dBi of gain for a fraction of the cost of an amplifier. The difference in dB might not seem like a lot but in performance it is substantial. I know lotsa guys who swear by QRP on top of Pikes Peak.
     
    Last edited: Dec 3, 2008
  4. dave

    Dave New Member

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  5. Leftyretro

    Leftyretro New Member

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    Your correct that antenna gain is the best way to increase effective radiated power and has the added bonus that it also increases your receiver's S/N ratio as the antenna gain is fully reciprocal for both sending and receiving.

    However 24dbi gain is really not achievable in any practical manner in the HF ham bands where long distant SSB contacts take place. Heck, 10db gain is going to cost some bucks especially in the lower frequency HF bands.

    To the OP about quality of SSB generation. Good carrier suppression is but just one requirement for a good sounding signal. Audio processing, bandpass filtering method and bandwidth is also equally important. Most hams these days use quite a bit of audio compression to keep the average RF power output higher while sacrificing a little audio quality for that extra punch.

    Make no mistake, SSB is not a hi-fi quality sounding modulation method, it's designed to generate the best S/N ratio signal for a given amount of power consumed. No power is wasted transmitting a carrier or the opposite sideband. It's power efficiency is it's best attribute, only CW (more code), received with a narrow bandwidth receiver has a higher power efficiency value.
     
  6. Space Varmint

    Space Varmint New Member

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    Hey thanks allot there Mr Papageorgio. I don't think the antenna will effect the carrier though.
     
  7. Space Varmint

    Space Varmint New Member

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    I know. It is awesome aint it? I think it's sounds better than regular AM.
     
  8. Leftyretro

    Leftyretro New Member

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    Well I think it sounds like Sh*t compared to good FM stereo modulation, but like in wine tasting, it's a very subjective thing I guess.
     
  9. Mikebits

    Mikebits Well-Known Member

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    I did not quite follow you. What is the reason for the VOX? A SSB xmitter with a well balanced modulator will not output any carrier until it is modulated with voice. That is the whole selling point of SSB.

    The key here is well balanced modulator. See some of your previous post.
     
    Last edited: Dec 3, 2008
  10. Space Varmint

    Space Varmint New Member

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    Mike! Your still my buddy, man.

    Is that it? That's all there is? I tend to think you will naturally have some noise come through the filter and will mix with an LO and give you some garbage. Follow me here. Remember, I'm up converting from 4MHz so I will have a VFO. Ovbviously I want to transmit on more than one frequency. So you will have another filter which select the output of the crystal filter plus or minus the LO. I saw where a guy had thrown an an attenuator right there. I think that's part of the overall signal performance. Then I did see where some of the big manufacturers were using VOX switching in the amplifiers for whatever reason...???
     
  11. Space Varmint

    Space Varmint New Member

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    Well, if your talking about music, yeah, no doubt. I should have stated A3 modulation. So I'm talking voice communication. I think SSB far exceeds all other types of modulation in quality of signal alone, not to mention the efficiency factor.
     
  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You're not making yourself very clear?, SSB is probably the poorest 'quality' you can use - BUT - it's one of the most efficient, and perfectly satisfactory for voice communications over long distances. Wideband FM isn't an option :D and even narrowband FM (with excellent voice quality) takes far too much bandwidth, and doesn't travel anywhere near as far.

    If you want to better SSB, then move to CW - goes considerably further than SSB, but it's also a lot slower and less convenient.
     
  13. Space Varmint

    Space Varmint New Member

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    All of that is true, but I think your missing the point, and yes it could be a matter of opinion as the other fellow said. Point being, in my opinion, SSB is the best sounding voice communications when done right. Also, not considering efficiency in the argument, it is the most effective mode of continuous voice intelligence. Meaning that it must be the fact that the receiver supplies a steady synthetic carrier that does not fade like the sent information, that the actual fading of the signal tends to be less noticeable and more solid than AM or un-aided (as in repeaters) FM.
     
  14. flat5

    flat5 Member

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    Problem with semantics here.

    Voice sound quality and voice intelligibility do not have the same meaning.

    Carrier suppression will be the result of a good balanced modulator. Good quality will involve all of the audio chain.
    Mic, amps, bandpass filter, carrier/bandpass offset
     
    Last edited: Dec 4, 2008
  15. flat5

    flat5 Member

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  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Of course they have the same meaning. The SSB postings sounded horrible like ducks quacking with zero intelligibility.

    Modern telephones sound adequate with voices because their transducers have a wide bandwidth and low distortion. Old telephones with their carbon mic and tin-can earphone had poor sound quality and poor intelligibility.

    Some cell phones sound horrible. My daughter's new cell phone transmits no high audio frequencies. My son's new cell phone transmits extreme distortion. When used handsfree, both cell phones chop the voices.

    I am watching live TV. When the people speak directly into a microphone the sound of their voice is crisp and clear. TV has a flat audio frequency response up to 15kHz and low distortion like wideband FM radio which produces excellent sound quality and intelligibility.
     
  17. flat5

    flat5 Member

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    I do not agree with you that sound quality and the ability to be heard over noise is the same thing. You are talking about another thread and not the meaning of words. You are also dog minded about hi-fi and want to apply it everywhere. You seem to dislike ham radio too, but I'm not sure about that.
     
    Last edited: Dec 4, 2008
  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The noise from The Varmint's SSB radio came from his poor circuit and from poor selectivity. The low audio frequencies were severely cut to stop hum from the power supply because decoupling was not used. The high audio frequencies were cut to stop hiss from the many transistor amplifier stages and many attenuator stages. Therefore the bandwidth was much too narrow for speech making voices sound like ducks.
    The BFO drifted its frequency which caused voices to sound like chipmunks.
     
  19. flat5

    flat5 Member

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    Once again, you are referring to another thread.
    We do not disagree on the sound of his receiver.
    I live in Holland. I'm well aware of people sounding like ducks :)

    Here, we were discussing carrier suppression and the benefits of SSB. I felt the discussion needed to be clarified as to what was being meant by quality of sound (or voice) and designing so that voice can best be heard through a very noisy environment.

    That is all, over and out. 73s old man. QRT
     
    Last edited: Dec 4, 2008
  20. Space Varmint

    Space Varmint New Member

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    But Uncle Scroogie. It's not supposed to sound high quality. In fact one thing I have been noticing looking over schematics is, alot of these quys go the extra mile to put in audio filters in front of the speech amp. My mike is already tailored to SSB so I think I can bypass that stage.
     
  21. Space Varmint

    Space Varmint New Member

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    Did you notice he said, "don't use an rf amp"? He stressed that with a big NO NO NO!

    Huh, this might be a problem. I better change my oscillator to a crystal osc. The problem is, I want to adjust for upper and lower sideband using one crystal but don't think I can warp it that far.

    What is the recommended difference frequency again? It's like 15K apt it?
     

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