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Deadkey vs swing

Discussion in 'CB and Export Equipment and Accessories' started by Simbalage22, Jul 23, 2010.

  1. Simbalage22

    Simbalage22
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    for all those that dont already know I have a Cobra 142GTL base and a little Texas Star 250 High drive. My question is whats better a low deadkey with alot of swing, Or a higher deadkey and less swing? I only ask because my 142 is currently set with a little under 2w dead key and swings slightly to 10.. People say it sounds really good and the modulation is clean.. So do I leave it or should I step that deadkey up a bit.. Furthermore if one has a mobile radio with/and without and amp what settings would be best? Basically how does deadkey and swing work together and whats the best setup with an amp and without one... and where does high drive fit into the equation?


     

  2. W5LZ

    W5LZ
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    Two good questions!
    An amplitude modulated signal is composed of two parts, a carrier ('dead key') and applied modulation ('swing'). The relationship between the power levels of these two signals determines the percentage of modulation of that AM signal. That percentage of modulation can be too low and too high, there's a 'sweet spot' for modulation. That usable range of modulation, the 'sweet spot' determines the efficiency of that signal and it's audio 'quality'. It runs from about 80% to 100%. Any less or more than that and you have a loss in 'quality' and efficiency. Why a 20% range in modulation percentages? Because a human voice has about that difference in volume and tone (that's probably not the best way of expressing that, but it's close enough). Music has an even greater difference in tone quantity and range. Music requires a wider frequency range which means that the resulting AM signal will be wider, 'fatter', than a voice signal of the same modulation percentage (why AM broadcast stations are spaced wider apart).
    So what happens when the modulation percentage is less than about 80%? The resulting signal sounds like it's sort of muffled. If the modulation percentage ever goes above 100% the result is a drop in output power or efficiency. That may seem 'wrong', but it's not, it's a fact. The addition of that carrier and modulation signals produces a 'zero' modulation for some fraction of a second, which means no power output for that fractional second, and that means a reduction in output power. That's where that 'backwards swing' comes from, and what it means. The percentage over 100% modulation determines the length of that 'fractional second' of no output power, so the greater than 100% the signal the longer that time fraction and the more 'backwards swing' there is. Small increases over 100% produce smaller time fractions of zero signal so the less 'backwards swing' you see, which may not even be noticeable. It's easy to see if you use an oscilloscope to look at the signal. There appear to be 'gaps' between the 'bumps' on the scope. Those 'gaps' are at the zero power line of the displayed signal, which mean that there's no power being measured so no output.
    {I can't show pictures of that cuz I don't have a scope and the other equipment required to do that. I also have problems posting pictures on forums! So if you want to see it, find someone who has the equipment or pick up a standard electronics text book which shows it happening. All things considered, find the text book, there are lots of people with scopes who don't know how to use them!}
    A too much or too little modulated signal sounds 'bad', and also wastes power and time. You decide how much you want to sound bad and waste power and time. Increasing or decreasing the carrier/'dead key' level in relation to the applied modulation/'swing' determines that percentage and efficiency. The standard ratio is 4:1, modulation to carrier. That does -<NOT>- mean you do the measuring with a watt meter, but with an oscilloscope! If you use a watt meter, it's a 2:1 ratio, that watt meter only measures the 'positive' half of the output power, it can not measure the 'negative' half! So, cut that '4:1' ratio in half, making it '2:1'.

    Ready for this??
    Am amplifier doesn't know beans about carriers and modulations, 'dead keys' or 'swing'! It only knows one thing, if the applied input power is too much or not. If that input power isn't very much, then the amplifier doesn't have much to amplify, so is working at less than 100% (which is good!). If the input power is too much, one of two things happen. Either the resulting (amplified) signal is distorted, or, the amplifier dies from being over fed. A distorted signal means lots of power, but that power is wasted cuz it isn't much in the same 'shape' as the signal coming in. Why have a very loud garbled signal? It's much better to have a less loud signal that's easily understood. Of course, that just depends on if you just want to be loud, or have a good signal, big difference.
    So why do people use 'dead key' to set how an amplifier is working? Because it's easier to do than doing it right! If that amplifier is built to standard specifications, the right ones, then you can get away with doing it that way. It won't be the best tuning in the world, but it'll be close. Those 'standards' assume a few things. The modulation percentage is right, the amplifier circuit is right, and the users knows what they are doing. There are so many variables in those things that I wish I had a penny for each! I'm sorry, but there are NO STANDARDS with 'CB' amplifiers, doesn't matter who makes them. And all bets are off for legal commercially made amplifiers when they are used incorrectly (which also means on the wrong bands). Wanna do it right? Great, then learn how to do it right, which ain't easy or simple. There is no such thing as 'Plug-n-Play' with radio stuff unless you are willing to put up with less efficiency, or a reduction in capabilities. You can cover that with 'air freshener', but the 'stink' is still there, it didn't go anywhere. If you are satisfied with hiding the 'smell', good for you. If not, then why not just do it right and not have the 'stink' at all?
    It's up to you.
    - 'Doc
     
    1 person likes this.
  3. Wire Weasel

    Wire Weasel
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    Your current set up is just right and it is sound good. Leave it alone.

    So where'd that "to swing or not to swing thread go?" Y'all know...that one that was as long as a book and all kinds of people were getting killed over it? Man....that thread cost thousands of lives and millions of dollars ! {Animal House}
     
  4. Simbalage22

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    Thanks for the wonderful info.. But its basically telling me no answer other then its beyond the scope of plugNPlay, and read a book on scopes. My question still remains should I bump up that deadkey..I know too much will make it sound like garbage and will possibly blow the amp, But where is the balance.. You said 4:1 with scope... 2:1 with meter but nowhere do I see how.. In Noob terms what is good starting point for deadkey with an amp, and a starting point without one? I understand all the theory, but I need realworld simple answer.. Sorry as I am new to cb's not electronics nor amps and how they work.. Just how I would get the max clean sound out of this radio, and get a general idea when working with radio's and amps where to set the deadkey..

    Example: Stock radio.. Is it better to have the deadkey high and have little swing, or lower and have more swing.. And how does this differ in everyday terms when using an amp
     
  5. Highlander_821

    Highlander_821
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    Tell me this, when you are using the amp with that 2 watt deadkey from the radio, what does the amp deadkey without modulation? It should be around 45-55 watts. If it isn't, adjust the radio deadkey up or down until you get it somewhere in that range.

    High deadkey with small swing=undermodulated (bad). Low deadkey with huge swing is overmodulated (also bad). Deadkey at 1/4 of full modulated power is just right. You are pretty close to that now (a little over) but since you are running an amp, a little more swing will probably be ok.

    But check what the deadkey coming out of the amp is with no modulation, and let us know what that is.
     
  6. Simbalage22

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    THANK YOU!!! OMG short and to the point.. I need to get another patch cord to check the power after the amp. I know stock radios are at 4W and mine is a little under 2.. So thats why I asked. You wouldnt happen to know what the max power the 142 can be set to confortably would you? I was told how to adjust the deadkey, but dont know how to get more max power.. Basically I want the most out of this radio with the amp confortably.. But also was considering an amp for the car cb, which has higher deadkey (4w) with about a 12w swing... Thanks for this info.. Will post results soon
     
  7. Highlander_821

    Highlander_821
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    I don't know about how to get the most power from that radio, but I'd suggest you leave it pretty much like it is. Not worth it to try to squeeze more out of it, IMO. You'd probably end up smoking either the rig or that amp eventually. Nobody is going to notice the increase anyway.

    Little amps like that one tend to work pretty well with 1.5 to 2.5 watts of carrier. More than that and you aren't leaving them enough headroom to amplify your signal when the radio is modulating.
     
  8. HomerBB

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    Doc,
    Thanks for the info.
    I can appreciate S22 wanting a short how-to answer (don't we all?), but the material you supplied is ultimately more vital to turning the lowly newb into a knowledgeable radio enthusiast.
    Homer
     
  9. Simbalage22

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    LOL.. I replied to this earlier but the storm knocked out the power as I hit send. I wasnt meaning it as I didnt like the info.. It was very interesting, at the same time I am new and didnt understand this info in noobie english :).. I've printed this info for learning literature in future applications
     
  10. Lazybones1222

    Lazybones1222
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    Dead key and swing. I love this. Let me pose a question and then try to make a point:

    1. RF is AC not DC current right? ok....

    2. If your dead key is 4 watts with 4 watts of forward swing (8 watts total), the negative part of the sine wave will go to 0 watts. Right? All is good.

    3. If you dead key is 2 watts and swings 8 watts forward (10 watts total) the negative part of the sine wave is at negative 6 or -6 watts. No there is no such thing as negative watts - so that part of your signal will clip off. Distortion is the result. Sounds like, well "a CB" instead of a what natural voice would sound like if a person was standing beside you talking.

    The older radios dead key 4 watts and swing to 8 or so as they should.

    The majority of the CBs I hear do not sound natural. So much distortion. The "Swing is king" thing is bullshit. Another old wives tail spread by meter watchers to those that have no clue.

    I agree with what someone said above - with a watt meter - the Deadkey should be 50% of the pep modulation, no 25% as some say. What ever your forward swing is, it should not go negative off the carrier to a point below ZERO on the negative part of the sine wave. Look at the pic below, the horizontal line represents the dead key out of radio or amp if used. The bottom or the vertical line is zero. DONT GO BELOW ZERO. lol

    forward swing
    [​IMG]
    represents zero
     
    #10 Lazybones1222, Jul 23, 2010
    Last edited: Jul 24, 2010
  11. HomerBB

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    Cool. a lot of stuff written on the forums goes over my head. Every time I read something else, a little more sinks in. Good practice to save and read the material later.
     
  12. W5LZ

    W5LZ
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    Oh me, there are several things about that post that just aren't right.
    In no particular order.
    The only thing that picture illustrates is a sine wave. It isn't the right shape for a combination of carrier and applied modulation. Drop that 'zero' line to the bottom of the lower cycle and you'd have one cycle of a carrier being modulated to 100%. But, only the 'positive' half of the signal. There is a 'negative' half of the signal depending on how it's displayed on an O'scope.
    More than 100% modulation always results in at least a very small fraction of time when there is no power being transmitted, 'small' gaps between the zero level of adjoining peaks/'bumps' in that scope figure. As the percentage of modulation get's higher, those 'gaps' get wider. That results in the 'backwards' swing of the watt meter you see sometimes. You're right, there's no such thing a 'negative' power, but there is such a thing as NO power and that's what's happening with that 'reverse swing' thingy.
    And then you get to the AVG and Pep power ratings. They don't mix without a lot of converting. Unless for very specific instances, there are no good reasons for mixing those two types of power ratings. 'Big numbers' is NOT a good reason except for idiots bragging. It only results in confusion and misunderstandings. So why even bother with it?
    Partial explanations do more damage than even misunderstood complete explanation, and without the background knowledge of this stuff it's all going to be 'partial'. Do yourself a very big favor and get the basic electricity stuff learned. This is very basic electricity you know.
    - 'Doc
     
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  13. Lazybones1222

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    no - I don't think you understand what I was saying. Nevermind.
     
  14. BOOTY MONSTER

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    A.M. TUTORIAL
     
  15. Wire Weasel

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    This might be what you've read out of some book somewhere, but apparently you are not actually a radio operator with an active station. Some book (no book presented) may (or may not) state that the situation you suggest will come out as "distortion," but that doesn't mean that "distorted," meaning rough, scratchy, poor, hard to understand audio is what receving stations are going to HEAR out their speakers...ya know....with their ears. No meters, no computers, just a real live transmission from a radio to a listening stations's ears.

    Low dead keys with much larger forward swings is most all AM radios produce and is certainly true of any mosfet-finaled radio on the market these days.

    These radiosSOUND GREAT !!!!

    You are suggesting that every Galaxy, RCI, Connex, Magnum, General Lee ect....are all distorted and sound bad. Well that's just crazy. Sorry guy but you are simply wrong.

    And so we have another highly entertaining thread of "to swing or not to swing," that will no doubt end up costing thousands more lives and millions more dollars. Because the history of those who refuse to learn are doomed to repeat it.

    harrumph
     
    #15 Wire Weasel, Jul 24, 2010
    Last edited: Jul 24, 2010

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