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AM CB Myths???

Discussion in 'CB and Export Equipment and Accessories' started by Simbalage22, Aug 8, 2010.

  1. Simbalage22

    Simbalage22 Active Member

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    Is any of this true? And If so why do we put swing kits in our radio's in the first place? I have been searching on what the right deadkey with and without and amp and this just tops the icing on the cake

     
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  2. jazzsinger

    jazzsinger Bullshit Buster

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    Wrong. An AM signal is fully modulated when the "swing" doubles the carrier. That is to reach 100% modulation a 4 watt key should swing no more than 8 watts. Anything more than that is distortion to your voice. The AM carrier is necessary for the receiver to properly demodulate the audio from the signal. If you add excessive swing it will distort your audio. It will not help you get out better.

    That part is partly true,the swing should double the carrier peak voltage,but it quadruples the pep power not doubles it p=v squared/r

    ie if peak carrier voltage was 50v then 50v x 50v /50ohms = 50w

    if peak voltage is doubled with 100% modulation added,then it becomes 100v x 100v /50ohms = 200w pep

    if you want avg of peak power (avg peak power = rms of 100 peak volts squared /50 ohms) then it would be 70.7v (the rms voltage of the 100v peak) x 70.7v /50 ohms = 99.9698w avg peak.which is probably where he got his doubling of power from by using a non powered peak reading meter.

    a 4w key should swing approx 15.6w pep for 100% modulation.

    whoever wrote that has confused voltage and power.anything over 100% modulation is distorted whether you can hear it or not.

    have a look at the bottom pic (a pic is worth a thousand words) in this link you'll see what happens when you overmodulate,the green graph is a spectrum analyser representation,watch as the harmonics either side of the fundamental frequency grow the more you overmodulate:

    Amplitude Modulation

    Keep it clean,sound mean.its not rocket science!!!
     
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    Last edited: Aug 8, 2010
  3. Buckshot555

    Buckshot555 Member

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    I too have read this article. Seems pretty interesting and informative. The ratio of modulation to carrier should be about 2:1 on a watt meter. So for every watt of carrier you need 2 watts of swing. This should equal about the right amount modulation. Anything more will just add to distortion of audio. So unless you want to watch the needle swing to the right as far as possible and don't care about someone understanding you, than I would say try to keep swing relatively low. I'm guessing if you add an amp, you would still need to keep the same 2:1 ratio to sound the best.

    Truckers and competition CBers like to put a swing kit in their radios. Yes, it DOES make the radio put out more power, No it probably doesn't make it "get out" any better, or sound any better. And if it does get out better, you probably won't understand it anyway. I've moded my buddies radio's to swing on their request and I warn them about what it will do, but most people don't care, they just want to see the needle swing and tell everyone their radio is badass. Honestly, a CB "peak and tune" usually just consists of the guy cutting the modulator limiting resistor, and then tuning the coils out. So the radio will splatter like hell.

    The newer radios' I've bought all seem to mostly have tuneable modulator pots that can be used to increase or decrease the modulation level to get that sweet spot, but it does it all within the limits of the radio, so you don't have to worry as much about splattering it unless you cut something out and tamper with it.

    Backward swing is also true, though I don't know the math or the theory behind it. Watt meters will only read forward power.
     
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  4. jazzsinger

    jazzsinger Bullshit Buster

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    people put swing kits on radios because they listen to folk who don't know half of what they make out they know,its that simple.louder isn't necessarily better and thats the concept they have difficulty getting their heads around,go turn your hifi up full blast till it starts clipping and you will see sure its louder,but it sounds rough as f@ck,exactly what you are doing when you modify radios.a small amount of clipping can help cut through in difficult conditions when signals are low,but it comes at the expense of audio fidelity and is tiresome on the person receiving its' ears.
     
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  5. packrat

    packrat Active Member

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    People put swing kits on radios because the average person wants to "SEE" something happening. The more they "SEE" happening, the happier they are. Since you cant "SEE" radio waves, per se, the swings the thing.
     
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  6. pro151

    pro151 KB4RMA

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    Nailed it on the head. Great answer, wish I had thought of it. (y)
     
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  7. jazzsinger

    jazzsinger Bullshit Buster

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    pity you can't see distortion either.if the average person could see and understand a spectrum analysis of their signal after adding a swing kit,they'd never do it.

    not to mention the increased strain they put on their final transistor/s which can only result in shortening their lifespan.
     
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  8. pro151

    pro151 KB4RMA

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    Tune the radio for "optimum" not "maximum" performance, install a good antenna and if that doesn't do it for you, add an "antenna stretcher". :whistle:
     
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  9. mackmobile43

    mackmobile43 Jock Supporter

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    The antenna stretchers don't work well in ssb mode unless you have the bob85 condensation method of distilling you rf path.:whistle:
     
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  10. pro151

    pro151 KB4RMA

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    Well, I personally prefer the "dirty" class of stretcher so that I am able achieve maximum splatter and distortion across all 40 above, center and below. :whistle::D

    Now let's get that argument started all over again and really side track this thread. :w00t:
     
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  11. mackmobile43

    mackmobile43 Jock Supporter

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    That class will cause you to go [​IMG]
     
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  12. pro151

    pro151 KB4RMA

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    Nah, haven't gone blind yet but I Do prefer the glowing "nads". Don't need a night light to go pee in the middle of the night anymore. :D
     
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  13. mechanic

    mechanic Active Member

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    :pop:
     
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  14. Simbalage22

    Simbalage22 Active Member

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    see on my other thread I've gotten the impression 1/4 of pep is deakey. I kinda was looking at it all like a gain on an audio amp.. the higher the Deadkey, the stronger your carrier is (IE: you wont get cut off it your keyed and stop talking) but not sound as clear.. I also was under the impression a swing kit is intended for lowering the deadkey for an amp, especially a low drive.. Thus maybe swing is bad barefoot, but is needed when power is applied

    See my last post here
    http://www.worldwidedx.com/cb-band-cb-radios/66805-deadkey-vs-swing-8.html#post219577
    as I use the 1/4 mark explained on this forum to illustrate my point with this cobra 25 with a swing kit.
     
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    Last edited: Aug 8, 2010
  15. mechanic

    mechanic Active Member

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    Learned this in my amateur radio studies.... :bdh:

    A carrier from a transmitter in AM mode is narrow in a bandwidth point of view. If this carrier is not modulated and is turned on and off in a pattern it can be CW, still narrow....
    If your voice or music or what ever is applied through some mixing circuits with a microphone then you have modulated AM. When the carrier is removed or filtered you will have DSB or SSB (reduced carrier usually).
    The more power you apply to the carrier, amplified, because of the circuit design, the more likely you will create harmonics.
    When you modulate with voice to the amplified carrier, the harmonics become greater and and propagate up and down the spectrum (frequency or channels).
    If the carrier is reduced and "overlayed" with greater or increased modulation, then you have what is called "swing".
    If you over modulate or use a wide bandwidth mode like music then harmonics can be created. These can be a bother as it is called splatter because the harmonics spread to other channels, channel 6 for an example!
    Over modulating the carrier or too much swing will lead to "flat topping the envelope". CB radio circuits are rather limited by design and cannot handle too much for it's envelope, distortion will result!
    So if you detune your radio then amplify the output it will be cleaner but still it will be amplified.

    Kinda like the GIGO principle! Garbage In - Garbage Out

    To monitor this stuff you need good equipment and cheap meters and just "S" meters will not give a correct view. We all want clean and loud signals don't we?

    Enough! as this is becoming a Rant for me! :oops:

    73 mechanic
     
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