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They said it couldn't be done; or did they say "shouldn't"?

Discussion in 'CB Radio Modifications' started by LeapFrog, Aug 5, 2019.

  1. LeapFrog

    LeapFrog Wielding Hanlon's Razor

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    FQP13N10 as the Driver..
    FQP13N10 as the Final..



    A.M. regulator modification, "wideband capable".
    VLC player from the P.C. to an outboard audio amplifier.

    This Cobra 29 LTD belongs to a friend of mine on the west coast.
    The Bird 43 has a 50 Watts Element, no PEP kit, and yeah it's swangin'.

    I think he did well, what do you think?
     
    #1 LeapFrog, Aug 5, 2019
    Last edited: Aug 5, 2019

  2. 543_Dallas

    543_Dallas Sr. Member

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    Good work. Thanks for reminding me why I quit listening to Stern.

    How strong is the signal on the sdr? I see some buckshotting but that may go away under normal use when you actually have some carrier.

    The positive peaks don't look like they are flat topped but the negative peaks look very under modulated. Eventhough they aren't anywhere near the baseline they looked square at times. This can cause the splatter. Looks a lot like a 3 diode keep alive circuit that's being used too much.

    I think it's a success but don't be afraid to run some carrier and lose some pep power. A bit over 100% modulation with the right amount of compression and a peak limiter at the end of the audio chain can still be very loud. You don't want the negative peaks to baseline but they need to be near 100% modulated....which will show less bird watts.
     
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  3. LeapFrog

    LeapFrog Wielding Hanlon's Razor

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    I think he was a little close to the SDR, and I agree a bit more carrier; the negative peaks should clean up and get close to 100%.
    At some times the EMin is a little fat but I don't really see "squaring".
     
    #3 LeapFrog, Aug 5, 2019
    Last edited: Aug 5, 2019
  4. 543_Dallas

    543_Dallas Sr. Member

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    I thought I saw the negative peaks start so square off a few times but it's really hard to tell on the fly like that. I understand the transmitter is physically close to the sdr. If the received signal was 40 over and you see some splashing it's not a big deal but if it's an s5.....

    Good work though. I like to see experiments like this instead of the usual how many watts can we get this sum bitch to do.

    What is he using for audio processing? Line level input or just a mic plugged into the rig?
     
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  5. 500kpot

    500kpot Active Member

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    Dear Mr. Dallas

    I went through the video at .06 times the speed and I did see about 90% on the negatives, albeit not a great deal of times, which leads me to believe there is no compression or limiting, which you have already stated, and to me, IMHO, the waveform shows a lack of audio power. On the other side of the coin if infact there is no compression or limiting, I then feel the audio was intentionally held "low" for max positive peaks and no cut off on the negatives. Which I would think this better than "straight lines" as a negative. Which many youtube techs suffer from. Again this is only MHO.

    I think distortion is a word. I.E. an audio equalizer is a form of distortion as the input isn't the same as the output, but the audio, assumed the EQ was setup properly, sounds richer and fuller. So it is in good prudence to discover where the distortion exists as it pertains to this said video from this so called "TT" . More specifically is this good or bad distortion?

    Thank you for your insight where you have posted and I look forward to hearing from you again.

    Any information you provide will not fall upon deaf ears.


    Best Wishes,
    500kpot
     
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  6. 543_Dallas

    543_Dallas Sr. Member

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    He's what I thought I was seeing. Not hitting baseline but squared off. Looks like a keep alive circuit is being used. Nothing wrong with that if you don't over do it. Screenshot_20190805-051754_Chrome.jpg
     
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  7. LeapFrog

    LeapFrog Wielding Hanlon's Razor

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    It is the audio being held low, he wasn't using any procecsing just VLC player line level out to the outboard audio amp.

    He is going to make a new video using compressor / limiter and the negative peaks will go beyond 90%. :)
     
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  8. 543_Dallas

    543_Dallas Sr. Member

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    Is it possible to just use a single tone test? This is a 1k tone on a uniden 78ltd with a mmm mauldulator clone. I can't remember what the carrier level was. I think it was a watt and a half.

    20161202_202036.jpg
     
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  9. nomadradio

    nomadradio Analog Retentive

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    A single-tone test is the tradition for AM.

    The two-tone signal is intended for sideband. If you feed a single tone into a SSB transmitter what should come out is a RF carrier. In other words a single RF 'tone'. Audio sinewave in, RF sinewave out.

    On a good day.

    The two-tone 'scope pattern makes it possible to guess how a sideband transmitter will behave with a voice signal.

    The added complexity of the two-tone RF-envelope waveform makes stable 'scope triggering a bigger challenge.

    73
     
  10. LeapFrog

    LeapFrog Wielding Hanlon's Razor

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    Here is the set with a function generator, the next test will be with an Alesis 3630.
     

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