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Sideband harmonics 7mhz away...wheres your test tone?

Discussion in 'General CB Services Discussion' started by 357, Nov 12, 2018.

  1. 357

    357 Walkin' the dog

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    Wtf bbi?
    Sideband "harmonics" are 1.5khz away, not 6.5mhz away and hello hello hello hello hello hello is not a 1khz test tone needed to give a proper reading.
    Are your customers that stupid?

    The span is from 2mhz to 52mhz and those "peaks" are 7mhz below and 7mhz above.



    No wonder he disables comments and likes.

    Plus he has a 30db attenuation on so you cant see the real readings.

    2018022.jpg
     
    #1 357, Nov 12, 2018
    Last edited: Nov 12, 2018

  2. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    It may just be the radio driving it, the spurries I'm seeing - 7.8MHz is from Cobras' 148/2000 or 142 series - even Grants or Washington's..

    Just proves the amp is not filtering out the IF mixing artifacts...So there may be more to the story than what is being told to the viewer...

    If the radios been modded - it says a lot about the producer of the videos...
     
  3. Martian

    Martian Well-Known Member

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    He doesn't know how to use the instrument.

    I need to know more but watching his videos is cancer, especially after the antenna video.

    Attenuation is likely needed. He could be running 1kW of his nasty signal thru a sample port that may generate a still dangerous level of RF for the instrument.

    After I have a few martinis later I may watch the video.
     
    Shadetree Mechanic likes this.
  4. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    The span on the analyzer needs to encompass the 54 MHz to show the third order harmonics. A little trickery goes a long way when dealing with display data.

    Also one of the things he is calling harmonics is just the side band of the modulation.
    In addition he shows the Oscilloscope and when he modulates it is well over 100% and shows dead spots where the carrier is gone altogether. Splatter box radio.

    The amp might be good but the radio is crap.
     
    #4 Tallman, Nov 12, 2018
    Last edited: Nov 13, 2018
    Robb, unit_399 and Handy Andy like this.
  5. Martian

    Martian Well-Known Member

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    There is that. I can't remember the last time I have seen in my short time looking at CB repair videos where someone shows EVERYTHING.
    They all seem to cut them off at ~52Mhz.

    The trickery is very real. I can't understand why Siglent is supposedly endorsing him, if that's to be believed.
     
    Handy Andy likes this.
  6. kopcicle

    kopcicle Sr. Member

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  7. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Bookmarked!

    Thank you!
     
  8. 357

    357 Walkin' the dog

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    Here's what it should look like.
    Span of 150khz, not 49mhz.
    Sorry it just hurts my head when I see this shit.



    2018023.jpg
     
    Dmans, kaos513 and Handy Andy like this.
  9. Shockwave

    Shockwave Sr. Member

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    I think Kopcicle is correct here. When you see spurs that go below the fundamental frequency and are this far out of normal bandwidth, that's happening inside the radio. What you are seeing may be the sum and difference of the IF frequency as it passes out of a mixer and is not properly filtered. Funny thing is if you run a TS-940 on this frequency in AM without the optional AM IF filter, this is exactly what you'll see on the spectrum analyzer.

    It's nearly impossible for an amplifier to create a spur below the fundamental frequency unless it's self oscillating and that would not have clean spurs equally spaced. As others have pointed out, we would need to see what's happening to at least the first harmonic frequency of 54 MHz. before we could judge the amplifiers spectral purity. This problem could also be as simple as just over driving the input to the analyzer.
     
    Tallman likes this.
  10. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Remember to keep this in context.

    If he's using a Cobra 142, Uniden Grant or a Gentronics - anything using 35MHz and S042 to downmix, one of the byproducts is the 7.8 MHz removed - which if not caught by the BPF - no matter how good the amp is, it's so broadbanded it picks up everything. Including what gets past the radios' own output filters.

    So really - to see both, lets' the end user decide for themselves. (If it were me...)

    Focus on the radio delivering spread spectrum technology the old-fashioned way of a bad tuneup...

    Or...

    Focus on the Radio and Amp together to pour in all the power into your frequency YOU are using - not everywhere else but there...
     
    Tallman likes this.
  11. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    CRAP IN=LOUDER CRAP OUT
     
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  12. Rwb

    Rwb Sr. Member

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    Smoke n mirrors or pure BULLSCHITT he is passing on to the buyer
     
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  13. kopcicle

    kopcicle Sr. Member

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    There was a doubt ? :)
     
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  14. Rwb

    Rwb Sr. Member

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    never a shadow of doubt kopcicle
     
  15. Martian

    Martian Well-Known Member

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    I checked a few older 8719 radios I have here that have the S042P and they did not have any leakage that I could see.
    I ran it into a 100W amp and checked again and still no discernible 7.8 or 35Mhz leakage.

    I can't say I have ever seen VCO or carrier osc leakage out of one of these radios substantial enough to notice. The bandpass filter post mixer is generally good enough to knock this down to almost nothing so it simply gets lost in the rest of the chain.

    I think BBI or whoever he is has a serious, serious problem with whatever radio he is using. Probably just fine by him since it makes the needles move a tad more to the right.
     
    Rwb likes this.

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