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Not sure what the mod is called to broadcast on multiple channels...

Discussion in 'CB Radio Modifications' started by mattsowders1989, Jul 19, 2017.

  1. mattsowders1989

    mattsowders1989
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    Anyone know what the mod is called and what it consists of? Of course it'll differ from radio to radio. I just wanted to do a little reading on it to have something to play with. Any help would be greatly appreciated. Thanks!


     

  2. Jim Dickey

    Jim Dickey
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    Basically what you are talking about is what about half of the idiots with wire cutters and screwdrivers do on accident. They Over-Modulate to over 120% which can cause the transmission to bleed 5 channels up and down. Generally not considered a good thing unless you just want to make a lot of noise and take up half the Band........

    I'm not sure there is a way to TX on Channel 3,17, and 35 using the same antenna and final transistor, without filling all the space in between those channels.
     
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  3. nomadradio

    nomadradio
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    What you're talking about is probably what we used to call the "Nuke Duke".

    One guy in eastern KY nicknamed it "World of Sound".

    I like to call it the "Clone Army", since that's what it looks like on the spectrum or waterfall display of a SDR.

    Dozens of exact clones of your on-channel AM signal, a dozen or more channels above and below it.

    20 years ago when someone asked "What are we gonna do to keep this old radio stuff on the air when you retire?" I said I would publish the plans for this trick. That would be the end of CB, and give them something to remember me by.

    Still have no plans to retire. Just can't understand why nobody else has figured out how to do this. I submitted a talk proposal to show how it works at a couple of hacker cons, but it was never selected for either con's schedule.

    Called that one "Analog Spread Spectrum". And yes, that's what the acronym spells.

    Back in the 90s there was some interest in finding a way to interrupt your car's FM radio when an emergency vehicle's siren would not be heard over your car's stereo and air conditioner. Never had any patent for this, only worked as a developer for the folks who did have patents. It never went anywhere. Getting paid for design work is the hardest part, so I walked away.

    Thought about selling the pc board ready to install in a CB, but it could attract the kind of attention I usually avoid. Should build a couple hundred and just find some third party to market them. Keep my name out of it.

    But here's the basic technique. Generate a square wave with an accurate frequency of 10 kHz and an amplitude of 5 Volts or less peak-to-peak. A potentiometer sets the actual drive level into a 56k resistor. The other end of the resistor goes to the cathode of the PLL's vco varactor diode.

    Easiest way to generate an accurate 10 kHz is to take a cheap 10.24 MHz crystal, and divide that frequency by two, ten times in a row. That's how a 40-channel radio's PLL chip does this on the inside.

    It's frequency modulation, pure and simple. FM produces sidebands like AM, but they behave differently. Each FM sideband, 10 kHz apart is a fairly-exact copy of your original single-channel AM signal.

    Thermodynamics still apply. Spread your 4 Watts across 40 channels, and that's 1/10th of a Watt per channel. Won't shut down much of anybody else.

    Works okay on a Cobra 29, or a RCI-made channel-selector radio. Never tried it on any kind of "Ranger" ham-type radio, only the ones with a 40-channel selector.

    Radios that have the VCO built into a flat-plate module are less effective. Works best when you can feed directly to the cathode terminal of the VCO's varactor diode.

    Need to post it on a YT vid.

    73
     
    #3 nomadradio, Jul 19, 2017
    Last edited: Jul 19, 2017
  4. Road Squawker

    Road Squawker
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    Well, most (all?) of the MMM setups that are on CB ch 28, also transmit on 28.380 @ the same time.

    YMMV
     
  5. 543_Dallas

    543_Dallas
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    That is a defect of the export rigs some people use the board in. I had a bone stock rci 2970 about 10 years ago that did the same thing. You could hear the spur for miles.

    The mmm board has nothing to do with the pll circuitry. It just modulates the final and driver in the radio.
     
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  6. mattsowders1989

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    Thanks NOMAD. Like I said, I find the modification fascinating. I know a few people in eastern Kentucky use it to play "Foggy Mountain Break Down" I guess to try and plug people up on the 11-meter band. Especially Frosty. Thank you for that info. It's greatly appreciated. There is a definit reason why you are know around the U.S.
     
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  7. bob85

    bob85
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    Back in the early 80's we had the RUSSIANS mod for maxon boarded uk fm cb's
    you got very low power on all the channels seemingly at the same time,
    you could take that and input it into a CP163 X2 wide band amplifiers 1/2w input and get significantly more power,

    later i discovered by accident that early 5 band president jacksons could act like a poor mans sweep generator,

    if you backed the supply voltage down to just the right spot while in tx they would rapidly switch between tx & rx outputting very low power everywhere from about 24mhz - 30mhz as the vco kept sweeping over and over, you could fine tune the sweep speed with voltage adjustments,

    take that and input it into a 163 x2 and nobody local was hearing anybody not very close to them.
     
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  8. Klondike Mike

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    Just what the band needs. :-(
     
  9. nomadradio

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    Pretty much my thought on the matter. But if CB is on its deathbed, one more unfiltered Camel king-size won't speed things up all that much.

    About the late-90s RCI2950 crock. Yes, one batch of those radios would BOTH receive and transmit on a half-dozen or more channels above and below the frequency selected. After a lot of head-scratching, staring at integrated-circuit data sheets and unanswered calls to RCI we found a surface-mount resistor on the solder side of the 2950's pcb, across two adjacent pins of one chip in the PLL. Wasn't on the schematic, so we removed it.

    Problem solved. No more "20-channel receive" problems, and the transmit shrunk back down to one channel.

    Never could get a straight answer out of RCI about it. Should have recorded the serial numbers of the affected radios, but never did. Hindsight is great, ain't it?

    But they found their error and never shipped another radio with that particular "personality trait" again.

    And if you want this trick to function on transmit only, your design must include a way to shut it down while receiving.

    73
     
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  10. w9cll

    w9cll
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    Why? What are any valid reasons to do this?
     
  11. 543_Dallas

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    I ordered square wave gen fully around around a 555 timer on eBay for a few bucks. It will be an interesting project.

    The 2970 I had seemed to only be transmitting out of band. I left the thing keyed up on the base and drove away in the mobile. After about 4 miles I could still hear the spur on the 10 meter band at an S5. I could hear audio from the television crystal clear.

    I would have never known if I hadn't stumbled across this article and decided to test it. I'm glad I did

    http://home.ptd.net/~n3cvj/rci2950.htm

    A couple of guys in town have newer radios with the same issue but not as bad. You have to be very close to them to hear the spur and the audio is unintelligible. One is a 2970n2 and the other a 2995.

     
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  12. jon666

    jon666
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    just get a class c amp.
     
  13. nomadradio

    nomadradio
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    Don't know about "valid", but there is a strategy that it supports. If you have a problem with jammers covering up your receiver, this makes it harder to tell what frequency you're listening to. And if the distant station you want to hear knows a "code" that tells him what channel where he should transmit, the jammer must guess it correctly to plug your ears. Naturally this assumes the jammer can transmit on only one channel at a time.

    Seems wasteful of spectrum to take up dozens of channels just so you can listen to one of them without being jammed. Maybe I should have called it a "tactic", more than a strategy.

    Anybody remember the cartoon in MAD magazine every month called "Spy Vs Spy"?

    If you use this trick to circumvent a jammer, he'll adapt and put one of these in his radio, most likely.

    73
     
    #13 nomadradio, Jul 19, 2017
    Last edited: Jul 19, 2017
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  14. Mustang 131

    Mustang 131
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    I have a pair of 29 modified by sidewinder that does exactly that. You can vary the amount of channels it transmits and recieves. It makes it impossible to be jammed but you needed a good amp. Also it was (still is) one of cleanest sounding radios I own.
    That radio was blast on the Jersey Shore back in th 90's when a lot of cabs, truckers, and drunks where on the band late at night. Ran a Dave 3cx3000 into an original Masedon Jay in the Mojave antenna at 100'..All that bandwith made that box hot!!
    Breaker channel 1,2,3,4,5,6,7....dammit forgot to break into the A channels..lets start again.

    Ahh memories....
     
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  15. 543_Dallas

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    To get a reaction out of you and waverider.;)
     

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