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NPC RC modification mod

Discussion in 'General CB Services Discussion' started by Happy_Hamer, Jan 13, 2010.

  1. MisterFatty

    MisterFatty Poppin Fresh!

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    Mol, I completely agree, The Internet has spawned a whole new breed of "Tech" they do NPC mods, "peek" :D radios, they "Clip" limiters, Build amplifiers, talk on amateur radio.



    They do all of this with very little knowledge, if any. I won't even bother with proper equipment part of it. A few go on to learn, but most just don't have a clue, and don't care to. Typically these are the same guys who argue with you because they know, or their buddy, the guy with the "Secret CB" books, the one that can tell you what to clip says its so...

    I enjoy the interaction of forums, because it forces me to keep up on new technology, brush up on old, and is a great learning tool.

    I'm constantly learning, and am far from knowing-it-all, the difference is recognizing and accepting the facts.
     

  2. Happy_Hamer

    Happy_Hamer Administrator
    Staff Member

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    Finding more and more

     
  3. C2

    C2 Sr. Member

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    Seeing is believeing, but only half of the time...

    Show me the spectrum.
     
  4. cbdoctor

    cbdoctor Member

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    I know that this is kinda old but I just now saw it!

    NPC does NOT stand for Negative Peak Clipping<-------That is the last thing that youu want. It is NP Compression! Huge Difference.

    BTW, the mod that is shown at the beginning of this thread is for a 148 Cobra and yes it was Bill Eitner's version but almost identical to my version. There is no similarity between this mod and the one done with the diode/resistor on the 3600XXX boards.

    Quote:

    "SS8541,,,,,,i think the npc/rc is trash, even though it is based on an old a.m. engineering(positive carrier shift) and ham(negative cycle compression) form of a.m. modulation. for one, it makes no sense to remove the limiter. the purpose of this modification is to increase positive modulation while keeping a clean signal(neg. peaks at 100% or less). removing the limiter completely voids the whole point of the mod. and volting the finals is also a wasted step. you may get another 5w that no one will ever see, while at the same time stressing the final/finals."

    I find it hard to believe that there are so many techs that want to talk bad about something that they don't even have a clue about.

    You could not possibly make a statement that could be more wrong than the paragraph quoted above. It is absolutely essential that the limiter be disabled!!!
    It causes NO TRASH OF ANY TYPE!

    I have explained numerous times on this forum and CBTRICKS that the limiter is removed for this mod--"not to void the Whole point of the mod", but because the NPC circuit takes the place of the limiter and does a better job. The job that the limiter does before the NPC-RC is being accomplished by the NPC circuit and the limiter is no longer needed because it will cause the NPC to be of no consequence--It HAS to be removed for the NPC to functuion properly.

    Your so-called "volting the finals" (which it is NOT) is NOT done to get more power or to raise the voltage on the finals--It is done to save the modulation transistor from burning up because of the extra work load that it has put on it with ANY modulation boosting modification. As a side-effect, the finals get extra voltage which is FINE AND DANDY! The finals could take another 4 or 5 volts without hurting them.

    If the radio is an SSB unit, the voltage on the finals during SSB transmission is the full voltage right off of the power plug--Same transistors--Same peak audio--NO HARM done to the finals because of voltage!!!!!!!!!!!!!1

    Anyone that believes that the raised voltage will damage the finals needs to study the topic of power dissipation. Then get the spec sheet of the final transistor and see what the power dissipation rating of that transistor is.

    The SAME TRANSISTOR seems to have no problem when you substitute it for the 2078 in a Cobra 29 WHICH HAS THE FULL VOLTAGE ON THE FINAL! Wonder why? The 29 uses a transformer for modulation which should be much more dangerous to the final with high voltage than the transistorized modulation.

    If you will notice, there has been a lot more of the "main Line" techs on the forums that are NOW agreeing with me on this subject.

    :D
     
    #19 cbdoctor, May 29, 2010
    Last edited: May 30, 2010
  5. thecbdoctor

    thecbdoctor Member

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    Once in a while I Google NPC/RC just to see what is being said about the mod and it amazes me that I find that this thread was last posted on by me two years ago next week. I Rebuttled a number of things that were in error and NO ONE came back to either argue the point OR to support.

    I would like to hope that it was because I did such a good job on my rebuttal that no one dares 2 question it--LOL!

    There has been statements on three different forums that the NPC/RC is now the most used mod on the planet--WOW!

    BDW**Jump_im**
     
  6. purenrg

    purenrg Member

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    ...
     
    #21 purenrg, May 24, 2012
    Last edited: May 24, 2012
  7. purenrg

    purenrg Member

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    Please give it a rest you just wont attention, it's been well proven that this is nothing but a trash mod:bdh:, with pictures using a spectrum analyzer.
     
  8. Onelasttime

    Onelasttime Well-Known Member

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    AMC tracks the negative peaks the portion that is under the curve towards the center on the scope. The waves you see on top and bottom on the scope that look like ascending and descending hills are both positive's the point towards the center where they appear to touch is the negative portion.

    He is keeping the AMC in place and setting the modulation prior to the NPC mod for 95%-100% modulation so his negative peaks will not get out of control. The AMC is still tracking the negative and limiting. The positive peaks where never controled by the AMC. The only thing here that is changing is the retio relationship between the positive and negative the positive is not directly copled to the negative now so it is allowed to go past 100% while keeping the negative at or bellow 100%. Not sure if that is truly NPC but the end result is much the same with out splater aka spurious harmonics.

    I am guessing that with this setup he selected 130% because it sounded much louder while still being clean and clear.

    If you toss enough processing at the problem you can get above 200% modulation on the positives with out flat topping if you have enough head room left in the audio and rf section of the radio which is not likely in the run of the mill stock CB radio or stock export. The RC portion of this sort of mod is meant to deal with the lack of headroom and allow for more modulation before flat topping.

    Back when Dinosaurs roamed the earth back in 1992 I played around with adding an additional audio IC, upgrading capacitors, voltage regulators and many of the transistors in the radio to gain more gain and less noise etc......I was aiming to add more headroom for NPC mod. In most all cases it worked but the effort and time was well not well spent for the gain in the real world. I was in H.S. and liked playing around with this stuff it was always a toss up girls and whisky or late nights with the smell of rosin core solder?!?!?!?LOL

    I have not met anyone else that ever played around with doubling the audio ic to increase headroom on the NPC or PPE modification. I am an old man now with 3 kids...lol I am cheating now and buying an NPC board and will likely cheat and have a real tech install it since I do not have a scope,signal generator, or even a huge well light magnifying glass anymore!LOL

    I like the NPC mod but I think at some point you need to stop chasing ever last bit of performance and just be happy and enjoy the hobby! If it is not clean sounding on the air what good is it? I was amazed to hear the gentleman above stopped at 130% it is both rare and refreshing to see someone in this hobby be prudent and not chase every last increment of performance!!!

    P.S. An iPhone with 1000 cycle test tone feed into the mic does not count as a signal generator. I hope their is not a O-Scope app for the iPhone or I am going to lay a golden egg.LOL
     
  9. TM86

    TM86 Ooohhh, shiny!

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    Hope your nest is ready: http://www.oscium.com/oscilloscopes/imso-204
     
  10. Robb

    Robb Yup

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    That scope is a no-go; it is rated at only 5mhz.
    For CB radios, you need at least a 50mhz scope, or a preferrable 100mhz scope to work with. The good news is that analog 100mhz scopes can be had on eBay for about $100.
     
  11. sonoma

    sonoma Sr. Member

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    wow, hard to believe this just got brought back up. since Billy dean Ward died the npc/rc mod seemed to pass with him. not as much talked about it any more.
    and as Robb mentioned a 5mhz scope is not bid enough for cb work. you can use it for some internal adjustments but not many.
     
  12. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    Removing limiters is always a bad idea. Asymmetrical modulation is the way to go. Allows the limiters to stay intact, and you can maintain full adjustability too.


    ~Cheers~
     
    NZ8N and Robb like this.
  13. TM86

    TM86 Ooohhh, shiny!

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    Until I found that link I didn't know anyone had even made a scope package for the iPhone, no matter how useless. At $400, I thought it was more funny than practical.
     
  14. Robb

    Robb Yup

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    I agree with ExitThirteen. In that asymetric modulation is the whole point with the NPC mod; but that same, popular way of doing it by clipping the limiter is the wrong way - for many provable reasons,

    I have still yet to try Exit's method for asymetric modulation; but I am planning to do it just the same. He has posted his proved results on this thread:

    http://www.worldwidedx.com/threads/over-130-modulation.163831/page-6

    Check it out; read the whole thread . . .
     
    NZ8N and Shadetree Mechanic like this.
  15. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Digging up info on the npc mods. Here is something to read, I have to go back and read it again. Bump.
     

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