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what NPC/RC mod looks like on a scope
- Thread starter Moleculo
- Start date
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Thanks for your cheer for me being here! I don't know about YOUR varmint. I do remember that I received 3 amplifiers that I still owe for to someone. I know what the other 2 are and would recognize their handle if it were still the same. What was your handle then.
You have to realize that I am living quite a different lifestyle now than I was back then. I have been through absolute HELL--which is exactly where I should have been living the lifestyle that I was living.
A year and a half ago I took a fall and woke up from a four day coma and was larthargic for a couple of months--didn't hardly know who I was or where for over a month.
I spent 11-1/2 months on my back or in a wheel-chair in 5 different hospitals and 2 convelesant homes.
I have a new hip (OCT 8-2008), a still broken knee on the same leg and two severely torn shoulder rotator cuffs. I am NOT making very much money at this time but I am heading for San Diego in the next few days to go to work with a will known amplifier company. Let me know the particulars on the Varmint. Most of my memory has returned but once in a while I find myself remembering things that I didn't know that I knew<---that does make sense--if your me! LOL!
BILLY DEAN WARD
i was starting to enjoy this......NOW we need the waders. after 846 years of CBers BSing each other over which mod is better then the last, how to get 50 watts out of a 4 watt transistor, my 17 watt CB does 10 pounds better then his 15 watter..........ARRRRRGGGGGGGGGGGGGGGGGGGGG!!!!! i play with magnums for entertainment purposes only, i play with ranger/galaxy/superstar chassis designed radios for target practice, and i play with uniden grant xl chassis radios when i feel like talking on a CB and sounding like a human. hasn't ANYBODY learned that yet???? the ALC on my antique FT101e just moves a little, the ALC on my 746pro & 756pro3 moves roughly the same, the bird meter on my XL keys at 2 and swings to 7 or 8 or 9. SO, if i can't be heard by who i need to be heard by, i turn on the amplifier. next kettle of fish. yeah, sometimes the texas star is OK. the davemades have been sold to finance new driver boxes. als500/600 are usually good. the 4cx4000 modified commander works well with ameritrons. if i still can't be heard, 4cx15000 modified commander always can! have a 4cx35000c in the works. power supply is currently being developed. the power company hasn't been too cooperative with supply requirements of a residential need this large. may end up moving the shack into my commercial entity, though i don't really care to do that.
point being-GIVE UP THE BS FOR AN ADDITIONAL COUPLE OF WATTS!!!! when will CBers (& hams) get it????? JUST LEAVE IT ALONE SO YOU SOUND LIKE A HUMAN!!!! while we're at it, give up that 16 transistor fatboy with 22 volt PS in the house. it severely compounds the CRAPPY sound eminating from MANY radios on 27.025. come on guys. you think hams don't abuse the 1500 watt rules? THINK AGAIN. 60db over S9 is NOT 'good conditions'. on 27.025. or 50.130. or 28.410. or 21.290. or 14.240. it is RAW WATTS. albeit CLEAN WATTS. trust me ;-). if somebody would like to start the next BS thread regarding 4cx100000 tubes & 250kw on 27.025......go ahead! show me the house it is xmitting from and i'll show you closer to 10kw coming through his 2-0 service wire. that AIN'T happening either, boys.
this place is almost as entertaining as 'the zed'.......
I understand the classic models, but we would need the same for our super whacked packed xcvrs...
Unless there has been some newer material published in the last 20 years, that document is pretty all-encompassing on the subject.
On the subject of carrier pinch-off:
"First, the intermittent disappearance of the carrier, which is believed by many broadcast engineers to be the cause of splatter, actually has very little to do with it."
Now, on the subject of negative peak clipping:
"Most important, it is apparent from Figure 3 that negative peak clipping is the major cause of splatter and that, theoretically, it matters little whether the clipping occurs as carrier pinchoff in the transmitter or as clipping in the audio prior to modulation. Comparing the spectra of
3 dB overmodulation in Figures 3f through 31, there is almost no difference between carrier pinchoff and audio clipping. The conditions of carrier pinchoff, -99% audio clipping, and -95% audio clipping, produce spectral
components which are stronger than -35 dB out to the fourth harmonic of the modulating frequency, and produce additional significant components even farther out."
It goes on from there, but you can go read the details for yourself.
I started this thread 5 years ago and would like to think that I've grown in my understanding of some things since then. Keep in mind that the first part of this thread is really chopped up bad and is missing quite a few posts due to system conversions. However, I wouldn't try to prove the same point again by using those methods.
First, I think we should stop using the word "distortion". That word has many different applications. Second, I think everyone can agree that what we are trying to avoid is splatter, IMD, and producing an all around "crappy" sounding device. The last part of that is subjective and can also mean a lot of different things to a lot of different people.
I get what CBDoctor is saying and what this mod is attempting to accomplish, and in a lot of cases is accomplishing. But there is nothing new about this technique...as W5LZ reminds us, people have been doing this since the inception of AM. This mod is just a basic negative clipper circuit with the built in modulation clipper disabled. The basic negative clipper circuit is widely available and is even shown here: Clipper circuits : DIODES AND RECTIFIERS
Look familiar?
In principle, I don't have a problem with limiting the negative peaks to just under -100% and allowing the positive peaks to extend beyond %100. Ham AMers and all commercial AM stations do this. Of course, they don't get crazy with it, either because of the splatter it can cause. As NU9N eloquently put it,
"Of course, like anything else, there are some purity issues and tradeoff when using real aggressive peak-limiting. There will always be a fine balance between low distortion and aggressive peak limiting. The trick is finding the balance that will satisfy both sides of the equation - Loudness vs. Cleanness. A little bit of peak limiting will go a long way, so don't get too carried away!"
The biggest problem that I have with this type of mod in a CB environment is that there are too many other factors and variables happening that are not being accounted for. On the test bench, we send a 1Khz tone into the radio, look at it on the scope and say, "see -95%/+150% (or whatever) modulation...nice and loud, sounds good". In the real world, what we DON'T know is how the operator is going to use his radio. What mic is he using? Is it a power mic cranked all the way to oblivion? What are the audio characteristics of the mic? What are the audio characterics of the person using the mic? Where is this operator going to set the mic gain? What other equipment is going to be put inline that will affect the overall audio quality and spectral purity? Without observing the radio on a scope (or other equipment) while it is in use by the eventual operator, you have no idea what the end result will be.
Again, quoting NU9N, "Even at low levels of speech, the dynamic content contained in normal speech is more than any transmitter can handle on its own! This is where vocal dynamic processing (Compressors, AGC Gain Riders, Peak Limiters, etc...) come to our rescue. They do exactly what is implied by their names; compress or limit the amount of the signal amplitude coming out as opposed to the signal amplitude that was going in."
[and]
"With good EQing, compression and tight asymmetrical peak limiting, even the most outrageous peaks cannot escape, insuring that a constant and controlled audio signal will be delivered to your transmitter, giving you the freedom to talk the way you want without worrying about excessive amplitude or distortion as a result of poorly controlled dynamics."
The standard CB station has no EQing, no compression, and I wouldn't call a simple negative clipper circuit "tight asymmetrical peak limiting".
When you hand the typical CB operator a radio that has the stock modulation limiter disabled with an NPC/RC mod introduced, they will hook it up with their power meter in line and proceed to crank the MIC Gain (and also crank the power mic up) until they see the most power output on their meter. So now we have a radio with no control on the audio side that is sending a lot of crap into a radio that is capable of modulating that crap at +125% to +200% while hoping our negative clipper circuit contains the crap to -95% modulation. So now we've created the potential for a loud, overmodulated, splattering monster. Even if they are careful with their mic settings, there still is very little control over the audio input to the radio other than whatever dynamics are introduced by combining some random mic with some random human voice characteristic. This is why some radios with mods like this sound "good" to our ears with some operators and the same radio with another operator's voice/mic will sound terrible.
So what do we really accomplish by doing this? For one, we've made it terribly easy for the CB operator to screw up the resulting output even easier than it normally would be. Second, we might have made it possble to be LOUD. Because of the operating habits of a lot of operators, it just ends up sounding like LOUD crap. If it were so easy to just add a simple negative clipper circuit to an AM radio to make it sound good, do you think NU9N would need all this equipment in the stack prior to the rig itself?
Now, I realize that the CB operator isn't attempting to put together an AM station like that...but I hope you can see my point. Doing a mod like this and saying it doesn't cause splatter when you're not accounting for all of the other things going on is like handing a loaded gun to an untrained kid and then saying it's not the gun's fault that it went off. OK, maybe that's a bit of an extreme analogy, but it makes my point. The end result is often a net LOSE.
BTW, here is a link to NU9N's AM site, which is a great tutorial: NU9N AM Transmitter Hi Fi Audio Modulation Processing
On the subject of carrier pinch-off:
"First, the intermittent disappearance of the carrier, which is believed by many broadcast engineers to be the cause of splatter, actually has very little to do with it."
Now, on the subject of negative peak clipping:
"Most important, it is apparent from Figure 3 that negative peak clipping is the major cause of splatter and that, theoretically, it matters little whether the clipping occurs as carrier pinchoff in the transmitter or as clipping in the audio prior to modulation. Comparing the spectra of
3 dB overmodulation in Figures 3f through 31, there is almost no difference between carrier pinchoff and audio clipping. The conditions of carrier pinchoff, -99% audio clipping, and -95% audio clipping, produce spectral
components which are stronger than -35 dB out to the fourth harmonic of the modulating frequency, and produce additional significant components even farther out."
It goes on from there, but you can go read the details for yourself.
I started this thread 5 years ago and would like to think that I've grown in my understanding of some things since then. Keep in mind that the first part of this thread is really chopped up bad and is missing quite a few posts due to system conversions. However, I wouldn't try to prove the same point again by using those methods.
First, I think we should stop using the word "distortion". That word has many different applications. Second, I think everyone can agree that what we are trying to avoid is splatter, IMD, and producing an all around "crappy" sounding device. The last part of that is subjective and can also mean a lot of different things to a lot of different people.
I get what CBDoctor is saying and what this mod is attempting to accomplish, and in a lot of cases is accomplishing. But there is nothing new about this technique...as W5LZ reminds us, people have been doing this since the inception of AM. This mod is just a basic negative clipper circuit with the built in modulation clipper disabled. The basic negative clipper circuit is widely available and is even shown here: Clipper circuits : DIODES AND RECTIFIERS
Look familiar?
In principle, I don't have a problem with limiting the negative peaks to just under -100% and allowing the positive peaks to extend beyond %100. Ham AMers and all commercial AM stations do this. Of course, they don't get crazy with it, either because of the splatter it can cause. As NU9N eloquently put it,
"Of course, like anything else, there are some purity issues and tradeoff when using real aggressive peak-limiting. There will always be a fine balance between low distortion and aggressive peak limiting. The trick is finding the balance that will satisfy both sides of the equation - Loudness vs. Cleanness. A little bit of peak limiting will go a long way, so don't get too carried away!"
The biggest problem that I have with this type of mod in a CB environment is that there are too many other factors and variables happening that are not being accounted for. On the test bench, we send a 1Khz tone into the radio, look at it on the scope and say, "see -95%/+150% (or whatever) modulation...nice and loud, sounds good". In the real world, what we DON'T know is how the operator is going to use his radio. What mic is he using? Is it a power mic cranked all the way to oblivion? What are the audio characteristics of the mic? What are the audio characterics of the person using the mic? Where is this operator going to set the mic gain? What other equipment is going to be put inline that will affect the overall audio quality and spectral purity? Without observing the radio on a scope (or other equipment) while it is in use by the eventual operator, you have no idea what the end result will be.
Again, quoting NU9N, "Even at low levels of speech, the dynamic content contained in normal speech is more than any transmitter can handle on its own! This is where vocal dynamic processing (Compressors, AGC Gain Riders, Peak Limiters, etc...) come to our rescue. They do exactly what is implied by their names; compress or limit the amount of the signal amplitude coming out as opposed to the signal amplitude that was going in."
[and]
"With good EQing, compression and tight asymmetrical peak limiting, even the most outrageous peaks cannot escape, insuring that a constant and controlled audio signal will be delivered to your transmitter, giving you the freedom to talk the way you want without worrying about excessive amplitude or distortion as a result of poorly controlled dynamics."
The standard CB station has no EQing, no compression, and I wouldn't call a simple negative clipper circuit "tight asymmetrical peak limiting".
When you hand the typical CB operator a radio that has the stock modulation limiter disabled with an NPC/RC mod introduced, they will hook it up with their power meter in line and proceed to crank the MIC Gain (and also crank the power mic up) until they see the most power output on their meter. So now we have a radio with no control on the audio side that is sending a lot of crap into a radio that is capable of modulating that crap at +125% to +200% while hoping our negative clipper circuit contains the crap to -95% modulation. So now we've created the potential for a loud, overmodulated, splattering monster. Even if they are careful with their mic settings, there still is very little control over the audio input to the radio other than whatever dynamics are introduced by combining some random mic with some random human voice characteristic. This is why some radios with mods like this sound "good" to our ears with some operators and the same radio with another operator's voice/mic will sound terrible.
So what do we really accomplish by doing this? For one, we've made it terribly easy for the CB operator to screw up the resulting output even easier than it normally would be. Second, we might have made it possble to be LOUD. Because of the operating habits of a lot of operators, it just ends up sounding like LOUD crap.
If it were so easy to just add a simple negative clipper circuit to an AM radio to make it sound good, do you think NU9N would need all this equipment in the stack prior to the rig itself?
Now, I realize that the CB operator isn't attempting to put together an AM station like that...but I hope you can see my point. Doing a mod like this and saying it doesn't cause splatter when you're not accounting for all of the other things going on is like handing a loaded gun to an untrained kid and then saying it's not the gun's fault that it went off. OK, maybe that's a bit of an extreme analogy, but it makes my point. The end result is often a net LOSE.
BTW, here is a link to NU9N's AM site, which is a great tutorial: NU9N AM Transmitter Hi Fi Audio Modulation Processing
I'm still waiting for people to put their money where their mouths are...
I've done these things before and while I can try and convince myself that it looks nice and pretty on the scope, that is not even half the story. A nice, close-in view of the Occupied Bandwidth with sufficient signal resolution (RBW) to see each of the IMD products would be quite interesting. Then, how about a peak at the 2nd and 3rd harmonics of the fundamental frequency.
Otherwise it's just a bunch of H&T to me, and no formula in a texbook is going to qualify it any way the same or differently because, you never know who is going to come up with some snake oil that actually works!
So lets have some real show and tell!
I've done these things before and while I can try and convince myself that it looks nice and pretty on the scope, that is not even half the story. A nice, close-in view of the Occupied Bandwidth with sufficient signal resolution (RBW) to see each of the IMD products would be quite interesting. Then, how about a peak at the 2nd and 3rd harmonics of the fundamental frequency.
Otherwise it's just a bunch of H&T to me, and no formula in a texbook is going to qualify it any way the same or differently because, you never know who is going to come up with some snake oil that actually works!
So lets have some real show and tell!
"First, I think we should stop using the word "distortion"".
transmitter overmodulation in any form is a non-linear process. a transistor or tube operating beyond the flat region of the turn on curve (af or rf) generates non-linear products, i.e., distortion.
overmodulation is only a minor component. major reductions in splatter type interference can only be achieved by reducing the high energy content of the modulating signal. this begins in the audio chain, starts at the microphone and encompasses not only sporadically occurring high energy levels but also unnecessarily wide frequency response. the wider the frequency response the further up and down the band audio frequency harmonics are generated, due to the adding and subtracting of multiple audio frequencies generating new frequencies far removed from the frequency response of the originating microphone in use and is the very reason that the audio frequency response for microphones used for communications purposes as well as the speech stages in AM (communications) transmitters are generally restricted to somewhere in the 300 - 3,000 Hz. region. the wider the frequency response, the wider the occupied bandwidth of the modulating signal. it has been shown time and time again that this limited range of frequency response is all that is required to produce maximum intelligibility in voice communications signals and maintain the proper occupied bandwidth limitations.
in a typical am transmitter used for communication purposes the upper 3Khz. limitation more-or-less guarantees that at 100% modulation total sideband power of the modulated signal does not exceed 6Khz. bandwidth without increased suppression of sideband energy beyond these limits. rolloff and attenuation of audio energy above 3Khz. ultimately determines the amount of bandwidth that is occupied, of course this is meaningless to most radio hobbyists.
in an am transmitter there are basically four types of distortion possible:
amplitude distortion
frequency distortion
intermodulation distortion
phase distortion
the asynchronous detector circuitry in am receivers is dependent on minimizing all forms of distortion at the transmitter in order to faithfully recover and reproduce the original modulated/transmitted signal while at the same time maximizing the usable signal-to-noise ratio at the receiver for weak signal work. as long as we have hobbyists who do not understand the core principles of am transmitter operation we will have distorted signals on the band.
non-linear operation of an amplifier at Audio or Radio frequencies constitutes DISTORTION.
transmitter overmodulation in any form is a non-linear process. a transistor or tube operating beyond the flat region of the turn on curve (af or rf) generates non-linear products, i.e., distortion.
overmodulation is only a minor component. major reductions in splatter type interference can only be achieved by reducing the high energy content of the modulating signal. this begins in the audio chain, starts at the microphone and encompasses not only sporadically occurring high energy levels but also unnecessarily wide frequency response. the wider the frequency response the further up and down the band audio frequency harmonics are generated, due to the adding and subtracting of multiple audio frequencies generating new frequencies far removed from the frequency response of the originating microphone in use and is the very reason that the audio frequency response for microphones used for communications purposes as well as the speech stages in AM (communications) transmitters are generally restricted to somewhere in the 300 - 3,000 Hz. region. the wider the frequency response, the wider the occupied bandwidth of the modulating signal. it has been shown time and time again that this limited range of frequency response is all that is required to produce maximum intelligibility in voice communications signals and maintain the proper occupied bandwidth limitations.
in a typical am transmitter used for communication purposes the upper 3Khz. limitation more-or-less guarantees that at 100% modulation total sideband power of the modulated signal does not exceed 6Khz. bandwidth without increased suppression of sideband energy beyond these limits. rolloff and attenuation of audio energy above 3Khz. ultimately determines the amount of bandwidth that is occupied, of course this is meaningless to most radio hobbyists.
in an am transmitter there are basically four types of distortion possible:
amplitude distortion
frequency distortion
intermodulation distortion
phase distortion
the asynchronous detector circuitry in am receivers is dependent on minimizing all forms of distortion at the transmitter in order to faithfully recover and reproduce the original modulated/transmitted signal while at the same time maximizing the usable signal-to-noise ratio at the receiver for weak signal work. as long as we have hobbyists who do not understand the core principles of am transmitter operation we will have distorted signals on the band.
non-linear operation of an amplifier at Audio or Radio frequencies constitutes DISTORTION.
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this thread was an awesome read.... only problem with it, is its hard to weed out fact from fiction...
All I know its a great mod for driving amps and only cost a dollar for parts and easy to do.
If dont like want the NPC mod you could always buy a Top Gun Modulator $17.95 + shipping.
Jjust my 2¢
If dont like want the NPC mod you could always buy a Top Gun Modulator $17.95 + shipping.
Jjust my 2¢
I am in California now and will be going to San Diego to do some design work and I will be leaving with two very good Spec/an's and two very nice scopes, and ALSO some 3 and 4 hundred amp power supplys. Once I get set up in my new CB shop In Arkansas, I will "put my money where my mouth is" so to speak. That will be no problem because, I DO KNOW HOW to use both a scope and spec/an and I have looked at many NPC-RC's and when I do one just as I have explained on this and other forums, they are beautiful on the instruments.
BILLY DEAN WARD
I've never understood how a circuit that just raises and lowers the static carrier lever in conjunction with the loudness of the modulation ever got named "negative peak compression" True negative peak compression works independantly of the carrier level. On a standard AM transmission, the carrier doesn't change amplitude. The sideband energy is what causes the envelope growth. The only reason the carrier doesn't pinch off with the so called "NPC" mod is because the modulator in any given CB radio is only capable of a finite amount of audio drive. When the NPC mod raises the static carrier level to maximum on high voice levels, it's merely driving the carrier too high for the limited audio available to modulate the transmitter to beyond 100%
It always seemed to me, that if you start with a double sideband, unsuppressed carrier, and want to eliminate part of one sideband and suppress part of the carrier to increase overall output, there's a much easier and efficient way of going about it. It's not a new idea, it's been around for a while. Care to guess what I'm talking about?
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