what NPC/RC mod looks like on a scope

[cbdoctor]

Regulated bias and output filter improvement are already on the way. That is one of the first things that I will be working on for My Personal designs and I believe I will have quite a lot of the power of persuasion in other designs.

About the Bird slug; Yeah, I wasn't trying to describe the bird slug in my post. I was attempting to give my opinion on what the perfect pass-band would be.

Actually, in most bird slugs there is more than just a wire for the pickup loop. It is usually a precision made silver plated metal strip--or least it used to be.

Can someone tell me about this forum from the standpoint of getting back to the same thread time after time? When I arrived on the forum this time, it took a while to locate this thread. Other times that I have been here, this was where it was at when I opened it with my browser.

BILLY DEAN WARD

 

[9C1Driver]

In the last 10 years I have had two radio's done with the non-volted final version of the NPC. One was an old 2950, the other a Delta Force. I saw the scope on both radio's and it looked nothing like those pictured way back when. Those were two of the best talking radio's I ever had.......even better then a radio tuned by Bob's cb and some dude named Justin. I have sold both but wish I still had that Delta and 2 pill Joker amplifier. What a talking combo.

 

[cbdoctor]

I never did do what I had planned to do so I will do it now. That is, rebuttel the following post. I have mingled my statements after each quote.

"I wanted to show everyone what an NPC/RC (diode/resistor) mod looks like on a scope, and the distortion that it causes. So I went over to F.G. Best, where we took a Galaxy off the shelf, and applied the mod to it. We then ran a test tone through it (so the signal pattern shows the easy to see sine wave) before and after."

Any variance from the exact sine shape of the wave would be considered distortion. Usin a mic compresser causes distortion. The question to be answered is how much distortion and what type of distortion is ok.

Bill Good loved the idea of NPC-RC. We talked about it over dinner in Rancho Cucamonga for a couple of hours back in 1994.

"This first pic is of a properly modulated AM signal with no NPC/RC mod. Note the nice symmetrical pattern."

Yeah, I notice the NICE SYMMETRICAL PATTERN! That is exactly what we do NOT want. That is the whole idea of NPC-RC! To make the radio NOT have a symmetrical pattern! What did you think Negative Peak Compression meant? If you are compressing the Negative peak and not the positive peak, it CANNOT BE symmetrical. So that is a Given!

No, it is NOT properly modulated. The limiter is working overtime as the percent of modulation is around 90% in that picture. It should be around 98-99%. The negative peaks should NOT show that very bright section near the zero line. It should be a very nice u shape from the top of the negative peak and a very nice inverted u shape from the bottom of the negative peak. They should ALMOST come together at the zero line. If they did touch, then it would be 100% modulation which is hard to achieve without clipping so that is the reason for the limiter--to keep it back at about 98% modulation.

Let me explain what NPC-RC is! The modulation circuit is modified so that the exponential curve of the added diode controls the Negative peak of the modulation cycle. During the positive peak, the circuit works in a normal fashion except if the limiter is removed the positive peaks can go higher than normal and can be allowed to go to just below the saturation point which means they will NOT flattop. The added diode--the compression circuit--takes the place of the limiter so the limiter can be removed with no problems resulting from it's removal.

As the Negative peak gets closer and closer to the zero line on the scope pattern, the modulation applied gets lower and lower accordingly because of the exponential curve of the diode.

"Now this is with the NPC/RC mod applied. I took a pic of the radio so you can see that the mod is there. This is also an "extreme" NPC mod so it's easy to see in the tiny picture on the internet. We did a more typical one as well, and the results were the same, just not quite as dramatic."

This is not the NPC-RC that I introduced to the internet about 10 years ago. In fact, on my site I state that this mod you show here should NOT be done to a radio because it causes flattoping to extremes if not done right.

I have been doing it properly for about 35 years. It has been done since the early to mid 30's. Other than having way to much compression, there is nothing wrong with that pattern. That is what it would look like at only about 50% modulation.

Shot of the mod:

What it looks like on the scope:

"Notice how the negative peaks (the part of the signal closest to the X axis. It's at the center, not the bottom of the sine wave) are totally trashed. This gets represented as distortion under normal voice operation."

Where in the world did you come up with the idea that the negative peaks are totally trashed? This is that extreme language that I was talking about on another thread. Similar to saying, "They completely GUTTED the amc circuit", when a single wire was cut.

There is ABSOLUTELY NOTHING trashy about that pic.

It is apparant that whoever was coaching you during these tests has no idea of what is going on in the mod.

The Negative peaks actually look great except for the fact that they are a way to much compressed. Get rid of the second resistor and the second diode and put back the original 560 resistor that came in the radio then place the resistor-diode combo across c-189 and you will love the sound of the audio and it will look great on the scope.

"Here's one last video clip of the mod being applied then disconnected while a steady tone is running. If you turn up your speakers, you can even here the tone change frequency as it distorts when the mod is applied and then disconnected."

This has no meaning! We don't apply that much modulation when we speak into a microphone. Any signal can be OVERDRIVEN--expecially if we are trying to prove something that does not exist.



Click here for video clip

"Hope everyone finds this educational and revealing."

I hope everyone reads this very correct rebuttel from someone who has done over 16,000 of these mods on Galaxy and other RCI-built radios with much success and very clean beautiful sounding modulation.

BILLY DEAN WARD



Moleculo


</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=moleculocdx363>MoleculoCDX363</A> at: 12/20/04 9:20 pm

 

[15minigrass]

Why not post a single 100 ohm and single Diode so we can actually see what the diff. is. Does it still looks the same on a scope with a human voice or whistle.

And how about some sound or voice of the NPC and w/o NPC on the recieving end. Both my radios has NPC done. The 959 I did the mod and the Pres. Grant came modded w/the NPC.

If its really that bad what can be done to the mod to reduce the distortion?

Mind boggling!!! Aloha, James....

 

[The Jerk]

quote:



that is what i wanted .

here we go again ....a dirty signal.....on what ?a machine.....we dont talk to machines or scopes we talk to people.if people say it sounds good and my "ears" tell me the same then who cares what it looks like on a scope or a machine.

The only time anyone would notice that dirty signal (besides a scope) is when your bleeding over all 40 channels and every other piece of electronics within a half mile radius. You won't really hear the difference (unless its YOUR toaster that's talking to you)...

I had (what was sold as) a PPE mod done once, it turned my Cobra 29 into a 45 watt "monster"...and I would bleed on every channel. So your talking on a single channel and wasting wattage on the other 39...how much wattage is actually on the channel your talking on??? A Bird can't tell you that.

 

[ButtFuzz]

You won't really hear the difference (unless its YOUR toaster that's talking to you)...

Hey, watch it, man! I was the 2008 WATT* award recipient!!!

(Worked All Them Toasters...)

 

[15minigrass]

Is there a cure for it not bleeding all over the airwaves w/o eliminating the NPC?

 

[cbdoctor]

Did you not Understand 15minigrass? The NPC-RC DOES NOT cause ill effects. For one thing the picture that the guy did at Best is NOT trashed on the negative peaks.

That picture is a beautiful example of EXACTLY what the compressed Negative peak should look like except it is compressed too much for it to cause a loud signal.

I don't know what a technician would think it means to compress the Negative peak and not compress the positive peak. It means that you will have assemtrical modulation--the exact thing you are striving for by doing any modification that causes low DK with Laterlots of modulation.

The first time I ever did NPC-RC. I flipped out when I say the modulation envelope. Later when I introduced it to the internet via my forum, The CB Clinics Of America.

Everyone there flipped out except Bill Eitner who argued with me for a month--until he performed the mod and from that time on he was sold on the mod and talked good about it for years!

Anyone on the internet KNOWS that if it had ANY problems, he would have NOTHING to do with it.

RFMATRIX, Tim had NPC-RC as part of his signature. He pushed it everywhere. If anybody doubts the mod, you need to look at the scope yourself.

I already have the short tutorial on the mod on my site but I am going to redo it so that everyone can understand what the scope readings mean. In other words how to interpret the scope patterns as it is evident that the ones that started this thread does not understand what he is looking at.

 

[15minigrass]

Thanx Doc. That I can understand. Great remedy. Well w/that said, Im leaving it(NPC).

Both my radios are NPC modded. The 959 I did my self by adding a 1N4001 doide to R264 and the President Grant Export I bought from 521 Houston on WWPDX already came w/it. It keys @ 2 watts swinging 25+. Im thinking of lowering it to .5 or 1 watt DK. Love it, it drives my 350V perfectly.

Peace out Doc. Aloha, James....

 

[freecell]

a properly modulated AM signal is where the RATIO OF PEP TO CARRIER POWER is defined as follows:

dB = 10 LOG(1 + M)2

while negative peak compression conservatively applied may be of some benefit the distortion level increases as the positive peaks exceed 100%. using reduced carrier levels AND NPC no longer constitutes an amplitude modulated signal and instead produces a DSB signal with suppressed carrier, the extend of which is defined by the formula above.

as in the example mentioned previously, that of 2W carrier & 25WPEP, the signal generated is a double sideband signal with suppressed carrier, NOT an AM (amplitude modulated) signal.

as a direct result of the peak-to-carrier expansion produced by both NPC & RC, not only is the signal able to be detected in AM mode, it is also perfectly detected and readable in both LSB and USB modes, including unwanted levels of annoying carrier power present in the passband.

audio compression rarely if ever contributes more than 1 dB. to signal readability under any conditions. conversely, rf compression and logarithmic audio clipping both provide much greater advantages in regard to signal performance and readibility.

practically speaking, NPC/RC is much to do about nothing.

 

[cbdoctor]

I am not going to get into a hot and heavy debate with you but Even if that formula may be called a properly modulated am signal. it is not the only proper way to do it. It depends on what you are trying to accomplish with what you are doing.

The NPC-RC is far from much to do about nothing! That is a rediculous statement and shows that you havn't a clue.

NPC-RC, as all AM signals, can be heard on SSB. Have you been in the business as long as you have and not ever heard AM with the switch in the SSB position. I think NOT!

Distortion is ANYTHING ABOUT THE OUTPUT SIGNAL THAT WAS NOT IN THE INPUT SIGNAL. The word is NOT A DIRTY WORD! Of course the way most of us use the word an amateur would be lead to believe that any distortion is undesireable.

However a perfect SSB signal has LOTS of distortion. You must know that a perfectly tuned in SSB signal DOES NOT sound like the voice speaking into the microphone.

Using an EQ system with your audio stereo is a form of distorting the signal.

THE ONLY THING THAT CAN BE DIFFERENT ABOUT THE SIGNAL AND NOT BE DISTORTED IS THE AMPLITUDE OF THE SIGNAL!

There are simply NO ILL EFFECTS caused by the properly done NPC-RC!

BILLY DEAN WARD

 

[cbdoctor]

While I have seen the formula you posted, I think, I do not know what all it is talking about so I Googled it with:

dB = 10 LOG(1 + M)2 as applied to amplitude modulation. I didn't do an hour search--only about 15 minutes. So, why don't you explain what everything in the formula means and HOW AND WHY it applies to AM

And are you, when you say a properly modulated AM signal, referring to a 4:1
ratio, which is the proper ratio for an AM signal if it is to be symmetrical.

By the way, have you ever placed a screwdriver in the carrier level pot and twisted it for maximum DK? If so, you have seen the highest power level the Positive modulated peak can reach; if the radio is properly aligned!

Yes, CW is a modulated signal by the EEE definition of modulation--The Application of Intellagence to a carrieer!


BILLY DEAN WARD

 

[freecell]

"Distortion is ANYTHING ABOUT THE OUTPUT SIGNAL THAT WAS NOT IN THE INPUT SIGNAL."

and there's no negative peak compression in the human voice. referencing the operators voice as the input signal, the introduction of NPC represents distortion in the output of the exciter/transmitter which IS NOT PRESENT in the original input signal. the only objectives are to exceed 100% positive modulation (index=1) while preventing the negative portion of the waveform from clipping. since the depth of the positive portion of the waveform is greater than the depth of the negative portion under these conditions then all symmetry in the X plane is lost. NPC destroys waveform symmetry.

if exceeding a modulation index of 1 is the only objective that can easily be done by simply expanding the peak-to-carrier ratio of the resultant output signal. no negative peak compression is required and waveform symmetry is maintained without being concerned with clipping of the negative waveform.

in either event, distortion is still present. after all has been said and done, all you've done is disabled the AMC circuits ability to prevent overmodulation on voice peaks.

resting, unmodulated carrier + 6 dB. total sideband power = 100% modulation.
M is modulation index, 100% modulation/M = 1

dB = 10 LOG(1 + M)2
db = 10 LOG(1 + 1)2
db = 10 LOG(2)2
db = 10 LOG(4)
db - 10 (.60205)
db = 6.0205

assign any value you like to carrier, whenever you add 6 dB. of total sideband power two things are constant, 100% modulation and peak power that is four times the carrier.

http://www.firecommunications.com/hlsos.shtml

the only legitimate purpose served by any form of clipping or compression is to improve the S/N ratio in the receiver front-end at the other end of the circuit.

EFFECT OF PROCESSING ON SIGNAL-TO-NOISE IMPROVEMENT AT RECEIVER

25 dB. of audio clipping can produce in excess of 5 dB. improvement in receiver S/N ratio. with rf clipping reserved for SSB transmitters, the only two forms left are audio (NPC) and rf compression. with 25 dB. of compression in either format the improvement in the S/N at the receiver front end is no more than 1 dB.

in an am transmitter, properly implemented audio clipping produces the greatest improvement in receiver S/N ratio of better than 4 dB. when compared to NPC.

reason, logic and plain old common sense dictate that the processing format that produces the greatest increase in receiver S/N ratio is the most effective in delivering a minimally distorted, highly intelligible signal under all possible conditions. simple preamplification, logarithmic clipping, audio frequency bandwidth limiting and removal of audio harmonic byproducts produced by clipping yields better than a 4 dB. improvement over NPC, again, a lot to do about nothing, for nothing.

 

[cbdoctor]

if exceeding a modulation index of 1 is the only objective that can easily be done by simply expanding the peak-to-carrier ratio of the resultant output signal. no negative peak compression is required and waveform symmetry is maintained without being concerned with clipping of the negative waveform.

You just don't get it! No matter how I say it, you are going to argue with me. I ain't got time for this right now.

If you expand the peak-to-carrier ratio, DISTORTION!!!!!!!!!!!!! It might be OK to distort in that case--depends on how you do it. As I stated, all distortion is not BAD distortion!

reason, logic and plain old common sense dictate that the processing format that produces the greatest increase in receiver S/N ratio is the most effective in delivering a minimally distorted, highly intelligible signal under all possible conditions. simple preamplification, logarithmic clipping, audio frequency bandwidth limiting and removal of audio harmonic byproducts produced by clipping yields better than a 4 dB. improvement over NPC, again, a lot to do about nothing, for nothing.

Removing the audio harmonic by products will still leave a distorted signal. Possibly distortion that is not bad but distortion anyway!

NPC-RC is as clean as your going to get a peak to carrier ratio. I don't understand why yoou can't understand that I DON'T CARE IF THE SIGNAL IS ASSEMETRICAL! I INTEND TO MAKE IT SO. THAT IS THE PURPOSE OF THE MOD!

BILLY DEAN WARD

 

[freecell]

you're not changing anything. the human voice by its very nature is defined as an asymmetrical signal, lacking balance and uniformity, simply because of the wide ranging values of voice energy produced between consonant and vowel sounds.

What is asymmetrical modulation?

that's the very reason that any form of processing is required in the first place, to suppress the wide disparity in energy levels between consonant and vowel sounds in human speech and to increase the amount of average transmitter power output when compared to the peak values.

the amount of distortion able to be tolerated in a processed audio signal reaches threshhold when no further improvement in intelligibility or receiver S/N ratio can be attained. the bottom line is that audio clipping, not audio compression, represents the best processing format of the ones mentioned for maximizing the S/N ratio at the receiver end of the circuit. period. using the same distortion threshhold percentage and comparing audio compression and audio clipping side-by-side, audio clipping provides a 4+ dB. INCREASE in receiver signal-to-noise ratio, pure and simple.

in your defense, you have explained absolutely nothing.