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That is NOT what is happening! If the negative peaks were not compressed and you modulate the positive peak as much as possible--but still below the saturation level--the negative peak would severly clip. The NPC components, normally just a single diode and a resistor, causes the gain of the modulation circuit to lower during the negative peaks. That is, the more modulation, the less negative peak gain. This causes assymetrical modulation with very nice shapped sine-wave type peaks on both the negative and positive peaks.

What a lot of "so-called" techs have to say is the the negative peaks are trashed, pointing out that they are "thick" in the middle of the modulation envelope. What they do not take into consideration is the fact that if you have the same number of peaks in the positive direction as you do the negative direction. the area that they occupy will be different for the negative peaks than it is for the positive peaks. Of course the center will look thicker because there are so many negative peaks that are compressed into that small area of the screen.

This simply shows that the compression circuit is working properly.

As stated already, the actual carrier does not change as modulation is applied. This can be seen on the spec-an. However, the term amplitude modulation came about because the early fathers of this science thought that the amplitude was being varied in accordance to the modulation applied.

using this idea simply as a teaching tool, it can be seen why they believed this to be so and there are many ham radio operators, and many more cb techs that still subscribe to this erronous thinking.

as modulation is applied to the carrier the carrier "seems" to expand during the positive peaks and go to zero size during the negative peaks.

With NPC-RC (RC = reduced carrier) the negative peaks hit about 98 percent modulation at the same time as the positive peaks PEAK OUT at somewhere above 200 percent.

The compressed negative peaks do not cause clipping and since compression takes over for the limiter, which is removed, there is no problem removing the limiter since compression does a better job anyway. Removing the limiter allows the positive peaks to reach their maximum usuable value WHICH IS JUST BELOW THE SATURATION POINT!

I gotta go--more later.

BILLY DEAN WARD

Awesome...

baloney:

CHAPTER 5 INTRODUCTION TO WAVEFORM INTERPRETATION
MODULATION MEASUREMENTS
Figure 5-1.—Antenna current increase with amplitude modulation
Figure 5-3.—Rf amplitude percentage modulation wave envelope
Oscilloscope Measurement Methods

CBdoctor,

i was reading through some old posts between you and Bill Eitner on the cbtricks yahoo group.

i noticed that you used to use a diode when doing the NPC mod to the 148GTL chassis, then after some time, it became increasing the value of a cap from 1uF to 10uF.

am i confused?
are there two ways to do this mod to the 148 chassis?

what is the way that you prefer nowadays?
thanks for any light you can shed on this for me.

oh, how is your NPC mod for the 29LTD chassis coming along?
last i heard, you were thinking of incorporating an echo along with the mod.
i think that an NPC mod board that also contains a GOOD sounding reverb would be a hot ticket item.
most people who use echo want it for the "big radio sound" and not for actual repeating echo. (unless they are just trying to be jerks LOL)

anyway, hope all is well with you.
i look forward to hearing about what you are working on these days.
LC

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Almost 5 years this thread has been running and still not one single spectrum analyser pic of this beautiful clean signal after NPC-RC mod.Am I the only one who thinks that is suspicious,spectrum analysers don't tell lies,so if there's nothing to hide then why not show the spectral purity of this mod?


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

In answer to that cb doctor,no high end audio manufacturer would ever consider adding an equalisation system to a top end hifi,they even grudge adding bass and treble controls because they know it degrades signal purity but do so because the consumer demands it because they are either deaf,thick or playing music at such volume levels and overdriving their amps that the impurity added by bass/treble controls is minimal compared to the impurity added by overdriving.

Audio distortion doesn't sound good,it is tiresome and causes listening fatigue.

Parametric & graphic EQ's are used to compensate for acoustically less than perfect rooms in many high end audio systems. I have a Denon PMA-900V (mid-fi IMO) integrated that I use a EQ with for this reason. The adjustment for the room deficiencies will more than make up for a little NOISE (not distortion) being introduced into the signal by a QUALITY EQ. Sorry for getting off topic, but I wanted to respond to the EQ distortion comment earlier.

wheeeee-haaaaawwwww.....they're still arguing about what an npc-rc looks like in 'free-space', that classic 'isotropic-receiver', & i just keyed over 'em & gone with 2 watts carrier from an 8719 chassis & a large tube. again. WHO F@<&!*G cares???? or is that......get a life? can never keep those straight. keep arguing, i'ma going back to the shack.

Hey DOC, I need this mod for a 146GTL cobra. Can you point me out to where to do the mod????

Thanx. 1-5

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