what NPC/RC mod looks like on a scope

[Moleculo]

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.



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

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.



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.



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.



Click here for video clip



Hope everyone finds this educational and revealing.



Moleculo


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

 

[Moleculo]

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.



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

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.



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.



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.



Click here for video clip



Hope everyone finds this educational and revealing.



Moleculo


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

 

[Happy Hamer]

No offense but I would like SS8541 to look at this because he seems to have good luck with a mod similar to the NPC and I have been happy with his work so I wonder if something is missing.



I sent Richard an email about this post

</p>

 

[Happy Hamer]

No offense but I would like SS8541 to look at this because he seems to have good luck with a mod similar to the NPC and I have been happy with his work so I wonder if something is missing.



I sent Richard an email about this post

</p>

 

[JustinDePolis2]

Well, there's a couple of ways to do it, but they all end up with the same result, that is, if done correctly, and that's negative peak compression. Everyone thinks that the top of the scope pattern is the positive peaks, and the bottom is the negative.... not so...where the lobes meet in the middle is negative, and the otp and bottom lobes are the positive, in English, it's because the scope only has the capability to display it this way.


Click Here To Go To FG Best Communications

</p>

 

[JustinDePolis2]

Well, there's a couple of ways to do it, but they all end up with the same result, that is, if done correctly, and that's negative peak compression. Everyone thinks that the top of the scope pattern is the positive peaks, and the bottom is the negative.... not so...where the lobes meet in the middle is negative, and the otp and bottom lobes are the positive, in English, it's because the scope only has the capability to display it this way.


Click Here To Go To FG Best Communications

</p>

 

[frbestcom]

No offense, but how come when I here a guy ask for a radio check, and he sounds distored, over modulated and at best like crap, but the guy tells him he sounds good? Most CBers do this (not all) over and over. If you do this mod It IS over modulating and distorting your radio period. Now if thats the sound your lookig for than that's what you will get. Bill Good would rip that mod out of every radio so fast it would make your head spin.



Frank.

Click Here For FG Best Communications Web Site</p>

 

[frbestcom]

No offense, but how come when I here a guy ask for a radio check, and he sounds distored, over modulated and at best like crap, but the guy tells him he sounds good? Most CBers do this (not all) over and over. If you do this mod It IS over modulating and distorting your radio period. Now if thats the sound your lookig for than that's what you will get. Bill Good would rip that mod out of every radio so fast it would make your head spin.



Frank.

Click Here For FG Best Communications Web Site</p>

 

[Moleculo]

I tell the local guys all the time they sound good when they sound like crap. I do it because it's funny to keep them talking like that for a while and make my station sound better! <img src=http://home.comcast.net/~shockwav/medium-smiley-002.gif ALT=":lfh"> ok, ok...after a while I clue 'em in that I was messing with 'em.... <img src=http://users.joplin.com/dutch64804/posticon24.gif ALT=":lmao">


</p>

 

[Moleculo]

I tell the local guys all the time they sound good when they sound like crap. I do it because it's funny to keep them talking like that for a while and make my station sound better! <img src=http://home.comcast.net/~shockwav/medium-smiley-002.gif ALT=":lfh"> ok, ok...after a while I clue 'em in that I was messing with 'em.... <img src=http://users.joplin.com/dutch64804/posticon24.gif ALT=":lmao">


</p>

 

[JustinDePolis2]

Well the mod is simple, and me and Tim saw it for our self that night. Alot of people think that the way to read an AM signal with a wattmeter is to read it in RMS mode to avoid seeing ...what did they call it... oh yes, "fake watts". By the way, real quick, does anyone have a fake watt filter, I need to pick one up...<img src=http://users.joplin.com/dutch64804/posticon24.gif ALT=":lmao">



Any way, it's simple, really. The TOTAL AM signal is made up of positive and negative peaks. Remember math class? RMS = root mean square, mean is the average. So, if you add a negative number to the equasion, meaning negative peaks, the wattmeter on the RMS setting will either stay fairly still, or in some cases move backward and forward with modulation applied to the carrier. Now, compress the negative peaks, and stop them from reaching 100%, and the positive peaks "outweigh" the negative peaks, therefore it makes the meter read higher.



REAL NPC works, and works well. (there I said it) and the fact is that alot of AM radio stations use this technology to increase the pocitive peaks over 100%, near 120%, and keep the negative peaks below 100%. The reasoning behind this is because when the envelope approaches zero on peaks, the total output power is reduced to zero for an infilite amount of time. (since you can't technically go below zero on negative peaks) Therefore, when the RF power approaches zero, there are alot of harmonics and spurs generated during this cycle, for a couple reasons. First of all, the PA stage in the radio starts acting like a switch, which produces unwanted signals, and secondly, it also produces not only harmonics related to the RF signal, but also harmonics related to the AF signal as well. This is why NPC is a good idea. (there I said it again) But also, it does change, or distort the origional signal.



But, the problem is, is that NPC needs to start early in the modulation process. Simply adding a diode and resistor doesn't cut it. I have yet to see a radio done correctly where the positive peaks are just over 100%, and the negative peaks are just before 90-95%. Usually the positive peaks are severely clipped, and the negative peaks are way too "compressed" and the radio sounds like garbage.



So, there's my opinion, so I am going back to e-bay to get a book on "maul vs. swing" and to find a "fake watt filter".



I personally prefer an AM signal properly modulated.


Click Here To Go To FG Best Communications

</p>

 

[JustinDePolis2]

Well the mod is simple, and me and Tim saw it for our self that night. Alot of people think that the way to read an AM signal with a wattmeter is to read it in RMS mode to avoid seeing ...what did they call it... oh yes, "fake watts". By the way, real quick, does anyone have a fake watt filter, I need to pick one up...<img src=http://users.joplin.com/dutch64804/posticon24.gif ALT=":lmao">



Any way, it's simple, really. The TOTAL AM signal is made up of positive and negative peaks. Remember math class? RMS = root mean square, mean is the average. So, if you add a negative number to the equasion, meaning negative peaks, the wattmeter on the RMS setting will either stay fairly still, or in some cases move backward and forward with modulation applied to the carrier. Now, compress the negative peaks, and stop them from reaching 100%, and the positive peaks "outweigh" the negative peaks, therefore it makes the meter read higher.



REAL NPC works, and works well. (there I said it) and the fact is that alot of AM radio stations use this technology to increase the pocitive peaks over 100%, near 120%, and keep the negative peaks below 100%. The reasoning behind this is because when the envelope approaches zero on peaks, the total output power is reduced to zero for an infilite amount of time. (since you can't technically go below zero on negative peaks) Therefore, when the RF power approaches zero, there are alot of harmonics and spurs generated during this cycle, for a couple reasons. First of all, the PA stage in the radio starts acting like a switch, which produces unwanted signals, and secondly, it also produces not only harmonics related to the RF signal, but also harmonics related to the AF signal as well. This is why NPC is a good idea. (there I said it again) But also, it does change, or distort the origional signal.



But, the problem is, is that NPC needs to start early in the modulation process. Simply adding a diode and resistor doesn't cut it. I have yet to see a radio done correctly where the positive peaks are just over 100%, and the negative peaks are just before 90-95%. Usually the positive peaks are severely clipped, and the negative peaks are way too "compressed" and the radio sounds like garbage.



So, there's my opinion, so I am going back to e-bay to get a book on "maul vs. swing" and to find a "fake watt filter".



I personally prefer an AM signal properly modulated.


Click Here To Go To FG Best Communications

</p>

 

[JustinDePolis2]

Yeah you can use pretty much ANY type of diode, if ya want I'll re-do it that way, with a 1N4001. I've seen people use any where from 40 ohms all the way up to 200 ohms, we used 100, and it wasn't as drastic, but for the sake of photos, we used two 100's.



Oh and yeah... the mic gain wasn't set any where, the AF was applied directly to the mic amp. If you watch the video, you'll see the AF level modulating to about 100%, then the resistor is "touched" back to the pad on the board, and well, just check it out.


Click Here To Go To FG Best Communications

</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=justindepolis2>JustinDePolis2</A> at: 12/21/04 3:27 pm

 

[JustinDePolis2]

Yeah you can use pretty much ANY type of diode, if ya want I'll re-do it that way, with a 1N4001. I've seen people use any where from 40 ohms all the way up to 200 ohms, we used 100, and it wasn't as drastic, but for the sake of photos, we used two 100's.



Oh and yeah... the mic gain wasn't set any where, the AF was applied directly to the mic amp. If you watch the video, you'll see the AF level modulating to about 100%, then the resistor is "touched" back to the pad on the board, and well, just check it out.


Click Here To Go To FG Best Communications

</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=justindepolis2>JustinDePolis2</A> at: 12/21/04 3:27 pm

 

[Moleculo]

Justin, can you do the mod again with the 1N4001 and a 100ohm, with a tone, use the same scope settings and take a quick pic?


</p>