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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>

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>

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=ju stindepolis2>JustinDePolis2</A> at: 12/21/04 3:27 pm

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=ju stindepolis2>JustinDePolis2</A> at: 12/21/04 3:27 pm

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?


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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>

OK I might be missing something here, so you guys help me out, here are the Pictures...





and







If I look at the two, the top Picture is what I was taught to look for in a properly modulated AM signal, and looks better (to me)than the bottom one. Not to mention that the work did not have to be done to modify the radio pictured at the top,is this correct, or am I not understanding something?





73

Jeff


<span style="color:orange;font-family:helvetica;font-size:large;">RadioActive</span>







</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=au dioshockwav>AudioShockwav</A> at: 12/22/04 8:50 pm

__________________
Radio-active

NASA/SOHO

OK I might be missing something here, so you guys help me out, here are the Pictures...





and







If I look at the two, the top Picture is what I was taught to look for in a properly modulated AM signal, and looks better (to me)than the bottom one. Not to mention that the work did not have to be done to modify the radio pictured at the top,is this correct, or am I not understanding something?





73

Jeff


<span style="color:orange;font-family:helvetica;font-size:large;">RadioActive</span>







</p>Edited by: <A HREF=http://p067.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=au dioshockwav>AudioShockwav</A> at: 12/22/04 8:50 pm

__________________
Radio-active

NASA/SOHO

Actually Audioshockwave, the NPC mod that was done to the 55 doesn't look like it's doing much at all. If you look at the center of the scope, the negative peaks are still approaching near zero.


Click Here To Go To FG Best Communications



</p>

Actually Audioshockwave, the NPC mod that was done to the 55 doesn't look like it's doing much at all. If you look at the center of the scope, the negative peaks are still approaching near zero.


Click Here To Go To FG Best Communications



</p>