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To swing or not to swing

hold on, im missing something here.

Joedirt, are you saying that what the NPC mod is essentially doing is turning the AM POWER control up and down at an audio rate along with your modulation?
LC
 
Joe, You have to understand if the radio actually raises the carrier momentarily as the audio increases, the effect this swing kit has really does nothing for audio and just makes the meter look good. From what you've explained, it seems that the NPC mod is raising the carrier to prevent the negative peaks from reaching cutoff. Problem with this method is it also reduces the true modulation percentage even on the positive peaks since modulation is referenced from the carrier point. Raise the carrier point for a given level of PEP and the modulation percentage goes down.

That explains why you could have these high PEP to carrier levels because with the increased carrier it offsets the over modulation. What you don't realize here is that you've traded the increased modulation the swing kit would normally offer for little more then an entertaining dance on the watt meter when you modulate. True negative peak compression does not manipulate the carrier point to prevent RF cutoff, it reduces the gain only on negative peaks and has no effect on the carrier point.

I think I've said it before but if the mod raises the 1 watt carrier to lets say 4 watts during modulation, you will sound identical if you just set the carrier to 4 watts. There is no way you're going to get a 1 watt carrier swinging to 40 watts PEP to sound good in another CB receiver. You've already recognized the carrier goes up when you modulate. Connect this with the fact it sounds no different then if you fixed the carrier at the higher point to begin with.
 
Shockwave said:
Joe, You have to understand if the radio actually raises the carrier momentarily as the audio increases, the effect this swing kit has really does nothing for audio and just makes the meter look good. From what you've explained, it seems that the NPC mod is raising the carrier to prevent the negative peaks from reaching cutoff. Problem with this method is it also reduces the true modulation percentage even on the positive peaks since modulation is referenced from the carrier point. Raise the carrier point for a given level of PEP and the modulation percentage goes down.

That explains why you could have these high PEP to carrier levels because with the increased carrier it offsets the over modulation. What you don't realize here is that you've traded the increased modulation the swing kit would normally offer for little more then an entertaining dance on the watt meter when you modulate. True negative peak compression does not manipulate the carrier point to prevent RF cutoff, it reduces the gain only on negative peaks and has no effect on the carrier point.

I think I've said it before but if the mod raises the 1 watt carrier to lets say 4 watts during modulation, you will sound identical if you just set the carrier to 4 watts. There is no way you're going to get a 1 watt carrier swinging to 40 watts PEP to sound good in another CB receiver. You've already recognized the carrier goes up when you modulate. Connect this with the fact it sounds no different then if you fixed the carrier at the higher point to begin with.
Click to expand...

Yes I realize that im not going to get any more mod out of the radio with the NPC but the thread is "To swing or not to swing" People were saying that radios that swing are dirty and sound like crap... Im just saying that its not the case in all radios and that it is possible to run a clean swinging radio without bleeding over on other channels and sounding like crap..... Thats all!

I run my radio with the factory mod limiter, 1 watt dead key swinging 40+ Into a 2x4. I have the limiter set so just before the wave starts flat topping it kicks in. Most Cbers say its sounds loud enough, I run a clean station and still run a 2x4 for all its worth.
 
OK, I'm lost then. If you understand that this mod raises the carrier during modulation and therefore does not constructively add to the modulation, what is the point of this swing mod? There are only two accurate answers. One would be just for the sake of seeing the meter move more when you talk with no gain in audio or range. The second would be the slightest reduction in average power consumption. That won't save you much in terms of power supply requirements since you still need the amps to reproduce those positive peaks.
 
Joe has also asked if it's possible to measure the true modulation level on a scope with this modification. You simply have to reference your measurements against the carrier level that the modification increases to under audio peaks. Since it's a compressor, it will have an "attack" mode, and a release time. The compressor will switch into the attack mode when it receives an audio peak. During this mode is when your modification pumps up the carrier.

After an audio peak, depending on the capacitors used in the compressor circuit you should see a slight delay in the release time as the carrier holds high after the audio peak. You have probably already seen signs of this and is what caused you to notice the modification effects the carrier with audio. That split second after strong audio is where you have to measure the true carrier on the scope with this modification since it manipulates the carrier with audio.
 
Shockwave said:
Joe, You have to understand if the radio actually raises the carrier momentarily as the audio increases, the effect this swing kit has really does nothing for audio and just makes the meter look good.
Click to expand...

AND will make the receiver AGC produce a lot of transient distortion while tracking the carrier.

Some people actually enjoy distortion.

Just another way around having a large enough final to do the job at hand properly.
 
"Just another way around having a large enough final to do the job at hand properly."

Which is basically the only 'good' reason for ever doing that 'swing' thingy. Anytime you 'shade tree' something, you wind up with some 'sap' mixed with the results. Do it right or end up a little 'sappy'.
- 'Doc

(all puns intended)
 
The NPC-RC DOES NOT manipulate the carrier! Most techs that I have posted with on this and other CB radio forums do not seem to understand that the term amplitude modulation is a term that should NEVER have been used to start with.

The amplitude of the carrier is NOT varied during the positive or the negative peak. The carrier remains the same throughout the 360 degree modulation cycle which can be proven by viewing the signal on a spectrum analyzer. The sideband power increases and decreases during the modulation cycle.

However, the idea that most of us grew up with--that is that is the carrier is varied in amplitude during the modulation cycle is EASIER to picture in our minds than the correct idea.

The GAIN of the modulation circuit is controlled by the NPC-RC components in such a manner as to cause the negative peak modulation gain to become less and less as the positive peak modulation gain remains "untouched" by the circuit.

Using THAT idea, we can picture the modulation circuit varying the positive peak in the normally understood manner while the negative peak is compressed so that the positive peak hits it's 250% to 400% point at the same time that the negative peak hits aboout 98%.

This is done because of the exponential curve of the diode.

I have had some radios to hit 65 watts from a dead key of 2 watts and sounded GREAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAATE!

I AGREE that under normal negative peak limiting done in such a manner as a Texas Star V-mod does, you CANNOT have 1 watt dead-key peaking to 35 or 50 watts and sound good--but there is no comparrison in a Class "C" clipped to the n'th degree and the NPC-RC Modification--They are two totally separate ideas.

:D
 
Well Booty Monster, I know you were only joking when you asked for someone to tell you that 1 watt swinging to 60 would sound good. We've got them claiming 2 watts swinging to 65 sounds GREEEAT!!! I mean it's only 3,200% positive peaks, there shouldn't be any distortion......right? I'd love to see that great sounding waveform on the scope connected right after the AM detector on the receiver.
 
I've heard Joe Dirt's radio (he's around the Exton area)...its loud, got lots of swing (on the receive end), and falls flat on its face after a certain distance. He does that every time I hear him...sounds loud up close, then falls completely off at a certain distance. I've been told that is the result of a large dead key to swing ratio??

One thing that someone said once is that while it looks distorted on a scope, the human ear can't really pick most of that distortion up.
 
The Jerk said:
I've heard Joe Dirt's radio (he's around the Exton area)...its loud, got lots of swing (on the receive end), and falls flat on its face after a certain distance. He does that every time I hear him...sounds loud up close, then falls completely off at a certain distance. I've been told that is the result of a large dead key to swing ratio??

One thing that someone said once is that while it looks distorted on a scope, the human ear can't really pick most of that distortion up.
Click to expand...

When AM is 100% modulated the peaks only reach 6 db higher then the carrier. When you start turning the carrier down to 1 watt with 30 watts PEP or 2 watts at 65 watts PEP that makes the audio peaks 15 db higher then the carrier. It stands to reason that the modulation that's 15 db above the carrier will propagate much farther then the carrier. In the distance this will sound distorted like side band because the carrier is too weak to copy while the audio peaks are still strong enough. At 3,200% positive peaks I'm thinking the scope won't be needed to spot distortion. But someone will post a recording claiming to show 2 watts carrier with 65 watts PEP sounding great.
 
The Jerk said:
I've heard Joe Dirt's radio (he's around the Exton area)...its loud, got lots of swing (on the receive end), and falls flat on its face after a certain distance. He does that every time I hear him...sounds loud up close, then falls completely off at a certain distance. I've been told that is the result of a large dead key to swing ratio??

One thing that someone said once is that while it looks distorted on a scope, the human ear can't really pick most of that distortion up.
Click to expand...

I have no clue where Exton is? I live south of Vernonia, Oregon 35-ish miles north west of Portland.

Its all about RMS wattage not the swing!
 

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