so.. I tried the npc

[Shockwave]

Do not do any modification to a Cobra 2000 that would require more current from its internal power supply. It's already close to maxed out running all those extra chips in the counter / clock and will just fall out of regulation if loaded heavier without rewarding you with noticeably more power. On the other hand, I know you can fit a 20 amp power supply inside that speaker box.

 

[Lil'Yeshua]

It's not the voltage in this case that will stress a weak final since the breakdown voltage of even the 2SC1969 is well above 12 volts. It's the current that if run too high into a poorly matched output can blow the final open. Dual final radios are not as susceptible to this like the old 148 could be.

Turning the voltage down will reduce the current but then you have to deal with the power and heat dissipated in the regulator. It's much simpler to just reduce the drive by lowering the carrier level. It's the added voltage that allows us to increase the output without exceeding the current limitation of the final. Modulating this voltage makes the PEP increase dramatically.

It's also worth mentioning that the required collector current on a final to produce a 4 watt carrier on a 6 volt series pass modulated radio like a 148 is twice the current required to produce the same 4 watts in the circuit the 29 LTD uses with a 12 volt modulated collector line. That means there is still ample headroom to reproduce some good positive peaks with this mod.

In principal,isn't that the same as 220VAC vs. 110 VAC. There's less current with say a 1 watt device through 220 volts than 110. Ohm's law. Go figure. Cool!

 

[Slowmover]

The old 148 is the exact radio that inspired me to figure out how to modulate the 12 volt line because it was notably lacking in audio if both stages were not modulated. If you set the carrier at 4 watts in both the 6 volt modulated condition and the 12 volt unmodulated condition, the audio lost in the final stage is very obvious to the ear.




If the distortion I'm talking about were in the stock audio chain, it would be more apparent in the larger positive peaks. Those peaks are relatively clean. Its the negative peak when the diode conducts and then opens that we see the sharp transition going in and out of the negative peak.

I don't argue that you can't make the waveform look good but I think what you're missing is once you've done that, the diode is no longer conducting or having any real effect on the negative peak. I agree many people can benefit from checking the microphone phasing on AM. Flipping two wires can sometimes make a huge difference depending on the persons voice.

“. . Checking the microphone phasing on AM. Flipping two wires can sometimes make a huge difference (voice-dependent).”

New to me (as are pretty much all tech issues).

Anyone?

.

 

[sp5it]

Which wires?

 

[Slowmover]

Which wires?

what I spelled out was quote from linked post at its end.

 

[Handy Andy]

That depends on if you're Right Handed or Left Handed...

Nothing like a little "Electron" humor to make a post more Electrifying...
​

(...a Loud groan emanates from the auditorium...)

Ok, you ask an interesting question - but in reality - the question may be more of which wire is best to use for the main Audio (live) wire.

There are times when wiring a speaker "back-wards" tends to emphasize a specific type of sound to enlighten a user or those that play with audio to obtain a specific effect -To or from- a type of sound for their album or song...

Since most Mics produce an AC (alternating current) type of signal - the main premise is to use the wire that has the most shielding or external location of winds to the outside - as negative - to provide some coupling shielding and even a common mode effect of noise pickup - closer to ground than to have the external part of the coil subjected to stray noise fields...

Here's an example...
(...besides sir, you have already played with these so you know pretty much the end of how this turns out...)

I'm being generalized here for a reason so we don't get bogged down with too much information...​

In reality, you may need to examine the "Cavity" or Capsule the mic is in.

Most mics to develop a strong return for the smallest of Vibrations - have to orient the Magnet to Coil in the right fashion to gather this energy from the Vibration without the process of self-cancellation - an effect caused by the reverse EMF the coil induces once the Signal is "caught" - by the expenditure of energy against the ohmic losses then can have a loss effect of signal degradation caused by the inductive effects and the dampening - as well as the energy the coil is trying to dissipate is now traveling thru the coil winds and thru the copper used - that has ohmic losses adding to this.

So to be honest, reversal of wires may not have the effect you wish to have, but in light of the potentials your working with, any effort to reclaim the losses the coil would otherwise had within itself - anything is worth a try.

But remember too - the capsule is the main culprit - if it isn't designed right or has no way to equalize pressure between the membrane and the external world - can stiffen the membrane's response and you get horrible results.

There's always another use for moms' Salad Bowls Collection​

You showed various Dynamic mics that you took out the "felt" and by doing so increased the pickup and changed the tone of the mics response. This is why they put the element in a capsule like they do to keep the sounds oriented to strike/vibrate that membrane to achieve their desired effects. This "desired" word is arbitrary - you can use any way you wish, including a parabolic dish and when the mic element is aimed towards the apex of the foci the dish has - you'd pick up a lot of audio signal from the effort but it's highly directional - partly due to what and where the Mie element is placed facing towards the dish.

One MAJOR aspect that tends to get overlooked...

THE SPL - Sound Pressure Level...
Too much - you lose QUALITY of signal (changed to Distortion)​

You don't want that....

So to entertain yourself - you did something like this already with other mics, just reposition - remove or otherwise adjust the dampening felt used in the capsule to lower/raise or change the tone and improve or lessen the pickup sensitivity. More Felt adds "bass" - too much you get more of a rattle. Less Felt gives you higher tones and sometimes it's too much for one's hearing to tolerate.

The Coil itself has a start and a finish. and a lot of winds in the middle. So the issue of stray noises and fields that can add aberrations to the signal does "try" to get addressed - they usually wind the coil to have it's negative to the case side - while the start of wind wire is more internal and closer to the suspension core - where the ring magnet or E magnet has it's stronger to strongest fields intersecting the copper closest to the core of the copper winds.

Again, knowing these are "mass assembled" in dark comers of the planet - wiring color does show a polarity and how to determine the polarity? Well, a small battery can usually reveal the coils initial direction of best POSITIVE flow.

The thing is a lot like a solenoid - so it too can show polarity - if done carefully and gently - just apply a small current to the coil wires then reverse the connection, and observe how the membrane "distends".

When hooked one way connection - it goes in, (which is what you want) the other pushes it out (lifts - the inertial return effect) where it is looking for it's state of rest.

The Coil of a GOOD element - rests in the center of the strongest fields - which tends to isolate it from external effects of noise - the membrane is where it hears the external world, the wires from the coil are sending the results of the effort.

Use what works for you.






.

 

[Slowmover]

Had a hunch that might be the concept

 

[Handy Andy]

There's a lot in that post, Unpack it as you deem necessary to get thru the day or night...

 

[Slowmover]

There's a lot in that post, Unpack it as you deem necessary to get thru the day or night...

I’m not finding info that sells me on NPC/RC mod on a 959. Felt obligated to look it up. (Gut feel not there)

Then came across that tidbit about phasing, looked worthy.

Messing with a mic makes more sense to me based on what (I think) I want.

Been buying mics for “no reason”. Time to find out why.

 

[Handy Andy]

Hey, that reminds me...

​

 

[Shadetree Mechanic]

Asymmetrical peak limiting about half way down the page.

http://www.nu9n.com/am.html#3

 

[Eldorado828]

This asymmetrical peak limiting is a very interesting subject to me, lots because I don't fully understand it. I see it's always connected to hi-fi audio in conversations, to which doesn't make a lot of sense to me because our transmitters or receivers aren't really capable of true hi-fi. Being mostly seasoned in the world of car audio where the musical spectrum goes far beyond the transceivers we use for 2 way in this world.

Now I much better understand the waveform in terms of positive and negative peaks to where this thread topic started but reading "asymmetrical" now brings to mind what is commonly related to hi-fi audio or high fidelity in the car audio world.

From a point of ignorance I ask, why are these 2 so commonly tied together and how can we call modified audio in this 11 meter Communications world high fidelity?

It's late and I'm tired, hopefully some of that makes some kind of sense

 

[Slowmover]

Some of this stuff is silly when you consider the objective of NPC is to increase the amount of volume without increasing the amount of distortion. The last thing you want to do is "volt the final". These radios modulate the final and the driver simultaneously for a reason. You cannot fully modulate any transmitter in the hi level mode (the type these radios use) unless you apply modulated DC to more than one RF amplifier stage. As soon as you disconnect the final from the modulated 6 volt line and tie it to the main 12 volt line, there is no modulation applied to the final power amp. You just went backwards to make a watt meter look impressive.

Effective NPC is much more than just a diode. Broadcast stations use very complex multi band compressors in conjunction with negative peak clipping that is always followed by many poles of filtering to move the harsh transitions any useable NPC is going to create. Most of these CB mods have been developed by people who think the goal is to stop the negative peak from reaching RF cutoff and if you look at the results, they sometimes do that. Problem is that has nothing to do with the unwanted distortion and actually removes headroom required to avoid it. Again, going backwards.

Most of us know when we see flat topping on the positive peak, we have distortion. The same is true of the negative peak in that we have to pay more attention to the shape of the waveform than the aspect of RF cutoff. An AM carrier perfectly modulated to 100% with a 1Khz. tone will hit RF cutoff 1000 times per second but not cause any objectionable IMD.

This is because at 100% modulation there are no flat portions in the waveform at the top or bottom. If nothing is flat, there is no DC component. If there is no DC component, there are no sharp transitions in the positive or negative peak. That all adds up to a clean signal with a carrier that is constantly going in and out of RF cutoff but the shape of the original audio is never cutoff on the top or bottom.

Now if you do some mod to your radio that clips off the negative peak at say 95% modulation, you just took out 5% of your headroom before the negative peak could become flat. Since that diode is not followed by a filter network anytime its driven over 95%, its output will be clipped, flat and have sharp transitions. Exactly what you want to eliminate. Most people would get more out of a good compressor before even thinking about how to compress the negative peak independently.

Best descriptive word, IMO, is that we want the words in our TX to have punch.

We’ve all experienced what some operators achieve by design or by accident where they simply come through better than do others.

A whole long list of reasons can apply.

After spending the best part of a day reading around on NPC-RC I believe I’ll leave it as an abstraction.

Matching best mic (one journey) to best radio (another journey) inside best Radio System Installation (main journey) is enough.

Screwing around with base station gear might change that approach. Or a second radio on which to experiment.

.

 

[Handy Andy]

We’ve all experienced what some operators achieve by design or by accident where they simply come through better than do others.

The NPC-RC - started out as a whacky way to show forward swing on a meter to impress ones' self in thinking they did something "KEWL" to their radio. (Circa 1990's)

Then as time progressed others took to the task to provide actual provable theories which turned into practice

(If this looks like I favor the mod - no, I'm not a real big fan of it but
- "When In Rome...Do as the Romans Do.")
​

It's when you see and know the effects this mod does to the audio envelope - it does not turn this into a "Louder" radio - it shoves (by apparent action) moves more voltage into the carrier power by changing the way the Regulator recovers from the negative swing - it gives an apparent effort to help (Help? Well, not really, just keeps the ,limiters from engaging) the radio provide greater larger, higher voltage peaks which is the Audio Envelope along with RF carrier - between these two - you "see" a forward swing - but not necessarily "Louder" audio - just envelope containing those voltage peaks.

What's been "trimmed off" is the part of the Audio signal that sinks below carrier power level.

• You need to dwell on that for a moment - Symmetry versus Asymmetry
• - because that "negative" swing is why people say you have to adjust the "resistor value" to recover some of that negative energy that ADDS Audio Punch to the radio that the NPC-RC REMOVES - it lessens those "troughs" - flattens them really - and the receiving side can't recover that missing information - it's simply lost during the conversion done at your radio.
• - it's not their fault in what they hear; for you did the conversion to your radio and that information contained in those negative sides, are lost forever..

Why?

• You don't "Fully modulate" those peaks unless you "trim" the mod per your power levels you use, and if you're going to do that, might as well run the radio between 2.5 to 3.25 watts - you achieve the same effects only you have 100% Fully modulated signal going out running without that NPC-RC.
• Limiter action - by default, in these lower power levels is not only fully adjustable - it can be "fully defeated" just by running lower carrier - the AMC and ALC don't have to struggle with the dynamics as much.
• To some that is their "smoking gun" and last-line of defense - in getting their words out - run it into an amp to do the rest - as best as possible.
• I have known this for some time and have taken flack for even making the suggestion of using a higher ohmic resistor value to restore the audio signal - That includes Punch
  • - there are many that are "Stiff necked" when it comes to understanding that Hi-FI and NPC-RC are NOT compatible methods to combine together in audio processing.

So, yes, you're right to hold back and not destroy the audio you are producing in a properly tuned radio.

Think about this for a moment...

• Do you see any "stock" radios using the NPC-RC?
• Seriously do you?
• You think that with all the hype - benefits and retirement package this mod tends to supply for those that use it - you'd think, for one minute, that all those crazy Asians would let this simple mod money-maker method be ignored and let a performance-based selling point pass them by?
• Otherwise the mod would be used by Qixiang and Uniden and Cobra - with CRE and Alan doing more business by using such mods - it simply would be used by now.

They don't...why? - Read above...you lose too much Audio Signal in the "NPC-RC the BW way" because the 100 ohm resistor described in the mod, takes away all the slope of the negative peaks and FLATTENS it .

• - you lose 50% of audio envelope this way - by using this value in his method is what turns off the limiter action in most radios.
• When you trim, increase that resistor - you then "offset" the envelope slope losses and slow down the "clamping effect" the Diode would otherwise perform on the audio, on it's own, had there been no resistor installed in the first place
  • - IF you had done just the diode - you already know how that sounds.
• The trimming also brings back some of the negative peaking the Audio Envelope has, then Realize this; the reason why the Limiters have to fiddled-defeated or otherwise played to restore the swing is because you're restored some of the negative peaking the limiters are detecting
  • - the trimming effect is restoring the symmetry of the Audio envelope

Hey - don't like to read that? Then Don't DO The Mod - save the radio by lowering the carrier power to more closely match the power draw, and let the Envelope, with all your audio - come through - it will take care of the rest.

Hell, you run an amp - so you turn down that radio to match in the thing anyway - why add more to the mess than you've already got? You got it working - don't keep fixing it!​

• Do we have to go into the fact that you radio runs cooler and would also last longer lowering the power demands?

I'm not here to start arguments - I'm here to help dispel the myths of "why" there are the issues around the NPC-RC mess to begin with.

 

[Shadetree Mechanic]

In my understanding, the NPC is used to prevent the negative peaks from flat toping. This will allow the positive peaks to exceed 100% while keeping the negative below 100%. So with the positive peaks at 150%, it will be louder than a radio that can only do 100%. Right?