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Clean Signals from C Class!!!

Hey Homer, I just stumbled across this video, (congrats on the great contact into Belfast!) you were also captured here and I can hear the class C biasing a little in your audio . . .


MARK 68CT1970 I QSO WITH 2CT004 - YouTube

Is it fair to say that there was an edginess to Marks voice, too, and he was recording himself from within the automobile, not as a third party recorder like the other recording?
I can hear what you refer to, but I seem to also hear his live voice with raspy distortion, too.
 
Is it fair to say that there was an edginess to Marks voice, too, and he was recording himself from within the automobile, not as a third party recorder like the other recording?
I can hear what you refer to, but I seem to also hear his live voice with raspy distortion, too.

Oh yes I did, but I presumed he also had a class C amp in line. I know it's not due any issues with the receiver on that IC-7000! I have nothing but respect for that little rig. I've heard a few of those sound better than a Pro3.
Your audio isn't all that bad really, I've heard multiple levels of horrid class C audio that is 20 times worse than yours, but I expect at some point you'll move into class AB1 and enjoy knowing you sound crystal clear. Maybe there's a Henry 2K just waiting for you out there somewhere! :D
 
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His voice is not over the air, but from within the automobile he is DXing from. There should not have been amp distortion in his voice. That's why I think there is some poor recording quality that makes a good assessment of the audio difficult to do on that one.
 
Oh yes I did, but I presumed he also had a class C amp in line. I know it's not due any issues with the receiver on that IC-7000! I have nothing but respect for that little rig. I've heard a few of those sound better than a Pro3.
Your audio isn't all that bad really, I've heard multiple levels of horrid class C audio that is 20 times worse than yours, but I expect at some point you'll move into class AB1 and enjoy knowing you sound crystal clear. Maybe there's a Henry 2K just waiting for you out there somewhere! :D

So My Palomar TX 75 says Bi-Linear on the face, is it AB1/2???
 
Just a few things if I may...... A "CB" style "class C" amplifier *COULD* sound ok on AM and SSB although this is not proper, and I would never recommend it. The reasoning behind this is because these amplifiers, while by definition ARE IN FACT class c, they are not biased deep into the class c region.

Meaning, in order to be completely deep into the class C region, they would have to have a negative bias supply pushing them deep into class C which would, just like a proper bias supply pushing the transistors towards B, or AB, cost the manufacturer money and time. Then you would have a true class C amplifier suitable for FM and CW only. And even them, some bipolar transistors do not like this deep "switching" mode and it can cause "hot spotting" and other phenomenon.

Ok back to it... so instead in most CB amplifiers the base (input) of the transistor is often just tied to CBG (circuit board ground) at 0 volts potential putting the transistors right at the border of class "C" and "B". True class "B" would call for forward bias, so we call them class C. Remember for class "C" conduction angle needs to be 90 degrees and for class "B" it is 180. What I usually see is something in between.

So..with a little forward bias, things go more into the B region, and then add a little more Ic (bias, idle current, etc) and we get more than 180 but less than 360 which is "AB" and fine for most operation as long as the bias source is a low impedance source and does not fluctuate all over the place, has proper RF bypassing and does not go negative on voice peaks which in some CB amps is typical.

On another note, I see a lot of people refer to their solid state, transistor amps as AB-1, AB-2, etc. This is IMPOSSIBLE. The reason for this, is AB-1, and AB-2 refers to a TUBE amplifier with the "1" or the "2" referring to which element in the tube is biased toward or against another element. This is NOT SO obviously with a bipolar transistor.

So bi-linear is misleading as well. It would tell you that is is a linear amplifier with a receive amplifier. I have even seen some CB amplifiers stamp AB-1 on the front. They obviously mislead and have no ideas themselves what they are building I guess.

To answer the question on the TX-75, it would be by definition a class C amp, but as referred to as earlier not deep into class C. But not "linear" either.

One last comment about class c. There is a push pull design phenomenon that does occur when two devices are put in stages once again common with CB amplifiers. It tends to replace the missing half of the cycle or part of it depending upon the design. To explain it all would be outside the scope of this post, but if anyone is interested I could do a write up on it.

This is all very old concepts, and technology. I suggest reading some older material such as ARRL handhooks from about 1945-1960 for information on AM, so called "NPC" that we see on here attempted a lot where modulated positive peaks exceed 100% and negative are limited to reduce interference and distortion. They also go into great detail about using class C for modulated modes, and the difference between feeding modulated RF through the amp and modulating the stage directly.
 
I always thought it was "garbage in, garbage out"...if there's no garbage in could garbage come out??? please explain...


3's


Basically a class C amp operates more like a switch, switching the RF current flow on and off during various parts of the cycle. When an RF signal is hard switched on and off it generates garbage moreso than if the switching is done slow and smooth. Even when using CW (mores code) you have to be carefull that the RF is not switched smoothly or it will result in "key clicks" that cause interference. That is pretty much it in a nutshell and in very basic terms,
 
Only way these people are ever going to understand amplifier biasing is to attend a class and be shown the plots of drive signal in vs the resulting signal out for the various bias modes and given the handout sheets to take home and look at again..
When this is shown then try the argument that it makes no difference right there in that class.
Even do an internet request on this subject and find out the answers from souces other than CB boards instead of keeping on denying there is no difference.
Short fact is you can not reproduce an input envelope signal other than CW or FM, with gain that is essentially distortion free in the output using class C conduction angles in any form.
Some one discribed class AB1 and 2 as appliying only to tube amps if I understood the reply.
WRONG.
Bias has the same intent, use, reason, conduction angle etc representations for solid state as it does for tube amplifiers.
Last I knew we still adjust idle current in solid state rigs that is for the class AB1 setting for general use.
Look in any CB or Ham radio service manuel and you will see the class AB1 setting idle current shown.
Now some higher end Ham radios have a class A bias option for those who want to work AM so distortion is at the min attainable with that radio.
Why would that be offered if is makes no difference?
.
A bi polar transister is a three port device the same as a triode tube.
Only difference is the voltage and current levels each operate at.
.
.On the first recording you can hear the amplifier come out of current (CONDUCTION CUTOFF) into conduction at the beginning of each sound. That's the mufflness. Part of the drive signal is missing.
The sudden fast rise into conduction also produces harmonics that are amplified and passed out that has many other frequencies in it.
.
Also, IMD has not even been mentioned here. Those are of unwanted signal "mixing" in the device and also causes wide band emmisions up and down the band.
Then add to all this, poor driver radio performance especially from a golden screwdrive that also gets amplified along with class C bias causing distortion and the result is a real mixed soup signal.
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On the second recording it didn't show as bad but was still there besides the recieve was not on frequency.
Listen again to them and rethink your positions on the subject.
.
Some how this thread reminds me of politics.
People stand before you will lie, distort the truth, are ignorent of the facts and just plain believe what they hear and try to make others believe it by passing it on as fact.
People who pass it on are called 'sheepels" and are worst than the lires.
At least the lies and the people who tell them are known by most others, when they hear them..
 
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KM3F,actually class AB1 and AB2 are in relation to tube amps only. The designation ab1 or ab2 pertains to wether or not grid current flows. Solidstate amps have no grid circuit and a solidstate equivalent has never been substituted in any wording of the definition of ab1 or ab2 that I have ever seen and I made a career in electronics.
 

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