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All things being equal: AB vs C

Free Cell said...
"When compared to a Class AB1 or Class AB2 amplifier operating at the same power input, a Class C amplifier will deliver a received signal increase of about 1db--in other words, 1/6 of 1 S-unit."

most people still run them 3 and 6 db higher . splatter splatter splatter .
 
Is war ever going be over at least once a year this has come up since the forum was created. There will be a few who will learn, and move foward, then there will those who want to be that "sniper" on bands. At the end of the day there will always be a bigger dog on the block. Get what makes you happy and use it, there are many on here that have led the horses to water, it's up to the horse to drink.
 
this thread is still going?

freecell said:
an AM transmitter produces a signal that constantly varies in amplitude.
an SSB transmitter produces a signal that constantly varies in amplitude.
Click to expand...

Its true, both AM and SSB varies amplitude, but AM has a carrier thats always there when transmitting, and this carrier will keep class C pills turned ON except in the case of 100% negative modulation where for that instant of negative peak there is no RF (or very little).

I'm sure you all know that SSB has no carrier, so there is nothing to keep class C pills on, which is why the biasing is needed.

Another item to be concerned with bipolar biasing, is that when temperature increases, the transistor will increase gain and burn itself up in a run-away condition, unless bias is reduced at high temperatures.
Bipolar transistor biasing - Wikipedia, the free encyclopedia
see "Note on temperature dependence".
Its something to be aware of with a 2sc2879 with biasing for SSB.

MOSFETs have an advantage here of having the opposite behavior of reduced gain at high temperatures, preventing the runaway condition.
 
rfoverlord said:
Is war ever going be over at least once a year this has come up since the forum was created. There will be a few who will learn, and move foward, then there will those who want to be that "sniper" on bands. At the end of the day there will always be a bigger dog on the block. Get what makes you happy and use it, there are many on here that have led the horses to water, it's up to the horse to drink.
Click to expand...

I wish I was on a different forum right now... I have a REALLY GOOD reply for this pointless reply...
 
dudmuck said:
...AM has a carrier thats always there when transmitting, and this carrier will keep class C pills turned ON except in the case of 100% negative modulation where for that instant of negative peak there is no RF (or very little).
Click to expand...

The carrier might keep the transmit relay closed, but it has nothing to do with keeping "class C pills turned ON". If the amplifier is biased Class C, it conducts for less than 180 degrees of the input cycle, by definition of Class C. The output is therefore not a faithful duplication of the input; the amplifier is therefore not linear. Non-linear means distortion, and distortion means splatter.
 
all really good input... the more you guys comment on this the more it forces me to research and the more I learn which is really the point... it also helps to hear simple/multiple explanations put to specific concepts.

good shiznit... apreciate it!
 
Beetle said:
The carrier might keep the transmit relay closed, but it has nothing to do with keeping "class C pills turned ON". If the amplifier is biased Class C, it conducts for less than 180 degrees of the input cycle, by definition of Class C. The output is therefore not a faithful duplication of the input; the amplifier is therefore not linear. Non-linear means distortion, and distortion means splatter.
Click to expand...

If you were talking about a single transistor, yes you are right.
But these pills are always used as a push-pull pair, so the inertia of the matching transformers fill in the gaps where both pills are off. But to maintain inertia needs at least a minimum RF input drive, which is why class C sucks at SSB.

A full cycle of 27MHz is only 37 nanoseconds, so the gap that needs to be covered by inertia is tiny amount of time.
 
I vote this the 2008 WWRF Thread of the Year award !! :thumbup:
A lot of good "truth" here fella's. :thumbup: and we all know that sometimes the "truth" don't sell guys. :( (many just buy the lie) I like that. :)

You were right about about the popcorn in the beginning Booty :drool: You just new it was going to get better. :) I like what you said rfoverlord , I'd say that was pretty much hitting the nail on the head dude. :thumbup:

Freecell , Doc (W5LZ) , Dudmuck , Beetle , and a few others tend to know there trades and hobbies well . After 6 years on these boards , they have truly been the teachers (weather you like them or not ) , the rest has been up to "us" to learn and take it for what it is , or just accept the lies for what they are and go about our businesses thinking we know what we know weather it's a bunch of B.S. or not. (kind of what rfoverlord said)

IM just a ballpark kind of guy when it comes to the numbers and my radio hobby (I try and keep it simple within my complacated brain) I'd like to think your question has been answered even alot more then you expected it would ROC1 :)

and yes , there are some decent "illegally made" cb radio amps out there. Even Texas Star's that are sold legally but converted for 11 meters (no longer legal) are good AB amps . You have the Messenger and Palomar/Cobra Blue face line that are AB (if you get them from the right source)

Yeap , clean in would be (as clean as your going to get) out. dirt in is dirt out no matter what amp it is. So in the end , if it truly means that much to you ? You take given radio and amp of choice to a good tech who knows his craft well and let them do it up as good as they can get it for you.......this way it's possible to utilize all your power on given freq rather then others above and below the one your on which would only be wasting your power to begin with.

I've said it before , it's like being a Alcoholic and getting nudge from a judge to go to A.A. meetings......1. you find out your a alcoholic and 2. after that , it has a way of screwing with your drinking there after and 3. you continue to stay in denile about the whole truth of the matter. :(

You can either deal with the truth or continue to buy the lie ? And what I've found out about this hobby is that folks plane and simple like ,can not and will not deal with the truth. IM just glad it's not my job to make them believe. If there happy ? So be it .
 
dudmuck said:
If you were talking about a single transistor, yes you are right.
But these pills are always used as a push-pull pair, so the inertia of the matching transformers fill in the gaps where both pills are off. But to maintain inertia needs at least a minimum RF input drive, which is why class C sucks at SSB.

A full cycle of 27MHz is only 37 nanoseconds, so the gap that needs to be covered by inertia is tiny amount of time.
Click to expand...

If you're running a pair of transistors in true "push-pull", it would make a lot more sense to do it right and bias it Class B. When one stops conducting, the other one immediately (i.e. much less than 37 nanoseconds later) starts conducting and vice versa. I'm sure the builders are familiar with this idea.
 
some info on amp classes .
Classes of Amplifier Operation

on another forum (partly sponsored by a class C amp builder) they were saying as a class c amp gets hotter it goes into class B mode . someone said they discussed this at their ham class and they all BOUGHT the idea their class c amps will be clean on ssb because of that . i just dont see how heat can compensate for a proper circuit design and i dont believe that BS for a nanosecond . but im a duck and somewhat of a parrot and lacked the knowledge to adaquately dispute that claim so i just didnt comment anymore .

i guess take the fans out and itll go into class AB then stick in in the oven while baking cookies and itll go into class A . hehehe
 
Last edited by a moderator:
SK said
"I've said it before , it's like being a Alcoholic and getting nudge from a judge to go to A.A. meetings......1. you find out your a alcoholic and 2. after that , it has a way of screwing with your drinking there after and 3. you continue to stay in denile about the whole truth of the matter. "

12 STEPC OF CCA . (class c anonymous)

1. We admitted we were powerless over splatter boxes - that our transmissions had become unmanageable .

2. Came to believe that a proper ab biased amp could restore our signal fidelity .

3. Made a decision to turn our amp biasing requirements over to the care of FREECELL as we understood Him .

4. Made a searching and fearless inventory of our signals sine wave on the oscilloscope .

5. Admitted to amp gurus , to ourselves and to our favorite forum the exact nature of our wrongs .

6. Were entirely ready to have class AB biasing remove all these defects of broadcasting .

7. Humbly asked e-bay/forum sales to remove our splatter boxes .

8. Made a list of all persons we had harmed , and prayed they didnt come knock on our door when we tore up their tvs and such .

9. Made direct amends to incorporate an actual bias design wherever possible, except when to do so would injure our pride .

10. Continued to take station inventory and only use amps with a actual bias in it .

11. Sought through forums and telephone to improve our conscious contact with FREECELL as we understood Him, asking only for knowledge of amps and antennas and the de-cyphering ability to carry that out.

12. Having had a RF amplifier awakening as the result of these steps, we tried to carry this message to class C addicts and to practice these principles in all our transmissions .
 
The only thing I could add to this has been highlighted and is part of the proper statement of AA.

BOOTY MONSTER said:
SK said
"I've said it before , it's like being a Alcoholic and getting nudge from a judge to go to A.A. meetings......1. you find out your a alcoholic and 2. after that , it has a way of screwing with your drinking there after and 3. you continue to stay in denile about the whole truth of the matter. "

12 STEPC OF CCA . (class c anonymous)

1. We admitted we were powerless over splatter boxes - that our transmissions had become unmanageable .

2. Came to believe that a proper ab biased amp could restore our signal fidelity .

3. Made a ( conscience) decision to turn our amp biasing requirements over to the care of FREECELL as we understood Him .

4. Made a searching and fearless inventory of our signals sine wave on the oscilloscope .

5. Admitted to amp gurus , to ourselves and to our favorite forum the exact nature of our wrongs .

6. Were entirely ready to have class AB biasing remove all these defects of broadcasting .

7. Humbly asked e-bay/forum sales to remove our splatter boxes .

8. Made a list of all persons we had harmed , and prayed they didnt come knock on our door when we tore up their tvs and such .

9. Made direct amends to incorporate an actual bias design wherever possible, except when to do so would injure our pride .

10. Continued to take station inventory and only use amps with a actual bias in it .

11. Sought through forums and telephone to improve our conscious contact with FREECELL as we understood Him, asking only for knowledge of amps and antennas and the de-cyphering ability to carry that out.

12. Having had a RF amplifier awakening as the result of these steps, we tried to carry this message to class C addicts and to practice these principles in all our transmissions .
Click to expand...
 

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