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From: (Dave=A0Hall)
On 6 Oct 2004 14:37:46 -0700, (Jim Hampton) wrote: Hello, Twist Dave was referring to 'S' units at the other end of the circuit. One 'S' unit is *supposidly* equal to 6 dB. 6 dB is an increase in power of four times. (You know that, I know that,) Jim has yet to answer, but here you are answering for him, Davie. What confidence you display. Again, for the record, Jim, are you in agreement that a "peak and tune" will increase S units on a 4 watt stock radio? most knowledgable people know that, Agreed, as you are the ONLY one arguing that you can change the net increase on a stck 4 watt radio in regards to S units. That alone should tell you what you lack and need to know, but your comprehension skills have been abused. and I suspect Twisty knows that as well. He just likes to argue for the sake of arguing. I exchanged ideas on this subject and in this thread with sideband and now Jim, and as usual, you are alone in your claims. *Only* you are referring to your exchanges as arguing, no one else. Get over yourself and educate yourself on how to conduct proper communication and public debate without allowing your temper to exhibit control. In other words, stop taking everyhting so personal. It's not my fault your ego makes you feel this way when you attempt to debate issues, but I don't mind being your sounding board for blame. It's true that most CB "S" meters are far from linear, and consistent. On the lower part of the scale, 1 "S" unit might be only 2 or 3 db. At the upper end, 1 "S" unit might be closer to 10db. But the theory is sound. Dave "Sandbagger" And has nothing to do with your ignorant and wrong claim that a peak and tune increases the S units on a 4 watt stock radio. |
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On Thu, 7 Oct 2004 10:05:13 -0400, (Twistedhed)
wrote: From: (Jim*Hampton) Hello, Twist Yo' Jim. Dave was referring to 'S' units at the other end of the circuit. When I took exception to his words, he was speaking of S units received by another radio, arrived via the peaking of the 4 watt radio that was of topic.. No, that's WRONG. Another shining example of your inability to comprehend. I stated that peaking a 4 watt radio will improve that radio's signal to another's receive station. But that improvement will be very minimal, as it takes 6db (4x increase) more in power to gain 1 "S" unit on the received end. Dave "Sandbagger" |
On Thu, 07 Oct 2004 07:06:26 -0400, Dave Hall
wrote in : On Wed, 06 Oct 2004 11:47:29 -0700, Frank Gilliland wrote: snip Compression -- a term usually applied to audio conditioning where the amplification of a signal is varied inversely to it's input level. One of the most common types of audio compressor is called "constant volume amplifier". That is but one type of compression. For a more detailed discussion of RF amplifier compression, please refer to the following related link: http://cp.literature.agilent.com/lit...5965-7710E.pdf Generally speaking, amplifier compression occurs when the input:output power ratio no longer increases db for db. You should know me by now -- I just -have- to disagree. The use of the term 'compression region' is really a misnomer. It's properly described as a nonlinear region. The reason is that different devices behave differently, and while a few devices (some transistors, a few tubes, incandescent lightbulbs) have nonlinear characteristics similar to compression, the fact is that nothing is being 'compressed', and the vast majority of other devices have nonlinear regions that do not resemble compression. And whether that nonlinear region is gradual or sharp, it's still clipping because it's a limitation of the device. It also causes distortion that is characteristic of clipping. And yes, saturation is within the nonlinear region. I'll give him this one. This may be a matter of semantics, like noting the difference between 'weight' and 'mass'. I had these things drilled into my brain by my profs for the simple reason that using the wrong term can cause a misunderstanding. And that's what I believe is happening when people substitute the term 'compression' for when the transistor has exceeded the limits of linearity and subsequently clips, be it hard or soft. But no matter what you call it, the result is distortion. But the problem here is that the term 'compression' has been adopted by voodoo techs as a euphamism for 'clipping', making it sound as if the distortion-causing effect is not only benign, but sometimes preferred. It is neither. After reading the link, you might want to revise your definition. There are a bunch of very talented engineers here who would be a bit insulted to find out that you refer to them as "voodoo techs". I'll stick with my definition. And while I may take issue with some of the more liberal definitions used by engineers these days, I should point out that I worked for HP (Agilent) several years ago and I'm not a big fan of their engineering department. But you are right about one thing. a -33dbc harmonic rating from a single carrier signal is pretty poor. Perhaps a chebychev lowpass filter on the output will fix it up..... That would be nothing more than a kludge. The fault is in the design. The response isn't even close to linear. That may be due to the bias class, the bias regulator, the choice of active device, or just crappy engineering overall. I suspect it's a little of everything. Usually, if it is a push-pull design, device matching plays an important part. Bias is also important, as is impedance matching. But even a "good" design should have a follow-up low pass filter to minimize any harmonic content. Absolutely. But even filters have limitations. Assuming Brian's amp has 350 watt noise figures in the neighborhood of -18 to -24 dB (not unrealistic), it would take a mighty stout filter to clean it up! |
On Thu, 07 Oct 2004 13:58:13 -0700, Frank Gilliland
wrote: On Thu, 07 Oct 2004 07:06:26 -0400, Dave Hall wrote in : On Wed, 06 Oct 2004 11:47:29 -0700, Frank Gilliland wrote: snip Compression -- a term usually applied to audio conditioning where the amplification of a signal is varied inversely to it's input level. One of the most common types of audio compressor is called "constant volume amplifier". That is but one type of compression. For a more detailed discussion of RF amplifier compression, please refer to the following related link: http://cp.literature.agilent.com/lit...5965-7710E.pdf Generally speaking, amplifier compression occurs when the input:output power ratio no longer increases db for db. You should know me by now -- I just -have- to disagree. That's what makes discussion interesting. Unless, of course the other party is nameless sociopath..... ;-) The use of the term 'compression region' is really a misnomer. It's properly described as a nonlinear region. A device can be non-linear without going into compression. The way I learned it, compression is a specific term that applies when a normally linear device loses linearity as it approaches it's maximum drive level. The reason is that different devices behave differently, and while a few devices (some transistors, a few tubes, incandescent lightbulbs) have nonlinear characteristics similar to compression, the fact is that nothing is being 'compressed', and the vast majority of other devices have nonlinear regions that do not resemble compression. Exactly! That's why compression refers to a specific condition, so as to differentiate it from other forms of non-linerarity. Certain class "C" "Modulator" type amplifiers, for example, deliberately run in the non-linear region just above device cutoff, to take advantage of the "swing" effect of the device. It's non-linear, but it's not compressed. And whether that nonlinear region is gradual or sharp, it's still clipping because it's a limitation of the device. It also causes distortion that is characteristic of clipping. And yes, saturation is within the nonlinear region. I differentiate the term "clipping" from "compression" by the application in which the terms are used. In an application such as a broadband amplifier with a broad spectrum of carriers (Such as a CATV amp), is applied to the input, the term compression applies as you reach the point of non-linear gain and the incidents of composite second order beats rises disproportionately. I look at "clipping" as a momentary chopping off of an otherwise linear signal reproduction, such as what you would encounter with AM modulation peaks which run out of headroom in an amplifier, which would otherwise be still in the linear range when unmodulated. You can still "clip" while not being fully into compression. Maybe I'm over-analyzing these terms, but that's me..... I'll give him this one. This may be a matter of semantics, like noting the difference between 'weight' and 'mass'. I had these things drilled into my brain by my profs for the simple reason that using the wrong term can cause a misunderstanding. And that's what I believe is happening when people substitute the term 'compression' for when the transistor has exceeded the limits of linearity and subsequently clips, be it hard or soft. But no matter what you call it, the result is distortion. No argument there. But the problem here is that the term 'compression' has been adopted by voodoo techs as a euphamism for 'clipping', making it sound as if the distortion-causing effect is not only benign, but sometimes preferred. It is neither. After reading the link, you might want to revise your definition. There are a bunch of very talented engineers here who would be a bit insulted to find out that you refer to them as "voodoo techs". I'll stick with my definition. And while I may take issue with some of the more liberal definitions used by engineers these days, I should point out that I worked for HP (Agilent) several years ago and I'm not a big fan of their engineering department. While the link I provided, was put out by Agilent, it was one of many examples. I don't work for them either, but I do work with some talented RF engineers, and we use the term compression frequently to describe the point where linear gain ceases, and distortion products increase disproportionately. But you are right about one thing. a -33dbc harmonic rating from a single carrier signal is pretty poor. Perhaps a chebychev lowpass filter on the output will fix it up..... That would be nothing more than a kludge. The fault is in the design. The response isn't even close to linear. That may be due to the bias class, the bias regulator, the choice of active device, or just crappy engineering overall. I suspect it's a little of everything. Usually, if it is a push-pull design, device matching plays an important part. Bias is also important, as is impedance matching. But even a "good" design should have a follow-up low pass filter to minimize any harmonic content. Absolutely. But even filters have limitations. Assuming Brian's amp has 350 watt noise figures in the neighborhood of -18 to -24 dB (not unrealistic), it would take a mighty stout filter to clean it up! A 5 pole filter should bring it into line. All he would need is an additional 30db of attenuation Dave "Sandbagger" http://home.ptd.net/~n3cvj |
On Fri, 08 Oct 2004 07:08:10 -0400, Dave Hall
wrote in : On Thu, 07 Oct 2004 13:58:13 -0700, Frank Gilliland wrote: On Thu, 07 Oct 2004 07:06:26 -0400, Dave Hall wrote in : On Wed, 06 Oct 2004 11:47:29 -0700, Frank Gilliland wrote: snip Compression -- a term usually applied to audio conditioning where the amplification of a signal is varied inversely to it's input level. One of the most common types of audio compressor is called "constant volume amplifier". That is but one type of compression. For a more detailed discussion of RF amplifier compression, please refer to the following related link: http://cp.literature.agilent.com/lit...5965-7710E.pdf Generally speaking, amplifier compression occurs when the input:output power ratio no longer increases db for db. You should know me by now -- I just -have- to disagree. That's what makes discussion interesting. Unless, of course the other party is nameless sociopath..... ;-) Which one? There are so many..... The use of the term 'compression region' is really a misnomer. It's properly described as a nonlinear region. A device can be non-linear without going into compression. The way I learned it, compression is a specific term that applies when a normally linear device loses linearity as it approaches it's maximum drive level. The problem is the application; i.e, the operational limits of the device. More below. The reason is that different devices behave differently, and while a few devices (some transistors, a few tubes, incandescent lightbulbs) have nonlinear characteristics similar to compression, the fact is that nothing is being 'compressed', and the vast majority of other devices have nonlinear regions that do not resemble compression. Exactly! That's why compression refers to a specific condition, so as to differentiate it from other forms of non-linerarity. Certain class "C" "Modulator" type amplifiers, for example, deliberately run in the non-linear region just above device cutoff, to take advantage of the "swing" effect of the device. ......huh? That statement looks like a train-wreck. Assuming we're talking Class C for both types, a device is usually pushed towards -saturation-, and the result is clipping which forms a psuedo-square wave that packs more energy than a sine wave, and making the stage more efficient (a design that evolved into the Class E amplifier). Also, Class C devices are -biased- above cutoff by definition. But what is this "swing effect" you describe? I have never heard of a -device- having such an effect unless it was a self-resonant device. Last time I checked, most transistors don't tend to be self-resonant below 30 MHz..... It's non-linear, but it's not compressed. That's the point. It's -not- compressed. I see no reason to place that label on a portion of a curve only because it loosly resembles one of the characteristics of compression yet doesn't fall within its definition. To me it's like using the word 'pill' to describe an RF transistor, or 'swing' to describe modulation. And whether that nonlinear region is gradual or sharp, it's still clipping because it's a limitation of the device. It also causes distortion that is characteristic of clipping. And yes, saturation is within the nonlinear region. I differentiate the term "clipping" from "compression" by the application in which the terms are used. In an application such as a broadband amplifier with a broad spectrum of carriers (Such as a CATV amp), is applied to the input, the term compression applies as you reach the point of non-linear gain and the incidents of composite second order beats rises disproportionately. I look at "clipping" as a momentary chopping off of an otherwise linear signal reproduction, such as what you would encounter with AM modulation peaks which run out of headroom in an amplifier, which would otherwise be still in the linear range when unmodulated. You can still "clip" while not being fully into compression. Maybe I'm over-analyzing these terms, but that's me..... I see the image in your brain -- "clipping" suggests a straight-line cut from the top of the wave. And I understand your definition of 'compression' as the transitional zone between linearity and clipping. But clipping, by definition, is caused when the signal exceeds the limits of the device. And that's exactly what happens when the output is pushed into the nonlinear region because it's operation is intended to be limited to the linear region (otherwise it's not a linear amp). I'll give him this one. This may be a matter of semantics, like noting the difference between 'weight' and 'mass'. I had these things drilled into my brain by my profs for the simple reason that using the wrong term can cause a misunderstanding. And that's what I believe is happening when people substitute the term 'compression' for when the transistor has exceeded the limits of linearity and subsequently clips, be it hard or soft. But no matter what you call it, the result is distortion. No argument there. But the problem here is that the term 'compression' has been adopted by voodoo techs as a euphamism for 'clipping', making it sound as if the distortion-causing effect is not only benign, but sometimes preferred. It is neither. After reading the link, you might want to revise your definition. There are a bunch of very talented engineers here who would be a bit insulted to find out that you refer to them as "voodoo techs". I'll stick with my definition. And while I may take issue with some of the more liberal definitions used by engineers these days, I should point out that I worked for HP (Agilent) several years ago and I'm not a big fan of their engineering department. While the link I provided, was put out by Agilent, it was one of many examples. I don't work for them either, but I do work with some talented RF engineers, and we use the term compression frequently to describe the point where linear gain ceases, and distortion products increase disproportionately. I've known many talented engineers who learned switch terminology backwards: for example, they would describe a 6-position rotory switch as a 6-pole single-throw. I've known some talented engineers who didn't know the difference between 'active' and 'passive'. I've even known a couple talented engineers who thought electrons flowed from positive to negative. I guess I'm just anal (like THAT'S a suprise!). But you are right about one thing. a -33dbc harmonic rating from a single carrier signal is pretty poor. Perhaps a chebychev lowpass filter on the output will fix it up..... That would be nothing more than a kludge. The fault is in the design. The response isn't even close to linear. That may be due to the bias class, the bias regulator, the choice of active device, or just crappy engineering overall. I suspect it's a little of everything. Usually, if it is a push-pull design, device matching plays an important part. Bias is also important, as is impedance matching. But even a "good" design should have a follow-up low pass filter to minimize any harmonic content. Absolutely. But even filters have limitations. Assuming Brian's amp has 350 watt noise figures in the neighborhood of -18 to -24 dB (not unrealistic), it would take a mighty stout filter to clean it up! A 5 pole filter should bring it into line. All he would need is an additional 30db of attenuation Don't forget that as you increase the power you need to increase the attenuation. This is because of the changes in the equipment rules regarding harmonic emissions. The limit is now absolute whereas before it was relative to signal strength. Regardless, a LP filter won't filter the splatter. |
From: (Dave=A0Hall)
On Thu, 7 Oct 2004 10:52:18 -0400, (Twistedhed) wrote: And has nothing to do with your ignorant and wrong claim that a peak and tune increases the S units on a 4 watt stock radio. You are a basket case. And your insultive demeanor and erratic behavior is beyond your self-control whenever you are reminded we are speaking of a topic that was being discussed, not a hypothetical radio invoked by yourself to change the topic. Your ability to comprehend even the simplest concepts is severely impeded. Complaining about me and blaming me for your radio incompetence isn't going to change your inability to remain on topic or take away your ignorance concerning S units. This is seconded only by your penchant to spin and twist words in order to avoid admitting that you misunderstood the concept. A concept only you appear to be familiar with. I'll let Jim or anyone else set you straight. Jim isn't bailing you out, In fact, no one has agreed with you, so stop looking to others for help. But suffice to say, you're in over your head. Dave "Sandbagger" I'm not the one that claimed S units can be increased on a 4 watt radio with a peak and tune,,,you did. Learn to accept your failures and those things you are unable to change without the need to blame others. |
N3cvj wrote:
When I took exception to his words, he was speaking of S units received by another radio, arrived via the peaking of the 4 watt radio that was of topic.. No, that's WRONG. Another shining example of your inability to comprehend. I stated that peaking a 4 watt radio will improve that radio's signal to another's receive station. Stop trying to tell the masses they misread you. Here is what you said(verbatim): "I won't go into the math here but in order to see even 1 "S" (signal) unit increase on another guy's meter, your radio would have to put out 4 times as much power as it did stock." There you have it. You even clarified which radio you were speaking of by identifying "YOUR" radio in your response to the post of the 4 watt radio. And you still haven't explained how that is possible, and you won't,,,,because it's not. Dave "Sandbagger" That self-contradiction is almost as direct and blatant as this one: "What Doug does in no way represents what I do here or on the air" N3CVJ, 2004 "Yes I'll admit I made a mistake allowing myself to get sucked into Doug's world But mistakes are how humans learn, so chalk this up as lesson learned." N3CVJ, 2003 |
On Fri, 08 Oct 2004 05:57:51 -0700, Frank Gilliland
wrote: You should know me by now -- I just -have- to disagree. That's what makes discussion interesting. Unless, of course the other party is nameless sociopath..... ;-) Which one? There are so many..... Does it matter? ;-) The use of the term 'compression region' is really a misnomer. It's properly described as a nonlinear region. A device can be non-linear without going into compression. The way I learned it, compression is a specific term that applies when a normally linear device loses linearity as it approaches it's maximum drive level. The problem is the application; i.e, the operational limits of the device. More below. The reason is that different devices behave differently, and while a few devices (some transistors, a few tubes, incandescent lightbulbs) have nonlinear characteristics similar to compression, the fact is that nothing is being 'compressed', and the vast majority of other devices have nonlinear regions that do not resemble compression. Exactly! That's why compression refers to a specific condition, so as to differentiate it from other forms of non-linerarity. Certain class "C" "Modulator" type amplifiers, for example, deliberately run in the non-linear region just above device cutoff, to take advantage of the "swing" effect of the device. .....huh? That statement looks like a train-wreck. Assuming we're talking Class C for both types, a device is usually pushed towards -saturation-, and the result is clipping which forms a psuedo-square wave that packs more energy than a sine wave, and making the stage more efficient (a design that evolved into the Class E amplifier). Also, Class C devices are -biased- above cutoff by definition. But what is this "swing effect" you describe? I have never heard of a -device- having such an effect unless it was a self-resonant device. Last time I checked, most transistors don't tend to be self-resonant below 30 MHz..... I know, swing is not a technical term, but I don't know what else to call it besides non-linear (distorted) modulation gain. A Class "C" amplifier is biased below cutoff (Hence the improved efficiency) so if your drive level is barely above that point, the region of gain there is significantly non-linear. At 2 watts of drive, the gain might be 6db. By the time drive hits 8 watts, it might be 10 db. The "swing effect", then results in a radio with a 2 watt carrier modulating to 100% at 8 watts, feeding into an amp and coming out with an 8 watt carrier with modulation peaks reaching 80 watts. It's dirty, it's distorted, but it sure makes that wattmeter swing forward... But the point of my example was to illustrate that not all non-linearity is a result of continual overdrive (Compression) or momentary overdrive (Clipping). It's non-linear, but it's not compressed. That's the point. It's -not- compressed. I see no reason to place that label on a portion of a curve only because it loosly resembles one of the characteristics of compression yet doesn't fall within its definition. To me it's like using the word 'pill' to describe an RF transistor, or 'swing' to describe modulation. Don't shoot me, I'm only the messenger. Whether or not the term is factually accurate, it is in common use. I adopted it from working with those who used it, and many other support companies which offer technical seminars on various conditions of amplification. And whether that nonlinear region is gradual or sharp, it's still clipping because it's a limitation of the device. It also causes distortion that is characteristic of clipping. And yes, saturation is within the nonlinear region. I differentiate the term "clipping" from "compression" by the application in which the terms are used. In an application such as a broadband amplifier with a broad spectrum of carriers (Such as a CATV amp), is applied to the input, the term compression applies as you reach the point of non-linear gain and the incidents of composite second order beats rises disproportionately. I look at "clipping" as a momentary chopping off of an otherwise linear signal reproduction, such as what you would encounter with AM modulation peaks which run out of headroom in an amplifier, which would otherwise be still in the linear range when unmodulated. You can still "clip" while not being fully into compression. Maybe I'm over-analyzing these terms, but that's me..... I see the image in your brain -- "clipping" suggests a straight-line cut from the top of the wave. And I understand your definition of 'compression' as the transitional zone between linearity and clipping. But clipping, by definition, is caused when the signal exceeds the limits of the device. Stop right there. You've got it. Clipping is when you exceed the absolute limits of the device to amplify further. Compression is less severe, the device can still amplify, but it is no longer linear db in for db out. But no matter what you call it, the result is distortion. No argument there. I'll stick with my definition. And while I may take issue with some of the more liberal definitions used by engineers these days, I should point out that I worked for HP (Agilent) several years ago and I'm not a big fan of their engineering department. While the link I provided, was put out by Agilent, it was one of many examples. I don't work for them either, but I do work with some talented RF engineers, and we use the term compression frequently to describe the point where linear gain ceases, and distortion products increase disproportionately. I've known many talented engineers who learned switch terminology backwards: for example, they would describe a 6-position rotory switch as a 6-pole single-throw. I've known some talented engineers who didn't know the difference between 'active' and 'passive'. I've even known a couple talented engineers who thought electrons flowed from positive to negative. I guess I'm just anal (like THAT'S a suprise!). That's the difference between the "hole" theory and the "electron" theory. I admit that current flowing from positive to negative makes more "sense", even if it has been shown to be the opposite. Absolutely. But even filters have limitations. Assuming Brian's amp has 350 watt noise figures in the neighborhood of -18 to -24 dB (not unrealistic), it would take a mighty stout filter to clean it up! A 5 pole filter should bring it into line. All he would need is an additional 30db of attenuation Don't forget that as you increase the power you need to increase the attenuation. This is because of the changes in the equipment rules regarding harmonic emissions. The limit is now absolute whereas before it was relative to signal strength. That's only true above a certain power output. I believe it's 1 KW but my mind's a little foggy on the exact level. Below those limits, harmonic content is still rated relative to dbc. It makes little sense to use absolute levels which would be higher than the -dbc ratings in a "low" power amp. -40dbc from a 1 KW amp is100 mW. But if CB makers were allowed to spec harmonic output at 100 mW, that would be much worse than current specs. I don't think Brian is playing in the big leagues yet. ;-) Regardless, a LP filter won't filter the splatter. That's certainly true. That has to be handled in the biasing, feedback, and by keeping drive levels in the linear range of the devices. Dave "Sandbagger" http://home.ptd.net/~n3cvj |
On Fri, 08 Oct 2004 09:57:07 -0400, Dave Hall
wrote in : snip for brevity I know, swing is not a technical term, but I don't know what else to call it besides non-linear (distorted) modulation gain. Good point. A Class "C" amplifier is biased below cutoff .....my bad.... (Hence the improved efficiency) so if your drive level is barely above that point, the region of gain there is significantly non-linear. Well, yeah, if by nonlinear you mean nonexistent. At 2 watts of drive, the gain might be 6db. By the time drive hits 8 watts, it might be 10 db. The "swing effect", then results in a radio with a 2 watt carrier modulating to 100% at 8 watts, feeding into an amp and coming out with an 8 watt carrier with modulation peaks reaching 80 watts. It's dirty, it's distorted, but it sure makes that wattmeter swing forward... Now I see what you mean. I thought you were talking about the flywheel effect. The train wreck must have been caused when my brain spilled on the tracks. But the point of my example was to illustrate that not all non-linearity is a result of continual overdrive (Compression) or momentary overdrive (Clipping). It's non-linear, but it's not compressed. That's the point. It's -not- compressed. I see no reason to place that label on a portion of a curve only because it loosly resembles one of the characteristics of compression yet doesn't fall within its definition. To me it's like using the word 'pill' to describe an RF transistor, or 'swing' to describe modulation. Don't shoot me, I'm only the messenger. Whether or not the term is factually accurate, it is in common use. I adopted it from working with those who used it, and many other support companies which offer technical seminars on various conditions of amplification. I realize that the term is used as you describe. My beef is that such use is inaccurate and inappropriate. And whether that nonlinear region is gradual or sharp, it's still clipping because it's a limitation of the device. It also causes distortion that is characteristic of clipping. And yes, saturation is within the nonlinear region. I differentiate the term "clipping" from "compression" by the application in which the terms are used. In an application such as a broadband amplifier with a broad spectrum of carriers (Such as a CATV amp), is applied to the input, the term compression applies as you reach the point of non-linear gain and the incidents of composite second order beats rises disproportionately. I look at "clipping" as a momentary chopping off of an otherwise linear signal reproduction, such as what you would encounter with AM modulation peaks which run out of headroom in an amplifier, which would otherwise be still in the linear range when unmodulated. You can still "clip" while not being fully into compression. Maybe I'm over-analyzing these terms, but that's me..... I see the image in your brain -- "clipping" suggests a straight-line cut from the top of the wave. And I understand your definition of 'compression' as the transitional zone between linearity and clipping. But clipping, by definition, is caused when the signal exceeds the limits of the device. Stop right there. You've got it. Clipping is when you exceed the absolute limits of the device to amplify further. Compression is less severe, the device can still amplify, but it is no longer linear db in for db out. Like I said, I understand what you mean by the 'compression region'. I just think it's not the appropriate label, mainly because nothing is compressed. I still think that 'clipping' is more appropriate, and I could even accept 'limiting' or 'squaring'. But not 'compression'. But no matter what you call it, the result is distortion. No argument there. I'll stick with my definition. And while I may take issue with some of the more liberal definitions used by engineers these days, I should point out that I worked for HP (Agilent) several years ago and I'm not a big fan of their engineering department. While the link I provided, was put out by Agilent, it was one of many examples. I don't work for them either, but I do work with some talented RF engineers, and we use the term compression frequently to describe the point where linear gain ceases, and distortion products increase disproportionately. I've known many talented engineers who learned switch terminology backwards: for example, they would describe a 6-position rotory switch as a 6-pole single-throw. I've known some talented engineers who didn't know the difference between 'active' and 'passive'. I've even known a couple talented engineers who thought electrons flowed from positive to negative. I guess I'm just anal (like THAT'S a suprise!). That's the difference between the "hole" theory and the "electron" theory. I admit that current flowing from positive to negative makes more "sense", even if it has been shown to be the opposite. You and I both recognize that current flow and electron flow are not the same thing, and so do most engineers. But the engineers I mentioned actually thought that -electron- flow was from positive to negative. Maybe it is under certain circumstances, but I haven't been to the anti-universe since high-school. Absolutely. But even filters have limitations. Assuming Brian's amp has 350 watt noise figures in the neighborhood of -18 to -24 dB (not unrealistic), it would take a mighty stout filter to clean it up! A 5 pole filter should bring it into line. All he would need is an additional 30db of attenuation Don't forget that as you increase the power you need to increase the attenuation. This is because of the changes in the equipment rules regarding harmonic emissions. The limit is now absolute whereas before it was relative to signal strength. That's only true above a certain power output. I believe it's 1 KW but my mind's a little foggy on the exact level. Below those limits, harmonic content is still rated relative to dbc. It makes little sense to use absolute levels which would be higher than the -dbc ratings in a "low" power amp. -40dbc from a 1 KW amp is100 mW. But if CB makers were allowed to spec harmonic output at 100 mW, that would be much worse than current specs. I don't think Brian is playing in the big leagues yet. ;-) Not if he can't jump into this discussion and defend his work. Regardless, a LP filter won't filter the splatter. That's certainly true. That has to be handled in the biasing, feedback, and by keeping drive levels in the linear range of the devices. If Brian appears and brings an open mind, maybe I'll show him how to use predistortion in the bias regulator to linearize the output. But that's a big 'if'. |
On Fri, 08 Oct 2004 07:22:54 -0700, Frank Gilliland
wrote: On Fri, 08 Oct 2004 09:57:07 -0400, Dave Hall wrote in : snip for brevity At 2 watts of drive, the gain might be 6db. By the time drive hits 8 watts, it might be 10 db. The "swing effect", then results in a radio with a 2 watt carrier modulating to 100% at 8 watts, feeding into an amp and coming out with an 8 watt carrier with modulation peaks reaching 80 watts. It's dirty, it's distorted, but it sure makes that wattmeter swing forward... Now I see what you mean. I thought you were talking about the flywheel effect. The train wreck must have been caused when my brain spilled on the tracks. No, nothing that elaborate. Just simple basic stuff, but it's the stuff that CB'ers seem to flock to, even if it isn't the cleanest use of amplification devices. But the point of my example was to illustrate that not all non-linearity is a result of continual overdrive (Compression) or momentary overdrive (Clipping). It's non-linear, but it's not compressed. That's the point. It's -not- compressed. I see no reason to place that label on a portion of a curve only because it loosly resembles one of the characteristics of compression yet doesn't fall within its definition. To me it's like using the word 'pill' to describe an RF transistor, or 'swing' to describe modulation. Don't shoot me, I'm only the messenger. Whether or not the term is factually accurate, it is in common use. I adopted it from working with those who used it, and many other support companies which offer technical seminars on various conditions of amplification. I realize that the term is used as you describe. My beef is that such use is inaccurate and inappropriate. You will find this true in many cases. But unless I'm in a position to correct the error, I just go with the flow, rather than calling unwanted attention to myself for making (standing) waves.... I look at "clipping" as a momentary chopping off of an otherwise linear signal reproduction, such as what you would encounter with AM modulation peaks which run out of headroom in an amplifier, which would otherwise be still in the linear range when unmodulated. You can still "clip" while not being fully into compression. Maybe I'm over-analyzing these terms, but that's me..... I see the image in your brain -- "clipping" suggests a straight-line cut from the top of the wave. And I understand your definition of 'compression' as the transitional zone between linearity and clipping. But clipping, by definition, is caused when the signal exceeds the limits of the device. Stop right there. You've got it. Clipping is when you exceed the absolute limits of the device to amplify further. Compression is less severe, the device can still amplify, but it is no longer linear db in for db out. Like I said, I understand what you mean by the 'compression region'. I just think it's not the appropriate label, mainly because nothing is compressed. I still think that 'clipping' is more appropriate, and I could even accept 'limiting' or 'squaring'. But not 'compression'. Ok, try looking at it this way, in the audio sense of the term "compression", a dynamic range of 90db, is often squashed into a range of less than 70db. In the RF amplifier sense, the amount of change for every 1 db of input signal changes from 1 db on the output to an amount less than that. A large variation of change (within the region of compression) on the input results in less of a range on the output. That change is therefore "compressed". That's the difference between the "hole" theory and the "electron" theory. I admit that current flowing from positive to negative makes more "sense", even if it has been shown to be the opposite. You and I both recognize that current flow and electron flow are not the same thing, and so do most engineers. But the engineers I mentioned actually thought that -electron- flow was from positive to negative. Maybe it is under certain circumstances, but I haven't been to the anti-universe since high-school. I actually knew a technician many years ago who thought that it would take a few seconds for CATV signals several miles away to bleed off after a line amp was disconnected. Hey, we're talking RF here not water pressure! Sheesh! Absolutely. But even filters have limitations. Assuming Brian's amp has 350 watt noise figures in the neighborhood of -18 to -24 dB (not unrealistic), it would take a mighty stout filter to clean it up! A 5 pole filter should bring it into line. All he would need is an additional 30db of attenuation Don't forget that as you increase the power you need to increase the attenuation. This is because of the changes in the equipment rules regarding harmonic emissions. The limit is now absolute whereas before it was relative to signal strength. That's only true above a certain power output. I believe it's 1 KW but my mind's a little foggy on the exact level. Below those limits, harmonic content is still rated relative to dbc. It makes little sense to use absolute levels which would be higher than the -dbc ratings in a "low" power amp. -40dbc from a 1 KW amp is100 mW. But if CB makers were allowed to spec harmonic output at 100 mW, that would be much worse than current specs. I don't think Brian is playing in the big leagues yet. ;-) Not if he can't jump into this discussion and defend his work. You noticed that too? Regardless, a LP filter won't filter the splatter. That's certainly true. That has to be handled in the biasing, feedback, and by keeping drive levels in the linear range of the devices. If Brian appears and brings an open mind, maybe I'll show him how to use predistortion in the bias regulator to linearize the output. But that's a big 'if'. Can you do that for RF amps? I've heard of the technique, but thought is was strictly for audio amps. Dave "Sandbagger" http://home.ptd.net/~n3cvj |
On Fri, 08 Oct 2004 11:54:22 -0400, Dave Hall
wrote in : On Fri, 08 Oct 2004 07:22:54 -0700, Frank Gilliland wrote: snip If Brian appears and brings an open mind, maybe I'll show him how to use predistortion in the bias regulator to linearize the output. But that's a big 'if'. Can you do that for RF amps? Absolutely. One method is to tap the input signal to a small RF power transistor with similar nonlinear characteristics and use it to shunt the input to the final. That method also eliminates the need for a base resistor and improves bias regulation. Overall, the amp requires a little more drive power, but the benefits are well worth the costs. There are other methods that work even better such as high-frequency OP-amps with nonlinear feedback, inductors with nonlinear saturation characteristics... just about any part of the circuit can be tailored to compensate for a nonlinear power device. ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Twist:
1. I don't have your email... Haven't for a couple of years. Mine's easy to find, if you know where to look. I've even been posting hints as to how to find it for years.... every time I post. 2. I mostly operate on the Amateur bands now, though I do run 19 to find out why I'm sitting in traffic, or to tell Swift he's a moron (like he doesn't know already, but it's still fun to yell at the guy who doesn't know how to keep it in his lane). 3. It wasn't voodoo.. Voodoo is expecting pushing over 100% modulation to make the radio "louder" on the receiving radio.... I've said it before, and I'll say it again.. 4 watts on one channel is alot louder than 40 watts on all 40. -SSB Twistedhed wrote: From: (sideband) Twistedhed wrote: You would be best served putting your voodoo radio bull**** to rest. Assuming a peak and tune job is somehow related to increased "S" units is imbecilic. _ Twist: Actually, there is a correlation. If two radios are set up in a "fixed" location, each, and one transmits a carrier, there will be a reading on the "s" meter of the receiving radio. Assuming the two radios are far enough apart so that the transmitted signal does not register above, say, s5 on the receiver, it is possible to get a relative power reading from the transmitting radio. Now if the transmitting radio increases power fourfold, say from 4 watts to 16 watts, the receiving radio should now show s6 on its meter. This of course assumes that the receiving radio's ALC is tuned properly and that the s-meter is calibrated properly. In a properly calibrated receiver, a 3db increase in received signal strength should show about 1/2 of an S unit. Doubling the power output is the equivalent a 3db increase. Whooa...you sure? It's a moot point, but output power does indeed have something to do with "s" units, to the receiving radio. There isn't a direct correlation, and most CB receivers probably aren't calibrated properly, but there is a correlation, nonetheless. Yes, thanks for the reminder. I am aware output has much to do with the S units on the receiving end. What was being discussed was a peak and tune of a four watt radio. No amount of tuning or peaking is going to render a difference in S units from 4 watts. To the original poster: as for the antenna advice, a Wilson 1000 is a decent antenna, and will do fine. You will notice increased receive and transmit range while still remaining legal. Hope this helps. -SSB SSB,,Im taking another road trip to the Carolinas real soon,,probably Myrtle Beach. In addition to seeing if Dwight wants to hang out awhile (I may have to drive to Surfside Beach, for that) you have to send me an email letting me know your times and freqs of operation. I'll try and hollah at ya' from the road. |
Alex wrote: Thanks so much. With all the trolls in here I wasn't sure I would get a decent reply. thanks again. Nary a problem.. Enjoy your radio, and the hobby. -SSB |
On Fri, 08 Oct 2004 17:26:07 -0700, Frank Gilliland
wrote: On Fri, 08 Oct 2004 11:54:22 -0400, Dave Hall wrote in : On Fri, 08 Oct 2004 07:22:54 -0700, Frank Gilliland wrote: snip If Brian appears and brings an open mind, maybe I'll show him how to use predistortion in the bias regulator to linearize the output. But that's a big 'if'. Can you do that for RF amps? Absolutely. One method is to tap the input signal to a small RF power transistor with similar nonlinear characteristics and use it to shunt the input to the final. That method also eliminates the need for a base resistor and improves bias regulation. That's sounds more like adaptive active bias. It's a bit tough to find a biasing device that tracks the precise non-linear characteristics of the amplification device, and you have to be especially watchful of thermal runaway. Overall, the amp requires a little more drive power, but the benefits are well worth the costs. This would not be a problem in the CB area, where the tendency is to overdrive them anyway..... There are other methods that work even better such as high-frequency OP-amps with nonlinear feedback, inductors with nonlinear saturation characteristics... just about any part of the circuit can be tailored to compensate for a nonlinear power device. I guess it all boils down to how much you want to invest in a good design. At some point, you reach that magical point of diminishing returns. I wonder why more ham and commercial two-way radio amps aren't using better designs than the simple basic stuff. Dave "Sandbagger" |
On Mon, 11 Oct 2004 06:57:51 -0400, Dave Hall
wrote in : On Fri, 08 Oct 2004 17:26:07 -0700, Frank Gilliland wrote: On Fri, 08 Oct 2004 11:54:22 -0400, Dave Hall wrote in : On Fri, 08 Oct 2004 07:22:54 -0700, Frank Gilliland wrote: snip If Brian appears and brings an open mind, maybe I'll show him how to use predistortion in the bias regulator to linearize the output. But that's a big 'if'. Can you do that for RF amps? Absolutely. One method is to tap the input signal to a small RF power transistor with similar nonlinear characteristics and use it to shunt the input to the final. That method also eliminates the need for a base resistor and improves bias regulation. That's sounds more like adaptive active bias. It's a bit tough to find a biasing device that tracks the precise non-linear characteristics of the amplification device, and you have to be especially watchful of thermal runaway. What I described is kind of a psuedo-Darlington connection. It has less gain than the classic Darlington, but has a higher frequency response and a lower VBEsat. It also has the Darlington's high linearity. And while the final will still saturate, it will do so with more difficulty. The problem of thermal runaway is avoided by mounting both transistors on the same heatsink. The real problem comes from the collector capacitances (the devices being RF power transistors), so the pairs must be carefully chosen and matched for phase using a few extra reactive components. Lot's of math. Needless to say, it's not a popular design except in some very high power amplifiers where other methods would be more expensive. Overall, the amp requires a little more drive power, but the benefits are well worth the costs. This would not be a problem in the CB area, where the tendency is to overdrive them anyway..... I'm sure they would find a way. There are other methods that work even better such as high-frequency OP-amps with nonlinear feedback, inductors with nonlinear saturation characteristics... just about any part of the circuit can be tailored to compensate for a nonlinear power device. I guess it all boils down to how much you want to invest in a good design. At some point, you reach that magical point of diminishing returns. The real expense is paid in the initial design of a custom component, and that's just an one-time expense. After the design is finalized even custom components are relatively inexpensive, especially when ordered in large quantities. (For custom inductors, Micrometals has been a real good company to work with over the years. They even have composite cores that would be ideal for applications just like this.) I wonder why more ham and commercial two-way radio amps aren't using better designs than the simple basic stuff. Well, many do. I'm sure you've looked at component lists and seen inductors that are listed only as in-house numbers. Sometimes that applies to semiconductors, too (such as the Peavey dual-diode I was talking about in another thread). Sometimes capacitors are chosen not for their linearity but for their -non-linearity. And everything I said here about linearity also applies to other factors -- seemingly run-of-the-mill components are sometimes carefully selected for specific temperature coefficients, equivalent series resistances, breakdown characteristics, etc. Even tubes and transistors are often selected for gain figures that fall within a range smaller than the defined tolerances of the part specification. What often appears to be an off-the-shelf part may not have an off-the-shelf replacement. An example is the use of sequential mic/keying relays used on many older tranceivers -- the modification to the relay is rarely documented, and replacement with a generic (synchronous) relay can quickly burn out the screens in the finals. Been there, done that, and the T-shirt is now a shop-rag. A good design requires a LOT of engineering, not just big heatsinks and pretty PCB artwork. The specs for Brian's amp don't demonstrate much engineering at all. Heck, even a little negative feedback would help that amp immensely but he won't even to -that- much. Oh well. I didn't notice, but is he still using a single relay to switch both the input and output? ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Hi Jim. Perhaps you missed the last post on which you chimed in and I
asked your opinion of the radio being discussed, so here it is again. For the record, do you agree or disagree with the statement "Peaking and tuning will not raise the S units of a 4 watt cb rdio"? |
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Twistedhed wrote: The voodoo comment wasn't in response to anything you wrote or posted. It was in response to claiming one could raise the S units on a 4 watt cb with a peak and tune. Besides, I don't even use 4 watts, I use 3 most of the time. You going to try and make this picnic thingy? Try being the operative word. With my schedule, it's impossible to tell if I'm going to be working after I deliver the freight I've currently got, much less next year... going to try. -SSB |
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