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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 =--- |
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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