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SkyWave 2879AB Amplifier
"Steveo" wrote in message ... jim wrote: Steveo wrote: "Telspam Electronics" wrote: http://cg/spam Things must be slow. didn't he get booted off a provider for spamming? Rumor has it. Very good layout PC board, that takes allot of work. Hope he sells them all day to CBers, I don't care where they go. Some of the so called BIG amps( Dave Mades, ect ) look crappy inside because the designers are not very bright.Some look like they were built in a cow barn. |
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SkyWave 2879AB Amplifier
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#3
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SkyWave 2879AB Amplifier
JSF... you're right about those "big amps". They are nothing but
hay-wired prototypes, mostly designed and constructed by persons having no electronic background. I have looked at many of them over the years and have found that they have major flaws such as inadequate cooling, improper tuning, and instabilities/oscillations caused by improper layout and long wires running around all over inside. Because of these issues, their owners must keep a steady stream of expensive output transistors flowing through them... if you know what I mean... LOL www.telstar-electronics.com |
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SkyWave 2879AB Amplifier
On a sunny day (22 May 2006 04:45:06 -0700) it happened "Telstar Electronics"
wrote in .com: JSF... you're right about those "big amps". They are nothing but hay-wired prototypes, mostly designed and constructed by persons having no electronic background. I have looked at many of them over the years and have found that they have major flaws such as inadequate cooling, improper tuning, and instabilities/oscillations caused by improper layout and long wires running around all over inside. Because of these issues, their owners must keep a steady stream of expensive output transistors flowing through them... if you know what I mean... LOL www.telstar-electronics.com Hi, I am reading on your website http://www.telstar-electronics.com/S...Amplifiers.htm about efficiency and conductingangle. My question, has anyone ever attemped a class D (pulse width) modulated amp with MOSFETS for 27Mc? The limit would be the switching time, say if we have 1nS switching FETS, and 37 nS period time, we use a bridge, so per 37 nS we switch 4x = 4nS We dissipate any power (not counting Rds-on losses), could we achieve 80% efficiency? There are also losses from transformer and Pi filter of course. And perhaps you would need a switchmode to get a higher operating voltage, mmm that would bring it down to .8 x .8 = 64 % + filter and other losses.... But it COULD take you into the kW range with cheap FETS? Whatdoyouthink? ;-) |
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SkyWave 2879AB Amplifier
Jan,
Sure you can run class D at 27MHz... the problem is distortion. Class D is very efficient but is really only meant for digital signals. www.telstar-electronics.com Jan Panteltje wrote: On a sunny day (22 May 2006 04:45:06 -0700) it happened "Telstar Electronics" wrote in .com: JSF... you're right about those "big amps". They are nothing but hay-wired prototypes, mostly designed and constructed by persons having no electronic background. I have looked at many of them over the years and have found that they have major flaws such as inadequate cooling, improper tuning, and instabilities/oscillations caused by improper layout and long wires running around all over inside. Because of these issues, their owners must keep a steady stream of expensive output transistors flowing through them... if you know what I mean... LOL www.telstar-electronics.com Hi, I am reading on your website http://www.telstar-electronics.com/S...Amplifiers.htm about efficiency and conductingangle. My question, has anyone ever attemped a class D (pulse width) modulated amp with MOSFETS for 27Mc? The limit would be the switching time, say if we have 1nS switching FETS, and 37 nS period time, we use a bridge, so per 37 nS we switch 4x = 4nS We dissipate any power (not counting Rds-on losses), could we achieve 80% efficiency? There are also losses from transformer and Pi filter of course. And perhaps you would need a switchmode to get a higher operating voltage, mmm that would bring it down to .8 x .8 = 64 % + filter and other losses.... But it COULD take you into the kW range with cheap FETS? Whatdoyouthink? ;-) |
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SkyWave 2879AB Amplifier
On a sunny day (22 May 2006 07:47:53 -0700) it happened "Telstar Electronics"
wrote in .com: Jan, Sure you can run class D at 27MHz... the problem is distortion. Class D is very efficient but is really only meant for digital signals. www.telstar-electronics.com Hi, you know class D audio amps exist I suppose? There are even class D power amp chips for audio. These use PWM (pulse width modulation). You can make any output waveform with PWM (as long as the switching frequency is much higher then the output frequency). This links shows some basics for a modulator (driving class D for example): http://www.netway.com/~stevec/ham/pd...lid_state.html I can also think of a 'digital' solution, say you have 8 RF amps, 1W, 2W, 4W, 8W, 16W, 32W, 64W, and 128W, now simply switching these on with an 8 bit digital audio signal (one on each bit) and summing the RF output together, will give you a 255W AM modulated transmitter with less then 1/255 (0.4 percent) distortion (have not tried)? Since these RF amps can be class C (no need for A, AB, B, any linear!!) you should get good efficiency. The stages are only 'on' or 'off'. So, maybe someone could combine some :-) Nice for experiments.... hehe |
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SkyWave 2879AB Amplifier
On a sunny day (Mon, 22 May 2006 15:32:12 GMT) it happened Jan Panteltje
wrote in : On a sunny day (22 May 2006 07:47:53 -0700) it happened "Telstar Electronics" wrote in s.com: Jan, Sure you can run class D at 27MHz... the problem is distortion. Class D is very efficient but is really only meant for digital signals. www.telstar-electronics.com Hi, you know class D audio amps exist I suppose? There are even class D power amp chips for audio. These use PWM (pulse width modulation). You can make any output waveform with PWM (as long as the switching frequency is much higher then the output frequency). This links shows some basics for a modulator (driving class D for example): http://www.netway.com/~stevec/ham/pd...lid_state.html I can also think of a 'digital' solution, say you have 8 RF amps, 1W, 2W, 4W, 8W, 16W, 32W, 64W, and 128W, Actually I think I have this wrong, should be Volts (RF output) ratio or powers of 2. So 1 W in 50 Ohm: U^2 / 50 = 1, so U = sqrt(50) = 7V eff, the next higher higher one would be 14V eff or 3.92 W, better start at the high side... So for your 300W in the highest bit: U^2 / 50 = 300, U^2 = 15000, so U = sqrt(15000)= 122V eff. The next lower one (bit 7) would be 122 / 2 = 61V eff, so 61^2 / 50 = 74.42W, bit 6 would be 61 / 2 = 30.05 V, makes 18.06W bit 5 would be about 15 *15 / 50 = 4.5W bit 4 would be 7.5 x 7.5 / 50 = 1.125 W etc etc. I have also been thinking about doing SSB this way. For SSB we need half the bits, and one bit to change the phase of the driving carrier 180 degrees. Hope I got that right. You'd be selling lots of amps!!! |
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SkyWave 2879AB Amplifier
On a sunny day (Mon, 22 May 2006 16:41:03 GMT) it happened Jan Panteltje
wrote in : I have also been thinking about doing SSB this way. For SSB we need half the bits, No, same bits, but bit 8 as sign bit changing carrier phase 180 degrees.... We'll get there.... |
#9
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SkyWave 2879AB Amplifier
Your statement about having the switching freq much greater then the
output freq I agree with. But if you wanted to make an amp for 27MHz... what switching freq would you have? 2X, 5X, 10X ? Also, with a high switching rate... with square-waves... you have tremendous harmonic content. You also would require much higher frequency amplifers... along with the quantum leap in complexity of combining all those amplifiers, A/D conversion, etc... I think your idea would work... it's just not practical in my mind. www.telstar-electronics.com |
#10
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SkyWave 2879AB Amplifier
On a sunny day (22 May 2006 10:29:39 -0700) it happened "Telstar Electronics"
wrote in .com: Your statement about having the switching freq much greater then the output freq I agree with. But if you wanted to make an amp for 27MHz... what switching freq would you have? 2X, 5X, 10X ?\ Look at that example link, it uses 100kHZ (KILO Hertz) in the PWM AM modulator, leaved the RF stage as is, but the PWM modulates it supply voltage. that way the output. In case of direct pwm to the RF, yes, I mentioned 1nS switching time, could be done. I like the digital idea better..... Also, with a high switching rate... with square-waves... you have tremendous harmonic content. You also would require much higher frequency amplifers... along with the quantum leap in complexity of combining all those amplifiers, no no, MOSFETS can switch that fast.... A/D conversion, Any PC gives 16 bit audio, just some shift registers or some i2c io expanders, no need for an AD converter, we are going to drive digital now :-)!!! etc... I think your idea would work... it's just not practical in my mind. Remember the modulation frequency is in the audio range, at that speed you have to change the PWM. You need a pi filter lowpass in ANY case to get good harmonic surpression. In the digital case (swithing 8 amplifiers), there are some more advantages. Problem is adjusting the exact power level (so a ramp (sawtooth) waveform has equal steps), adding (summing) the output takes inductors couplers... impedance matching. Hey, I have done that DA thing for up to 10 MHz or so.... the big boys can do it, why not we? Probably will be worth a fortune on ebay 50 years from now. |
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