Of course Doc, but the point is the maximum output power is way more then 167 watts per transistor and you can reach 252 watts output without exceeding maximum dissipation or collector current on the 2SC2879.
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Of course Doc, but the point is the maximum output power is way more then 167 watts per transistor and you can reach 252 watts output without exceeding maximum dissipation or collector current on the 2SC2879.
I never have understood the why of wanting to drive the hell out of anything in the first place.
Buy or build more than you want in the first place and then "under drive" it for want of a better term.
Less heat, longer life, etc.
I personally run nearly everything I own at 12-13V and am happy with performance and life of the equipment.
That's the way I do it and my humble opinion. give me hell now guys.
Buy or build more than you want in the first place and then "under drive" it for want of a better term.
Less heat, longer life, etc.
I personally run nearly everything I own at 12-13V and am happy with performance and life of the equipment.
That's the way I do it and my humble opinion. give me hell now guys.
I never have understood the why of wanting to drive the hell out of anything in the first place.
Buy or build more than you want in the first place and then "under drive" it for want of a better term.
Less heat, longer life, etc.
I personally run nearly everything I own at 12-13V and am happy with performance and life of the equipment.
That's the way I do it and my humble opinion. give me hell now guys.
The "buy bigger in the first place" is good advice however, it doesn't work in the competition classes many of these guys run in. They are limited to a specific number of transistors and alternators for a given class of competition. You can then see why it's important to them to squeeze every last watt out of each transistor.
That's also why there are differences in a competition amp that was designed to make maximum power from each transistor for a 15 second keydown and something designed for a longer duty cycle like talking skip.
I never have understood the why of wanting to drive the hell out of anything in the first place.
Buy or build more than you want in the first place and then "under drive" it for want of a better term.
Less heat, longer life, etc.
I personally run nearly everything I own at 12-13V and am happy with performance and life of the equipment.
That's the way I do it and my humble opinion. give me hell now guys.
Would ya be surprised if I agreed with you instead?
I do; it is the best way of keeping radio equipment out of the shop - and your money back in your pocket where it belongs in the first place.
OK. I didn't read the competition connection into this thread. I was speaking of general everyday use and didn't even think about competition.
That's why in drag racing I always preferred a big block over a small block. Never turned a big block over 7500 RPM. If you needed more power out of it, put a blower on it. Same principle applies to radios and amps. Don't "over-rev" your equipment and it will have "repeatability" and reliability.
Now there's something else I like, big block engines. Your post brought back memories of all the times guys with a 350 would beat me off the line thinking they had it all wrapped up, only to see the power of the big block come on half way down the 1/4 mile and eat em up. I ran a 427 CID 435 HP tri power vette engine in a 67 Camaro. It was bad but there were still bigger 454 LS6 and LS7 engines that came out later. OK, now back to watts.
so, what if the signal going into the amp is rife with harmonics like most CB signals are?
lets assume for the sake of argument that most Cbers run their radios with the AMC disabled.
this adds harmonic content to the fundamental 27mhz signal.
if a linear amp were used to amplifiy this particular "dirty" signal; would the amp
amplify the harmonics as well?
if it did, could this cause the condition where a wattmeter placed after the amp would add all this amplified harmonic content up and show the total on the meter?
could this cause a high SWR reading?
would placing a low pass filter after the amp and before the meter shunt these harmonics to ground and allow the meter to show only the 27mhz funamental signal?
could the wattage reading be reduced by a significant amount in this scenario?
im just trying get a handle on all this. LOL
LC
lets assume for the sake of argument that most Cbers run their radios with the AMC disabled.
this adds harmonic content to the fundamental 27mhz signal.
if a linear amp were used to amplifiy this particular "dirty" signal; would the amp
amplify the harmonics as well?
if it did, could this cause the condition where a wattmeter placed after the amp would add all this amplified harmonic content up and show the total on the meter?
could this cause a high SWR reading?
would placing a low pass filter after the amp and before the meter shunt these harmonics to ground and allow the meter to show only the 27mhz funamental signal?
could the wattage reading be reduced by a significant amount in this scenario?
im just trying get a handle on all this. LOL
LC
Now these are the right questions to ask. All of the things you mention will contribute to harmonic content. The amplifier will amplify any harmonics that arrive at it's input and make them larger too. Here is the key. If the harmonic content is high enough to cause highly inflated forward power readings, it will most definitely exaggerate the reflected power reading by much more. This is because the CB antenna will be reflecting much more power at the harmonic frequencies then at the fundamental.
Obviously installing a low pass filter after the amp will have a major effect on the harmonic attenuation. What doesn't seem so obvious is the fact this will not lower the power meter by any significant difference. If the reflected power into a resonant antenna is low, then harmonic content has not inflated your meter reading. This in no way is an indication that harmonics are absent, just that they are no where near the level of causing severe inaccuracy in the meter.
You did mention one thing that probably contributes to inflated power readings more then out of band harmonics. That's overmodulation with a disabled AMC. Power meters will show a higher average reading the more you overmodulate and flat top the envelope. That's because of the way the mechanical meter movement responds to different waveforms. The scope will show you that no more RF voltage is being developed into the load once you start flat topping. The meter will read higher because the flat tops hold the average higher for a longer duration then a sine wave would.
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Wouldn't it be more effective to put the filter between the radio and the amp - and in this way - eliminate all of the unwanted harmonics from becoming amplified? Wouldn't this force the amp to only amplify ~27mhz (so long as the filter chosen will do just that freq only)? And if so; then the amp becomes more efficient to amplify just the desired frequency - run cooler, give off an accurate wattage reading to the meter, and keep the Hams off of one's back?
LOL!
But seriously....
LOL!
But seriously....
I would love to see the IMD ratings of a 2SC2879 producing 252 watts. Lowest IMD for a 2SC2879 is when it is producing about 60 watts. Anything above (especially) or below thgat causes the IMD performance to deteriorate. It is for exactly that reason that ham rigs using 2SC2879's run a pair of them at about 100-125 watts output.
http://www.rfparts.com/pdf_docs/2SC/2SC2879.pdf
If it weren't for the fact that amplifiers generate harmonic content themselves, it would make more sense just to filter the input. The problem is the amplifiers don't just amplify what's on the input, they also create their own harmonic content. More so with broadband transistor amplifiers then with tubes. This is why it's mandatory for a solid state amplifier to be followed by the correct harmonic filter for the band in use in order to meet the standards for harmonic emissions. It's also not a bad idea to filter the input as well as the output.
Captain, the topic wasn't how to design a quality final power amplifier for the next HF rig to hit the market. I won't begin to dispute the fact the spectral purity sucks when you run every spec right to the maximum. I believe the basic topic of the thread was if it's possible to obtain hundreds of watts from a 2SC2879 on the fundamental frequency. The transistor is rated for 250 watts of dissipation. Anyone should understand it's quite possible to obtain 250 watts of output all the way down to 50% efficiency without exceeding the parts real specifications.
B
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when i read the article i thought the point was that those hundreds of watts shown wernt on frequency and that it is the combination of the primary frequency and the harmonics making the meter give an exaggerated reading .
Isn't this the same as saying "if it's possible to obtain hundreds of watts from a 2SC2879 on the fundamental frequency"? In order to get 250 watts from a 2SC2879 you have to keep the reflected power very low. Some of the fanatics involved with the competition amps strive for 1 watt reflected out of every 1000 forward. Knowing that the bandwidth on a 1/4 wave whip is plus or minus a few hundred KHz of it's resonant point, I ask what harmonic would these hundreds of watts be on and still not generate significant reflected power?
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