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Author Topic: Realistically priced mobile HF amps...  (Read 23098 times)
KD8MJR
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Posts: 5156




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« Reply #15 on: May 30, 2015, 04:30:30 PM »

I would have thought the biggest problem is not the BPF but the amp biasing design. That's where all the harmonics get generated from.

Amp Bias design is fairly straight forward and adds little to the cost, but then again that depends on how one looks at it.  If you want a 500W class "A" biased amplifier then yes it's going to cost a lot more than a Class "B" biased amplifier doing the same 500W and Class "C" gets even cheaper and dirtier and less linear.  The thing is that it's a choice at the design stage, do I want a clean very linear but not very efficient class "A" amp thats using the same finals heatsink etc but will only do 300W or do I want a Class "B" amp using almost all the same components that will do 500W.   Of course for Ham use we would use class AB and get the best of both worlds (Almost Wink ).

BTW you would never need to use a BPF, only a LPF and either way that would clean up most of the harmonics.  Your overall point has merit in that a cheap CB amp may have such a bad design that doing any kind of modifications would be pointless.  On the other hand I have opened up a Palomar CB amp (i think it was Palomar) and found the design to be class AB and pretty well laid out. It even had a band selector and contrary to what some would say it was actually going through a LPF filter board that was unfortunately crap.  An amp like this could be redone and used on the ham bands but unfortunately the price for the new finals it needed plus the other work involved in making a new LPF board made it a waste of time.  Oh and I almost forgot, as per typical of CB amps it had Zero protection circuitry.
« Last Edit: May 30, 2015, 04:46:17 PM by KD8MJR » Logged

“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
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