[600MRG] Amp

[Brian Pease]

The idea in a non-linear amp is to keep the MOSFETs fully OFF (open 
circuit) and fully ON (short circuit) while spending minimum time 
(nanoseconds) in the linear transition region.  This minimizes heat 
losses.  A high-current MOSFET driver IC works well.  The amps are 
indeed like switching power supplies whether Class D, E, or whatever.  
My 100W amp is more than 90% efficient, with most of the loss in the 
toroids of the output circuit and low pass filter.  The MOSFETs run cold.
On 8/3/2015 3:40 PM, Kenneth G. Gordon wrote:
> On 3 Aug 2015 at 15:03, Jim Miller wrote:
>
>> The way I'm thinking about this is the drive to the finals (FETS usually)
>> needs to be hard and square at 472khz in order to achieve the desired
>> minimum switching transition times.
> I'm sorry, but I am not following you: the first question that hits me is "Why?".
> What type of amp are you suggesting? Why does it REQUIRE a
> square-wave input?
>
>> This means the drivers need to hit the
>> finals with a 472Khz square wave. Anything less than a square wave at this
>> point will result in excessive power dissipation if this is a continuous
>> occurrence. Obviously not desirable.
> Again, I am not following you here. The amp in question sounds rather odd
> to me.
>
> It sounds to me that rather than an amplifier, you are essentially using a
> switching-power supply to drive an antenna.
>
>> OTOH a finely shaped, e.g, raised cosine (ok, I know its not optimal...) RF
>> envelope coming into the amp will have around a 5ms period of rising and falling
>> signal. How the predriver, driver and final stages deal with this ramp will
>> determine whether or not "key clicks" will result.
> ALL amplifiers tend to "sharpen up" the wave-form applied to their inputs.
> Linear amplifiers tend to do this to a lesser extent, but it can still happen with
> them too.
>   
>> It seems to me that the amp will necessarily sharpen those transitions in
>> order to ensure than switching time at 472khz is minimized and therefore
>> produce broader CW signals than if a linear was used.
> Well, I must again ask, what kind of "amplifier" is this? It sounds rather odd
> to me.
>
>> This should be easy to test on the air. I have a P3 and I'm used to seeing
>> "clicky" CW all the time in contests. I usually see a handful of 2-3khz
>> signals each time and occasionally a 5khz monster.
> Please remember that at HF, at least, clicks can be not only accentuated, but
> even generated, by propagation effects. In my 59 years as a ham, I have
> heard this effect often. I spend most of my ham time on CW.
>
> Ken W7EKB
>
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