[hpsdr] 400w Class E linear amplifier

[mike]

Yes, thanks all around. Great stuff!

73

Mike
WO1U

Bob McGwier wrote:
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Phil Harman wrote:
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> Horst, DL6KBF, has kindly translated DJ7AW's 400w Class E PA article into 
>> English. It's at
>>
>> <  http://www.hamsdr.com/personaldirectory.aspx?id=739  >
>>
>> Many thanks Horst!
>>
>> 73's Phil...VK6APH
>>   
> 
> 
> Indeed,  many thanks.
> 
> The things to consider in the article as immediately relevant and of 
> interest to us are the discussions concerning the envelope and phase 
> channels and the group delay between them and how we can do better with 
> DSP techniques in our SDR transmitters and consider the practical 
> limitations he ran into.
> 
> 
> Mathematically what is happening with envelope elimination and 
> restoration transmitters could not be easier to understand if you 
> consider the signals in their natural state as complex or analytic 
> signals.  So we will start out immediately doing exactly that since all 
> of our SDR code that is open source does this.
> 
> Consider the single sideband (for example) signal to be
> 
> i(t) + j q(t)  
> 
> where i and q are the real and imaginary signals as a function of time.
> 
> All that is happening in an EER transmitter is the conversion of this 
> signal from rectangular to polar form.
> 
> i(t) + j q(t)  =   r(t) exp(j phi(t))
> 
> r(t) is the envelope or modulus.  It is found in the article by use of 
> an HK-demodulator
> exp( j phi(t)) is the constant envelope or "phase channel".  It is found 
> in the article by a limiter.
> 
> Fortunately for us,  we can just do the computation in our software
> 
> r(t) = sqrt(i^2 + q^2)
> and
> phi(t) = atan2(q(t),i(t))
> 
> Since exp(j phi(t)) is constant envelope it is easily amplified by very 
> very nonlinear amplifiers.   r(t) is impressed on the highly amplified 
> signals by modulating collector voltage (say) of the transistors of the 
> final or the final and driver.   Please note Marc Franco's notes I have 
> uploaded into the repository.
> 
> I offer Nick Sokal's QEX article up for people to read from ARRL TIS:
> 
> http://www.arrl.org/tis/info/pdf/010102qex009.pdf
> 
> The thing to note about a Class E amplifier is what the current and 
> voltage ideal goals are.  Hard limited voltage is on  when current is 
> zero and hard limited voltage zero when current is high.   This is not 
> practically possible. The extent to which it is NOT possible leads to 
> the loss which decreases the efficiency from 100% to whatever the 
> practical limits are.  The practical limits are determined by the 
> devices and the components chosen in a class E amplifier circuit.  The 
> circuit slams even harmonics into an open  or infinite load and pass odd 
> harmonics unattenuated to the extent possible.   The higher the number 
> of odd harmonics passed and the greater the degree to which even 
> harmonics are suppressed, the closer to the theoretical 100% efficiency 
> we get because the sharper the transitions from on to off and back will be.
> 
> Nick Sokal has been gracious enough to donate the Design Automation 
> design and simulation suite to AMSAT.
> 
> What will our goals be?  We need to identify good parts that will pass 
> lots of harmonics to get high efficiency.   The phase or hard limited 
> channel and the envelope channel in the polar coordinate amplifier will 
> be distorted by the circuits.  So when the amplitude is "plate 
> modulated" back onto the phase signal,  these distortions will lead to 
> intermodulation distortion.
> 
> With our digital signal processing there are multiple things we can do.  
> We can observe and determine the appropriate pre-distortion filters to 
> apply to the signals while they are still in rectangular or (I,Q) form 
> so "undo" the distortions once by measurement.  Or, we can do this but 
> allow for dynamic measurement to take care of any deviations.  These 
> will inevitably be there because hams will not accept the need to run 
> their signals into perfect dummy loads!  
> 
> I hope this helps.
> 
> 73's
> Bob
> N4HY
> 
> 
> 
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