[Elecraft] Why predistortion ?

[Dave B]

Pre-distortion is often used in modern cellular base-station 
transmiters, and perhaps digital broadcast systems where they have to 
handle multiple carriers simultaneously, "at power".

It dramatically reduces transmitted intermodulation to very low levels, 
allowing such multi carrier systems to co-exist very close to each 
other, improving the reception of the base station by the mobile/handset 
device.  (Lower Bit Error Rate numbers.)  Without spending mega bucks 
for a PA system grossly over rated and inefficient, just to stay in it's 
very linear region, well below the 1dB compression point!  (As was 
common not that long ago.)

As mobile phones these days are also almost all SDR in nature, even they 
may apply pre-distortion to their TX signal, for the same reason.  
Smaller lower cost and lower power consumption PA, but keeping it clean.

"Docherty Amplifier" systems are also often used in other cases, where a 
clean low power class A amp in effect "corrects" the output of a much 
more powerful, more efficient but not as linear (class B) amplifier by 
means of a combiner, dynamically adding or subtracting "signal" as 
needed in analogue real-time.  (Crude over simplification!)

The techniques are as yet not common in Amateur circles, but are 
becoming widely used in several commercial scenarios, so it is only a 
matter of time...  As more and more mainstream radio transceivers adopt 
SDR principles in both RX and TX paths, the cost savings at the high 
power stages become significant, once the software is developed and 
fully engineered.

73.

Dave G0WBX.


On 14/09/2020 17:00, elecraft-request at mailman.qth.net wrote:
> Re: [Elecraft] Why predistortion ?

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