[Amps] Grounded Grid (Screen) 4CX250B power gain

[Joe Subich, W4TV]

> Hopefully, one or more of the adaptive pre-distortion 
> techniques being used are not subject to patent protection 
> and associated licensing fees.  It would be a great time to 
> incorporate this technology into all new SSB exciters.

I seriously doubt that adaptive predistortion is covered by 
any enforceable patent and it is certainly not limited to 
digital modulation.  

Phillips, Marconi and others, used predistortion with analog 
NTSC exciters more than 25 years ago.  I fondly remember 
adjusting the predistortion on UHF transmitters to minimize 
(cancel) the regenerated lower sideband and other IMD like 
products in the pulsed power amplifiers.  

In those days the predistortion was not adaptive ... it had 
to be adjusted manually as the finals aged and the operating 
point shifted.  However, adaptive controls are much easier 
to implement with digital systems ...  since the data should 
always fall within limits of the ideal locations in the 
"constellation."  It is far easier to implement correction 
algorithms with discrete as opposed to analog values. 

73, 

   ... Joe, W4TV 
 




> -----Original Message-----
> From: amps-bounces at contesting.com 
> [mailto:amps-bounces at contesting.com] On Behalf Of Paul Christensen
> Sent: Tuesday, July 21, 2009 2:12 PM
> To: amps at contesting.com
> Subject: Re: [Amps] Grounded Grid (Screen) 4CX250B power gain
> 
> 
> > "Tokyo High Power marketed a cathode driven 2 X 
> 4X150/4CX250 amp that 
> > had
> > IMD
> > on par with grid driven.
> 
> I did a "double-take" the first time I had seen one since 
> Tokyo Hy-Power is 
> more commonly known as a SS amp manufacturer.  What's really 
> got me excited 
> is the use of adaptive pre-distortion in the new ADAT 
> ADT-200A transceiver. 
> The transceiver is now in production and has the ability to 
> sample RF at the 
> output of an external amp and apply complimentary non-linear 
> distortion to 
> offset inherent non-linearities in the PA chain between the 
> rig and external 
> amp.   Adaptive predistortion is being used in the digital broadcast 
> industry, although its root can probably be traced to the MIL sector.
> 
> Typical 3rd-order IMD coming from the ADT-200A's 50-watt SS 
> PA is -55dB, 
> although specification is -45 dB.  If the typical figure is 
> correct, that's 
> ~ 20 dB better than most commercial amateur SS HF amps.  But 
> the real power 
> of that type of algorithm is its extension to any external SS 
> PA.  So, it 
> would seem quite possible that one could utilize the 
> ADT-200A, coupled with 
> say...a Tokyo Hy-Power SS kilowatt amp and achieve IMD 
> numbers unheard of 
> with some of the best vacuum tube designs.
> 
> Hopefully, one or more of the adaptive pre-distortion 
> techniques being used 
> are not subject to patent protection and associated licensing 
> fees.  It 
> would be a great time to incorporate this technology into all new SSB 
> exciters.
> 
> Paul, W9AC
> 
> 
> 
> 
> 
> 
>  
> 
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