[Amps] Pre-Distortion Linearizer

[Roger (K8RI)]

On 5/3/2013 8:11 PM, Tom Thompson wrote:
> As long as the transceiver manufacturers give us transceivers with poor
> IMD, it does little good to get the IMD on the amplifier good, unless
> you home brew your own transceiver.
>
> Tom   W0IVJ
>
>
> On 5/3/2013 8:39 PM, Leigh Turner wrote:
>> That's right Bob, complex indeed. Such linearization and intermodulation
>> distortion correction techniques are not the panacea they might first
>> seem;
>> their practical implementation in ham-radio gear is not trivial and the
>> costs generally outweigh the meagre gains and benefit. As Paul points out
>> the other impediment for commercial equipment manufacturers is the
>> complex
>> IP and licensing minefield.

It's my understanding that the analogue version is relatively simple and 
good for about 10bd decrease in IMD, beyond that it gets complicated and 
expensive.

With exciters running on the order of 30-35 db a 10 db increase to 40 or 
45 db would certainly seem worth while.  With the better the exciter the 
better the amp output so the FTDX 5000 in the 40 db range (AB1) as well 
as the new Kenwood would produce amp outputs with around 50 db IMD which 
sure sounds like a worthwhile goal. Admittedly we are talking expensive 
rigs in the $5000 to $800 range to drive an almost equally expensive amp 
but QRO amps with 50 db IMD would be practically unnoticed except for 
strong, clean signals.

More than 10 db requires complex digital circuitry, but sooner or later 
some one is bound to develop a system on a chip or 2, or 3 with 
relatively low cost.

Am I missing something?

73

Roger (K8RI)
>>
>> For the average ham it's far easier to run an amplifier conservatively to
>> steer well clear of the amplifier's compression transfer curve where the
>> gain and Po depart from a linear relationship with input power, i.e.
>> practice power and drive back-off to attain maximum linearity.
>>
>> The majority of common ham-radio amplifier tubes respond nicely to this
>> simple approach and yield sufficiently adequate IMD characteristics when
>> deployed in a well designed amp.
>>
>> Compensation techniques to linearize an imperfect amp abound, but are not
>> simple to implement in a 1500 Watt PEP Tx system.
>>
>> Leigh
>> VK5KLT
>>
>>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Robert
>> Carroll
>> Sent: Saturday, 4 May 2013 11:37 AM
>> To: amps at contesting.com
>> Subject: Re: [Amps] Pre-Distortion Linearizer
>>
>> As a former Bell Labs design supervisor in the cellular wideband linear
>> amplifier design area, I can say that predistortion schemes as well as
>> feedforward linearization were being studied intensely and resulted in
>> many
>> patents at BTL and elsewhere.  It was a very complex problem both
>> practically and theoretically.  The simpler means of incorporating
>> predistortion quickly became inadequate to meet FCC requirements as
>> mobile
>> telephony moved away from its FM roots.
>>
>> Bob W2WG
>>
>>
>>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Paul
>> Christensen
>> Sent: Friday, May 03, 2013 8:35 PM
>> To: amps at contesting.com
>> Subject: Re: [Amps] Pre-Distortion Linearizer
>>
>>> Check out US Patent 4588958 by Allen Katz K2UYH.  It's a common way to
>>> linearize solid state PAs for the cellular market back in the day.
>> Great info, Jeff.  Looks like K2UYH has multiple, related linearization
>> patents.   Also, thanks for passing on the references.
>>
>> In looking at his patent citations, work really accelerated around the
>> time
>> of the cellular industry explosion.   I imagine AT&T/Bell Labs was faced
>> with similar spectral efficiency issues with its Long Lines carrier
>> microwave systems, but they had more usable licensed spectrum way up
>> at 6 &
>> 11 GHz where fixed, point-to-point communication is possible at those
>> wavelengths -- but not roving communications.
>>
>> Often when the subject of pre-distortion comes up, the usual questions is
>> "why doesn't manufacturer X have this technology?"  Peering through the
>> patent data is one reason why.  It's easy for us to want the
>> technology --
>> not so easy for the manufacturers to wade through the intellectual
>> property
>> landmines or secure licensing agreements.
>>
>> Paul, W9AC
>>
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