[Amps] SPE 1.3K-FA and FTDX-5KMP / IMD at rated PEP

[Joe Subich, W4TV]

On 11/15/2015 11:09 PM, Leigh Turner wrote:
> The only other way around this intractable dilemma is the use of
> linearity correction pre-distortion techniques in either analog or
> digital form, the latter being implemented with an SDR Tx exciter
> running the requisite correction algorithm.

Even linearity correction will not work if the devices are being driven
into saturation - the TV transmitter designers know that very well.
Linearity correction works as long as there is some headroom left in
the Pin/Pout curve but once you've lost the ability to increase drive
to compensate for the compression you've reached the limit of
correction.

73,

    ... Joe, W4TV


On 11/15/2015 11:09 PM, Leigh Turner wrote:
>
> Yes indeed Joe. The VRF-2933 FETS are good / arguably best of breed in
> today's generation and offerings of modern RF Power semiconductors.
>
> The key to success here is de-rating the combined module's PEP to steer well
> clear of their 1 dB power compression and subsequent saturation points. Then
> you will attain those desirously clean IMD numbers with good TLT output
> xfmrs, diplexer style terminated harmonic output filter, etc, and FET bias
> optimisation.
>
> This has been shown to be so in practice.
>
> The only other way around this intractable dilemma is the use of linearity
> correction pre-distortion techniques in either analog or digital form, the
> latter being implemented with an SDR Tx exciter running the requisite
> correction algorithm.
>
> Leigh
> VK5KLT
>
> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Joe Subich,
> W4TV
> Sent: Monday, 16 November 2015 1:55 PM
> To: amps at contesting.com
> Subject: Re: [Amps] SPE 1.3K-FA and FTDX-5KMP / IMD at rated PEP
>
>
> On 11/13/2015 4:50 PM, Leigh Turner wrote:
>>
>> That sensible criteria Joe just about excludes all solid-sate
>> commercial amps that are currently in the ham-market...rather sadly
>> :-(
>
> Which is a shame because the Quadra and PW-1 with 8 x MRF-150 *should*
> *be* capable of -40 dB(PEP) at 800W output and -35 dB(PEP) at their
> rated 1 KW output.  Given the age of those designs, it is amazing that
> the new designs are so sloppy.
>
> A pair of BLF-188A based amplifiers with splitter/combiner each running
> 800W PEP for 1600W PEP total should be able to make the -40 dB(PEP) as
> long as the designer takes care to keep the bias stable and avoid any
> saturation of the output transformers.
>
> I suspect, but have not seen the IMD curves, that the two of the old
> EB-104 boards updated with VRF-2933 VFETs and new output transformers
> could also make the grade (again 800 W (PEP) per board with transistors
> capable of 2400W total saturated power).
>
> 73,
>
>     ... Joe, W4TV
>