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@contesting.com] On Behalf Of Joe Subich,
W4TV
Sent: Monday, 16 November 2015 1:55 PM
To: amps@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
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