Charles,
I'm presently designing, building and testing a homebrew solid state HF
amplifier with similar specs to the DX2400L. The amp comprises a twin pair
of 1200 Watt pallet modules based on 4 x SD2943 parallel-push-pull / total
of 8 x 50V MOSFET devices that are being combined with a homebrew 2-port
combiner to produce a 2400 Watt nominal output capability with lots of Po
headroom for power back-off down to clean legal-limit operation.
I can say it's a challenging tall order to design a rugged, robust and fully
bullet proof SS amp to work at full rated Po spec above a 2:1 load VSWR with
today's available RF power semiconductor devices. I can empathise with the
Dishtronix designers and their pragmatism by passing off non-resonant
antenna loads as being too hard to deal with...at a cost hams would be
willing to pay. The Dishtronix amp is already an expensive high-end product
appealing to limited market segments.
The antenna VSWR here at my QTH is pretty flat on my favourite DX bands that
I use, and on the couple of bands where its rises at the band edges I simply
use my trusty AT5K manual tuner to tweak up the VSWR to near 1:1. The Alpha
4040 auto-ATU would also do a competent job with the DX2400L or any other SS
amp.
Turning on a tube amp and waiting for the heaters to warm up seems like an
inordinate amount of time when you hear that rare DX station calling CQ; the
solid-state amp being instantly ready for service!
I see the load matching requirements of QRO solid state amps as being quite
a minor negative aspect when weighed up against all the other plus point
advantages.
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Charles Harpole
Sent: Saturday, 17 November 2012 7:45 AM
To: amps@contesting.com
Subject: [Amps] interesting statement in Dishtronix
The Dishtronix web page for their amp, DX 2400L 1, makes the following
statement, " Beam antennas and multiband verticals are not designed for use
with a tuner."
This odd statement is made in the context of the company not offering an
automatic antenna tuner inside or external to this amplifier. That site
goes on to explain that wide range matching of an amp to various antennas
...which may have higher swr like 3 or even 4 to one... should not be done;
instead, the amp user should make his antennas more resonant and with swr of
2 to 1 or less. That passes the issue of amp matching antennas on to the
antenna and handily off the task of the amp. I have had a few resonant
antennas but none which presented a flat swr over the whole of one band.
Makes me go huummmm.
I guess if one can afford the 2400L, one should be able to afford a whole
lot of antennas which can then present a flat swr to this amplifier
regardless of frequency. Or a few StepIRs, maybe?
Am I being too hard on Dishtronix's web site wording?
Added note... an Alpha 9500 added to the cost of their Model 4040 high power
auto tuner will be less than the DX 2400, QSK version. I am making these
notes in the context of this reflector's continuing conversation about solid
state amplifiers.
73,
Charles Harpole
k4vud@hotmail.com
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