*******Direct email reply to my post from Mark--NU6W (who appears to be
having some issues getting comments posted to the reflector)******
I have built several LDMOS linears over the last 5 years. I completed one
last year using most of the components that are now in the RF2K+. I used
the same exact extruded heat sink (10" x 10" x 3.5") and the same 80MM 38
CFM fans used by W6PQL legal limit design used by Mark, WH7W. Most
recently, I built the current RF2K+ kit and have compared the two. The
RF2K+ heat sink is a more modern (and expensive) design that has a
significantly greater surface area of serrated cooling fins. The C/W/3"
thermal rating is over double the extruded heat sink. The RF2K+ heat sink
is not an extruded and provides a greater surface area with less weight.
In addition, the standard 120MM fans are in a push-pull arrangement for a
total of 150 CFM (vs 114CFM ) at standard speed and 30% more when jumpered
to run on 14.7 Vdc. 110 CFM fans (220 CFM total) could also be used at
the expense of more noise. The benefit of 120MM fans over 80MM fans is
noise. They can move a lot of air with less noise. In addition, we benefit
from the development on the water cooled radiator PC fan market. It has
resulted is some amazing performance.
In a A/B test clearly the newer RF2K+ heat sink/fan arrangement runs
cooler and with less noise. In addition, the PWM speed control keeps the
linear almost silent during casual operating and speeds up as needed.
BTW, I have a Acom 2000A which is still my most quiet amp.
It also seems everyone is getting a lot more comfortable running the LDMOS
devices at high temperatures. Where as a few years ago I preferred to keep
them under 55C, the manufactures are running them up in the 70 to 80C
range. It does not seem to effect there life. With MTTF of well over a
million hours with junction temps over 170C, I doubt we will see many
failures due to heat.
To clarify the comment on diplexed filters, the 3rd harmonic can be down
as little as 10db (not IMD products). The RF2K+ with its output design, run
around 13dB which is still 75 watts at legal limit. Pure signal will not
have any effect on the 3rd harmonics, only the IMD products which are down
-37dbc PEP or better. The RF-kit.de has the 0 dbm RF monitor ready for
Pure Signal. This is exciting technology, especially if everyone were to
use it. Hopefully Flex will develop their version soon.
RF-kit.de has experimented with diplex filter design and will probably
revisit it again. The same heat is still generated and needs to be
removed from the cabinet one way or another. It may be of a greater benefit
on the efficiency of the LDMOS in addition to heat reduction. My very first
LDMOS linear used diplexed filter design.
The TRX relays on the RF2K+ are mechanical that will probably be a little
noisy for the avid QSK CW operator. The software is fast enough to keep
up but a PIN Diode solution or vacuum relay solution would be preferred.
That is a project I expect RF-Kit to undertake.
The RF2K+ is just now being released for the US kit builder. I would expect
it will get exercised in some contests later this year. The Flex Power
Genius has been in development for almost 1 1/2 years and have taken 100s
of pre-orders but I don't know of any contest experience to date. It will
come.
It is great all the choices that Ham radio operators will have !!
73...Mark NU6X Sedona, AZ
===================================================
====================================================
Yes, Mark, I stand corrected. It is harmonic energy not IMD products that I
was referring to. I apparently spent too much time worrying about spelling
and typos than I did about technical accuracy.
And I agree, all of this new technology makes for educational reading and
new projects to work on.
73--Mark WH7W (in Honolulu)
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