[Amps] RF2K+ LDMOS linear

[Mark Mumaw]

I am still_*not*_ getting messages to my email so I hope this goes to 
the proper thread.

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