[Moon-Net] combining pallets 13cm SSPA

Alex Artieda hb9dri at emeham.com
Wed Nov 2 13:52:25 CET 2016

Dear Friends

After following the recommendations of several people I finish my new 13cm
PA based just in two MRF5P21180R6, that LDMOS is rated to 180 watts at
2.1GHz.  I combined two of them installed in a MRF21120 PCB harvested from a
damage Ericsson SSPA, For the output combiner I used the DB6NT MKU DIV2300-1
7/16 rated up to 1KW, the input combiner was a W6PQL rated for 300 watts I
guess,  I never imagine how difficult was to preserve amplitude and phase on
13cm, for hours the combining process didn't work, after rebuild my input
cables 6 times and install 3 small flappers on the in/out strip lines
finally the Amplifier deliver 310 W with 24 watts input, this is a gain of
11.1dB, not bad for a 2.1Ghz LDMOS (internal marched) running at 2320MHz.
What surprises me is the power start at 310 watts and after 45min of
continuous carrier the power just drop to 304 watts. My two original
Ericcson SSPA with 3  transistors always drop at least 50 watts after 30
sec.s of carrier and the temperature go up horrible high, on my new SSPA the
temperature in the heat sink was 55 Celsius at 31 Celsius room temp (yes
South African summer is coming). Monitoring the isolated port in the output
combiner with a 100 watts attenuator and a power meter I read no more than
300mW, any attempt to try to cero that value finish always in a little less
power and due the fact I will keep that 100 watts attenuator on the setup I
don't se a problem. I didn't measure the consume but I'm using 12amp 28vdc
separate power supplies for each amp., both are warm almost equal and i
never trigger the internal protection ,assuming each pallet is consuming
their maximum (12 amps this is translated in a efficiency near 50%,  again
not bad for a 2.1GHz internal matched fet.

The MRF5P21180R6 is a perfect candidate to replace the MRF21120 in your
Ericcsson amplifier, what I did is just remove the complete PCB and cut-off
one part with one fet, then keep two only, replace with the 21180, re-adjust
bias for 2 x 800ma and tune, you will have a more robust PA without the
heating problems, the pallets are mounted in a copper spreader 14mm and
later in a SK200 heat sink running with forced air with two turbo fans at
5m/sec. No thermal problems at all. The nice part is the 21180 cost just
17.00 USD, something to consider if you own a Ericcsson UMTS amplifier with
the fet MRF21220

Again thank you very much for all the valuable tips I receive off line, the
most critical part was the input coax, some ones differ just 1mm and I think
this is more than 2 degrees in phase error @13cm, really critical. Now I
will upload the new SSPA on my tower and concentrate my job in 5.7Ghz, hope
before Christmas South Africa will return to 6cm with 3.6m dish and 65 watts
on the feed.

Best regards 

73 de Alex, ZS6EME

-----Original Message-----
From: moon-net-bounces at mailman.pe1itr.com
[mailto:moon-net-bounces at mailman.pe1itr.com] On Behalf Of Alex Artieda
Sent: Donnerstag, 27. Oktober 2016 12:14
To: moon-net at mailman.pe1itr.com
Subject: [Moon-Net] combining pallets 13cm SSPA
Importance: High

Dear Friends

I'm in the process to rebuild my SSPA for 13cm, I have separate modules
harvested from Ericsson Amplifiers and I replace the original MRF21120 for
MRF5P21180R6, one single transistor is giving 160 watts (@2320 MHz) with
just 3 watts of dropping power after 45min carrier, the gain is 12dB and I
need just 10 watts driver, input RL is -26dB now my question, with the Idea
to combine two similar pallets how dissimilar is acceptable the output power
of both amplifiers? I just finish one but I'm tweaking the other one and the
second is giving me only 150 watts, I don't know if 10 watts difference is
acceptable, i will use 90 degrees hybrid couplers to combine both pallets,
maybe the 10 watts difference is dissipated on the isolated port with a
dummy load??

73 de Alex, ZS6EME

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