How to increase 2 XRF
286 to 250W CW
Some modifications to the W6PQL kit
By HB9BBD
Observations
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The PQL layout may be ideal for some XRF286
but not for all due to variing internal match of
the transistors
Unfortunately matched pairs cannot be figured
out because of soldering/desoldering issues
The board did not fit to some used transistors I
got so I had to fit the boards to the transistors
I built 10 double boards and try to summarize
the findings
At a glance – some visible
imbalances
Thermal analysis of the original board at 94 W out
Output capacitor is thermally
the hottest part
Mismatch at input and
output is detected by
different temperatures
High power dissipation
at 50 Ohm load!!!
Some just layed on flaps distribute the heat
peak to the center of output hybrid
Now at 10W in 180 W out
in
The hybrid is still
lossy but now
symmetrically
loaded
First try of
improvement
by mobile flaps
out
Less power loss at 50 Ohm load!!!
Parts to be replaced
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Omit the tiny ceramic trimmer TC1 and TC2 and take a
variable air capacitor (muRata)* or similar
Replace C2 and C12 by ATC 800A 22pF
*Thanks to Mike,
JH1KRC I have these
on my bench..!
How to find out what to do?
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As mentioned earlier, each transistor is unique in it‘s capacitance
etc. This is why I recommend to find out on your board yourself,
what is needed to improve. Do the following:
Prepare a teflon stick with little flap at it‘s end
At reduced drive (5W) carefully position the flap to the board (
without shortening DC !)
At position where positive effect is detected, lay down a flap and
so on
Once no further improvement can be seen, solder all mobile
flaps to the board
Beware of excessive RF exposure to your eyes, man!
These flaps helped to balance the
amplifier in power and phase
Input termination
Output termination
muRata 1-5pF
These flaps helped to balance the
amplifier in power and phase
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Output lines remarkably different..
Due to high current, generously solder the
cathode to the board! Thicknes improves here!
These flaps helped to balance the
amplifier in power and phase
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The hybrid also may need little mods
(C2 still original size)
Final results
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At input power of 14W the amplification is 14dB at
28VDC 16A
At 250W key down for 1 minute is possible with
moderate heatsink without fan, max. pwr out 320W
Enjoy these amps and call me off the moon in CW !
73 HB9BBD Dominique JN47ee
Another Issue..
The host of my EME site is a farmer.
 Since farmers in HB9 get lots of subsidies, he wants a
new barn for more cattle..
… and I want a better window to West!!
… and a solid shack too!!
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So the dish has to move
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Since I did not want to disassemble and put together,
the move was to be done in one piece
Total weight tower and dish is 5200 kg
Distance to relocate 28 m
All cabling off now..
The Hole
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An engineer found out that the dish requires the
Dishbase to be 1.5m above gnd for not touching the
roof when turning..
He further found out that this hole had to be made:
New shack will be in here!
The Steel
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1400 kg was to be invested.. And welded too.
The Fit
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Happily, the stainless steel base could be lasered along
the plans, which had been designed in 1996
So it needs to fit at first try.. 10xM33 in V4A quality
Steel into Hole
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Next comes concrete.. But before, welding the
grounding wire to the steel
The Concrete
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48 tons for the next 2000 generations!
The Move
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If something may go wrong, it does!!
The Move
The End, and..
(please, CW, USB or FM only!)