Presentation on theme: "How to increase 2 XRF 286 to 250W CW"— Presentation transcript:
1How to increase 2 XRF 286 to 250W CW Some modifications to the W6PQL kitBy HB9BBD
2ObservationsThe PQL layout may be ideal for some XRF286 but not for all due to variing internal match of the transistorsUnfortunately matched pairs cannot be figured out because of soldering/desoldering issuesThe board did not fit to some used transistors I got so I had to fit the boards to the transistorsI built 10 double boards and try to summarize the findings
3At a glance – some visible imbalances Thermal analysis of the original board at 94 W outOutput capacitor is thermally the hottest partHigh power dissipationat 50 Ohm load!!!Mismatch at input and output is detected by different temperatures
4Some just layed on flaps distribute the heat peak to the center of output hybrid Now at 10W in 180 W outinThe hybrid is still lossy but now symmetrically loadedFirst try of improvement by mobile flapsoutLess power loss at 50 Ohm load!!!
5Parts to be replacedOmit the tiny ceramic trimmer TC1 and TC2 and take a variable air capacitor (muRata)* or similarReplace C2 and C12 by ATC 800A 22pF*Thanks to Mike, JH1KRC I have these on my bench..!
6How to find out what to do? 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 endAt 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 onOnce no further improvement can be seen, solder all mobile flaps to the boardBeware of excessive RF exposure to your eyes, man!
7These flaps helped to balance the amplifier in power and phase Input terminationOutput terminationmuRata 1-5pF
8These flaps helped to balance the amplifier in power and phase Output lines remarkably different..Due to high current, generously solder the cathode to the board! Thicknes improves here!
9These flaps helped to balance the amplifier in power and phase The hybrid also may need little mods(C2 still original size)
10Final resultsAt input power of 14W the amplification is 14dB at 28VDC 16AAt 250W key down for 1 minute is possible with moderate heatsink without fan, max. pwr out 320WEnjoy these amps and call me off the moon in CW !73 HB9BBD Dominique JN47ee
11Another Issue.. The host of my EME site is a farmer. Since farmers in HB9 get lots of subsidies, he wants anew barn for more cattle..… and I want a better window to West!!… and a solid shack too!!
12So the dish has to moveSince I did not want to disassemble and put together, the move was to be done in one pieceTotal weight tower and dish is 5200 kgDistance to relocate 28 mAll cabling off now..
13The HoleAn 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!
14The Steel1400 kg was to be invested.. And welded too.
15The FitHappily, the stainless steel base could be lasered along the plans, which had been designed in 1996So it needs to fit at first try.. 10xM33 in V4A quality
16Steel into HoleNext comes concrete.. But before, welding the grounding wire to the steel
17The Concrete48 tons for the next 2000 generations!