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You will check swr between the LDMOS and the Filter board and adjust the length of coax between them to get the SWL Down. I changed out the 5.2v zener for a 6.2v and set for. That means the W6PQL design needs some slight modifications.įirst the Bias requires a slightly higher voltage. The output curve is slightly steeper so its a little harder to control low wattage outputs (below 200 watts) The MRFX1K80 has a slightly higher HF output Impedance of 4.7 ohm, compared to the BLF188XR (3.6 ohms). They even make a Plastic molded version of the MRFX1K80 that has a higher (better) thermal transfer (since the ceramic version is just a ceramic cover with an air cavity, and does not come into contact with the transistor circuitry) And I have no issues with heat dissipation now. Then polish and apply heatsink grease between the Copper heat spreader and the aluminum heatsink. Then I polished the mating surfaces and uses a high thermal transfer heatsink grease (i.e. I drilled and threaded holes to secure the LDMOS tab, then I created a solid brass clamp that sits over the top of the LDMOS to allow the mounting screw head(s) to sit above the LDMOS. I have also determined that its not necessary to solder the LDMOS directly to the copper plate. I find AM mode actually runs cooler than running SSB.Keep the SWR flat to avoid dumping any extra heat back into the heatsink. Then I moved them right up to the edge of the heatsink, and found that much better (pulling air through the fins of the heatsink). I had the fans on the back of the enclosure about 1" from the heatsink and could not control the heat properly. I found its easy to keep the operating temperatures below 40 ☌ while running FT8 or CW or SSB. Keep your fans close to (on the fins of) the heatsink. Originally designed by Motorolla, then renamed Freescale, then sold to NXP The Laterally Diffused MOSFET (LDMOS) is an asymmetric power MOSFET designed for low on-resistance and high blocking voltage. Single MRFX1K80H (1800watt CW 65vdc LDMOS)