My QDX Rev 2 works great. I have put a number of hours of constant activity with no issues. Rx sensitivity is great and transmit power is nominal.?
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However, I am concerned about the heat generated by the finals. I built mine for 9 volts, but put a 7809 regulator inside with the case as a heatsink. This way I can power the rig from 13.8 volts, but give 9 volts to the finals and the input to the P-channel MOSFET.?
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I noticed the case got warm on prolonged transmit activity. So at 21 C ambient, I checked temperatures with my IR thermometer. The case was 40 C after a half hour of constant FT8 activity (~45% Tx duty cycle). On opening the case, the finals bolt was 77 C and T1 was 60 C. While I believe the junction can take up to 150 C temp, I also know the TO92 case does not conduct heat very well. Leaving the case open only lowered the temps by about 4-5 degrees. A fan lowered temps by 20-30 degrees.?
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These seem to be excessive temps and would only get worse with high ambient temps in a field environment, such as SOTA or POTA, which is where I usually use this rig. So I mounted a small 12 volt CPU cooler on the case with holes drilled to allow air to enter the case from the fan and exit through the end plate. I powered the fan from the 9 volt 7809. This gave marked improvement in temperatures. Fan noise is low and power draw at 9 volts is only a trivial 25 mA additional. Additional case height is only about 12 mm more.?
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Temperatures after the mod are 29 C on case and 32 C at the finals bolt and T1 (case closed) after prolonged FT8 transmit activity. Again, this was at 21 C ambient. This is 35 degrees less than before! Pics are below. My write up and more pics will also be on Skyview Radio Society¡¯s ¡°Q5er¡± newsletter ( www.skyviewradio.net/newsletter/ ) for December 2022. I am hoping this will prolong the life of my finals.
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73, Dan? NM3A
