QDX now running cooler

Elwood Downey

Yes, according to my Elecraft W1 wattmeter, there is no change, all bands still report about 5W.

BTW, I built the 12V version.

Mitch Winkle

For the same power output as before?

Elwood Downey

Greetings all. Just an FYI to share a recent experience that ended up with my QDX running much cooler.

I often run my QDX as a WSPR transceiver while I'm in the shack. I set it to 30% proportion of transmit time. I use the purchased case and in this scenario I found the case ran quite warm to the touch (not unlike a powered iron hand warmer packet, if you've ever used one of those).

But then one day when I turned it on, the LED blinked once and then no more. Turns out Q7 had literally blown up, and I mean literally, there was bits of plastic in the case and the pads were burned black. I suspect this was because of the known issue that the MCU sets all lines as inputs at power up and thus might randomly drive the TX power amp line full on to draw a lot of current for a brief time, but that's just a guess.

Whatever the reason, I didn't have this part in my junk box and just decided to forgo the polarity protection so I just shorted the D and S pads together. Wow, the heat difference is dramatic. The QDX is back on the air but the point of this story is that the case now runs much cooler, just slightly above room temperature. I did not take any temperature measurements but it sure feels a lot cooler.

Have fun with your QDX, it's a amazing little unit.

73, Elwood, WB0OEW