Re: QDX 2.0 Q11 Smoked


Johan Bodin
 

Hi

An autotuner can present *very* bad loads to the transmitter during the tuning process. Overvoltage will kill the MOSFETS quickly while overcurrent will take some time to achieve the same result since heating of the chip has a handful of milliseconds delay. I use an old LDG Z11 autotuner with my QDX but, since I suspect that the QDX PA is slightly fragile, I always use some kind of attenuator between radio and tuner while tuning the antenna. This prevents the radio from seeing ridiculous impedances. I have had no problem whatsoever since Hans released firmware 1.02.

I have a simple resistive SWR bridge that attenuates -6dB in case of 50+j0 ohms antenna load. The rig will see worst case impedances of 33 to 100 ohms when the antenna load varies from a dead short to open circuit. A simple -6dB attenuator (Pi or T) would work equally well for protecting the radio, in fact even slightly better than my resistive SWR bridge.

73 SM6LKM

Daniel Walter wrote:

Curt,
with the Palstar Auto tuner, could that present transiently very high voltages to the QDX? Could that be the reason for the failures? I realize that the SWR would not be high for a long time period, but if the voltage was high enough, it would take no time.

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