Re: 12V to 9V Converter : QDX ?


On Sat, May 28, 2022 at 01:53 AM, Afghan Kabulldust wrote:
Voltage converters, especially buck converters are quite noisy, I would just recommend some  Si diodes in series, maybe 4 thus dropping the voltage by 2.8V on Tx. A lot lower noise. 
I built my REV1 QDX for 12v operation and I have been running it at 12v with no issue. I had ta similar idea for a "poor man's voltage regulator" by stringing 3 or 4 rectifier diodes in series to drop the typical 13.8v provided by most power supplies to something closer to 12v, giving me more power options. I have done this before for my my KD1JV MTR3B.  It is "cheap and dirty" and a little bit wasteful but there are no concerns about switching noise. 

I also have  a REV3 QDX coming that I might try to use with a small amp which requires less the 5W for drive. Looking at the output power vs supply voltage curves in the QDX manual, I think that easiest way to drop the output power of the QDX to drive an amp is to reduce the supply voltage so I think that the "poor mans voltage regulator:" could be used for this as well. 

Michael VE3WMB

P.S. You can get a little more sophisticated and add one or more switches to add or or subtract additional diodes to vary the voltage drop as needed. When using a rig with a Mosfet final it is always best to reduce the supply voltage when adjusting an antenna tuner that doesn't have a resistive bridge to protect the PA. The BS170s will be more tolerant of a reactive load with a lower supply voltage present. Switching in some extra series diodes during antenna tuning would do the trick. 

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