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Hello all,

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When I go portable, I use a 12V Makita drill battery which voltage varies between 12 and 10.5V. It is really convenient, the circuitry protects against shorts, it is in a robust case and it lasts a good while.

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Nevertheless it doesn't play well with the QMX, for some reason sometimes the tension goes up while in RX. I imagine, there is some unintended interaction between the QMX regulation and the battery while the current draw is low.

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I can't really "afford" the 0.5V drop of a regulator in emission thus I would like to add in between the two a simple linear regulator that auto switch itself in the circuit as soon as the input tension goes above 12V.

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Anybody would recommend a circuit that is a good starting point ? Even if I need to make modifications/adjustment, a "scheme design" would help me.

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73 de Yannig - F4IUJ

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I would use a pre-made buck-boost converter, like this one I got from amazon:

or just search for buck boost converter -? there are multitudes of models, some with meters, etc.

You set its output for 12.0V (as measured by your DVM), and if the input voltage is higher, it regulates it down, and if the input voltage drops lower, it boosts it up to 12.0V.? Works very well to give a constant regulated voltage to the QMX.? And it is very small, so you can attach it to the housing of your battery.? Like any converter, it is not 100% efficient (varies between 85% and 95% depending on voltages), but that only reduces the runtime from your battery a small amount, while it removes any concern about the voltage level into your QMX.

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Stan KC7XE

Thank you Stan,

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This is so obvious I am not sure why I did not think about it!

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Sure, I loose autonomy but I will get my 5W till the end. I just hope that it isn't going to be noisy (was my thinking behind the linear regulator).

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73,

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Yannig - F4IUJ

Hello all,

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For those lucky enough to be GQRP members, there is an answer to my question in the latest SPRAT which got to my letterbox yesterday!

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72 de Yannig - F4IUJ

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I've tried. Similar, just 2 Amps (is enough). Works ok, keeps voltage stable as set. But it does give some annoying buzz. I would not recommend.?

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I use this without any problems:

works very well since a year in shack and portable

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may you give it a try?

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vy 73 de Udo DF4BJ?