On Fri, Dec 6, 2024 at 09:58 AM, Lasse wrote:
Had to turn off SWR protection in the radio to get the tuner to work but it doesn't seem like this was a problem.
Personally, I do not use full auto tuning with a QRP Labs radio (or any other small, "hobbyist" QRP radio) at "full" power (4W even). I define "full" auto tuning as? the rig deciding when to tune. I also do not tune with more than 1W with my QRP rigs. I've been experimenting with the ATU-100 and, just because it tunes without misfortune one time or even 100 times is not an indicator that little QRP rig finals are safe. The transitions an auto tuner takes are dependent on its initial state and initial conditions, which are not visible to the user. Sometimes a high SWR might be present until the tuner finds an acceptable tune.
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The QMX+ABS project on this groups.io group has a custom ATU-100 tuner (by Sardar / AC8L) and it tunes well below 1W. It's integrated into the QMX+ chassis and it permits the use of QMX "tune" mode at 50% voltage (25% power). In order to realize reliable tuning under 1W, Sardar and friends had to give up SWR/power meter accuracy, but the QMX/QMX+ has those SWR/power meter features built-in and we are running the tuner "headless" anyway. I believe that changing the EEPROM cell values and Stockton bridge windings ratio can also be used to lower the power requirement for an ATU-10, similarly, tune well below 1W too.
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Another approach that I've found to work safely with external auto tuners, like the standard ATU-XXX or my Antuners, is to use an SWR bridge, like the "Tuning Indicator" sold by QRP Guys. The bridge reduces output power to the antenna and the worst SWR your rig will see is 2:1, into a short or open. When using the bridge on a QRP rig like the QRP Labs designs, there's no need to reduce power at the rig. However, one must deactivate auto-tuning when the tuning indicator is switched to "operate" mode after a tune cycle to obtain full power. I assume that the ATU-10 permits auto tuning deactivation, if only by powering it down, given its latching relays.
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Why do have the above opinion? Well...most recently, I blew the finals (and the gates that drive them but all now repaired) in my QMX+ while experimenting with the QMX+ABS ATU-100 based tuner. Sadly, I have acquired a bit more of a bone pile of finals than that mishap produced over the years while I learned the hard way!
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I only enable full auto-tune (where the tuner decides when to tune) with my commercial rigs, like my IC-7100 and IC-7300. They have very well-proven protection, including rapid power roll-back. Even then, I'm not in a big hurry so I'm not a big fan of full auto tuning. Pressing the button for each tuning cycle, when needed, works fine for me.
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73,
Cal (AD8Q)
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