There is one thing I would like to say though.

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You need to complain to those radio designers that use inferior techniques and parts… that design radio PAs that can easily be blown up.? It’s just not that hard to design something decent.

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Hi Dan, thanks for the note.

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Well… Switching a tuner in and out basis SWR is a very easy thing to do.? The real problem is the tuning.? If the SWR is 5:1 (and you are not using one of my indestructible 20W or 100W PA retrofits for your QRP radio)…. you will always risk the chance of blowing up your PA in the tune phase.? You can also get into “hunting” issues if you are on the edge of the tuner trigger (say at 2:1… where the SWR bounces between 2.01:1 and 1.98:1 with the antenna movement in the wind).? I’m also not a fan of “Hunt-and-peck” tuner algorithms that all of the hobbyists tend to use. ?Using the direct transform method seems way more appropriate so that the initial guess would be? right in the vicinity of where the actual tune solution actually is and may save your PA when tuning under full power.?? Another way to do this is to tune under reduced power… where you give tune into a resistive load and just use a small sample of the power from that load to determine the tune parameters.?? Of course the real way is to back the power down on the PA to a place where it won’t matter.

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I do have a tuner on the drawing board that I build for te uBITx that uses a lot of this… has a signal at tune initiation that tells the radio to go to low power (that could mean switch to a resistive load with a very lower power tap for tuning), uses phase and magnitude info to determine the transform from the radio to the antenna… and then solves for the inverse transform (read that tuner parameters) to present a 50 ohm load to the radio from the transform solved for the proper structure, L, and C values all within a few milliseconds.

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This project works well for all of the QRP radios I’ve worked with and is in the queue to get designed for board sales.? I have a few projects in front of it… like six… so it will be a while.? The T41 is just about finished… the 100W module is almost ready to be put up for sale as a kit. (the 20W module is available right now).

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Sorry there is only one of me.

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Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ VP2EHZ

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Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

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Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it:

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Moderator: North American QRO Group at Groups.IO.

Moderator: Amateur Radio Builders Group at Groups.IO.

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email:? bill@...

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Bill,
?I posted this to the QRP Labs reflector:

"There have been quite a few posts about ATUs and possible damage to QCX, QDX, and QMX finals. So it seems that someone should design and market a QRP ATU that has a resistive/absorptive bridge built-in which is automatically switched in every time it is triggered. And the bridge would only be switched out if the resulting VSWR is below 2.0 (or whatever programmed value you want.) and it should be the same size and run from the same voltages as those rigs."

So there is one other consideration for a lot of QRP rigs. That is to protect the finals when tuning. Yes, protection could be integrated into the radio, but why not have a tuner that protects the radio?

Any thoughts?
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Dan
NM3A at mail dot com