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Re: Tuned input

 

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I have tried this in the past. It's a huge KLUDGE and would not recommend it.? That tuner is going to try to tune while you are transmitting, You're constantly showing your radio a bad match every time you change frequency as it has to retune.?

Unless you can somehow make it stop with hard ware or software it never works.??

The old LDG amplifier version had special code that made it work for an amplifier and it had board changes as we only need a small change to work with cathode drive.

Then, The biggest issue, Is the Q is never correct.? The Q is important here for properly function and flywheel effect.? The antenna tuner is never going to match the correct Q.? It's super narrow and will have to retune even with slight changes in frequency.? If you jump from 14.100 to 14.250 its gonna ratchet away as you try to make a contact OR if its disabled, the SWR on the input will be 6 to 1.

What people end up doing is to remove the AUTO portion and just hard wire the relays for each band.? At that point, Just build a board and tune it.

C

From: [email protected] <[email protected]> on behalf of Brian Moran via groups.io <brian.moran@...>
Sent: Sunday, December 31, 2023 7:17 PM
To: [email protected] <[email protected]>
Subject: Re: [ham-amplifiers] Tuned input
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Yes, you would mount the tuner inside your amplifier somewhere; the output of the input network should be close to the tube. Controls for the tuner, and potentially the display, would be on the front panel.

The AT-100 can be put in automatic mode -- it reads the frequency that is being transmitted, and will switch to the L and C for that frequency.?

There's a different button that is pressed to cause it to "tune" for the current frequency.? Here's a link to an AT-100 manual for a particuar version of the software:?https://www.oz9f.dk/wp-content/uploads/2020/02/ATU-100_Extended_Board_User_Manual_eng.pdf?

If you expect a large variation in the input impedance to the amplifier, with a set of switched tuned circuits, while operating, do you expect to tune your input network while you are tuning your load and plate capacitors? or do you expect to tune the input network for some estimated input impedance and just switch between bands? Are you going to share this band switch with an output tank band switch??

I believe there was an auto-tuning 8877 amplifier project published in either one of the ARRL Handbooks, or the older Bill Orr Radio Handbooks, that did use the LDG module (which is now out of production).? That might also be a nice reference for the theory of why they did that.

-Brian N9ADG

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