Re: Tuner? Well Sure!

K9HZ <bill@...>

MFJ.  Huh. Glad to see them using science for a change.


I’m a little old school when it comes to RF design, and particularly with matching circuits like a tuner.  The best tuners I’ve ever owned were military tuners… specifically the old Collins 601 and the Harris RF-2601 devices.  If you are a study of these devices you know that the control circuits for the tuners operated essentially transform space with phase and amplitude information to effectively minimize SWR by determining the right transform to make the input see a purely resistive load.  Is that hard to do?  Nope.  You just have to think in a different coordinate system.  Rather than go into several pages of background here, for those interested… there is a wonderful and complete chapter on this very subject in Sabin & Schoenike’s book “Single Sideband Systems and Circuits”, Chapter 16.  This book is a must for the serious RF designer.  You can get it off Amazon.  Other chapters in the book will answer questions like why you don’t see grounded gate power amplifiers (a recent topic here), and why the very best IMD and linearity in an RF amplifier comes from a tube design in grounded screen configuration (common in broadcast transmitters… the cathode is at minus screen potential!).  Yikes!


I’ll put together a paper on the various loads the tuner will match once I have all of the calculations done.  Off the top of my head, it should match real impedances of 2ohms-10Kohms and reactances of +/-8Kohms.  I’ve configured the capacitor bank to sit on either side of the inductor to complete the entire transform space (read that work for those really low impedance antennas that are usually not covered by antenna tuners).


The hardware for me is a breeze… what is not so easy for me is figuring out the Raduino side… for display and setting… like Power, SWR, Bypass, frequency for memories, etc.  I may just build in all these things and ask someone else who is more familiar with the uBITx code to help out.  I have decided to make the tuner an I2C device though…so that should help with the communications.  I originally was gonna use RS232 (makes it work with a lot of other radios then too… and even stand-alone) I2C is better for integration.


I should have the hardware drawings dome tomorrow…



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email:  bill@...


From: [] On Behalf Of Gordon Gibby
Sent: Friday, December 29, 2017 6:37 PM
Subject: Re: [BITX20] Tuner? Well Sure!


If you guys can come up with something that works, it might provide a chance for Asher to provide employment for many many more people.


Remember the most recent MFJ products measure impedance and use smith chart type calculations to predict the solution in jump to it quicker.   



But that is not at all beyond the capabilities of many on this forum.


Sent from my iPhone

On Dec 29, 2017, at 19:25, bill richardson <ng1p.bill@...> wrote:

I have been wondering about an internal tuner for my uBitx and/or my BITX40’s. This sounds great please count me in on one.. love to see enough inductance to work on 160m also maybe a mod a future design.

thanks Bill ng1p

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