?

Bill,

I'll be looking forward to see the design...

Mike N2MS

On 11/08/2023 7:42 PM EST K9HZ <bill@...> wrote:


Most of the commercial antenna tuners for hams (MFJ, Elecraft, LDG, etc.) are built with fixed components (fixed caps and coils) in a series L parallel C (either side of the L to ground)… and an SWR bridge is part of the thing that reads power and SWR. Then tuner… when requested… starts at the beginning (typically with no coil and no capacitor) and starts trying all of the combinations to get to a low SWR. If all you measure is SWR that’s all the information you have… find a minimum SWR… and there is no relationship between the solution and the minimum SWR other than… since you are using the “L network” type of tuner… a smith chart would tell you that there is only one solution… so guess away. There can be something like 256*256 different guesses to get to a solution, and NO a prior guess does not give you any information on what the next guess should be. Typically these bridges can just be transformers and diodes to generate a voltage that is logarithmically related to SWR. Some more advanced ones will use two AD8307 devices (Log amps) instead of the diodes… and they can work pretty well… but the tuning is still slow.

But there is a better way. The Intelligent antenna tuners work differently… they actually measure phase and magnitude of load transmission… So why is this so important. Well (and this is all in Sabins book…) if you know where the load is on a smith chart… then you know EXACTLY what you need (what transform) to do to get to 50 ohms real and minimize the non-real parts. Right? So if you measured the REAL part (magnitude different than 50 ohms) at 100 ohms… and the non-real parts at -300j… you instantly know to add inductance to bring the 100 0hms to 50 ohms… and then add capacitance to move the -300j to zero (and you can see this on the smith chart). WOW! Smart. So how do you measure MAG and Phase? Well…….. there’s this part… AD8302… It’s in your LP-100A watt meter. It generates Mag and Phase info from a bridge (look at your LP-100A schematic). ALL OF THE MILITARY tuners do this The 601 and the Harris that you have all do this (granted doesn’t use a AD8302 to do it, but rather a different type of bridge).

So I have designed and prototyped the tuner for a very nice small 100W tuner that is generic to work with any radio. It uses an Arduino as smarts to do the tuning and a bunch of small latching relays to keep the power consumption low for QRP radios. It works using the stupid method of tuning above but I want to switch to a smarter tuning algorithm using the phase and mag. That’s why I want to completely understand the coupler design… so I can get the thing right for the AD8302. This little tuner of mine costs about $35 to build.


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