How does automatic antenna tuners work ?

[biff44]

I recently became aware of the AD5933 chip. It appears to be a full impedance measuring circuit at 100 KHz. I was thinking it could be made into a microwave network analyzer with the addition of an upconverter mixer, and downconverter mixer, and a shared LO PLL oscillator. With some proper directional coupling, you could probably measure S11 and S21.

http://dkc1.digikey.com/us/en/tod/ADI/AD5933_NoAudio/AD5933_Noaudio.html

p.s., this chip is the reason you can not buy a cheap LCR meter running at anything other than 100 KHz these days, they all must run off of this chip.

 

[chuckey]

Do you want to build a stand alone AE tuner or is it part of a complete TX? I spent some time working on 2 KW HF TXs tears ago and we had various versions for tuning the PAs. One point is that while tuning the PA or AE, the input power must be kept low and the drive muted while any switching is going on. To cover the whole of the HF band is impossible without band switching the capacitors. The inductors we used were not switched, but took the form of a coil wound on a ceramic former mounted on central bearings in ceramic end plates, as the former was rotated a wheel engaged on the coil would run along a shaft and progressively short out the turns of the coil, so the coil could be reduced from 30 turns to .5 turns. As well as tuning the the circuits must present the correct impedance to the PAs (loading), this was done by increasing the drive until the screen current was correct, then trying to dip the screen current then upping the drive again, until the Ia and IG2 were both correct (Ia = 1 A, Ig2 = 50mA) then ther transmitter was running 2kW CW or 1.5 KW p-p. Some of these transmitters had phase meters with which we tuned to, but you can't load on them.
Frank

 

[tony_lth]

Murata has developed a new antenna tuner chip. I will tell you the part number the day after tomorrow.
In the tuner, there is a VSWR detector. So the MCU adjusts the L / C to get the minimum VSWR.

 

[tony_lth]

Sorry, it's not Murata, it's EPCOS.
Closed Loop Single Feed Antenna Tuner
Freq range: 700-2700Mhz
Ordering code: B30680D7005Y725
Series/Type: D7005

The D7005 is a closed-loop antenna impedance tuner with integrated microcontroller, mismatch
detector, tunable matching network and DC/DC converter. The on-board 8051 microcontroller hosts
the tuning algorithm, ensures protocol synchronization and controls the power management system.
Inside the microcontroller data-flash is available to store tuning specific variables, which vary from
phone to phone.