Trimming and tuning
with no knowledge about S-parameters etc. Radiodesign as it was done in the old days....
Example take a look at the tuner applet at :
http://fermi.la.asu.edu/w9cf/tuner/tuner.html
How to tune this ?There must exist a method for finding SWR=1, with a reasonable amount of work. I cannot tune this...There must be a jungle-trick that one can do here..Is there a book that describes how to do it?
If one is going to tune the input output matching networks to an amplifier it must be even worse. If you start finding the optimum input match, and then trim the output matching network, the input matching network won't be the optimum anymore:
Gamma_in =s11 + s21*s12*Gamma_load/(1-....) and Gamma_out is looking similar but a function of Gamma_source. Whats is the jungle trick?
These kind of practical trimming and tuning issues should be adressed in the book I am loooking for. Is there such a book ?
Found info for the first time about how to measure L and C parasitics as well as unloaded Q in Vizmuller's book. It cannot be the only textbook about it ?
Hoping for some help
Kindest regards,
StoppTidigare
I worked with trimmers and screwdrivers for years.
Now i use simulator, but i don't forgot the screwdriver.
I don't answer to you exactly, but i give an opinion.
- The matching is a "tecnique" supported by mathematical algoritms.
- The manual tuning is more similar to an "art" , it may be learned but, once skilled, some one make it better than other peoples.
Tuning isn't related to impedence matching only, Historically, frequency has been the most tuned...
have you experienced the tune of a SSB radio receiver?
So to learn please prefere prectice than books.
Coming back to the matching, for my opinion, when you should match ona circuit, 1st use a simulator, then, place tuning (variable) elements. In the best case you'll not use it, but in the worst case you'll find very comfortable the presence of tuning elements.
A final note about tuning: the Q factor.
Due to the path choosen (for the tuning on the Smith Chart), you may "touch" far circles.
This mean that the Q factor of the tuning element became important for :
- Circuit loss (the loss is more effective if you are far from the centre)
- Fire azard (if you use large power), right side of Smith Chart >> spark risk, left side of Smith Chart >> extracurrent risk.
bye
Hello friends,
i am trying a similar project , an HF automatic antenna tuner, based on PIC16F876 that will check for best SWR achieved and then issue a command to a L-type matching network.(i.e. binary arranged capacitors and serial inductors)
so far i managed to check the SWR (in floating point) and then came accross the complex math of impedance part. I can also find the plot of initial state of output impedance BUT:
the main thing that i am missing is how to use the Smith chart for impedance matching. I need some algorithm or something to start coding in for microcontroller.
regards
mgf
Hi ,check
http://www.elektroda.pl/eboard/searchtopic61688-.html
StoppTidigare: I guess what sergio mariotti explained is true. Practice is more practical than theory. Currently you want to get some theoretical understanding of the tuning and trimming. I believe you can understand the theory after a lot of so called "on board tuning".
In fact, I have done a lot of tuning on high/medium power amplifier where the non-linear model is not available.