PI-Network Test Fixture

[MaryBeth]

Hi all, I'm writing about a Pi-Network Test Fixture because I may need to attempt to build one, but I'm trying first to understand what it actually does (basically I'm a poor grad student without the budget money to buy one). It is an "industry standard" used when measuring impedence, frequency, ect, of quartz crystals. I've been using a network analyzer to look at the frequency of a crystal I'm working with which I have submerged in a solution (I'm a chemist) and the only time I've seen the frequency stabilize was when Agilent lent me the Test Fixture, but I can't understand why it helped. I thought my problem was going to be due to stray capacitance of my system which is simply connected to ground, but the Test Fixutre didn't require any special set up (my crystal is in a glass jar at the moment). I'm hoping to find someone to talk about this with that can use simple language for someone still struggling with the idea of impedence. Any insight would be greatful.

Mary Beth

 

[stevez]

I use pi-networks to match the output of a transmitter to a 50 ohm line to the antenna. I use the values and circuit diagrams given but I also dig in to see if I can understand what is going on. In these applications the impedance transformation is significant - several thousand ohms to 50 ohms. The networks are also used to match the 50 ohm line to an antenna that might look like something significantly less than or more than 50 ohms. I've fooled a little with the calculations.

I'd like to understand more about what I am doing too. I think that by knowing the values of the pi-network, once adjusted for a match, that I can do a little math and determine what the load looks like in terms impedance, sign, real, imaginary, etc.

So, I understand a little and would like to know more. Feel free to email me at WA2EKL@ARRL.NET - my ham radio call. ARRL (American Radio Relay League) publications, particularly handbooks, explain the pi-networks well in more common language.