Smith (1905–1987), 1 is a graphical aid or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits. The Smith chart, invented by Phillip H.Wikipedia gives a better than average concise summary: So - see attenuator articles below and then Smith chart articles.Ĭarbon resistors may be carbon film or carbon composition?Ĭarbon film are not suitable for UHF work as they are formed by cutting a spiral track in a carbon film cylinder, so have very substantial inductance.Ĭarbon composition have a solid carbon body and may be suitable for UHF work depending on other factors. but doesn't that just help attenuation? Thanks again.Ī Smith Chart is not so much an attenuator design aidĪs a means of evaluating and adjusting a design. If I'm just trying to reduce signal power at the output, does it matter where/how the loss happens? So I know poor impedance matching as indicated by my charts means a higher VSWR. Here are the log plots of attenuation over the frequency range I am interested in:Īlso, another question struck me. This is the SC of my cable WITH the attenuator in the middle of it This is the SC of my taken apart coaxial cable WITHOUT the attenuator My questions are as follows: What is a Smith chart and how do I use it to improve my attenuator+cable design? Is this a feasible method for creating basic fixed RF attenuators given that they don't need to be super accurate and only need to function over a very specific range of frequencies (905-920 ish MHz)? Basically I took apart a coaxial cable and hand soldered in some close-to-calculated carbon 5% resistors in between the two SMA connector ends. Now I should mention that my prototype is very shotty. However, the smith chart is all over the place when I measure S11. I have prototyped one using just off the shelf resistors in a T-pad configuration that gives me a decent level of attenuation (pretty flat 19dB) when I perform an S21 measurement using my network analyzer. I need a few different levels of attenuation but each different attenuator can be fixed. I'm working on designing some hopefully simple RF (912 MHz) attenuators.