Filter question

Discussion in 'General Electronics Chat' started by Key, Jul 29, 2013.

  1. Key

    Thread Starter New Member

    Jun 21, 2013
    Greetings everyone, I have a small question regarding filters.

    I work as a technician in Ericsson (have worked for 6 months or so, have studied electronics for 2 years, working and schooling myself at the same time), and one of our main products is a bandpass filter.

    My job there is to maintain the testing stations, to make sure that they work properlly. I am full aware of the hardware side of things, which is all that is required. And a fair bit of the software side to make sure thigns run smoothly.

    But my question is about the filters. I never really thought about them before, but I got sort of interested in them after seeing the insides. Ive never really asked any of the working engineers about them, as we speak different languages and they have their own things to do.

    This filter, except for the small PCB inside (for troubleshooting and testing) has no electrical components that make it work as a classic passive or active bandpass filter (electronic components), instead it is a hollow metal slab with mushroom shaped resonators inside, that you have to tune it to specs with the screw on the "roof" of the chassis. The Rx/Tx inputs/outputs are essentially connected to a network analyzer, through a system of switching relays. How exactly is this filter called ? I would like to learn a fair bit more about it. Either by searching for the name or perhaps recieveing a small explanation here ? Another question I have is regarding a certain test, called IM-test, I assume its impedance test ? Workers are equipped with hammers, if needed they have to hammer the sides of the tuned filter to reach the required measurement values. What exactly does hammering do to the filter ?

    Thank you for taking your time reading this and perhaps answering.
  2. Papabravo


    Feb 24, 2006
    At high frequencies the geometry of the cavity acts like passive components at low frequencies. Hammering on the sides changes the dimensions ever so slightly and adjusts the frequency response. I think they still use very small surface mount resistors to build attenuators and power dividers.
  3. crutschow


    Mar 14, 2008
    Do you know the frequency range of the filters?
    t_n_k likes this.
  4. Key

    Thread Starter New Member

    Jun 21, 2013
    Depending on the product, somewhere at the 850ish MHz or 1.8GHz, ive searched for "cavity filters" surprisingly little info about them, ive read that they are suited for upto 1GHz, what happens after 1GHz ? Also I couldnt edit my post before, the filter doesnt have only one screw, they have tuning screws on top of every resonator along the cavity.
  5. WBahn


    Mar 31, 2012
    Try looking for "waveguide filter".