A temproary diversion from the Antenna installation --- Homebrew Crystal Filters
A Diversion from the Antenna Installation
My life seems to be consumed with installing the new two element beam; but it appears that the goal of having an new antenna may take a bit longer than thought (or desired). There has to be a workable solution that does not involve spending $3000 on a small tower. I have received some new inputs that will require a bit more noodling so the antenna project is now in the "needing more evaluation" stage.
So we don't lose your interest in this blog I want to share some tribal knowledge about building homebrew crystal filters. There is much information about the actual selection and characterization of homebrew filters and I will not cover that aspect. My bent is once you have the filter crystals and the selected capacitors how do you translate that into hardware.
In a recent project of mine called the LBS - II, I decided to use a 5.185 MHz homebrew crystal filter principally because I misplaced my normal stash of 4.9152 MHz crystals which happens to be my most favorite IF frequency behind 9.0 MHz. Because the LBS - II was (by design) to utilize Surface Mount parts to make the radio more compact I needed a way to install the crystals in a small footprint. Some noodle time came up with a layout that works and in fact is ideal if one elects to use the 9.0 MHz SSB Filter Kit Model #351 sold by INRAD. Here are the specifics:
- The footprint involves five pad areas of 0.2 inches wide by 0.4 inches long. Thus the overall size is 1 inch long by 0.4 inches wide.
- All of the filter capacitors are soldered along one edge of the assembly (this makes adjustments very easy to accomplish).
- The design provides a good ground plane area under the crystals which is very important to achieve the stop band attenuation
- The board can be made by etching, milling or ugly style with a hacksaw and xacto knife
- The board area being small is ideal for retrofitting into existing designs
- An all important final step is to connect all of the crystal cans to ground which is another factor in the stop band attenuation.
Drum Roll Please
|Layout for the 9.0 MHz INRAD Crystal Filter|
|The 5.185 MHz filter installed on the LBS-II. The Ground Wires have not been added at this point.|
Stay Tuned de N6QW