A Home Brew 224 MHz Repeater Project. May 2009 Once in a while I get back to building enjoyable repeater projects and this text is part of a description of a recently completed 224 MHz Repeater Project. One could easily apply the same techniques toward a repeater project in different frequency ranges.
A lot of different influences directed the choices made regarding what materials and equipment were used. There are many obvious (and some not so obvious) possible choices available to reach the same or similar end result. I will try to list and detail some of the choices and reasons why specific items where chosen/used. Pictures of this project will be placed in the group files section where/when available. Part One - The chassis or base plate: Aluminum boxes are common repeater chassis candidates, but their retail prices have increased dramatically for a classic 17 X 12 X 3 inch box. Since most all the electronics related to RF will be mounted in top mounted separate boxes there should be no major reason why an open-frame mounting scheme wouldn't work and be much easier on the budget. Not to mention obtaining the materials for constructing and open frame wood based chassis is much easier in non-metro areas. Wood base, sheet metal overlay chassis are by no means new. I have home-brew amplifier equipment constructed in the late 1940's using this technique and I've seen many similar examples in older ARRL Handbooks. Many repeater sites use common 19-inch wide telecom racks with various types of screw in shelf assemblies. Many of the more popular "rack shelves" are at least 12 inches in depth. So a section of scrap recycled 1-inch thick plywood was cut into a number of 16.5 X 12.5 inch squares and painted any dark color with common spray paint. Paint helps to seal the wood from moisture and improved the visual appearance over original scuff and paint markings. My local ACE hardware store sells small 24 X 24 inch squares of Steel and Aluminum sheet metal. Prices tend to increase dramatically by thickness and type of material. Just about any reasonable material should work well for the base plate material. I chose a 24 X 24 inch square of thin galvanized sheet for less than $20 and set about the process of measuring and cutting. A friend with a sheet metal shear offered to cleanly cut my galvanized sheet into any desired size. I had planned on cutting it myself using an electric saw outfitted with the proper blade. Caution to the reader is advised to always properly secure metal during the cutting or shearing process. A number of metal cutting techniques can be used to achieve the same end result. I measured and shear cut two 16 X 12 inch squares, which allows about a 1/4-inch wood top edge around the assembled package. Multi-use metal & wood screws with both flat and lock washers are used secure the sheet metal plate to the wood base. I simply chose to place four main anchor screws about 1/2 inch in at each corner. Other anchor screws are later mounted as desired. So the 224 MHz Repeater base plate chassis is now constructed and ready for use. Please view the available pictures in the group files section as we move on to the next stages. Cheers, skipp skipp025 at yahoo.com
