A rack mount bracket, by Karl Shoemaker, AK2O


The bracket project is support for equipment for the 147.20 repeater. Mounting remote radios are various site has space issues in most cases. This project was to keep a rack "footprint" to a minimum, since some sites require 19" rack mounted equipment and a small amount of RU's to boot. (RU=Rack Unit) therefore, a special universal bracket was developed.

Mounting issues

The old (motrac) receivers are eventually being replaced with micor type with the Spectra-Tac type chassis. The old receivers are mounted behind an up-front panel. Therefore, space is used efficiently. The newer Spectra-Tac type chassis use a different method. They have "ears" that mount the electronics about 7" in front of the 19" rails. The micor unified chassis is mounted similarly. Both can reduce space efficiently. This is especially important with some site owners that require only open rack mounted equipment. Most of the time only a few RUs are granted for the SRGs equipment.

Therefore a better way to mount equipment was researched and developed. While the newer receiver chassis takes 3 RUs the associated link transmitter can be mounted directly behind it, thus re-using the same RUs. Two thoughts come to mind:

  • The link Tx could be directly mounted to the back side of the receiver chassis, so to make this one Rx-Tx unit as a large FRU.

  • The link Tx could be directly mounted behind the receiver chassis, but on it's own bracket, so to make separate Rx and Tx units as smaller FRUs. This would allow better flexibility in the event of a swap-out for repair or updates, etc.

    The latter was decided. Therefore, a bracket need to be designed and a prototype built to allow most any link (Tx) radio to be mounted horizontally directly behind the receiver chassis, but allow access to all part of the receiver as well as the link transmitter. A couple of large "L" brackets with 3 crossbars attached to it appeared to be the solution. The cross bars can be either bolted or welded to the "L" sections. For this project the latter was utilized.

    Starting with flat steel stock of 3/4" x .188 " thickness, make the first cut 12 1/2" for each "L" section. One bracket will need two of these.

    It works much better to batch them if you have several to make. For this project 5 complete sets were made. The plan (left imagine) can be enlarged by clicking on it.







    After cutting, line them either in some clamps or a vice with the ends even on one side. From that side a template guide was made to make were the 3RU holes, or notches to be made. Using a 4" grinder all of the pieces had their notches started. Next, into 4 3/4" from the end made a 90 bend. Each "l" piece will be on each rail, therefore, the bend will be opposite for each set. Next, finish out the notches, making them 1/4" in diameter, using a bolt to check this. This will accommodate most any mounting situation, right up to using 1/4 bolts.






    Using a (pre-made) template (shown, here in blue) provides easy notch making locations. Using a 1/4" bolt for checking the proper notch width.













    In the picture the other "ends" needed a final cut. From the 90 bend this will be 7 3/4". Both dimension given are outside to end for length. As you can see there's some wrong angles to some of the "l" sections. By putting the bad ones back in the vice and giving the "tail" a tweak, up or down, they can be trued up.




    Here's a few of them rough finished.












    Because of the heavy thickness (.188") of the "L" sections bending them cold, 90 is not very practical in the vise. By cutting the bend point with a saw about half way greatly allows this. After the bend is correct the cut can be welded closed, on both sides. This actually increases the strength of this section somewhat.




















    Just another view of this procedure.












    Remember to bend each side opposite ways for each set.Shown here is several sets of the "L" sections.
















    Shown here are the cross bars installed on each side of the "L" sections. The right shows several completed brackets on the bench for final inspection before painting.















    This is the prototype used to develop the now, heaver duty version. When painting try to get at least 3 light coats of paint.









    Notes and after-thoughts

    The "L" section's notches were made for any size screw/bolt, up to 1/4". Most racks use the following size scew threads:

  • 10-32

  • 10-24

  • 12-24

    These sizes should work satisfactory without further consideration. However, for smaller screws the mounting may be too loose. At minimum, you might consider using a washer for small screws. Another consideration is to make the notches a little smaller, then enlarge them as needed for future installs. Another consideration is to use a little wider "L" section, such as 1". This will give you more flexibly in the notch size/depth for such future installs. Remember to keep at least 30% of metal (no notch) for adequate strength.



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