Building a Stratum-1 GPS Based NTP Server with a Soekris net4501

Make a Plan & Execute:

I originally bought my Soekris net4501 (just the bare board) off eBay for like $40 a couple years ago. I was planning on installing it in a custom enclosure with some other time equipment, but that project never happened. My particular net4501 board is a stripped down OEM model that only has a single Ethernet port, and was (what I thought) missing the second serial port, and no PCI slot on the side. For the curious, to interface with the net4501 console you use a null-modem serial cable and a terminal emulation program.

One day the board was sitting on my desk along with some other GPS hardware I was tinkering with, when a light went off in my head. I knew people have used the net4501 before for NTP servers and other purposes, but I thought man it would be cool to put the GPS receiver inside a stock Soekris enclosure. I went to the Soekris website and looked up the dimensions of the enclosure, did some measuring of the hardware, and realized it *should* be doable. So I ordered an enclosure from Soekris for ~$25.

Below are some pictures of the stock enclosure and my net4501 board. Note that there are no LEDs on the right side as there are in the picture on the first page, I added those in later. The reason there is so much empty space is because the same enclosure is used when adding in an optional PCI card with more Ethernet ports (and there are obviously more holes in the back of the enclosure).

As mentioned on the previous page, for the GPS I used a Motorola Oncore UT+ Timing receiver. Another of my past purchases on eBay, I think I paid like $30 or $40 for it. Its size is just perfect to be mounted in the enclosure.

To drill the holes in the proper location for the GPS module, I made a little paper template from specs given in the PDF manual. I just taped it to the enclosure and used a hand drill (and crossed my fingers... but not while drilling). Drilling the hole in the back of the enclosure for the GPS antenna input was a major pain as it *had* to be precisely in the center. The back of the BNC bulkhead connector was so large that it didn't give much room for error. In the end, everything fit perfect. Patience really pays off, take your time to measure and mark everything, then re-measure to verify your points before making any holes.

As you can see in the last picture, the receiver with antenna pigtail connected clears the top of the case with room to spare.