Wednesday, October 14, 2015

Denuo GPS Retrofit Board

Here is another quick post about some progress I've made toward developing a retrofit board for the Lucent KS-24361 REF-0.

Denuo GPS Retrofit Board for the KS-24361 REF-0

The Denuo GPS is a drop-in retrofit board for the REF-0. It uses the u-blox NEO-6M GPS module. There is a microcontroller on the board that translates the UBX serial messages from the u-blox to the Oncore format for the REF-0. The microcontroller also replicates control functionality of the REF-1, in that it automatically sends the appropriate messages with the correct timing for the GPSDO to operate. This enables standalone operation. While the NEO-6M is not a timing GPS, the board is still able to send sawtooth correction and other timing-related information.

The board is a significant step up from my previous prototyping efforts. It installs just like an Oncore GPS would in a REF-1. Power and signaling are handled through the 10-pin header used by a real Oncore. There are a small number of modifications that need to be made to the REF-0 to enable this, such as mounting standoffs and removing two SMD jumpers. The normal antenna mounting location is not present on a REF-0, so I opted for a u.FL connector and a pigtail to the outside. I think the finished install looks pretty nice. What do you think?

The Denuo GPS board mounted inside of a REF-0.

The board also has some neat features that are enabled by the modern GPS receiver. Sensitivity is hugely improved compared to the Oncore. Time to first fix is several seconds instead of several minutes. Also, the board breaks out the USB connector of the u-blox GPS. I can now monitor GPS status and tweak settings using the free u-center application.

So you might be thinking, "Where's the beef?" Or rather, where's the timing GPS module? The REF-0 is a GPSDO after all, and the original Oncore GPS was of course made for timing. Don't worry, that version of the board is in the works too.

A sneak peek at the Tria GPS Timing Module.

So that's it! I have a REF-0 with the Denuo GPS humming away in a quiet corner. Over the next few weeks, I'll be collecting data on the performance of the GPSDO with this retrofit board.

More to come.

Thanks for reading!

- Dan W.


  1. Dan -
    Great work. When you complete the "tweaking" of this Denuo GPS board,
    I would be interested in one board - bare, partial, or complete (don't have a REF-0 yet). I may have access to a uBlox LEA-6T -- but I think the LEA footprint is different than the NEO size.
    Very familiar with the standoff issue (GPS board) from the TAPR TAC-2 board build (now 20 years ago).

    1. Yeah, the NEO footprint and size is very different from the LEA unfortunately. The Tria board (minus the GPS module) actually has a similar bill of materials cost to the Denuo, despite the far more powerful microcontroller. The GPS module is what makes or breaks the final cost. Which is why I decided to develop both.

  2. Good stuff, Dan. I await availability of both boards for purchase. Thanks for all this work you've done.

  3. What I did not realize, until earlier this week, is that u-blox made 3 different versions of the LEA-6T module.
    Timing and Raw data features are available in three Module versions, the LEA-6T-0, LEA-6T-1 and LEA-6T-2. All are pin-compatible Modules.
    The LEA-6T-1 and LEA-6T-2 include internal Flash memories for firmware updates.
    u-blox 6 GPS Modules
    Dara Sheet

  4. I went to the u-blox North American on-line store, to check current pricing.
    Once you hit quantities of 10 or more, the pricing drops significantly

    LEA-8MT module - Qty and Pricing each.
    1 - 9 pcs $ 199.00
    10 - 49 pcs $ 92.46
    50 - 99 pcs $ 78.60
    100 - 249 pcs $ 62.91

    1. Yup, the LEA-M8T becomes very reasonably priced when purchased in quantity. The LEA-6T is still cheaper, but of course we are now relying on the surplus market for those, as the 7 and 8 series are the current models. I'll try to get my hands on an M8T to test the board with both possibilities.

    2. Dan -
      u-blox USA should sample you the M8T, especially if you show them how far along you are in development.

  5. Dan

    I think that the most interesting piece of data will be how the non timing receiver compares to the timing type. There has been lots of discussion about this on time-nuts with no clear consensus.
    Fred WA7AII

    1. That will indeed be interesting. Let's see, objectively, what a modern $10 receiver can do compared to the expensive T/F models.