I am very new to the (tr)uSDX but already looking for ways to modify and tinker with mine. One upgrade I identified right off the bat is a TCXO upgrade. I know that the PCB is not set up to support one, but perhaps it can be bodged in.
One thing I discovered while exploring this possibility is that the PLL chip on my board is not a genuine Si5351, but a MS5351M. This article suggests that it performs well and is a suitable substitute, but it was an interesting discovery. It shouldn't have any impact on a TCXO mod.
I designed a small PCB (15mm x 10mm) that I plan to test for a TCXO mod. My thought is to remove the 27 MHz crystal and then use two of its four pads for the clock signal input (to Xa on the MS5351M) and ground. VDD for the TCXO will be connected at the cathode of D2 where the 3.3V supply for the PLL chip is generated. That diode pin and the two necessary pads from the crystal footprint are all in line on the main board. My small PCB has castellated vias that will be placed next to / above those pads. Connection will be made with a tiny bodge wire or perhaps just a blob of solder, depending on how things line up. The mod PCB will be glued to the top of two larger, nearby ICs for support. I don't like that very much, but there's really no where to secure the board otherwise.
- tcxoupgrade918811.png (5.35 KiB) Viewed 883 times
The TCXO I picked is a 27 MHz +/-500ppb part from Digikey that costs about $3 USD. The entire assembled mod PCB would cost perhaps $4 USD in parts, ignoring shipping and such.
If my idea works out I will update. It probably won't in its initial form but tinkering is the fun part! Any input is welcome.
Thank you.
Dan Watson
N4XTL
Who knows.