Thursday, March 4, 2021

Ultimate 3S, modded

I have Sverre LA3ZA to thank for posting details to his blog regarding the compatibility of the QRP Labs TCXO with the Ultimate 3S. Until recently, the TCXO was an optional replacement meant only for the crystal synthesizer in the QCX-series of transceivers.

Despite being a regular reader of I somehow missed the announcement that the little TCXO circuit board that Hans offers as an option for the QCX is also compatible with the Ultimate 3S.

Sverre recently added the TCXO to his U3S with an excellent improvement to stability and, with today's POTA activation postponed till tomorrow, I decided to do the same.

The Ultimate 3S is a handy device for using WSPR to explore propagation but I have always limited my use of it to 14 MHz and below. Above 20 meters, the drift of 4 Hz or so was annoying to me. At 10 meters, it's worse yet, and don't even think about using it on 6 meters.

As luck would have it, I have a TCXO available due to not yet having built the second of two QCX kits that I recently ordered, so I gave this tiny 1X1 cm board a new home.

Leads from a couple old diodes provide stand-offs

Sverre mentions that the new Rev4 version of the synthesizer board has pinouts and labels for installing the TCXO. My Rev 3 did not, but with Sverre's clarification and the schematics, it was easy enough to find the three connections I needed: VCC, ground and output.

It won't win any beauty contests but it works FB

Twenty minutes later, the much improved U3S is WSPRing on 15 meters with no drift at all. Previously, there would have been 4Hz of drift on this band.



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