Raj VU2ZAP has found good reduction of spurs with the following mods:
1. Replace L5 with an SMD inductor 680nH or 681nH. Mount at right angles to old toroid
2. Replace L7 as above. Note that C211 is bypassed with this mod.
Don’t be distracted by the missing C216 and C210. These parts were never populated.
An additional 45MHz filter is not required and, therefore, you should get almost the same power out as stock boards. If you ALSO use the second 45MHz filter the spurs get further reduced, but with some loss of output power. Raj used Murata inductors 1210 size. 1206 size will do.
With Mikes W0MNE relay fix and this mod, Raj has the uBitxv3 and v4 boards now operating within normal emission standards.
Raj thinks that a combination of high Q, small size and possibly internal shielding contribute to the reason why. Another hypothesis is that the original inductors caused ringing. Raj has also replaced L1-4 with 330nH SMD and that helped a little on one test board. His interest was to fix the problem of spurs with the simplest solution and without major surgery.