TX balun lacks DC block

[mossmann]

Balun T4 pin 1 is shorted to GND, but there should be a capacitor between pin 1 and GND. It is possible but tricky to bodge in a capacitor by cutting the GND trace and soldering a 33 pF 0201 capacitor in its place.

An untested bodge that might be easier would be to cut both traces between U13 and L10 (unpopulated), scrape away some solder mask, move T4 there, and then install two 33 pF 0201 capacitors onto the original T4 footprint.

An easier workaround with degraded RF performance is to cut the GND trace without installing a capacitor. This results in reduced TX output power at the intended frequency and increased LO leakage.

[mossmann]

The root cause of this is that the schematic symbol for T3 and T4 was drawn with an incorrect topology.