Mike W0MNE has come up with a fix for the harmonics problem with the µBITX that is simpler than other fixes …
He has two Ver 3 and one Ver 4 uBiTX rigs. He simply replaced K3, KT1, KT2, and KT3 relays with Axicom relays.
This has knocked down the 3rd, 5th, and 7th harmonic levels from -35dB to below -50dB on all 3 rigs. No board modifications are required, and no changes to the LPF circuitry is required. This may not be reproducible on all rigs, but with 3 rigs showing the same results it may be something constructors should consider.
Mike purchased the relays from Mouser – part # 655-V23105A5403A201. Cost was US$2.89 per relay plus shipping.
Raj VU2ZAP found a picture of the “innards” of the Axicom relay, and suspects the improvement in isolation is the result of the contacts being closer to the ground plane (as the relay coil is on top in this relay, whereas the standard relays supplied with the main board have the relay coil underneath the contacts).
Before the fix on 40m …
And after the fix on his Ver 4 rig …
