Faulty TX/RX relay

Glenn  VK3PE suggests, “For anybody trying to get their uBITX to work in Tx mode.  Mine was working then started to become intermittent. I would key the Mic PTT switch and the display shows it’s in Tx mode, but with no power out.

“Tracing signals etc, I found that the K1 changeover relay was not switching 12V to the Tx section. I could hear the relay ‘operate’ but it didn’t actually switch.    I replaced the relay and all is fine.”



Relay K1 mod

Fred PE0FKO asks a question about relay K1 after looking at the very nice schematic of the uBITX.

“The K1 relay is used for the RX and TX power switching and also for connecting the antenna in RX to the LP filter.   On RX (and TX) the LP filter is also a connection to the TX power amp by C80, that will give a (very) small load on the antenna signal at RX and a mixer (Q90 diode BE) for strong received signals?  Could it be improved by switching pins 12 and 14 of K1 and connecting pin 16 of K1 to C80 (removing the connection to the Low Pass filter)?”

Jerry, KE7ER responded:

“It’s a good idea to make use of K1-16 to disconnect Q90 during receive.  This would also protect Q90 from local QRO transmissions into a local antenna,   The similar Q13 on the Bitx40v3 is often blown in such situations, even when the rig is powered down.”

Alf Baranda asks:

“Can it be the Mod that I have highlighted?”

Of course it is the same mod!   Alf goes on to  attach images with the signal paths in the RX and TX modes.