Tuesday, May 2, 2017

BITX40v3 Mod - C91 & C92

When the BITX40v3 is using the Raduino, the two capacitors C91 and C92 should be removed from the circuit board. These capacitors attenuate the signal coming from the Raduino which is not as big a problem on LSB (injected RF around 5 MHz or less), but is more of a problem on USB (injected RF around 19 MHz). In the newest Raduino sketches (such as v1.0.9) the drive level for LSB and USB can be set in the software.

The above picture shows an older BITX40v3 board where L4 had to be removed; on the newer boards, both L4 and the variable cap above it are not installed.
The wires from the Raduino to the connector shown above, should be kept as short as possible and routed in an arc up away from the circuit board. Even better is to replace the two wires with mini coax such as RG174. This will minimize the Raduino signal that could enter the circuit and cause other problems such as the harmonic mixing that causes a "birdie" on 7199 KHz.
I can still hear the birdie on 7199 on my BITX40, but it is quite low and doesn't interfere with signals on or near that frequency.  73,  AL - VE3RRD

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