My friend have found the cause of spurious of 75 KHz. He said the cause of spurious was the noise of VCC around 19 MHz of 0.15V. As the result of the modifications of Bitx40 to reduce the noise, such as adding the big condenser and choke coil etc , the spurious level went down below of the criteria.
By this modification, my Bitx40 meets the criteria of the spurious of Japanese regulation. So I am going to submit the application for obtaining the certification of Bitx40 from the relevant authority.
There are two criteria for the spurious. 1) Baseband area : under -40db of power of fundamental frequency This frequency range is the 2.5 x occupied band of frequency of TX mode. 2) Spurious area : under -50db of power of fundamental frequency. This frequency range is the out of Baseband area for super harmonic spurious.
The attached files are 1) The picture of noise of VCC 2) The picture of Spurious of 50KHz/div after the modification. 3) The picture how the modification were added.
