Showing posts from March, 2021

FM band undersampling

Why Use Oversampling when Undersampling Can do the Job? - Texas Instruments  :    “..If we use the sampling frequency less than twice the maximum frequency component in the signal, then it is called undersampling. Undersampling is also known as band pass sampling, harmonic sampling or super-Nyquist sampling. Nyquist-Shannon Sampling theorem, which is the modified version of the Nyquist sampling theorem, says that the sampling frequency needs to be twice the signal bandwidth and not twice the maximum frequency component, in order to be able to reconstruct the original signal perfectly from the sampled version.“ Justin Peng tweeted the result of his RX888 undersampling the FM band on At my location the FM band stations are very strong and internal HF LPF of RX888 is not enough to cancel the FM band alias. I need to add an external HF Low Pass Filter with higher attenuation of FM band. So I decided to bypass the internal filter alw

Filter in a box

 In 2018 I read this paper  Band Pass Filter with Low Insertion Loss for 2m   by Dipl ing Tasić Siniša –Tasa YU1LM/QRP, I made my  PCB version for SMD components with a ground plane dimension of 50 x 20 mm so that  a  PCB of 10 x 10 cm  houses 10 filter boards . I mounted my first prototype with tin shield box and verified that the filter was fine in 2018. The point was that the  spacing of the inductors' turns requires some instrumentation to do easily the tuning. The tin shielding soldered box I made was quite laborious for me.  So the pcbs has been unused for two years. I placed the PCB gerber files and scheme in  repository Now with the very nice  SATSAGEN  by  Alberto IU1KVL the tuning of filter is fast and easy,  see .  SATSAGEN  requires  a   ADALM-Pluto    or   Pluto+    device. I used the 3D printer to make a PLA box to shield the filter

Another kind of bug. The thermal bug

During the evolution of ExtIO_sddc code the Co-Authors and I made many  tests on different computers to verify operation.  One of the PC candidate was the laptop (Asus UX330U | 2017 | i7-7500U cpu) that I used  during early development of BBRF013 / ExtIO_sddc.dll. Starting January 2021 I noticed something very strange. The application HDSDR was on but the  audio stream was discontinuous and sometimes crashed.  I thought about some software bugs.  After some testing with different code versions and on other PCs I installed Open Hardware Monitor on this PC and I noticed that the problem was related to CPU temperature. I thought that the CPU cooling was not efficient even though the internal fan was spinning. When the CPU temperature reaches high value the CPU clock is decreased to dissipate less heat. The behavior modulates speed performance of the CPU. The PC is 4 years old so I fear dust inside, not good thermal conductivity of the heat pipe and many other nightmares. I opened the lapt