The T03DSP High Performance Transceiver with DSP IF processing

Designed by Oleg Skydan UR3IQO

The Noise Blanker

I had no plans of including the noise blanker in T03DSP since I did not know any hardware design that will not degrade receiver IP3 performance.

The situation changed when a very annoying pulse noise appeared on the 160/80m bands. It was so strong that only local stations could be heard. So, I realized that I needed a noise blanker.

The other problem was the state of the transceiver's hardware - it was finished in the mid of September 2003 and all that I changed after that was the software. I was very satisfied with the other parameters of my transceiver and did not want to change anything in the hardware, so I decided to try to implement noise blanker in software.

I did not try to realize any sophisticated algorithm (like one in the Linrad by SM5BSZ). Just tryed to keep things as simple as possible. So, the blanker operates in a very dumb fashion - it measures the power of the received signal before the DSP filtering and if it exceeds threshold (which changes according to the average signal power) it produces a blanking pulse (with the length adjustable by user).

Here is the oscillogram of the real life SSB signal corrupted by impulse noise. You can see the noise blanker doing its job.

You can also listen to the above sample by downloading .WAV file from here.

All materials provided here are copyright by Oleg Skydan. In all cases, materials are provided for the purpose of self education and training in Amateur Radio. No use may be make for commercial purposes without permission of the author. Please send any comments and questions to Oleg Skydan UR3IQO.
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