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N2ADR filter board
James Ahlstrom, N2ADR, has developed a filter board that can be easily connected to the Hermes-Lite 2.0; it provides filters for the TX output to reduce its output harmonics and spurs and a RX high-pass filter that can be used to remove strong broadcasts signals below 2 MHz.
Here below are some measurements of the filters responses on two versions of this board:
- The initial revision E1 board
- The revision E5b8 built for the Hermes-Lite v2.0 build 8
Revision E1 board
This is an initial revision of the board.
Filters response, showing the passband losses:
Wideband response, showing the stopband rejection:
Revision E5b8 board
This is the board version used in the Hermes-Lite v2 build 8. The board design files can be found on GitHub.
The filters response is very close to the original E1 board, with a slightly higher losses in the HF bands. This could be partly due to the board traces having an impedance around 60 Ω rather than 50 Ω due to a different ground clearance.
Filters response, showing the passband losses:
Wideband response, showing the stopband rejection:
