Found couple FT240-31 chokes and measured their attenuation. Here are results in dB for attenuation for 20 turns, 26 turns and both of those chokes connected in series. Right table side shows difference between two chokes in positive attenuation dB. For example at 28.3MHz going from 20 to 26 turns produced 3.2 dB less attenuation. At 7.1MHz 26 turn choke had 1.5 dB extra attenuation over 20 turn while both of them connected in series produced 9.3 dB extra attenuation compared to 26 turn alone and 10.8 dB extra attenuation compared to 20 turn choke alone.
| MHz | 20 turns | 26 turns | 20 + 26 | 20 to 26 | 26 to S | 20 to S | |
0.6 | 19.6 | 25.2 | 29.8 | 5.6 | 4.6 | 10.2 | |
1.8 | 29.9 | 36.1 | 39.6 | 6.2 | 3.5 | 9.7 | |
3.7 | 34.8 | 39.8 | 43.7 | 5.0 | 3.9 | 8.9 | |
7.1 | 37.1 | 38.6 | 47.9 | 1.5 | 9.3 | 10.8 | |
14.2 | 39.7 | 36.4 | 47.1 | -3.3 | 10.7 | 7.4 | |
21.1 | 35.0 | 31.7 | 41.7 | -3.3 | 10.0 | 6.7 | |
28.3 | 33.1 | 29.9 | 39.3 | -3.2 | 9.4 | 6.2 |
Last edited:
