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ICOM IC-746/756/761/765/775/781 Inrad #116 455 KHz 400Hz CW Filter. 1. Ultimate rejection: > 90 dB 3. Typical Insertion Loss: < 6 dB What's the difference between IF filters from Inrad vs. Icom? Inrad filters tend to have a superior shape factor to Icom's (smaller numbers are better) as well as deeper stopbands. They also tend to be cheaper. When dealing with adjacent channel interference, the filter shape (depth and slope of the attenuation curve) is generally the prime factor. Inrad filters tend to outperform the Icom filters for this application. For example. The stock Icom filter in the 455Khz IF has a -6db bandwidth of 2.4Khz and a -60db bandwidth of about 5Khz. That gives it a shape factor of about 2.1 The comparable filter from Inrad has a shape factor of 1.6, a -6db bandwidth of 2.4Khz and a -60db bandwidth of 3.8Khz. This all means that the Inrad filter has a steeper attenuation curve, resulting in better extraneous signal rejection and improved selectivity. The Inrad filters tend to have greater ultimate attenuation than the Icom counterparts. Thus, Inrad filters tend to do a better job of adjacent signal rejection than Icom's filters. However, while the 455Khz Inrad filters are drop-in replacements for the Icom counterparts, the 9Mhz filters are not. They need a short piece of coax and a connector to wired up to the filter first. The adapting connector plugs into the filter slot, thus alleviating any mods to the radio itself. Reported assembly times range from 1-4 hours per filter, depending upon the skill and care of the installer. Finally, some claim that there is an insertion loss to the Inrad filters vs. the Icom filters. However, it's been demonstrated that dropping the noise level also drops the S-meter reading, possibly accounting for the reports. Bench tests do not show any insertion loss. Your ears may vary. (please look at our rules and privacy policy) |
heaton@machine--tools.com (Harriet Eaton) for additional information. This email is used for forwarding to newsgroup user.
