rats@cbnewsc.att.com (PRO-2004) (05/23/91)
I need a 50 Mhz low-pass filter for a portable scanner. Is there anyone out there that could modify the following filter to use normal spec components such that it would function as such? ========================================================================== Elliptic Filter for FM Radio Electronics World + Wireless World June 1990 Proliferating Band II local radio stations may cause reception problems for existing stations if the receiver is close to a new transmitters. Modern receivers should be immune but, if not, this low pass filter may help. The filter is a 6th order elliptic with two finite frequency zeros, passing frequencies up to 98Mhz (-3dB). A modest 15-20 dB rejection in the upper part of Band II attenuates new local radio frequencies without preventing reception. Group delay variation in any radio channel is negligible (<5nS). Inductors L2 and L4 are 2 and 3/4 and 2 turns of 26swg on a 5.33mm former (Cambion). L6 is a fixed choke. Construction without test gear is practical, but if availible L4 can be trimmed to precisely place a rejection notch at an interfering frequency. K. Williams Wells Somerset 18pf 47pf L6 --o o--o--o--||--o--o--o--||--o--o--CCCCC--o o-- | | | | | | | | 120nhy | \ === |-CCCC-| | |-CCCC-| | \ 75 Ohms / 10pf| 92nhy ===18pf 49nhy=== 18pf / 75 Ohms \ | L2 | L4 | \ | | | | | --o o--o------------o------------o---------o o-- NOTE: L2, L4 are varible. 0dB ---_________ 0.5dB loss \ 10 --- \ __ \ / 20 --- \ \/ 30 --- 40 --- 50 --|--|--|--|--|--|--|--|--|--| 80Mhz 90 100 110 120