26-04-2012, 08:54 PM
Lawrence: the 32 MHz H.G. filter. (Ref. your post #27)
To my understanding, in essence it's just like any other LPF: ideally, flat response to 32 MHz then a roll off to full attenuation. The highest freq. required from the filter is 32 MHz. The next 'available' freq. is 33 MHz, which isn't 'far away', and that must be suppressed: I would expect something like -20 dB at 33 MHz. I doubt if insertion loss is critical - which gives some latitude to the coil design - provided that the flatness of the pass-band (for the freqs. 1 MHz to 32 MHz) is fairly even (say +/- 2 dB), so that the output harmonics of the 1 MHz input are at all about the same level.
So overall, a LPF with quite a demanding performance: stop band -20 dB within 1 MHz (32 - 33 MHz) and a 'flat-ish' pass-band. Hence several L/C sections required; R/C sections won't do.
Al.
To my understanding, in essence it's just like any other LPF: ideally, flat response to 32 MHz then a roll off to full attenuation. The highest freq. required from the filter is 32 MHz. The next 'available' freq. is 33 MHz, which isn't 'far away', and that must be suppressed: I would expect something like -20 dB at 33 MHz. I doubt if insertion loss is critical - which gives some latitude to the coil design - provided that the flatness of the pass-band (for the freqs. 1 MHz to 32 MHz) is fairly even (say +/- 2 dB), so that the output harmonics of the 1 MHz input are at all about the same level.
So overall, a LPF with quite a demanding performance: stop band -20 dB within 1 MHz (32 - 33 MHz) and a 'flat-ish' pass-band. Hence several L/C sections required; R/C sections won't do.
Al.
