Bob, Thanks for the confirmation. I have spectrum lab - will take a look after FD. I also think the level drops several db (to the ear) as the filter switches from 150hz to 100hz, most noticable on weaker sigs.
73's Gill You may be on to something. Using the 100 Hz FIR filter and injecting a steady carrier, I looked at the receiver output using Spectrum Lab. I observed multiple spurious tones, 2 of which are only 15 dB down from the desired signal. The freq spread between the desired signal and the 1st spur is 2x the difference between the signal and filter center, so you have zero beat at filter center. And so on. Take a look at it with an audio spectrum analyzer, it's interesting. Zero beat with the other -15 dB spur is at the upper filter skirt. Aliasing? The result is the same for the 50 Hz filter, but the 50 and 100 Hz IIR filters are squeaky clean under the same conditions. Subjectively speaking, when listening to on air signals, the signal starts to sound bad to my ears as you tune it close to the upper filter edge zero beat point, but within 20 Hz of filter center the effect seems subtle, and easily overlooked. However, viewed on the spec an, it's clear that something isn't quite right. I observe no such problem with ver 1.78 FIR filters under the same conditions. Maybe someone else can take a look at this. Bob NW8L -- View this message in context: http://www.nabble.com/2.10B-narrow-filter-anomaly-tp18171265p18176510.html Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
