Larry Lopez wrote > So you need a linear phase filter. > Is the DSP filter linear phase ?
I teach DSP and filters at the University of Oslo. Of the two DSP filter types, FIR (Finite Impulse Response) and IIR (Infinite Impulse Response), only an FIR filter can be designed to have exact linear phase and constant group delay. But an FIR filter can also have a non-linear phase, but that is the exception. Therefore I assume that the K3's FIR filter is linear phase (I couldn't find this mentioned in the manual). If you really need the presumably linear phase response of the FIR filter, then that requires that the DSP filter is much narrower than the roofing filter (crystal filter) so that the DSP filter is the main contributor to the passband and transition band responses. This is however not the usual way to run JT9 and JT65, but rather that the filters in the decoder software running in the PC provide the narrow bandwidth. I believe they are FFT-based filter banks which is also a kind of FIR filter with linear phase. The K3 manual has this to say on the DSP filters and how to select: "Narrow DSP Filter Types For bandwidth settings of 100 Hz or lower, the K3’s DSP normally uses a type of filter that minimizes ringing: the Finite Impulse Response or FIR filter. If you’d like steeper filter skirts, and don’t mind a small amount of ringing, you can select Infinite Impulse Response” or IIR filters for these bandwidths. Locate CONFIG:FLx BW menu entry, then tap 7 until you see IIR ON. Both main and sub receivers will use the same setting. IIR filters take longer to change from one bandwidth to another, so you may hear audio artifacts when adjusting the DSP controls. If this is objectionable, use the default FIR filters." 73 Sverre ----- Sverre, LA3ZA K2 #2198, K3 #3391, LA3ZA Blog: http://la3za.blogspot.com, LA3ZA Unofficial Guide to K2 modifications: http://la3za.blogspot.com/p/la3za-unofficial-guide-to-elecraft-k2.html -- View this message in context: http://elecraft.365791.n2.nabble.com/How-to-outfit-a-K3-for-JT65HF-or-JT9-tp7587584p7587641.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
