That is very useful information Stuart. As a VHF operator I do not care about the LSB response, but I do care very much about USB.
I think for most SSB use the 5 pole filter will be fine. SSB operating is not like CW, filter shape factor is less important as you can't operate within a filter bandwidth of a strong signal because of the inevitable transmitted IMDs. The DSP will clean up the close in response and what really matters is the absolute rejection from several kHz away and beyond. I think I would stick with the 5-pole until something better comes along, like a variable bandwidth filter perhaps. While the 8 pole may be better, it is quite a lot more expensive and if you do want to spend that money ir might be better if it was spent on a CW filter. Mike Stewart G3RXQ wrote: > > Having run a quick test switching between USB and LSB on a quiet > band 10m, I noticed an appreciable difference in the tone of the > noise spectrum. > > I dug out my noise generator and examined the audio response using > Spectrum Lab. I set the DSP B/W to the maximum as what I wanted to > see was the 2.7KHz SSB roofing filter response. > > On USB the trace was substantially flat with the -3dB points at > 430Hz and 2.77KHz. Not too bad and could probably be improved by > moving the carrier offset frequency. > > On LSB, however the trace was far from flat having a slope from > audio LF to HF of about 6dB. Not very good at all... > > I tried adjusting the FL FRQ, but all this did was shift the > overall position of the sloping trace. > > Although the crystal filters are spoken about as being roofing > filters designed to keep strong signals away from the DSP > filtering they do affect the wanted passband. > > On the K2 there used to be a big difference between the USB and > LSB response until a modification to the output of the filter was > added. The KSB2 uses a 7 pole filter, giving a more or less > symmetrical response. I wonder if 5 poles is just too few ? > > Or maybe I have a duff (defective) 2.7KHz filter ? > > I wonder if others have plotted their 5 pole filters. > > 73 > Stewart G3RXQ > > > > > _______________________________________________ > 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 > > -- View this message in context: http://www.nabble.com/K3-SSB----Is-the-5-pole-filter-good-enough-tp15664900p15667715.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
