Bill and all, I must disagree - when the SSB filter widths and corresponding BFOs are correctly set, the variable XTAL filters can be quite usable for SSB reception.
First of all, the lower -3dB frequency corner of the passband must be near 300 Hz to maintain intelligibility. The high frequencies may be cut without sacrificing a lot of intelligibility. The filter width must be determined by using Spectrogram or a similar means - the numbers given by the K2 display for the wide filter settings may be grossly in error (the actual filter width is usually quite a bit wider than the numbers indicate at the wider filter settings - it is close to actual at 400 to 500 Hz widths, which is the design center for the filter). If the SSB filters are set for FL1 = OP1, and FL2 thru FL3 are set for progressively more narrow filters, then a properly tuned SSB signal will remain intelligible as the filters are narrowed, and high frequency QRM will be reduced. Assuming the 2.4 kHz width is used for OP1, centering the filter passband between the following Spectrogram markers will result in quite usable filters: FL1 width = OP1 -- 300 and 2600 Hz FL2 measured width = 2200 Hz -- 300 and 2400 Hz FL3 measured width - 2000 Hz -- 300 and 2200 Hz FL4 measured width = 1800 Hz -- 300 and 2000 Hz The DSP can be used as a supplement to these filters, but I find that the IF filters are adequate in most cases, freeing the DSP to be used for noise reduction and notch filtering purposes in SSB mode. Again, I find the most prevalent 'error' in setting the variable filters for SSB use is in assuming that the filter width is what is indicated on the K2 display - and that actual width may be quite a bit wider than indicated - measure the width with the Spectrogram display and ignore the width numbers shown in the display. 73, Don W3FPR > -----Original Message----- > > > On SSB, there's basically one XTAL filter - OP1. The variable > bandwidth filter is pretty asymmetric for use on SSB. OP1 also has a > very modest shape factor. > > I use the DSP filter to clean up the shape of the OP1 filter. I have > a couple of variants programmed that cut the high and low end of the > filter. These are useful during contests or any time there's lots of > QRM. Narrowing the filter may slightly reduce intelligibility, but it > also cuts adjacent signals. > > _______________________________________________ Elecraft mailing list Post to: [email protected] 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
