Roofing filters are selected by either of two ways. One is by directly selecting FLx on the K3 front panel. The other is by changing the DSP bandwidth via WIDTH, LO CUT or HIGH CUT. When the DSP bandwidth is decreased to the crystal filter bandwidth, then that roofer is selected. (Or, when the DSP increases beyond the current roofer's bandwidth, then the next wider roofer is selected.)
It is important to note that the "roofer bandwidth" is specified by the user in the K3 CONFIG menu, and you are not constrained to use either the "marketing" bandwidth or the actual bandwidth of the filter. You can put in any bandwidth you want because all you are doing is telling the K3 what DSP bandwidth to engage that particular crystal filter. Most users specify the marketing bandwidth of the filter, e.g., 250 Hz for the 250 Hz 8-pole filter. So, as you decrease the DSP bandwidth and reach 250 Hz, that crystal filter will engage. (Or, if you select FLx, then crystal filter 'x' is selected and the DSP bandwidth is set to 250 Hz.) But you can specify 350 Hz, which is actually rational since the real bandwidth of this filter is 370 Hz. Some people even specify a wider DSP bandwidth engagement point such as 400 or 450 Hz, because they want their crystal filter bandwidth INSIDE the DSP bandwidth. So, think about the relationship of the two filters (crystal and DSP), the resultant cascade bandwidth of the two, the shape factor of the two filters, and the passband shape. Decide the DSP bandwidth at which you want your particular crystal filters to engage. There are arguments for keeping the roofer wider than the DSP at all times and vice versa. Remember that when the DSP bandwidth is near the roofer's actual bandwidth, the cascade bandwidth will be significantly less. When one is much narrower than the other then the narrow bandwidth dominates the IF bandwidth, but other RX characteristics like IMD performance will be determined by the roofer bandwidth. Setting the DSP engagement bandwidths for your crystal filters affects both the resultant IF passband width, shape and "sound" of the audio, as well as the RX performance characteristics such as IMD. If your head hurts thinking about all this, just specify the bandwidth number in the part number of the filter! That is a good default and the radio will work great. Ed - W0YK ----------------------------------------------- Ed Muns Muns Vineyard - www.munsvineyard.com FaceBook - www.facebook.com/munsvineyard W7QQ wrote: > Im trying to configure the K3 receiver for diversity > receive. Im populating the roofing filter slots in both > receivers with matched filters, and the question came up: > When the K3 automatically selects the correct roofing filter > to match DSP filter bandwidth, does the K3 do this by filter > bandwidth, or by FLx number? > > In other words; when I use the width control, and > decrease DSP bandwidth from 3.0 Khz to 2.0 Khz on the front > panel, the K3 switches from the 2.8 Khz roofing filter > located in FL3 to the 2.1 Khz roofing filter located in FL4. > With the sub-receiver on, and in diversity receive, does the > K3 switch the sub-receiver roofing filter from FL3 to FL4, > like the main, or is it smart enough to know that my > sub-receiver has its 2.8, and 2.1 Khz roofing filters in FL1 > and FL2 respectively? Does the K3 select the correct > roofing filter by bandwidth, or by FLx number? Is the > selection logic the same for main and sub-receiver? > > > > > > The KRX3 manual is a little foggy on this. It says you have > to have at least one roofing filter, and if that happens to > be the KFL3B FM filter, it MUST be in the FL1 location. It > also says that you must have the widest bandwidth nearest > FL1, but does not say it must be located at FL1. ______________________________________________________________ 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
