There can be reasons to configure a roofing filter differently from its nominal bandwidth.
For example, I have a "250 Hz" filter. According to the filter plots on the Elecraft web site, the 6 dB bandwidth of this filter is actually closer to 375 Hz. I configured my filter to switch in at 350 Hz, which makes it much more useful to me than it would be if I had configured it to switch in at 250 Hz. If this filter is configured to switch in at 250 Hz in agreement with the label, then when you set your DSP bandwidth to 300 Hz or 350 Hz, you will be using the next wider filter in your receiver. Strong signals outside the DSP bandwidth but inside the wider roofing filter's bandwidth can still have bad effects, whereas if the filter is configured to switch in at 350 Hz, you can take advantage of its ability to reduce those unwanted signals with relatively minor impact on signals within the DSP bandwidth. Of course, if the bandwidth of the 250 Hz filter really was 250 Hz, configuring it to switch in at 350 Hz would render the 300 Hz and 350 Hz settings of the DSP filter somewhat less useful, since the actual bandwidth of the filter combination would now be close to 250 Hz regardless of what the DSP control said. There might be reasons to go in the other direction as well, i.e. to configure a filter to switch in only at a narrower bandwidth than the bandwidth marked on the filter. For example, if you had 500 Hz and 1000 Hz filters and often used a digital mode whose bandwidth was, say, 750 Hz, you could configure the 1000 Hz roofing filter to switch in only at 700 Hz and below. This would give you better filtering between 500 Hz and 700 Hz than without the 1000 Hz filter, while still permitting the 750 Hz mode signals to pass through at DSP settings of 750 Hz and above without being restricted by the roofing filter. 73, Rich VE3KI KA1J wrote: Is there any advantage to setting the 1.8 above, say as 2. in the utility. Or to have the 200Hz filter engaged at say 250? ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
