On Tue,1/13/2015 7:52 PM, Mike Zbrozek wrote:
And how many cw ops use a sharper 200 or 250 Hz filter?
I'm primarily a contester, but also a DXer. My K3s have all 8-pole filters. 250 Hz and 400 Hz for CW, 1.8, 2.1, and 2.8 kHz for SSB. I bought the 1.8 kHz before the 2.1, and I like the 2.1 better.
Remember that these are ROOFING filters -- IF selectivity is set by turning a knob to control the DSP IF. The roofing filters do two things. Most important, they protect the DSP IF from overload by very strong signals very close to you frequency. Second, and also quite useful, their selectivity CASCADES with selectivity of the DSP IF. That means that when, for example, the IF is set to 250 Hz and the 250 Hz filter is switched in (it happens automatically) the skirts get nearly twice as steep. We have the rejection of the IF plus the rejection of the filter.
We can set the filter to switch in wherever we want, simply by defining it's bandwidth in the setup menu. I have my 250 Hz filter set to switch in at 350 Hz, and I do most CW operation with a 250 Hz IF setting. These are settings you can play with.
I use a 400 Hz IF for RTTY, except under conditions of extreme QRM, when I might narrow it down to 200 or 250 Hz.
Another important point. If you're not a contester, you may not need any roofing filters other than the 2.7 or 2.8 kHz TX filter. If that's the case, I'd hold off buying additional filters until you've decided that you need them.
Note that I didn't answer the question about 5-pole or 8-pole. I buy 8-pole filters because it is my understanding that filters with more poles can be made to have flatter response in the passband. I started with 2.7 kHz 5-pole, and later bought a used K3 with an 8-pole 2.8 kHz filter in it. It is noticeably flatter when transmitting RTTY, and i've since replaced by 5-pole 2.7 kHz filter with the 2.8 kHz 8-pole filter.
73, Jim K9YC ______________________________________________________________ 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
