Brett Howard wrote: > > So am I to assume that the 8-pole filters are not going to need to worry > about this as they are all at 0 anyway? What is the advantage of > getting two matched pairs of 5-pole filters when you can get two 8-poles > for only 10 bucks a filter more? > > I'm assuming that its 100 + 100 + 30 for matched 5-pole filters or 125 + > 125 for the 8-pole filters. I can see there being a great advantage if > you already have a 5-pole and want to match it in your sub RX. But if > you're just getting 2 at the same time it seems like the 8-pole makes > for a good option too.. At least I hope so cause diversity receive was > the main reason I figured I'd go for the 8-poles... :) >
You're correct that 8-poles have no offsets and avoid this problem. When I ordered my 5-poles there was a $40 per filter discount to 8-poles and nobody (including Elecraft) understood that the Sub RX filters needed to matched if using 5-poles. EI6IZ on the Field Test team discovered this in December when he saw slight frequency offsets as the WIDTH control toggled different filters. But the real reason I ordered my 500 and 200 combination is purely bandwidth. Here are Elecraft's measurements: Filter BW(-6dB) Shape Factor 200 224 4.0 250 370 2.1 400 435 2.1 500 565 3.1 For weak CW signals or in contests I prefer a wider bandwidth. For weak signals the additional bandwidth gives my ears a better context in which to apply my ear/brain's internal 50 Hz filter. In contests, I also want to be able to hear stations calling me off-frequency as well as hear what's going on around my run frequency (so I can chase off those folks who send "?" once and then start CQ-ing 250 Hz above me). I would actually prefer 8-pole filters for rejection reasons, but the bandwidth choices above are simply wrong for my use. The 400 is too narrow and the 250 is too wide (and only 65 Hz between the two!). When I need a narrow filter, I want a *truly* narrow filter. The main use I have for the 200 is in nearly simplex pileups with lots of S9+++ signals (think 160m DX pileups). Another reason one might want 8-poles is when using N8LP's LP-PAN and SDR software for a panadaptor/waterfall display. The 5-pole offsets can cause a similar problem here as you rotate WIDTH through different filters. However, with the recent addition of Elecraft's programming commands to read the internal filter offsets, N8LP says WU2X can correct for the offsets in his PowerSDR-IF software. The bottom line to me is that I choose filters primarily for their bandwidth and I prefer the 500/200 combination even with their offset warts. If Elecraft offered different BW choices in the 8-poles, I might prefer them. Quite frankly, given the current $25 price differential, I don't see why Elecraft doesn't go to all 8-pole filters and make some better bandwidth choices (e.g. at least octave differences at the low end...say 600 and a *true* 250...not the one above which is actually 370). I wouldn't be surprised to see Inrad eventually do this even if Elecraft doesn't. 73, Bill -- View this message in context: http://www.nabble.com/K3%3A-KRX3-question-tp18280281p18301358.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
