Bruce this is from a similar question on the Yahoo Groups K3 list: -- In [email protected], Hector Padron <ad4c2006@...> wrote: > > The 1.8 roofer today with so much band noise and fool ops close to your > freq disrespecting the spectrum, its a must.This 8 poles filter together > with the DSP makes brick rx easy to work dx or contesting.The trick to > recover the lost audio quality when using it is to move counterclockwise > the shift control down to 1.2 and inteligibility is back.
This is very misleading and I must strongly disagree. I preface this by saying I made ~2500 QSOs on 10m single band in the CQ WW (high-claimed USA SOSB/10 score) and was never able to effectively use the 1.8k filter even though I tried in vain several times. Here's what a 1.8k will and will not do: 1. It *WILL* keep your AGC from pumping if there's another strong station within the 1.8 kHz passband. However, do you really think you could copy a weak signal while a S9+30 interfering signal is inside your 1.8k bandwidth? I don't think so. With any typical SSB filter bandwidth, AGC pumping is not a practical issue (it IS a big deal for CW however). 2. It *WILL *NOT* keep splatter from adjacent signals out of your passband. If an interfering signal is 5 kHz wide and partially falls within your passband, NO filter can remove it. Splatter is a real signal which NO filter (XTAL or DSP) can remove. 3. It *WILL* require very careful tuning for intelligibility. With callers that are off frequency by only 100 Hz, you'll miss off-frequency callers the first time which will slow your run rate. I had one caller even 500 Hz below my run frequency and I'm certain I would never have heard him if I was using the 1.8k. The most effective use of a 1.8k is probably for copying an extremely weak DX signal in white noise (not strong splatter or QRM). By tuning VERY carefully, you may slightly reduce the noise floor by reducing the noise bandwidth (potential reduction of 1.8k BW versus 2.1k BW is 10*[log (1.8/2.1)] = -0.67 dB). I really doubt many of us can detect a 0.67 dB improvement in signal/noise. The 1.8k is mainly a DXing tool...not a contesting tool. It cannot magically overcome the basic laws of physics. 73, Bill W4ZV -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Filter-question-SSB-tp6981339p6981505.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ 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
