K3 250Hz Filter gain maxed yet low
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I spent a few minutes today checking the filter gain balance on K3
1210. I fed in a 1uv signal from my XG2 and qualitatively measured the audio out when switching (XFIL) between filters. I started by finding the XG2 signal and zero beating it using the CWT/SPOT features and then switched between filters. I have an 8 pole set as follows: FL2-2.8, FL3-1K, FL4-400, FL5-250. I have gains as follows: FL2-0db, FL3-0db, FL4-3db, FL5-8db. The audio is good with these settings except for FL5 which even though maxed out has a very noticeably lower output. By fiddling with the FL4 setting and doing comparisons it appears that FL5 could use another 3db to bring the output up to equal that of the other filters. Just to make sure I was in the center of the 250hz filter I tuned around with the FINE setting and moving around made no improvements in the output only the expected decrease as I moved outside the filter BW. Is there any remedy for this? Should I send my 250hz/8pole back for replacement? tia jim ab3cv _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Hi Jim:
Not sure if this will help. There was a thread a few days ago where the comment was that the audio level was reduced at tighter filter widths. The factory commented on the effect of the RX EQ on filter gain. The suggestion was to make sure none of your RX EQ frequencies are set positive. Instead, set those undesired frequencies negative and leave the desired frequencies at zero. I tried this on my unit and it absolutely was the case. 73, Mike K2MK _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Mike
Thanks for the tip but after going to the RX EQ menu and using the CLR function as described in the manual I'm left with the same low output from the 250hz/8pole filter even when maxed at +8dB. Any other ideas welcomed. tia jim ab3cv _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
Re: K3 250Hz Filter gain maxed yet low
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In reply to this post by Jim AB3CV
Jim,
Your problem may be that you are centering the filters. There was a post by Lyle Johnson a while back which explained that the filters are not operated at their center, but are used closer to the slope than center to take advantage of the better rejection provided. I don't recall the exact circumstances, so you might want to look for that post in the archives. 73, Don W3FPR Jim Miller wrote: > I spent a few minutes today checking the filter gain balance on K3 > 1210. I fed in a 1uv signal from my XG2 and qualitatively measured the > audio out when switching (XFIL) between filters. I started by finding > the XG2 signal and zero beating it using the CWT/SPOT features and > then switched between filters. > > I have an 8 pole set as follows: FL2-2.8, FL3-1K, FL4-400, FL5-250. > > I have gains as follows: FL2-0db, FL3-0db, FL4-3db, FL5-8db. > > The audio is good with these settings except for FL5 which even though > maxed out has a very noticeably lower output. By fiddling with the FL4 > setting and doing comparisons it appears that FL5 could use another > 3db to bring the output up to equal that of the other filters. > > Just to make sure I was in the center of the 250hz filter I tuned > around with the FINE setting and moving around made no improvements in > the output only the expected decrease as I moved outside the filter > BW. > > Is there any remedy for this? > > Should I send my 250hz/8pole back for replacement? > > tia > > jim ab3cv > > Elecraft mailing list Post to: [hidden email] 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 |
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Hi Don
How do I center the filters (or not) I've not done any special setup or played with EQ (in fact just made sure it was zeroed out) on this unit. I went to the nabble site and searched on Lyle Johnson and could not find the info you mentioned. tia jim ab3cv _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
Re: K3 250Hz Filter gain maxed yet low
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The thread was about the ARRL review and on Nov 27.
73, Gary W7TEA
73,
Gary W7TEA K3 #1001, #5763 |
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AB3CV wrote:
>How do I center the filters (or not) I've not done any special setup or played with EQ (in fact just made sure it was zeroed out) on this unit. I went to the nabble site and searched on Lyle Johnson and could not find the info you mentioned. W7TEA replied: >The thread was about the ARRL review and on Nov 27. Here's the post W7TEA was referring to: http://mailman.qth.net/pipermail/elecraft/2008-November/100401.html Relevant excerpt from above post by KK7P: >The second question has to do with the difference between the above and below values for a given filter when the signal spacing is less than the nominal width of the filter. >This asymmetry is due to the way in which the K3 aligns the roofing and DSP filter passbands. The signal is not necessarily centered in the roofing filter passband; rather, the signal is shifted towards an edge to maximize the use of the roofing filter's skirt selectivity. >Why is this important? >Consider the case in which you are using a wider filter in a crowded band while operating CW. A huge signal appears very close by, perhaps 1 or 2 kHz away. The use of CW REV or CW may make a considerable difference on the impact of that signal on the receiver. If the passbands were centered, this tool would be less effective. >And if huge signal are on both sides? Time to get a narrower roofing filter! To explain this another way, the K3 normally has the roofing filter centered about the chosen PITCH in the CW passband. For example, if you use a 600 Hz pitch, the "250 Hz" filter (actually 370 Hz) would have 6 dB points at 600 +/- 185 Hz or a passband of 415 to 785 Hz. *HOWEVER* when using low PITCH (as I prefer), the K3 may shift the filter passband so that its lower end is no lower than 200 Hz. For example, if using a 300 Hz pitch, the above filter's passband would cover 200-570 Hz and therefore the chosen 300 Hz pitch is not centered in the passband. The reason for doing this is to reject the negative IF response which might allow signals from the negative side of 0 Hz (if you've used older analog radios, you probably remember this problem). There's another possibility that could be causing some apparent loss. Even though the 8-pole filters are advertised to have zero offsets, in fact I believe some have discovered they may have up to 80 Hz offsets. This has negligible effect at the wide filter bandwidths but could cause some problems with the 250 Hz filter. I would try the following test to troubleshoot the above problems. Se PITCH = 600 and apply a steady signal (e.g. XG1 or XG2). Now tune slowly and note the frequencies at which the signal drops by 6 dB. You've eliminated the passband shift issue by setting 600 Hz pitch and you should be able to determine if the filter's actual offset is something other than zero. You can use the internal AFV/dBV meter to do this without any test equipment other than a source (in fact you can even do this with the K3's internal 49380 image as the source). Turn AGC OFF, apply your test signal at what you believe is the center frequency (i.e. 7040 the XG1). Hold METER and tune VFO B until you see AFV...you should see AFV #### in the display. Allow the #### numbers to settle, then rotate VFO B slightly clockwise and you should see 0.0 dBV. Now slowly tune above and below 7040 and note the two frequencies at which you get -6.0 dBV readings. This should tell you whether the filter is correctly centered. Of course you could simply have a defective filter with high insertion loss, but doing the above will help both you and K3support@elecraft.com determine what your actual problem is. 73, Bill W4ZV |
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Followup:
I followed the directions given by Bill, W4ZV, and noticed my 250hz filter wasn't centered well. In fact the response increased by 1.4dB as I moved up frequency 30hz or so. I then recalled that I didn't really get comfortable with the REF CAL results when I first (impatiently) turned on my rig. I redid the REF CAL using WWV @ 10Mhz and moved it quite a bit and now get a very nice zero beat per the instructions. Now the 250hz filter centers perfectly and @8db of GN matches the 400hz filter "goodnuff". Thanks to all! jim ab3cv _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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