K2 Filter attenuation?
Locked
 
|
I have spent hours tweaking the CW filters on my K2 and am not sure that they are all that good yet. (I am in no hurry to complete this radio, my actual goal is to build a K2 that is comparable to the best). I built a K2 five years ago and do not recall filter attenuation like what I am experiencing on this new one.. To give you an idea what I am seeing I have posted a spectrogram screen shot with all three filters superimposed on each other. Does it look typical to you? CHART setup ============= Center freq is 570 hz (My favorite spot for CW) AGC is OFF. Noise source is a Palomar R-X Noise bridge. Audio is measured from the headphone jack. L34 is peaked Chart can be viewed at http://www.vtc.net/~ken/filters.jpg Here is what I have done so far. 1: I have CAREFULLY inspected T7 ensuring that: a: It has 20 turns red and 5 turns green b: Pin 3 is sourced from inner red wire Pin 1 is sourced from inner green wire (exactly as per diagram 6-18 in manual) c: Each of its solder joints are shiny and good. I reheated them (twice). There is no apparent PTTL 2: Inspected X7 - X11 = a: Each are labeled 4.9136 - S (verified) b: Each have good shiny solder joints c: Each have two excellent ground connections (on each side). 3: Carefully peaked L34 with AGC off (it peaked exactly one turn down from the top) Ken Lotts aa7jc _______________________________________________ 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 |
|
|
Ken Lotts wrote:
> To give you an idea what I am seeing I have posted a spectrogram screen shot > with all three filters superimposed on each other. Does it look typical to > you? It looks fine, although I would move the two wider filters a bit to the right. There looks like about 6-8 db difference in attenuation between the widest and narrowest filters, which is probably on the high side of normal (although this tends to vary). I see about 4 db on mine, which is #709 but has had the crystals replaced and T7 rewound to current spec. I would be interested in knowing how much difference in attenuation others are seeing. I know that K1JD has an ANCIENT K2 (field test vintage) which has zero db difference! -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ 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 |
|
|
Deni F5VJC wrote:
> I have kept my K2 (1188) up to date with all the A/B mods, however at times > I see references such the one below about T7 where a toroid may have been > changed from the original windings to a revised spec. Are these documented > anywhere, which toroids are now different and why? I haven't seen anything specifically on toroids, other than what's in the A-to-B modification documents <http://www.elecraft.com/manual/k2a2binstr.pdf> and <http://www.elecraft.com/manual/k2%20rev%20B%20comp%20kit%20rev-1.pdf>, which you have probably seen. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ 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 |
|
|
Thanks for the many replies, after spending HOURS of tweaking and reading
and retweaking and listening I have a better picture of what my K2 CW filters are capable of.. There is an interesting dent in each of the curves that I can not explain.. any ideas? Worth noting, I found out by accident that I can produce a chart that shows zero attenuation between filter settings simply by turning on the AGC. So if you do this, you are not getting realistic attenuation readings. The below chart is the best I can produce with the AGC turned off. Bottom line is that I get about 6 db of attenuation when I switch to the 200 Hz filter. The manual says the filter is designed down to 250 hz so I think that I should be just a tad better than what I am. How far down in db is the filter bandwidth measured ? (I seem to recall it is 6 db?) http://www.vtc.net/~ken/filters2.jpg Ken Lotts aa7jc _______________________________________________ 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 |
|
|
Ken Lotts wrote:
> The below chart is the best I can produce with the AGC turned off. Bottom > line is that I get about 6 db of attenuation when I switch to the 200 Hz > filter. I would say this is typical. But...your widest filter shouldn't be centered on 570 Hz, since this allows significant response on the wrong side of zero beat. You should move the passband of this filter a bit higher; you would get slightly more output at 570 Hz if you did this, too. There's no rule that says the filters must be centered. It's probably not useful to have any response below about 200 Hz. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ 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 |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |