KSB2-Filter Measurements
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Having had to today off work because of the snow, I had a chance to look at my
KSB2 SSB filter characteristics. My biggest interest was whether the filter had blow-by and if so, how much. First I modeled the filter input and output switching networks using 150 ohms as the source and filter load impedance. I expected more leakage from the switching, and was pleasantly surprised when I got 110 dB of isolation. Of course the real thing will have greater leakage, but at least it is in the Ball Park. To get a rough idea of the crosstalk between the input and output connectors on the RF board and also the tracking I used the CW filter. Using a signal generator I injected a low level signal and peaked it in the filter. I then removed the CW filter and increased the signal generator level until I got the same S meter reading. Although rather crude this measurement gave me a measurement of around -95dB. Again not bad. Using Spectrum Lab set to 24bit sampling I got a K2 OFF on screen noise floor of about -115dB. Switching the K2 ON raised this to -95dB. I connected a noise generator and set my K2 to 28MHz, AGC OFF, and PreAmp ON. I made the following measurements:- 0dB 1kHz -6dB 2.7kHz -60dB 3.5kHz -90dB 3.9kHz Shape factor 1.3 The noise floor was intercepted at about 4.5kHz. Both sidebands were nearly identical. Switching off the PreAmp improved the reading slightly. This performance was very much better than I expected. The passband has, however about a 2dB ripple in it. Any suggestions on a cure for this ? I tried to improve the filter response by adding brass shim as screening on the top and bottom of the board, but it made no noticeable difference. No blow-by here... I think that the filter is working just about as well as the design permits and I am very pleased with the results. 73 Stewart G3RXQ _______________________________________________ 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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G3RXQ shared with us some measurements he made & commented:
>This performance was very much better than I expected. The passband has, >however >about a 2dB ripple in it. I think it is this ripple that makes using my K2 on SSB seem tiring to listen to as compared to other rigs. Reducing the bandwidth on the K2 makes it even more tiring as compared to other radios that derive variable bandwidth filtering with two filters & the usual IF gymnastics. G3RXQ's comment that the KSB's filter working about as well as it is probably spot on. The same could probably be said for the CW filter. The ripple - along with ultimate rejection (either due to filter or layout) - could be much better & become obvious when using the K2 in more demanding situations. After a weekend of contesting, I get a headache listening to a TS-950S - but I just can't pull some things through on the K2 that I can with the 950 fitted with decent after-market filters. Even with the nasty high-frequency crud that comes from its SCAF CW audio filter, I find I gravitate towards the 950 more than the K2 as my running rig. Whilst there are number of things about the 950 that stick out as being inferior to the K2 (like phase noise), IMHO the filters make a big difference - making me wonder what a K2 would be like if we could INRAD it like other rigs. Again, maybe not an issue for some, depending on one's operating interests. I agree with W3ICT - such "criticisms come only because the K2 is a history making radio in most other respects". 73, VR2BrettGraham _______________________________________________ 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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> -----Original Message----- ... - but I just can't pull some things > through on the K2 that I can with the 950 fitted with decent after-market > filters. .... Comparing the K2 to any other rig outfitted with after-market filters is not really a fair comparison. It does make me wonder how the K2 would do with similar after-market filters -- alas, those filters do not seem to exist. With almost 5000 K2s out there now, I wonder if InRad is having second thoughts about providing filters for the K2 - it may require a non-SSB K2 to fit them in physically, and with the small market created by that simple fact, they may still not be interested. Actually, the filters on the K2 are not shabby by any means, but like most anything else, could be improved with sufficient bucks and effort. 73, Don W3FPR _______________________________________________ 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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W3FPR - Don Wilhelm wrote:
> Comparing the K2 to any other rig outfitted with after-market filters is not > really a fair comparison. It does make me wonder how the K2 would do with > similar after-market filters -- alas, those filters do not seem to exist. > > With almost 5000 K2s out there now, I wonder if InRad is having second > thoughts about providing filters for the K2 - it may require a non-SSB K2 to > fit them in physically, and with the small market created by that simple > fact, they may still not be interested. Actually, INRAD did make a prototype K2 CW filter -- 400 Hz with great shape factor. I have one. I first used a partial SSB board so that it could be switched in and out, but I could not get an acceptably low degree of blowby. Then I removed the SSB board and just hardwired the filter to the headers where the SSB board would go...still poor. I tried lots of things with shielding and grounding but never succeeded in getting results as good as the standard CW filters with the KI6WX mod. Just to be clear, this was NOT a problem with the filter, which looked great when tested stand-alone. It had to do with interfacing it with the K2. -- 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 |
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In reply to this post by Don Wilhelm-3
W3FPR added:
> > -----Original Message----- > ... - but I just can't pull some things > > through on the K2 that I can with the 950 fitted with decent after-market > > filters. .... > >Comparing the K2 to any other rig outfitted with after-market filters is not >really a fair comparison. It does make me wonder how the K2 would do with >similar after-market filters -- alas, those filters do not seem to exist. Yes, one could say it is unfair, so instead consider any rig with OEM filters against that rig with decent after-market filters - especially those from say INRAD - anyone who has used an INRADed rig will no doubt appreciate what after-market filters might do for our K2s! >With almost 5000 K2s out there now, I wonder if InRad is having second >thoughts about providing filters for the K2 - it may require a non-SSB K2 to >fit them in physically, and with the small market created by that simple >fact, they may still not be interested. Actually, the filters on the K2 are >not shabby by any means, but like most anything else, could be improved with >sufficient bucks and effort. An INRAD CW filter for the K2 is already available, but W2VJN suggested to me I might not want to buy one as it's hard to use - no ability to select it - so no point in doing more than a limited production run & call them prototypes. Even then, the cost was not far into the USD three-digit range - easily justified based on the expectation of what it could do, but perhaps a bit too dear seeing how it ended up in the junk box (being stuck having to always listen through the INRAD filter equally wasn't on). One INRAD filter can be made to fit in a K2 w/KDSP, KPA, KSB & KNB & I believe I can find space for another. To be able to complement the K2's stock filters with one good CW & one good SSB filter would be fantastic & definitely nowhere near as costly as doing what many of us do to other rigs (like coming up with something in the area of USD 1k to INRAD most of an MP, for example). No connection with INRAD here other than 20+ years of using their products & purchasing one of the last K2 filters George had made up despite the difficulties using it. Perhaps there is more to it than we realize, but INRAD sales are not detrimental to Elecraft as they are for Brands I, K or Y. Instead of building something from scratch, it's unfortunate that with the K2 it is not possible to easily use any alternative filter from the front panel. 73, VR2BrettGraham _______________________________________________ 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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VR2BrettGraham wrote:
> An INRAD CW filter for the K2 is already available, but W2VJN > suggested to me I might not want to buy one as it's hard to use - no > ability to select it - so no point in doing more than a limited production > run & call them prototypes. Even then, the cost was not far into the > USD three-digit range - easily justified based on the expectation of > what it could do, but perhaps a bit too dear seeing how it ended up in > the junk box (being stuck having to always listen through the INRAD > filter equally wasn't on). ...and also it hasn't been possible to take advantage of the filter characteristics, as far as I know. I have one of these prototypes in my junk box because even by hard-wiring it into the circuit I was unable to get sufficient isolation to reduce the blow-by to an acceptable degree. The stock filter arrangement is better. George (JVN) did some work, but I don't know if he found a way to use it successfully. -- 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 |
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