K2 XTALS
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I am buiding a K2 sn 004149 from an earlier non built K2 sn 000571 up to rev 'B' on the new 'B' pc boards.
I also have an early KSB2 SSB unit. All the above has the original XTALS for the CW filter and SSB unit.ie 4.195MHz -20. I have read lots of comments on the audio quality because of the tight band pass of the original SSB unit. I know that Elecraft have produced some modifications in the form of 14 new XTALs and a capacitor upgrade kit. Does anyone have experience of these mods ? Is there a basic capacitor upgrade that one can do first of all? Or is changing all the XTALs and adding new capacitors the best solution? Or is the original configuration ok? Regards Colin M1BNW _______________________________________________ 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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Colin,
There are 2 separate things here - Elecraft's specs to the xtal vendor for motional inductance were tightened on or about SN 2600. If you have a set that is older, you will likely benefit from installing a new set of crystals (do not mix new with the older crystals in any one filter (CW or SSB). Secondly, yes Elecraft has widened the SSB filter bandwidth from 2.0 to 2.3 (or 2.4) kHz. Only a few capacitors in the filter are changed, and you likely have the capacitors for the narrower filter. Weigh the pros and cons of the wider or narrower bandwidth - the narrower filter provides a bit more 'punch' to a QRP SSB signal, but is a bit more critical in positioning the passband correctly. The wider passband results in a more natual sounding transmitted signal. Take your pick based on your operating desires, both work well. If you do decide to change the fiilter bandwidth, it is easier to install the capacitors during initial construction - it is not really difficult to do it after assembly, but decidedly easier to put the capacitors in before the crystals are installed. 73, Don W3FPR > -----Original Message----- > > I am buiding a K2 sn 004149 from an earlier non built K2 sn > 000571 up to rev 'B' on the new 'B' pc boards. > I also have an early KSB2 SSB unit. > > All the above has the original XTALS for the CW filter and SSB > unit.ie 4.195MHz -20. > I have read lots of comments on the audio quality because of the > tight band pass of the original SSB unit. > I know that Elecraft have produced some modifications in the form > of 14 new XTALs and a capacitor upgrade kit. > > Does anyone have experience of these mods ? > Is there a basic capacitor upgrade that one can do first of all? > Or is changing all the XTALs and adding new capacitors the best solution? > Or is the original configuration ok? > > Regards Colin M1BNW > No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.322 / Virus Database: 266.11.16 - Release Date: 5/24/2005 _______________________________________________ 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 m1bnw
Morning Colin,
My K2 is #3255 and the KSB2 Build is Revision C-3. The envelope that contained the KSB2 crystals is marked 3.7 (as was the envelope containing the K2's IF filter crystals), and the KSB2 crystals are marked 4.9136. I have not made any modifications From 'swept' measurements the KSB2's filter -6db bandwidth is 2.1 kHz approx if I remember correctly Please note that this is not a 'noise loaded' measurement, e.g. Spectrogram. The exact figure is in my notebook which is packed away due to an invasion of plumbers, carpenters and others - sorry about that. Using this data and the measured audio response, mic connector to and including the modulator, to set the carrier oscillator frequencies (BFO), the BFO is no more than 200 Hz away from the frequencies suggested in the KSB2 manual. With a Heil ProSet Plus and no audio mods, full specd PEP is obtained and unsolicited audio reports are complimentary. My personal opinion is that the 2.1 kHz bandwidth is satisfactory with the K2, for ragchewing and DXing. Because the same intermediate sized crystal ladder filter is used for both USB and LSB, increasing the bandwidth could result in problems with unwanted sideband suppression when the BFO is on the low frequency skirt of the filter. This assumes that the filter is properly designed and terminated. It is possible to fiddle things to steepen the LF skirt, but usually at the cost of increased ripple in the passband. 73, Geoff GM4ESD ----- Original Message ----- From: "m1bnw" <[hidden email]> To: <[hidden email]> Sent: Friday, May 27, 2005 7:18 PM Subject: [Elecraft] K2 XTALS I am buiding a K2 sn 004149 from an earlier non built K2 sn 000571 up to rev 'B' on the new 'B' pc boards. I also have an early KSB2 SSB unit. All the above has the original XTALS for the CW filter and SSB unit.ie 4.195MHz -20. I have read lots of comments on the audio quality because of the tight band pass of the original SSB unit. I know that Elecraft have produced some modifications in the form of 14 new XTALs and a capacitor upgrade kit. Does anyone have experience of these mods ? Is there a basic capacitor upgrade that one can do first of all? Or is changing all the XTALs and adding new capacitors the best solution? Or is the original configuration ok? Regards Colin M1BNW _______________________________________________ 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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Geoff wrote:
Because the same intermediate sized crystal ladder filter is used for both USB and LSB, increasing the bandwidth could result in problems with unwanted sideband suppression when the BFO is on the low frequency skirt of the filter. This assumes that the filter is properly designed and terminated. It is possible to fiddle things to steepen the LF skirt, but usually at the cost of increased ripple in the passband. --------------------------------------- Geoff brings up a number of legitimate concerns when messing with the filter bandwidth. Fortunately, one of our most thorough and experienced technical guru's, John Grebenkemper, KI6WX, took these issues into consideration in designing the filter mods for increased bandwidth and less passband ripple. That's why the modifications are "official" Elecraft options and one can order from Elecraft (SSBCAPKT). The mod kit includes all the capacitors needed for one of several of different bandwidths. This mod kit assumes one has the new crystals and, for pre S/N 3000 units, the 2ND XFIL mod has been installed. The 2ND XFIL mod is required for best sounding receive SSB. It does not affect transmit audio. My modified filters are a full 2.6 kHz wide. I made the change as much for CW than SSB. While I'll pick up the mic on occasion, I work CW 99% of the time and I enjoy scanning the bands with a very wide bandwidth in which I can hear several QSO's at once. I only crank down the bandwidth when an unwanted signal become so loud it's obnoxious. Still, getting the best quality audio was an interesting project, even if I don't do a lot of SSB work. The receive audio is really surprisingly good. AM stations at the upper part of the North American AM broadcast band sound as good as they do on most regular AM radios when properly tuned in. Of course, accurate tuning is critical. A 10 or 20 Hz error is obvious and irritating when listening to music. The issues with opposite sideband suppression that Geoff raised do not come up because there is no need or desire to move the lower edge of the audio bandpass closer to the carrier frequency for transmit. What John's mods did was to provide a smoother, flatter, wider bandpass while maintaining the roll-off at the skirts. Normally, this wider bandwidth will be used to pass the higher-frequency sibilances that are so important for best speech intelligibility. Passing more of the low-frequency tone in human voices is usually a waste of power. That low frequency energy is simply what is called a "drone", or the fundamental note, produced by the throat. It's rich in audio harmonics, and it's those audio harmonics spread across the audio spectrum up to several kc/s that get modulated by one's mouth to make speech. My voice has been, on occasion, described as sounding a bit like a metal trash can being dragged along a gravel road. That's my natural, sometimes rough, low frequency drone. I find the most natural and intelligible setting for my voice rolls off the low frequencies from about 400 Hz down. Other voices might sound better passing frequencies down as low as 300 or even 200 Hz. That's where actual listening tests are important. When listening to our own voice in headphones, much of that low frequency sound comes right through our bones. Unless that bone conduction is taken into consideration, it's easy to arrive at a filter setting that sounds great when listening to oneself in the headphones but which sounds unnatural and tinny to others on the air. I suggest recording your signal then playing it back to hear what others actually hear. Keep in mind that only FL1 is used on transmit! No matter what filter is selected for receive, the K2 switches to FL1 when the PTT is pressed. So only FL1 need be set for optimum transmit audio. FL2, FL3 and FL4 can be set to move the passband up or down to adjust the bass/treble response on other signals or to help move away from nearby QRM. It works a bit like "passband tuning" in some rigs. For example, I have one position set to bring the low frequency rolloff down to about 100 Hz for listening to broadcast stations. Of course you can also assign some of these filter positions to the CW filters to provide a more restricted bandpass for listening to weak signals in difficult band conditions. Ron AC7AC _______________________________________________ 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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On Sat, 28 May 2005 07:26:21 -0700, Ron D'Eau Claire wrote:
> My voice has been, on occasion, described as sounding a bit like a metal > trash can being dragged along a gravel road. That's my natural, sometimes > rough, low frequency drone. I find the most natural and intelligible setting > for my voice rolls off the low frequencies from about 400 Hz down. For any LF voices such as your Ron, it might be worth reducing the value of coupling C's in the mic audio chain of the KSB2. The values supplied let enough low frequency component get through that Humped Back Whales would have no difficulty working the DX.... 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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Stewart G3RXQ wrote:
For any LF voices such as your Ron, it might be worth reducing the value of coupling C's in the mic audio chain of the KSB2. The values supplied let enough low frequency component get through that Humped Back Whales would have no difficulty working the DX.... -------------------- Excellent suggestion Stewart! The lower frequencies in my voice are more rough than "low". Unfortunately, I don't have one of those voices that is usually pressed into service for broadcast work. The capacitor technique is a good one. I used it in a couple of tube-type AM rigs over the years. With the K2, I really appreciated the flexibility of the BFO and Filter setup that allowed me to tailor the speech bandpass without resorting to swapping component values. It does leave open the issue of whether some of the low frequency components that are being cut off intentionally by the SSB filter might be triggering the compressor or audio ALC functions, affecting the overall speech amp gain. I seem to have adequate for full output across the spectrum on SSB, so I hadn't looked into it further. Ron AC7AC _______________________________________________ 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 Ron D'Eau Claire-2
Ron,
Thank you for your comments. Forgive me if I split up my reply. On May 28, 2005 at 3:26 PM you wrote: The issues with opposite sideband suppression that Geoff raised do not come up because there is no need or desire to move the lower edge of the audio bandpass closer to the carrier frequency for transmit. ---------------------------------------------------------------------------- -- Perhaps. If the only consideration is the transmitted audio spectrum, yes I would agree. As you correctly point out, passing more of the low frequencies is usually a waste of power. Of course the frequency response of the microphone and Tx audio circuitry needs to be included in this consideration. But the group delay characteristics of the filter should also be thought about. A typical Cohn ladder filter, for example, has wicked gyrations at the corner frequencies which requires that the carrier frequency be moved up the filter's skirt to reduce distortion at those audio frequencies that contribute to intelligibility. This of course increases the level of unwanted sideband unless at the same time, the Tx audio rolls off very sharply at the lower audio frequencies. To avoid this, Gaussian, Gaussian to 6db or 12db or the equiripple families of ladder filter which approximate constant delay can be used, and are the most useful from the distortion viewpoint. Although not relevant to this discussion, a narrowband Cohn ladder as might be used in a CW receiver will ring. Without seeing the delay and frequency response plots of the modified filters, any further comment would be guessing on my part. ---------------------------------------------------------------------------- -------- My voice has been, on occasion, described as sounding a bit like a metal trash can being dragged along a gravel road. That's my natural, sometimes rough, low frequency drone. Pass!! ---------------------------------------------------------------------------- --------- That's where actual listening tests are important. When listening to our own voice in headphones, much of that low frequency sound comes right through our bones. Unless that bone conduction is taken into consideration, it's easy to arrive at a filter setting that sounds great when listening to oneself in the headphones but which sounds unnatural and tinny to others on the air. I suggest recording your signal then playing it back to hear what others actually hear. Totally agree. 73, Geoff. GM4ESD _______________________________________________ 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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Geoff, GM4ESD, wrote:
Of course the frequency response of the microphone and Tx audio circuitry needs to be included in this consideration. But the group delay characteristics of the filter should also be thought about. A typical Cohn ladder filter, for example, has wicked gyrations at the corner frequencies which requires that the carrier frequency be moved up the filter's skirt to reduce distortion at those audio frequencies that contribute to intelligibility. This of course increases the level of unwanted sideband unless at the same time, the Tx audio rolls off very sharply at the lower audio frequencies. To avoid this, Gaussian, Gaussian to 6db or 12db or the equiripple families of ladder filter which approximate constant delay can be used, and are the most useful from the distortion viewpoint. Although not relevant to this discussion, a narrowband Cohn ladder as might be used in a CW receiver will ring. Without seeing the delay and frequency response plots of the modified filters, any further comment would be guessing on my part. ----------------------------- Those are good points that I haven't addressed since I'm not a filter specialist. As an operator I've heard first-hand some of the awful stuff a filter can produce in response to signals on the edge of its bandpass. The K2 filters went through a long cycle of testing and optimization at the hands of John Grebenkemper, KI6WX, with consultations with Wayne at Elecraft and possibly others. I presume these issues were considered at that time. Obviously, a complete redesign that would involve more crystals or a different filter topology was out of the question since such changes wouldn't fit on the SSB module. So I won't speculate on what compromises he may have made in his choices. He did publish a detailed "how-to" description of his recommendations in a paper that can be downloaded: http://tinyurl.com/8emeu. This is a document written for the typical Elecraft builder and does not go into the analytical work behind his recommendations. If you're curious, I'd suggest visiting John's web site (http://tinyurl.com/8cs8w) and perhaps dropping him an e-mail. I've always found him to be a very knowledgeable and patient in describing his work. Ron AC7AC _______________________________________________ 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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