+++++++++++++++++ See also K2_L33-7_or_BFO Stability +++++++++++++++++ Date: Sun, 03 Nov 2002 16:30:15 -0800 From: Wayne Burdick Organization: Elecraft To: k6se at juno.com Cc: elecraft at mailman.qth.net Subject: [Elecraft] Re: BFO Drift (and a solution for it) Earl, Removing one crystal tends to cut VFO drift by 30-40%, but this will not work for the BFO. (The amount of "pull" possible with one crystal is, unfortunately, not proportional to carrier frequency. It gets harder as the frequency goes down.) The good news is that we recently found a way to substantially reduce BFO drift, and had planned to announce it next week. Now is as good a time as any. (By the way, your past observations about drift were very helpful when we started looking into the problem in depth.) We have determined that nearly all of the BFO drift is due to L33. As you know, we had to use a toroid at L33 in order to minimize BFO leakage into adjacent circuitry. In order to keep the number of turns on this toroid reasonable, we originally used a core with a high permeability and a moderately-good temperature coefficient (about 250 ppm/degree C--a lot better than ferrite). But since this turned out to be the source of most of the drift, we have decided to begin supplying a new, pre-wound, highly stable inductor. This new inductor uses a T44-7 core. It's the same size as the old T44-8 but has a temperature coefficient a factor of 8 smaller (30 ppm/degree C). In order to get enough inductance on the T44-7, we had to use over 90 turns of #34 wire. This is not a winding we could ask customers to do, so we are having them professionally wound. We've tested the new inductors on about half a dozen K2s. BFO drift was reduced by as much as 80%. The average was about 75% (a factor of 4 improvement), and the worst case was around 70%. It may be possible to further reduce BFO drift by using N750 capacitors in the BFO, but we haven't received our test samples of these capacitors yet. In actual operation the difference is dramatic: the BFOs remain much more closely aligned with the selected filter's center frequency. Within a week or two we will begin offering a mod kit that includes the new toroid, as well as a single, wide-range PLL reference oscillator crystal. (We're already including these parts in new K2s.) If the N750 capacitors help, too, we'll also add these to the mod kit. I appreciate your patience while we've tried to resolve this. I'll be sending you one of these kits the moment it becomes available, at no charge. Please try it on your K2 and let us know if the degree of improvement is satisfactory. 73, Wayne N6KR orig-msg To: elecraft at mailman.qth.net Date: Sun, 3 Nov 2002 15:11:55 -0800 From: k6se at juno.com Subject: [Elecraft] BFO Drift When I first got my K2 (S/N 2622) running last May, my biggest beef was the VFO drift with temperature. I had grown so used to my FT-1000MP's stability (whose VFO drifts a maximum of about 10 Hz with extreme temerature changes with its stock oscillator (which is a non-TCXO) that I expected the K2 to be as good. Even in a stable temperature environment, my K2 drifted more than the 100 HZ spec given for the rig by Elecraft and after I griped about it, Gary Surrency sent me a new pair PLL reference oscillator xtals. The new xtals got the rig within Elecraft's specs (barely), but when the shack temperature changed, the VFO would drift much more than 100 Hz. >From a cold start with the new xtals, 10 MHz WWV will drift from about 9999.05 to 10000.04 MHz on my K2's VFO display (if the shack temperature is stable). The 4 MHz oscillator is set to as closely to 4000.000 kHz as possible, BTW. I came to accept the VFO's inaccuracy as long as I was careful that I did not operate near the edge of the band. The only other ramification is that the frequencies given on DX packet cluster spots might not agree with my VFO readout. However, BFO drift in my K2 is intolerable. The main reason I bought the K2 was that I thought it might make an ideal portable rig to use at my favorite salt lake bed location here in the Mojave Desert during 160-meter CW contests. The problem with the BFO temperature drift is that, when using narrow CW filters, the received signal may, or may not, be centered in the filter passband. Narrow CW filters are essential for best S/N ratio when receiving weak signals such as those encountered on 160. Gary Surrency also sent me a new pair of BFO xtals, but they were even worse than the originals, so I reinstalled the original xtals. Even at home, where the temperature does not change as widely as it does in a tent trailer at the salt lake bed, signals are outside of the K2's narrow CW filter's passbands more often than not. For this reason, I've given up on the K2 and it now gathers dust in a corner of the shack. The thread on removing one of the PLL oscillator xtals to alleviate VFO temperature drift has given me new hope, however. If it works, this should cut the BFO drift problem if half, possibly making the K2 usable for my purposes. The manual states that the BFO must be able to tune from 4912.7 to 4916.3 kHz, or a range of at least 3.6 kHz. Because the PLL 12.096 MHz xtals must have a 10 kHz range (and one xtal works in some cases), this corresponds to a range of about 4 kHz at 4.915 MHz, so maybe it's possible. I would appreciate it if anyone has removed one of the BFO xtals to reduce BFO drift that they let me know the results. 73, de Earl, K6SE ++++++++++++++++++ Date: Sun, 03 Nov 2002 20:13:54 -0800 From: "John, KI6WX" Subject: Re: [Elecraft] Re: BFO Drift (and a solution for it) To: Elecraft Mailing List Dave; The first design of the K2 used a solenoidal inductor, but this was changed to a toroidal inductor around S/N 1200. The solenoidal inductor has less drift than the toroidal inductor, but from what I have seen of Wayne's stability measurements, the new toroidal inductor should be better than the previous versions. -John KI6WX > Wayne: > I'm kinda confused. L33 in my K2 is not a toroid, but a 39uH solenoidal, > shielded inductor. I believe there may have been a mod to replace this with > a toroid, but I never did. Does the solenoidal inductor have the same > problem relative to drift? Would it be better to switch this out with your > modification kit when it becomes available? > > thanks, > > dave belsley, w1euy +++++++++++++++ Date: Sun, 03 Nov 2002 22:25:11 -0800 From: Wayne Burdick Organization: Elecraft To: "David A. Belsley" Cc: elecraft at mailman.qth.net Subject: [Elecraft] Re: BFO Drift (and a solution for it) "David A. Belsley" wrote: > > Wayne: > I'm kinda confused. L33 in my K2 is not a toroid, but a 39uH solenoidal, > shielded inductor. I believe there may have been a mod to replace this with > a toroid, but I never did. Does the solenoidal inductor have the same > problem relative to drift? Would it be better to switch this out with your > modification kit when it becomes available? Hi David, The new T44-7 toroid is a factor of 8 more stable than either the old T44-8 or the original solenoidal inductor. It also has less leakage, so it's a win-win solution. On the other hand, it's costing us a lot to get them pre-wound, but we feel that it's worth it to reduce the drift for those who have been inconvenienced by it. We'll announce the mod kit price and availability next week. 73, Wayne N6KR ++++++++++++++ From: "Robert Fanfant" To: "Wayne Burdick" , "David A. Belsley" Cc: Subject: Re: [Elecraft] Re: BFO Drift (and a solution for it) Date: Sun, 3 Nov 2002 23:18:59 -0800 I've been watching this discussion over the past week with interest. To me, its pretty amazing to see the expectation levels this low cost home brew kit has produced. In the end, another upgrade/mod is proposed that some my chose to install. To me it's just another example why the K2 is in a class of its own; continued improvements to an already fantastic radio. Can't say that about my factory produced rig. -rob K2 #1406 +++++++++++++++ Date: Tue, 05 Nov 2002 14:56:16 -0800 From: Eric Swartz WA6HHQ - Elecraft Organization: Elecraft To: Phil Wheeler Cc: "George, W5YR" , Bob Nielsen , elecraft at mailman.qth.net Subject: Re: [Elecraft] Re: BFO Drift (and a solution for it) Everyone who has a BFO MOD KIT on order will also receive a new 12.096 MHz reference oscillator crystal. We were originally planing to offer the crystal as a separate part, but we were flooded with so many questions yesterday asking if it was included in the BFO MOD KIT that we decided to go ahead and include it :^) The new BFO toroid parts and new single PLL reference osc crystal are both standard in currently shipping K2's, serial number 3000 and above. Those of you who put BFO MOD KIT orders in at the yesterday's lower price will not be charged extra. 73, Eric WA6HHQ Elecraft ========== +++++++++++++++ To: elecraft at mailman.qth.net Date: Sun, 10 Nov 2002 16:07:57 -0800 Subject: Re: [Elecraft] To PLL mod or not From: k6se at juno.com Lou, W7DZN's last post regarding combined PLL and BFO drift was excellent and enlightening. I want to briefly reiterate one of the things he pointed out: BFO drift causes the filter passband to shift and can cause the desired signal to not be in the passband, while PLL drift does not cause this. After doing the PLL and BFO (toroid) mod in my K2 (#2622), the BFO drift is virtually nil. Using Spectrogram with a 50 Hz xtal filter passband centered on my 400 Hz pitch marker at power on, no drift was noticed after 3 hours of warmup. I'm extremely pleased about this, as it has cured the problem which caused me to remove my K2 from active duty. 73, de Earl, K6SE ++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: "'Mike Harris'" , Subject: RE: [Elecraft] To PLL mod or not Date: Mon, 11 Nov 2002 08:05:50 -0800 We're taking bits and pieces out of previous messages. No wonder it's getting confusing. I define "side tone" as the locally-generated audio frequency that you hear whenever you press the key to transmit CW. It is not affected by drift of either the LO or the BFO. It is affected only by what you chose in the St P command from the menu. What I call the LO is using classic superheterodyne receiver terminology. It is the "local oscillator": the oscillator that heterodynes the incoming signal to the i-f. In the K2 it is what is often called the "PLL" because the K2 happens to use a phase-locked loop to generate the LO signal. Finally, the BFO or "beat-frequency oscillator" is the oscillator that heterodynes the i-f to audio. It runs close to the i-f frequency. The BFO frequency is what determines the audio frequency we hear in the speaker when a CW signal is centered in the i-f bandpass. It is set up using CAL FIL so that we hear a beat frequency equal to the sidetone when a signal is centered in the i-f bandpass. That means that the BFO frequency must be changed with different filter bandwidths, which is the whole point of running CAL FIL. In SSB reception the BFO frequency determines how the SSB signal will line up with the i-f filter passband to produce the most pleasing audio quality. But let's stay with CW for this discussion. My original point was that while drift in either the LO or BFO require retuning to put the received signal beat frequency back zero beat with the sidetone frequency, the effects of LO and BFO drift are different and easy to identify. My apologies for not reposting the whole message again with the replies. It has caused confusion. Here's what I was saying: IF the signal is tuned in 'properly', that is, so the CW note is zero beat with the sidetone AND the LO drifts in frequency (which, of course means that you must re-tune slightly to adjust for the change in pitch and put it back zero beat with the sidetone frequency) there will be NO change in the position of the signal in the filter bandpass. No matter how narrow the i-f filter bandpass is set and not matter how badly the LO might drift, when a signal is tuned in so it is zero beat with the sidetone frequency, it will still be centered in the i-f filter bandpass. IF the BFO drifts, the pitch of the received signal will change. Again, it can be placed back to "zero beat" with the sidetone frequency by adjusting the tuning control, but now the signal will have shifted in relationship to the i-f filter bandpass. If the BFO drifts far enough, the signal may move completely out of the i-f filter bandpass. Sorry for the confusion. And, yes, you are absolutely right. If the BFO frequency drifts we can adjust the receiver tuning to put the signal back in the center of the i-f bandpass, but now we will hear a different beat frequency in the speaker. The beat frequency will no longer be zero beat with the sidetone frequency. But that's not an acceptable procedure because it will move the transmitter frequency since the same oscillators are used for both, unless we are using SPLIT mode to give us two independent LO's: one for receive and one for transmit. That's WHY we zero beat the incoming signal to the sidetone frequency. It puts the K2 transmitter frequency exactly on the received frequency. So the first step in tuning in a signal is always to zero beat the incoming signal to the sidetone frequency. Ron AC7AC K2 # 1289 +++++++++++++ From: "Bob Tellefsen" To: "Rod N0RC" , , Subject: RE: [Elecraft] To PLL mod or not Date: Mon, 11 Nov 2002 08:49:45 -0800 Rod If you are looking at a received signal or marker with Spectrogram, center the signal in your narrowest passband. If the vfo is stable and the BFO is drifting, the signal should stay put within the passband (determined only by vfo and filter) but the pitch should change. If the vfo is drifting, the signal will move in the passband and the pitch will change. This should allow you to determine whether vfo or BFO is drifting. 73, Bob N6WG -----Original Message----- From: elecraft-admin at mailman.qth.net [mailto:elecraft-admin at mailman.qth.net]On Behalf Of Rod N0RC Sent: Sunday, November 10, 2002 10:07 AM To: rondec at easystreet.com; elecraft at mailman.qth.net Subject: Re: [Elecraft] To PLL mod or not Ron, et.al., After some thought, I'm not sure either of or methods can discriminate between VFO/BFO drift. (I know mine can't ;-) Consider this: Assume that the BFO is stable and constant, then if the VFO drifted, a stable RX signal would shift position within the passband. A result of the 1st mixer operation. And the RX tone would change, a result of the mixer action between BFO (stable) and the shifted IF signal. Now consider the VFO stable and constant, and a drifting BFO. Given a stable RX signal, the drifty BFO would cause the RX tone to change. Detection with ear or spectrogram detects the tone shift in either case, but can't isolate the cause, BFO, VFO or both. I think the only sure answer is a frequency counter at TP3 to measure the PLL and/or TP2 to measure the BFO. 73, Rod N0RC ++++++++++++++++++ To: n6wg at earthlink.net, elecraft at mailman.qth.net Date: Mon, 11 Nov 2002 09:27:03 -0800 Subject: Re: [Elecraft] To PLL mod or not From: k6se at juno.com Bob, N6WG wrote: "If you are looking at a received signal or marker with Spectrogram, center the signal in your narrowest passband. If the vfo is stable and the BFO is drifting, the signal should stay put within the passband (determined only by vfo and filter) but the pitch should change. If the vfo is drifting, the signal will move in the passband and the pitch will change. This should allow you to determine whether vfo or BFO is drifting." ========== A much easier way to see if you have BFO drift is to set up Spectrogram with a marker at the sidetone pitch you selected via the ST P menu. Then select your narrowest CW filter and look at the spectrogram display on just noise (no signal!). If the BFO is set up properly (CAL FIL), the marker will be in the center of the filter passband. If BFO temperature drift occurs, you will see the passband move up or down in frequency on the Spectrogram display (resulting in the sidetone pitch marker no longer being centered in the passband). 73, de Earl, K6SE +++++++++++++++ Date: Thu, 14 Nov 2002 09:42:46 -0800 From: Wayne Burdick Organization: Elecraft To: Ken Wagner Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] PLL / BFO Mod Kit Hi Ken, The crystal we're supplying with the kit will have been pre-tested for adequate range, since some older K2s may have crystals that won't cover this range used individually. If you're getting enough range from one of your present crystals, as well as an improvement in temperature stability, then you can stick with it. 73, Wayne Ken Wagner wrote: > > Elecrafters: > > A questions... > > Is there any characteristic, other than the increased range, of the new, > wider range, crystal that is being provided with this mod kit that is > critical to the success of the mod? I recently built s/n 2888, have removed > one of the 2 reference crystals, have the requisite >10khz range, and have > successfully run CAL PLL, etc. Everything seems to be great. Guess I need to > know if there is a need to install the NEW crystal that will come with the > mod kit. If adequate pull range is the only reason for the new crystal, then > I guess that I'm OK, but, since there is soooo much that I don't know, I > gotta ask! > > Thanks to whoever answers... > > 73, > Ken Wagner > K3IU K2/100 #920, K2 #2888 +++++++++++++++ Date: Tue, 10 Dec 2002 19:21:57 -0800 From: Wayne Burdick Organization: Elecraft To: Jim G Cc: Elecraft at mailman.qth.net Subject: [Elecraft] Re: New Problem after Stability Mod Jim, Let's take these one at a time. BFO: The resolution (increments) possible in setting the BFO vary a bit, but 20 Hz is pretty typical. Because of this, there's no guarantee that you'll be able to hit 4916.30 exactly. Getting to anywhere within 10 to 20 Hz of your target is more than adequate since the narrowest filter bandwidth you can get from K2 filtering is 4 to 5 times that. PLL: If you have an instability in the PLL, the first thing to check is the value of R19, which you no doubt soldered on the bottom of the board (it isn't present on the rev A RF board). Unfortunately some early BFO mod kits were sent out with 220 ohm resistors for R19, and this value turned out to be too small. This was the subject of a recent builder alert. The value should be between 1.8 and 3.3 k. It is 2.7 k in the Rev B K2. Let me know if this helps. 73, Wayne N6KR Jim G wrote: > > Installed the PLL/BFO kit to my K2 (s/n 2105 with Rev A board). When I > began re-entering the BFO settings I noticed that the last digit would > jump around; for example, if my BFO setting was 4916.30, it would jump > from .29 to .31. I was not able to set it exactly on .30. I've also > noticed that I have a frequency instability that shows up every 5 Khz > when tuning. > > Reading the Rev B PDF indicates that this is a PLL instabilty problem. > However, I notice this problem every 5 Khz across the entire 40 meter > band. It's also showing up on 20 meters. > > Any ideas on what I should be looking for? > > Thanks- > > Jim > K4GT ++++++++++++++++++ Date: Tue, 10 Dec 2002 20:45:34 -0800 From: Eric Swartz WA6HHQ - Elecraft Organization: Elecraft To: Jim G Cc: Elecraft at mailman.qth.net Subject: Re: [Elecraft] New Problem after Stability Mod Jim, The problem repeating every 5 kHz may indicate that you need to rerun CAL PLL (on 40M). Did you rerun it after making the change? 73, eric WA6HHQ ------ Jim G wrote: > > Installed the PLL/BFO kit to my K2 (s/n 2105 with Rev A board). -- snip -- ++++++++++++ Date: Thu, 12 Dec 2002 09:25:30 -0500 (Eastern Standard Time) From: Helmut Usbeck To: elecraft at mailman.qth.net Subject: [Elecraft] BFO Mod I installed the BFO mod, l33 and R116. So far so good. I seem to remember that for even less drift to remove X3 or X4, not to be confused with the removal of X1-X2 pll Xtal. Anyhow in removing either X4 or X5 I get only a 1.8 khz spread, instead of 3.6 khz or better. Of course the BFO mod sez nothing about removing a xtal but I though several of you out there tried it and gained a bit more stability. Do I add a cap or two somewhere or should I just leave it with 2 xtals installed. Regards Helm. WB2ADT +++++++++++++ From: "Don Brown" To: "Helmut Usbeck" , Subject: Re: [Elecraft] BFO Mod Date: Thu, 12 Dec 2002 09:45:34 -0600 Hi The only place you remove a crystal is X2 in the PLL reference oscillator. The BFO needs all of the crystals to have enough range. The drift in the BFO was in the toroid and that is corrected with the new pre-wound toroid L33. You may have seen a note about adding a cap in the BFO to get more range but that was with both crystals. Don Brown ++++++++++++++ From: "Dave" To: Cc: Subject: Re: [Elecraft] BFO mod kit instructions? Date: Sun, 11 May 2003 21:31:46 +0100 Lee They are part of the A to B mod instructions: http://www.elecraft.com/manual/k2a2binstr.pdf It's worth adding the PLL thermistor modification as it makes more difference than the A to B PLL/BFO mod on it's own. 73's Dave, G4AON K2 #1892 www.astromag.co.uk/k2/ ++++++++++++++ Date: Mon, 19 May 2003 18:00:43 -0700 From: Eric Swartz WA6HHQ - Elecraft Organization: Elecraft To: Larry - WA2DGD Cc: Elecraft Reflector Subject: Re: [Elecraft] K2 Temp. compensated PLL mod Yes the BFO toroid mod does alter the relationship between the DAC numbers and the actual BFO frequency. The inductor the toroid replaces impacts what frequency the BFO oscillates at. A slightly different value inductor (the toroid) will change the natural frequency of the oscillator, requiring a different varactor voltage (controlled by the DAC voltage) to reach the same operating frequency. Always write down your filter BFO frequencies, not the DAC numbers. Also don't forget that the BF1t frequency also sets the SSB transmit audio range and that a very small change in this parameter (+/-100 Hz) can make a big difference in the quality of your transmitted SSB audio. (There is a different BF1t setting for USB, LSB and Data modes.) 73, Eric WA6HHQ ---- Larry - WA2DGD wrote: > Hello all, > > Yesterday I did the BFO Toroid and PLL Xtal upgrade and the Temperature > Compsensation Mod to K2 #`1672. > The first step is to write down all the filter BFO frequencies. Well instead > of recording the actual frequency, I always record the 3 digit BFO control > parameter. I did the mods, all went well, and then I re-entered my BFO > control parameters. > Well I had quite a surprise.. USB was receiving LSB and vice versa, and CW > sounded like a direct conversion rcvr, I heard both sides of the cw signal > and my filters were totally screwed up. > Rather than going into a complete panic, I pulled out the KSB2 SSB manual > and entered the BFO Frequencies given in the manual as a starting > point.....everything went back to normal and I was able to use spectrogram > to set up my filters as before...now my K2 works great again. > > My question is this... do these mods alter the relationship between the BFO > frequencies and the BFO control parameters? After the mod, my BFO control > parameters are significantly different than the pre-mod numbers. The K2 is > working great but I'm curious as to what happened. ++++++++++++++++