+++++++++++++++++ From: "Don Brown" To: "David A. Belsley" , "Elecraft" Subject: Re: [Elecraft] K2 alignment after removing X2 (Logic Check?) Date: Sun, 3 Nov 2002 09:03:25 -0600 Hi You can cut the VFO drift with temperature in half by simply removing one= of the reference oscillator crystals. I remove X2 then check the referen= ce oscillator range as described on page 57 of the manual. If the range i= s at least 10 KHz then you can use that crystal by itself. If it does not= have enough range try the other crystal. Most of the newer crystals will= have just a little over the required range and are fine but you may need= to order a new set if yours won't make it. This also makes the VFO calib= rate more accurate because the 12 bit DAC's 4096 counts are spread out ov= er 10 KHz rather than 12-15 KHz. This makes each step a finer adjustment = of the range between the steps of the PLL chip. This allows the CAL PLL r= outine to calibrate the dial more accurately. =20 If you remove the crystal then you must make sure the 4.000 MHz clock is = accurate and then run CAL PLL. The only time the 4.000 MHz clock needs to= be accurate is while CAL PLL is running or when you are setting up your = filters. It is not used at any other time except as a clock for the MPU. = Just follow the instructions in the manual on page 57 and/or 98 to get th= e clock on frequency and run CAL PLL on 40 meters (assuming you have 2.XX= firmware). I prefer the page 98 method as it is more accurate because it= uses WWV as the standard. There has been some discussion about which is = the better method lately but after re-reading the procedures on page 57 a= nd 98 and performing both methods on 7+ K2's, either will put the K2 on f= requency within the stated specification. That is assuming the counter is= accurate. I don't think I need to worry about WWV's accuracy ;-) =20 Don Brown KD5NDB ----- Original Message ----- From: David A. Belsley Sent: Sunday, November 03, 2002 8:10 AM To: Don Brown Subject: Re: [Elecraft] K2 alignment after removing X2 (Logic Check?) Don: I've been a way for a month and a half and missed the issue behind this= =20 thread. Could you kindly fill me in? many thanks, +++++++++++++++++ From: "Don Brown" To: "Lyle Johnson" , "Elecraft" Subject: Re: [Elecraft] K2 alignment after removing X2 Date: Sat, 2 Nov 2002 12:54:15 -0600 Hi The way to check the range of the reference oscillator is on page 57 of t= he manual. Connect the counter probe to the reference oscillator TP3 and = use menu to turn on the counter. Tap the band+ and read the frequency the= n tap band- and read the frequency. The difference should be 10 KHz or mo= re. You may want to recheck your crystals, 5-6 KHz sounds very low. Nearl= y all of them will swing 10 KHz by the above method. If your crystals are= really that narrow I would order a new set. Then install only one and ch= eck the range. All of the newer crystals should swing 10 KHz Don Brown KD5NDB ----- Original Message ----- From: Lyle Johnson Sent: Saturday, November 02, 2002 12:36 PM To: elecraft at mailman.qth.net Subject: RE: [Elecraft] K2 alignment after removing X2 Hello Roy! > Once the X2 crystal (or X1 whichever the case may be) is removed, > the Cal PLL > is run again. Does rerunning the Cal PLL cause any change that would > necessitate a realignment and rerun of the Cal FIL? No. In my case, I didn't get enough range and had to use both crystals. One crystal gave about 5.8 kHz, the other 6.something. With both, I get arou= nd 12 kHz. I am not sure if there is a way to get a reading that says how far the oscillator was pulled during the Cal PLL task. I just wrote down the fir= st frequency, then watched it carefully until it was done and wrote down the last frequency it displayed. If the difference is not at least 10 kHz, it won't work. Cal PLL doesn't tell you it won't work, but you'll find if you tune aroun= d that there are large "dead" spots where the VFO just doesn't tune, even though the display shows changing numbers. 72, Lyle KK7P +++++++++++++++++++ Date: Sat, 02 Nov 2002 10:01:42 -1000 From: John Buck To: Elecraft Subject: Re: [Elecraft] K2 alignment after removing X2 (Logic Check?) I have not checked this out yet but I wonder if the change is necessary or desirable if the original crystals have the narrower swing capability stated below. Perhaps this setup is more stable than the "updated" crystals with more swing capability. Aloha, John KH7T +++++++++++++++++++ From: "Don Brown" To: "John Buck" , "Elecraft" Subject: Re: [Elecraft] K2 alignment after removing X2 (Logic Check?) Date: Sat, 2 Nov 2002 14:51:15 -0600 Hi I don't think so. I was told by Eric that a single crystal will have 1/2 = the drift due to temperature of the circuit with 2 crystals. If the cryst= al will swing 10 KHz that's all you need for the VFO to cover the range b= etween steps of the PLL chip. Any more and you are really wasting some of= the range of the DAC. I have done this mod on 4 K2's and all of the crys= tals had enough range. The oldest SN was 1808 and the newest was in the 2= 9XX range Don Brown KD5NDB +++++++++++++++ From: "Lyle Johnson" To: "Elecraft" Subject: RE: [Elecraft] K2 alignment after removing X2 Date: Sat, 2 Nov 2002 17:24:51 -0800 Hello Don! In my particular case, only 1 crystal did not provide enough swing. I just rechecked it using the method on page 57, and I show the same ~12 kHz with both crystals that my "watch the numbers and note them" method provided. If the swing is less than 10 kHz on 40m, then on 160m it will be less than 5 kHz and the tuning system will not work properly. At least, that was my observation. With the 5.8 kHz crystal, the radio worked fine on 40m and the bands I checked that were higher, but didn't work properly on 160m and 80m. With 12 kHz on 40m, the swing on 160m is about 6 kHz. This is enough to cover the 5 kHz needed by the PLL reference frequency pulling method used to provide < 5kHz stpes on the K2. FWIW, my current K2 is S/N 1971 purchased April, 2001. > You may want to recheck your > crystals, 5-6 KHz sounds very low. Nearly all of them will swing > 10 KHz by the above method. If your crystals are really that > narrow I would order a new set. Then install only one and check > the range. All of the newer crystals should swing 10 KHz. They really are that narrow. But my K2 works fine as designed with 2 crystals in the PLL reference oscillator, so I'll leave it alone for now. 73, Lyle KK7P +++++++++++++++ From: "Don Brown" To: "Randy Moore" , "'David A. Belsley'" , "Elecraft" Subject: Re: [Elecraft] K2 alignment after removing X2 (Logic Check?) Date: Sun, 3 Nov 2002 11:28:13 -0600 Hi I have Rev C manual and it lists 11.5-25 KHz as the acceptable range. But= I was told by Eric a month or so ago, as long as it will make 10 KHz or = more, it will work with one crystal and the drift will drop by a factor o= f 2. Since then I have done this mod on 4 K2's and it works fine. I have = not found any crystals that would not make 10 KHz but that's not to say t= hey all will. "Your mileage may vary" ;-) The crystals are cheap if you = should need to buy a new set and the mod is easy, so I think it's worthwh= ile. Don Brown KD5NDB ++++++++++++++ Reply-To: From: "Sverre Holm - LA3ZA" To: "'Elecraft'" Subject: RE: [Elecraft] K2 alignment after removing X2 (Logic Check?) Date: Sun, 3 Nov 2002 18:26:27 +0100 Don, That was a nice description of the VFO crystal mod for reduced temperature drift. I have referenced it in the unofficial mods list, at http://www.qsl.net/la3za/K2/mod.html 73 Sverre LA3ZA www.qsl.net/la3za +++++++++++++++++ From: "Lyle Johnson" To: "Elecraft" Subject: RE: [Elecraft] K2 alignment after removing X2 (Logic Check?) Date: Sun, 3 Nov 2002 10:52:21 -0800 Hello! I have gotten several private emails about all this. So, to be clear, I thought I should make one more post... The K2 uses a phase locked loop to generate the VFO frequency. This signal goes into the mixer to produce the IF of about 4.9152 MHz. A second oscillator, the BFO, mixes with the IF to produce the audio signal you hear, be it CW, SSB, PSK31 or ... The PLL is based on a Motorola MC145170 PLL chip, which uses a standard "divide-by-N" counter for the variable, or in the case of the K2, VCO, channel, and a "divide-by-R" channel for the reference, in this case the 12.096 MHz PLL Reference. The K2 uses the PLL chip operating at a final frequency near 5 kHz. Thus if the VCO needs to be at, say, 11.920 MHz to receive a signal on the low end of 40 meters, the MC145170 will set to divide the VCO by 2384 (11.920 Hz/2384 = 5 kHz) and the reference divider will be at its normal divide-by-2419 (12.095 MHz/2419 = 5 kHz). As you tune the radio such that the VCO moves from 11.920 to 11.925, the PLL Ref Osc will be pulled by a voltage from 12-bit DAC U5. When the VCO needs to be at exactly 11.925 MHz, the MC145170 will have its divide-by-N reprogrammed to 2385 (11.925 MHz/2385 = 5 kHz) and the DAC will "step" such that the PLL Ref Osc is at 19.095 MHz once again. In between the steps, the PLL Ref Osc is "pulled" via DAC U5 to fill in the gaps. For example, let's say you needed the VFO to tune up to 11.923 MHz from 11.920 MHz. The MC145170 divide-by-N is still at 2384. The required reference frequency is now (11.923/2384 =) 5.0013 kHz. This value multiplied by the divide-by-R value (2419) = 12.098 MHz. This is 3 kHz higher than the nominal value of 12.095. If you work out the math, you'll soon see that the necessary range that the reference oscillator must be pulled to cover 5 kHz at the output frequency is the ratio of the VFO frequency to the Ref Osc frequency. On 160 meters, the K2 VFO's lowest frequency (for 1.8 MHz) is about 6.7 MHz. SO to cover the necessary 5 kHz range, the 12.096 MHz Ref Osc must be able to be pulled at least (12.096/6.7)*5 = 9.03 kHz. This is the reason for the requirement for "at least 10 kHz" of reference frequency range. At the other extreme, for 17m or 10m, the VFO operates around 23 MHz. If the Ref Osc can be pulled 10 kHz at 12.096 MHz, then you will have (23/12.096)*10 = 19 kHz. So the lowest VFO frequency defines the need for the "pulling range" of the Ref Osc (10 kHz) and the highest frequency defines the need for the resolution of the DAC creating the pulling voltage. The frequency change per volt is not linear, but if we assume it is, and we have 12 kHz of pulling range at the Ref Osc (this is the case for my particular K2), then we have 22.8 KHz shift at 17m or 10m. A 12-bit DAC gives 4096 steps, or about 5.5 Hz/step. Due to the nonlinearity of the pulling system, this yields a practical resolution of about 10 Hz on 10m, and better resolution as the VFO frequency drops. This is explained in the theory section of your K2 manual, pages 105 and 106. Hopefully, the detail above may help you better understand the dynamics. Bottom line: you need 10 kHz of pull on the Ref Osc. If your K2 has crystals such that only one is needed to get this range, then you may get better temperature stability of your K2 by using only one crystal. In the case of my K2, I need both. Only one crystal limits me to about 6 kHz of pull, which is not enough for 160m and 80m - but is fine for 40m through 10m. Since I'm willing to live with the temperature drift, so there is no need for me to change the reference oscillator crystal(s). 73, Lyle KK7P +++++++++++++++ From: "Don Brown" To: "Lyle Johnson" , "Elecraft" Subject: Re: [Elecraft] K2 alignment after removing X2 (Logic Check?) Date: Sun, 3 Nov 2002 13:13:38 -0600 Hi Very good explanation. Maybe this will help people decide if they want to= do or not. I really see no downside to it if your crystal has the range. Don Brown KD5NDB ----- Original Message ----- From: Lyle Johnson Sent: Sunday, November 03, 2002 12:55 PM To: Elecraft Subject: RE: [Elecraft] K2 alignment after removing X2 (Logic Check?) Hello! I have gotten several private emails about all this. So, to be clear, I thought I should make one more post... The K2 uses a phase locked loop to generate the VFO frequency. -- snip -- ++++++++++++++++++ From: "Lyle Johnson" To: "Elecraft" Subject: RE: [Elecraft] K2 alignment after removing X2 (Logic Check?) Date: Sun, 3 Nov 2002 11:25:37 -0800 Hello Don! > ... I really see no downside to it if your crystal has the range. I agree. If either of my crystals had the range, I'd have done the mod! 73, Lyle KK7P +++++++++++++++++