There's a "built in" 20 or 30 Hz error in the dial readout, Jean-François. It is not intentional; it is an engineering trade-off in the design to balance cost and performance.
The K2 sets the frequencies of the VFO and BFO by adjusting a voltage on tuning diodes. Changing the voltage changes the capacitance of the diode and therefore the frequency of the BFO or Local Oscillator/VFO. When you align the K2, these voltages are set to produce the correct frequencies. When doing the alignment, the frequency display is acting as a frequency counter. That's why you must place the test probe on the correct test point, so the display can measure and display the frequency. The accuracy of this display is controlled by the master 4.000 MHz clock oscillator. That's why it is important to have this oscillator set a closely as possible. Once you have the BFO or VFO set, the K2 then measures the frequency, converts it to a digital number and stores it in a digital memory. It does this using an "analog to digital converter" chip or DAC. When you are using the K2 in normal operation and, for example, tune in a specific frequency as shown on your frequency display, the K2 looks up the voltage levels the oscillators need to tune to that frequency in the digital memory. This number is then converted to a voltage by the DAC and supplied to the tuning diodes. The error occurs in the DACs. Greater accuracy in reading and reproducing the exact tuning voltage needed means that a bigger digital number must be stored in memory. Elecraft used a DAC that guarantees that your actual frequency within 20 or 30 Hz of the indicated value, provided the 4.000 MHz master clock in the display was calibrated very accurately when you did the alignment. (Note that changing the frequency of the 4.000 MHz clock has NO effect on the accuracy of the tuning once you've done the alignment and stored all the tuning values). That seems to be what you are seeing. A 20 or 30 Hz error is quite normal. Some ops have gotten their accuracy closer. That can happen when the value the DAC stores happens to be the exact value needed. It is a matter of luck. After calibrating your 4.000 MHz master clock, you can often run the PLL and BFO alignments repeatedly and sometimes find that you have no discernable error, but it's rare. Where most CW ops really try to get the settings as close as possible is in setting the BFO frequencies for the CW filters. With a little luck, you can often get the values so close there's no audible jump in the beat frequency as you switch from one filter to the next or from CWn to CWr. Ron AC7AC -----Original Message----- Hi, I follow carefully the new document regarding the calibration of the 4 Mhz oscillator, and I can find that after each completed tasks, I have always a few cycle different... Example: before doing the tuning procedure, 14.150.12 was correct instead of 14.150.00, so 120 Hz offset... I did the application note entirely, and after I should tune to 14.150.03 to have the correct frequency... I always have a 0.03 or 0.02 difference.... Is it a normal behavior ? Maybe I'm a little bit to clumsy about calibrating my K2 ;-) 73 =============================================== Jean-François Ménard / VA2VYZ Elecraft K2 #4130 [EMAIL PROTECTED] Club d'Astronomie Amateur de Sherbrooke Club Radio Amateur de l'Estrie Mon site web personnel : http://homepage.mac.com/jfmenard =============================================== _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
