On Thu, 25 Nov 2004 20:03:33 -0800, Ron D'Eau Claire wrote: > That's not the case for the 4 MHz oscillator in the K2, Jean-François. > First of all, the 4 MHz clock on the control board and the trimmer capacitor > C22 have nothing directly to do with the PLL. That's why adjusting C22 > doesn't change your frequency. But what you read in the handbook is right. > Let's look at that first. > It is true that a PLL requires a reference oscillator, and the output > frequency is based on the reference oscillator frequency. One problem with > PLL's is phase noise - jitter in the frequency caused by the loop constantly > correcting the output frequency to agree with the reference oscillator. > Elecraft provides superb phase performance by doing something unusual. They > vary the frequency of the reference oscillator. The K2's reference > oscillator is varied over a 5 kHz range. The Phase-Locked Loop tunes in 5 > kHz "steps" and the reference oscillator is tuned to provide continuous > coverage within those 5 kHz steps. If you look in the archives (or have an > older K2) you'll see that a year or so ago some effort was put into adding a > temperature compensation circuit to the PLL reference oscillator in the K2. > That was because of a basic rule in radio: If the frequency of an oscillator > can be varied, it will try to drift! The K2's reference oscillator sometimes > showed annoying levels of drift, and the circuit was improved to stop that. > Let's get back to that 4 MHz oscillator on the control board. The K2 does > something else a little differently from many radios. The frequency readout > you see on the LCD display is *not* produced by constantly monitoring the > oscillator frequency in the K2. Instead, the K2 frequency readout is a lot > like the old vacuum-tube-day dials, in which you turned a knob, that knob > varied the frequency of an oscillator, and it also moved a pointer. The > pointer moved over a scale with numbers on it that showed the frequency. The > numbers on the scale were produced by hooking up a frequency counter to the > rig and checking the frequency produced as the tuning knob was turned. The > correct numbers were then printed on the scale behind the pointer so it > could be set back to any desired frequency later. Not every frequency was > recorded - just frequencies at regular intervals. Frequencies in between the > numbers could be estimated by "interpolation". That is the frequency exactly > halfway between 7000 kHz and 7010 kHz could be assumed to be 7005 kHz, and > so on. > That's how the K2 works, but its all done electronically. First of all, > there are no variable capacitors or other old-style tuning mechanisms used > in the K2. The oscillators - the beat frequency oscillator or BFO, and the > phase locked loop reference oscillator (called the variable frequency > oscillator or VFO in the K2 literature) are both tuned with voltages. > Voltage-variable capacitors replace the old big mechanical variable > capacitors. The voltage-variable capacitors change capacitance and therefore > the oscillator's frequency in response to the level of a direct-current > voltage applied to them. > When you run CAL PLL, a frequency counter built into the K2 measures the PLL > frequency. The K2 applies a tuning voltage to the PLL reference oscillator > and notes the frequency measured by the counter. This information is > recorded in memory so it can be looked up later. The K2 tunes through the > whole range of frequencies the PLL can cover noting the actual frequency > measured at regular intervals, and then recording the voltage applied to the > reference that will produce the frequency. > After CAL PLL is done, all of that data has been stored. > Now, in normal operation, you choose a band and spin the frequency dial to a > specific number on your LCD display. When you do that, the K2 looks up the > proper voltage from the data that was stored when your ran CAL PLL and > applies it to the PLL reference oscillator. That will put the reference > oscillator on the correct frequency, according to the data that is in > memory. Of course this happens very quickly so it appears that the tuning is > happening in direct response to your turning the knob. > Notice that the accuracy of the readout depends upon how accurately the > frequencies and tuning voltages were stored when you ran CAL PLL. That's > where the 4 MHz clock and C22 come in. The Control Board 4 MHz clock is the > time base for the frequency counter! So the closer it is to 4 MHz the more > accurately the K2 will measure the K2 PLL frequency and the more accurately > the dial calibration of the K2 will be in use. > That's why the procedures for setting C22 all remind you to re-run CAL PLL > (and CAL FIL) after adjusting it, in order to make the K2 store new > frequency and tuning voltage data in memory. After you do that you will > notice the change in the dial calibration. > Wayne published an excellent method for setting C22 on the Elecraft web site > (www.elecraft.com). Look under Builder's resources for "Adjusting C22 to > calibrate the K2's Frequency Display". > Ron AC7AC
>> What an excellent explanation, well done.... 73 Stewart G3RXQ > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Jean-François Ménard > Sent: Thursday, November 25, 2004 5:56 PM > Cc: Elecraft - Maling List > Subject: Re: [Elecraft] VCO relationship with 4 Mhz ocsillator > > Sorry to bother you.... > I read in my ARRL handbook about PLL... and now I understand that the > PLL must have a fixed, precised, reference to phase lock it's loop.... > the 4 Mhz oscillator clock... > I will find the place to put my scope probe to see the 4 Mhz oscillator > also... just for my understanding. > Thanks and sorry again for your time. > Le 04-11-25, à 19:49, Jean-François Ménard a écrit : >> Could someone tell me the short story about the relationship between >> the PLL reference oscillator and the 4 Mhz oscillator from the control >> board ??? >> I'm asking this question because when I calibrate the PLL reference >> oscillator at TP3 using the internal frequency counter of the K2 and >> also using my external Instek frequency counter also connected at TP3, >> trying to match the K2 PLL frequency on both display.... Well.... I'm >> turning C22 on control board, associated to the 4 Mhz oscillator.... >> and that make the PLL oscillator to change.... Why ?!?!? >> I can see the on the control board that the MCU have an output /PLLCS >> that go to the PLL synthetizer.... that must be there, but why ? >> This setup seems to be particular to the K2 concept ?!?!? Right, wrong >> !?!? >> Thanks for your time... >> >> Sincerly, >> =========================== >> Jean-François Ménard / VA2VYZ >> [EMAIL PROTECTED] >> Elecraft K2 #4130 >> http://homepage.mac.com/jfmenard >> =========================== >> _______________________________________________ >> Elecraft mailing list >> Post to: [email protected] >> 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 > =========================== > Jean-François Ménard / VA2VYZ > [EMAIL PROTECTED] > Elecraft K2 #4130 > http://homepage.mac.com/jfmenard > =========================== > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > 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 > > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > 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 _______________________________________________ Elecraft mailing list Post to: [email protected] 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
