[Elecraft] 4 Mhz oscillator

Sun Dec 29 11:09:08 2002

Hi

The 4.000 MHz oscillator only needs to be accurate while CAL PLL is actually
running. At any other time it is just the clock for the MPU. If you can get
it dead on then it only needs to stay accurate for about 5 minutes, so a
more accurate oscillator module would not buy you anything.

Don Brown
KD5NDB

----- Original Message -----
From: "Mike Rioux" <[email protected]>
To: "'Don Brown'" <[email protected]>; "'Mike McCoy'"
<[email protected]>; "'Helmut Usbeck'" <[email protected]>;
<[email protected]>
Sent: Sunday, December 29, 2002 10:01 AM
Subject: RE: [Elecraft] 4 Mhz oscillator

Would one of those 4Mhz 'oscillators in a can' be more accurate? You
know,
the ones a little bigger than an 8 pin DIP.  They have 4 pins, one
at each corner.  At least there would not be a cap to twiddle with.

73, Mike W1USN

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Don Brown
Sent: Sunday, December 29, 2002 3:40 PM
To: Mike McCoy; Helmut Usbeck; [email protected]
Subject: Re: [Elecraft] 4 Mhz oscillator

Hi

You cannot accurately measure the 4.000 MHz oscillator directly with a
frequency counter. Most counters have a 1 meg ohm paralleled with about
50
Pf on the input plus the added capacitance of the cable and you may have
more than 100 pf in capacitance. This loading will upset the frequency
of
the oscillator. If you use a X10 probe on the counter the probe
capacitance
is still around 10-12 pf more than enough to pull the oscillator off
frequency (remember C22 is at most 50 pf and paralleling 10 pf makes
quite a
change). The manual has you measure the 12 MHz reference oscillator with
the
internal and external counter and adjusting the internal to agree with
the
external. This will get you much closer but you are still depending on
the
accuracy of the external counter's timebase. The probe loading is why
the
manual has you connect both probes at the same time so the frequency
shift
is the same for both probes. This is why the method is more accurate
than
simply connecting the probe to C22

I prefer using spectrogram to align the 500 and 600 Hz audio tones
broadcasted by WWV so they line up with a 500 and 600 marker on the
spectrogram display. Then moving the indicated 12 MHz internal
oscillator by
the same amount with C22. Then re-run CAL PLL and recheck, after a
couple of
tries I can put The K2 dead on frequency. WWV is much more accurate than
any
counter, in fact all counters are calibrated to WWV so why not use the
most
accurate standard?

The beating of the 5th harmonic of the 4.000 MHz oscillator with WWV at
20
MHz is also a good method if you have another radio that will tune 20
MHz
and will put the K2 dead on frequency. I have tried both methods but I
like
the Spectrogram method best because you can do the CAL PLL and filter
alignment with the same setup.

Don Brown
KD5NDB

----- Original Message -----
From: "Mike McCoy" <[email protected]>
To: "Helmut Usbeck" <[email protected]>; <[email protected]>
Sent: Sunday, December 29, 2002 8:58 AM
Subject: Re: [Elecraft] 4 Mhz oscillator

> Yes... After an hour warmup I initially used a HP freq counter to set
the
> oscillator directly to *exactly* 4 Mhz (measuring right off left side
of
> C22) and after PLL found the display to be off. I then used the
recommended
> method of matching the display to the freq counter and it is still
off.
I'm
> 99.44% positive my freq counter is in calibration so I don't know what
the
> problem is.
>
> As soon as I can hear WWV on 20Mhz I'm going to try the zero beat
method.
>
> 73,
> Mike K5PU
>
> >
> > -Always noticed that my display reading of stations being received
> > seemed 50 Hz high.  I figured that the 4Mhz oscillator needed a
tweak.
> > I originally aligned it by the frequency counter technique described
in
> > the K2 manual, page 57.  Upon checking it I found it to be right on
and
> > hadn't changed since I originally did it. So just for kicks I
checked
the
> > 4 Mhz oscillator and found it sitting at 3.85 Mhz. That seems to
explain
I
> > think my high display reading.  Problem I see is if I used a counter
and
> > did it by the book, how come the low 4Mhz reading?  Anyone used a
counter
> > and have this problem?
>
>
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