[Elecraft] K3/K3S receiver and high-precision frequency determination?

Fri Apr 24 17:23:28 EDT 2020

With the TXO on the order of one every few minutes, without on the order 
two a minute or so.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 4/24/20 2:15 PM, donovanf at starpower.net wrote:
> Each of these frequency jumps causes phase discontinuity that is likely
> to cause bit errors in during PSK modulation and demodulation.
> 
> How often do they occur?
> 
> 73
> Frank
> W3LPL
> 
> ------------------------------------------------------------------------
> *From: *"Dave Cole" <dave at nk7z.net>
> *To: *elecraft at mailman.qth.net
> *Sent: *Friday, April 24, 2020 9:09:52 PM
> *Subject: *Re: [Elecraft] K3/K3S receiver and high-precision frequency 
> determination?
> 
> Thanks for the explanation, I have always wondered why...  I'm good with
> low phase noise, Low phase noise means less splatter from radios!
> 
> All the folks close to me have purchased K3s, so even though they are
> close, it is not too bad.  I had a friend that lived 700 feet from me,
> and had a Collins S-Line, including the KW...  It was horrid for being
> far too wide...  He switched to a K3, and for the most part things were
> far better.  Prior to the switch, I could not operate on the same band
> when he operated, after he switched to the K3, I could!
> 
> I took P3 screen shots of the change from old to new synthesizer, as I
> changed to the new one, and as he changed to the new one.  It is totally
> obvious how much better the new synthesizer is than the old...  See:
> 
> https://www.nk7z.net/k3/
> 
> for the screen shots.
> 
> 73, and thanks,
> Dave (NK7Z)
> https://www.nk7z.net
> ARRL Volunteer Examiner
> ARRL Technical Specialist
> ARRL Asst. Director, NW Division, Technical Resources
> 
> On 4/24/20 1:03 PM, Frank O'Donnell wrote:
>  > Dave,
>  >
>  > Thanks, that may have been the thread I was remembering.
>  >
>  > While searching old messages, I also came across a post from Ed Cole
>  > KL7UW from June 2018 in which he stated that, even if an external
>  > reference is connected, the K3 frequency "is established by the
>  > [internal] TCXO and the external reference merely performs a periodic
>  > check. ... the EXREF system does not phase-lock the TCXO.  It
>  > periodically corrects the error but the TCXO drifts normally between
>  > freg corrections ... . Now if you want to know why Elecraft chose
>  > periodic freq correction over true phase-locking, the answer is low LO
>  > phase noise.  Much harder to get low phase noise in a PLL than in a 
> TCXO."
>  >
>  > 73,
>  >
>  > Frank K6FOD
>  >
>  >
>  > On 4/24/20 12:37 PM, Dave Cole wrote:
>  >> Hi,
>  >>
>  >> That was me...  I used to use my Icom 756 Pro, to watch the Doppler on
>  >> changes in the ionosphere, and on Meteors.  The K3 uses steps to
>  >> correct frequency, while the Icom did not.  Analog vs. Digital
>  >> corrections.
>  >>
>  >> Accuracy is not an issue, it is the steps...  They destroy the
>  >> continuity of the tracking...  I should have some captures if you are
>  >> interested.  Email me off list and I'll send a set.
>  >>
>  >> The issue for me, I am looking for changes in frequency, on the order
>  >> of sub-1 hz., not looking to get an exact reading on the frequency,
>  >> just changes in frequency across minutes, not days or hours.
>  >>
>  >> I don't need to be dead on for frequency, but I do need to have a
>  >> straight line that is affected by Doppler, and path changes.  I can't
>  >> get that with my K3 without those annoying steps.
>  >>
>  >> Keep in mind we are talking worst case 6 or 10 Hz., and the steps
>  >> appear to be far, far, smaller than that...
>  >>
>  >> So...  I have given this aspect of the hobby up.  I did just get the
>  >> TXCO installed along with a lot of extras on my K3, and the steps are
>  >> longer, but still there...  I will get some older rig that is analog
>  >> in nature and return to that aspect of the hobby then...
>  >>
>  >> I was able to watch echos from aircraft between Eugene, and Portland
>  >> Oregon, (about 100 miles apart), using the KGW TV, (Ch. 2), aural
>  >> carrier as a source.  I got the coolest traces of Doppler shifts
>  >> caused by the aircraft movement.  Meteors were far more
>  >> interesting...  Anyway, it is not an issue of Frequency accuracy, bit
>  >> one of how the rig makes adjustments.  I would love to just turn off
>  >> the steps, and accept the drift over longer times.  Oh well...  Hope
>  >> that helps...  It is NOT the K3 having an issue with measuring
>  >> frequency...
>  >>
>  >> 73, and thanks,
>  >> Dave (NK7Z)
>  >>
>  >> On 4/24/20 10:11 AM, Frank O'Donnell wrote:
>  >>> Sometime (probably last year) I remember seeing a discussion of why
>  >>> the K3/K3S receiver isn't suitable to do high-precision frequency
>  >>> measurement tests at the level of hundredths of a Hertz. As I vaguely
>  >>> recall, the receiver is designed so that its frequency actually
>  >>> varies a bit intentionally, and I remember someone posting a plot
>  >>> demonstrating this. However, I'm striking out on finding any of those
>  >>> posts. Can anyone either help with them, or point to any other
>  >>> discussion/explanation on this?
>  >>>
>  >>> Thanks much,
>  >>>
>  >>> Frank K6FOD
>  >
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