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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