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

[Frank O'Donnell]

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