I don't recall that discussion you're talking about, but I can say the K3(s) has
nowhere near that stability or resolution. (At least mine doesn't) I don't know
why Elecraft would design intentional instability into the radio.
During a recent thread about the TCXO option, I did some quick-n-dirty
measurements of my old K3 with standard reference and my newer K3S with the high
stability reference. I have a cable that I can run from the reference board to
a frequency counter (BG7TBL FA-2 w/Bodnar GPSDO reference). For this I have to
remove the top covers on the radios. I found the old radio to be inaccurate but
precise. I could touch the crystal oscillator and see the frequency move from
temperature effects but recover quickly. The TCXO was another story. It moved
around when I just laid a sheet of paper over the open box. I didn't quantify
this as I had to move on to other things; maybe later.
The frequency conversion scheme in these radios is proprietary but it entails a
lot of fussing around, with sideband switching, bandwidth adjusting, etc. All
of this AFAIK is done with DDSes which are not exact, they move in steps, albeit
little steps, but steps nonetheless.
If you want better you might look at the past results of the ARRL FMT (which
coincidentally was held last night) to read the soapbox comments of what other
folks are using.
http://fmt.arrl.org/fmtresults.php
Wes N7WS
On 4/24/2020 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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