20 October 2015

QST Review of KSYN3A synth in K3 has erroneous TX phase noise plot

Hi all,

although I am not re-posting the articles from the other sources to my blog over here in that case I am doing it as it is very important for many of Elecraft K3 users.

In order to better understaning the situation about the KSYN3A boards and parameters after the upgrade and for explaining the QST Review results there is the latest statement from Wayne, N6KR...

"Hi all,

You may have noticed that QST recently reviewed the K3's performance before/after swapping in a new KSYN3A synthesizer. While the review text was accurate (and complimentary), there was a significant error in the KSYN3A TX phase noise plot (Figure 10). This error made it appear as if the original synthesizer had lower (better) wide-spaced phase noise than the KSYN3A (starting where the plot lines cross), which is not the case.

We should have caught this ourselves before the article went to print. We greatly appreciated the League's efforts to determine the source of error -- equipment setup -- and re-test. The digital-print version of QST will be corrected, and a correction will also appear in the December QST.

The ARRL sent us the revised TX phase noise plot for the K3+KSYN3A that they tested. You can see it here: 

In addition they're testing a K3S. Its TX phase noise plot looks as good or slightly better: 

These plots (used with permission) were for 20 meters, and are also representative of the other bands, including 6 meters. The bottom line is that the K3S, or a K3 with a KSYN3A, has extremely low phase noise at both close and narrow spacings. In the case of narrow spacings, the new synth also significantly improves the RMDR (reciprocal mixing dynamic range) over the original, as described in the article.

Note that the above plots show *transmit* phase noise. In receive mode, phase noise with the new synth is even lower, especially at close spacings (under 3 kHz from the carrier).

There's one other measurement in the QST review that needs a disclaimer. As you may know, the KSYN3A allows the K3 (or K3S) to be tuned down to as low as 100 kHz, thus including the 137 kHz band. The review showed an MDS of -44 dBm at this frequency, while in fact it is more like -115 dBm. It appears that the K3 under test didn't have the RF board modification required, or the modified KBPF3A filter module.


I hope it helps and it will clarify more the results and measurement done by labs reviewed in QST magazine.

73 - Petr, OK1RP

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