N7RR:
>he praises the optional u-Tune units, which "are hi-Q motorized
preselector circuits designed to enhance weak signal operating." (p.70)
He states "As shown in Table 1, use of the u-Tune units
makes a noticeable improvement in third order intercept in many
cases." For direct comparison, I converted ARRL's results with
u-Tune to IMD (for which we have data with K3):
dB IMDDR3, 2 kHz spacing, 500 Hz filter
2000 K3
71 (69) 94
(69 for stock...71 for u-Tune
u-Tune only makes 2 dB difference in IMD...not "noticeable" in my
book. To achieve this on 160-30, you'll buy 3 u-Tune units at ~$500
each (if my memory is correct).
>I'm wondering whether the optional KAT3, as an impedance-matching
device, will serve in practice as a practical substitute for a high-Q
preselector. If not, perhaps a similar auto-tracking external
preselector might be a popular K3 accessory.
To be perfectly candid, the 2000 has *terrible* performance
for both IMD and BDR at close spacings in the presence of strong
signals. Perhaps Yaesu recognized this and added u-Tune in an
attempt to improve things, but the bottom line is that it remains
terrible. IMD: ~70 dB versus ~95 for the K3. BDR: ~87 dB (with or
without u-Tune) versus ~140 for the K3. (Both at 2 kHz spacings
although Elecraft has not published final BDR results).
Bottom line, the K3 simply does not need a pre-selector to
achieve outstanding performance...and the 2000 is still terrible even
with ~$1500 worth of pre-selectors.
73, Bill W4ZV
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