[Elecraft] KX3 VFO tuning noise reduced or eliminated

[Wayne Burdick]

Some KX3 owners hear a pulsing or clicking noise when tuning the VFO on higher bands, especially when atmospheric noise is low. We discovered that the KXFL3 filter module is responsible for nearly all this noise, and that it can be reduced or eliminated with a simple modification to the module. This modification, which does not require any desoldering, is described in a document on our website:

    http://www.elecraft.com/manual/KX3%20Tuning%20Noise%20Reduction%20Mod.pdf

Factory assembled KX3s from serial number 4668 up, and kits from serial number 4753 up that include the KXFL3 option have been shipped with the updated board. (Note: The modification performed at the factory is slightly different from the one described in the document, but the resulting decrease in noise is the same.) Any KXFL3s purchased after July 4th for field installation will also include the modification.

You can tell if your KXFL3 board has been factory modified by opening the KX3 case, as if to change batteries. Inspect the KXFL3 module. If pins 11 and 12 are removed from the board, the KXFL3 has been modified. If not, you can easily perform the modification yourself using the instruction sheet.

In rare cases, such as when an extremely low-noise antenna is in use, you may still hear some very weak tuning noise even with a modified KXFL3 or with no KXFL3 module installed. In such cases we recommend trying the following firmware-based approaches to reducing the noise:  (1) set MENU:VFO NR to ON; (2) turn on the noise blanker and set it to a low level; (3) set MENU:RX SHFT to 8.0 instead of NOR. These settings are all saved per-band, so you only need to use them on affected bands.

73,
Wayne
N6KR