Elecraft KRX3 - Manual (Page 26)

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Auxiliary KRX3 Antenna Input (Optional)
Normally, the KRX3 subreceiver will share whatever antenna is in use by the K3 main receiver.
If you plan to use the KRX3 subreceiver to listen on one band while the main K3 receiver is on another band
sharing the same antenna, there are limitations on the combinations of bands you can choose because of the
effect of the bandpass filters used by the main K3 receiver. See Sub Receiver Antenna Selection on page 46 for
details.
The KRX3 has an Auxiliary Antenna input that you can use to have a separate antenna input to the KRX3 rather
than share the common main receiver antenna. There are two ways to route a separate antenna input to the
KRX3.
1. You may bring out the KRX3 Auxiliary Antenna input to a BNC connector on the K3 rear panel directly
below the ANT2 connector. This is the preferred way to connect an isolated receive-only antenna to the
sub receiver.
2. If you have the optional KAT3 installed, you may have the KRX3 subreceiver use the antenna
connected to ANT1 or ANT2 that is not being used by the K3 transmitter and main receiver. A relay in
the KAT3 switches the antenna. For example, if ANT1 is selected for the K3 transmitter and main
receiver, the KRX3 Auxiliary Antenna input will be connected to ANT2. This arrangement requires
well isolated antennas on all bands, otherwise the carrier-operated relay may switch during keying on
some bands. This will compromise QSK operation and may inject noise into your transmitted signal.
See Sub Receiver Antenna Selection on page 46for more information.
Only one of these options can be installed at a time. You can use the front panel menu controls to select either
the antenna shared with the main receiver or the optional antenna input you have installed.
If you do not want to install an optional auxiliary antenna input, go directly to Assembling the KRX3 Subreceiver
Module on page 31 to continue with installing your KRX3.
Installing the Auxiliary KRX3 Antenna Input via the KAT3
This option requires that you have a KAT3 Automatic Antenna Tuner installed.
With this option, the antenna connected to ANT1 or ANT2 that is not being used by the K3 transmitter and
receiver is connected to the KRX3 auxiliary antenna input. If you switch between ANT1 and ANT2 at the front
panel, the input not used by the K3 transmitter and main receiver is automatically switched to the KRX3
auxiliary antenna input.
Locate the 12” (30 cm) TMP cable.
Connect one end of the TMP cable to J43 on the KAT3 board (see Figure 29). J43 is next to the mounting
screw for the standoff in the corner of the board.