Specifications

37
Using the Sub Receiver
The KRX3 option adds an independent, high-
performance sub receiver tothe K3. Sub receiver
installation is covered in the KRX3 manual.
You can use the sub receiver to monitortwo
different frequencies or bands, using different
bandwidths or modes. Diversity receive is possible
if the main and sub receivers use different antennas.
Dedicated Sub Receiver Controls
SUB turns the sub receiver (and SUB icon) on.
Turn the subreceiver off when not needed.
This bypasses the main/sub antenna splitter,
improving main receiver sensitivity by 3 dB.
VFO B controls the sub’s frequency, and is also the
TX frequency during SPLIT (see details at right).
Holding SU B links the VFOs, allowing diversity
receive (details at right). VFO A is the master,
moving both VFOs in tandem. VFO B can be offset
from VFO A, or set equal to it by tapping A B .
SUB AF gain sets the sub’s volume level. With
stereo headphones or dual speakers, you'll hear the
sub on the right and main on the left. Otherwise
main and sub receiver audio are added together.
SUB RF gain normally sets the sub receiver’s
RF GAIN level. Ifthis knob is assigned to main/sub
squelch (CONFIG:SQ MAIN), then both main and
sub RF gain are controlled by MAIN.
BSET: Additional Sub Receiver Controls
Normally, receive controls such as SHIFT and
WIDTH, as well as the MOD E control, apply only
tothe main receiver (VFO A). To change sub
receiver settings (VFO B), hold BSET. VFO A will
show BSET, and the S-meter will show the sub
receiver's signal level. Tap AN T to select the
sub receiver’s antenna (details at right).
Some controls, including B AN D , PR E , ATTN ,
N B , and NR cannot be set independently for the
sub receiver unless CONFIG:VFO IND is set to
YES. If it’s set to NO, you’ll see =M AIN when
using these controls during BSET.
Tap A/B or hold B SET again to exit BSET.
Sub Receiver Antenna Selection
The sub receiver gets its RF input either from the
main receiver (sharing ANT 1-2 or RX ANT IN), or
from its auxiliary antenna input. (Also see pg. 40.)
During BSET, you cantap ANT to switch the sub
between M AIN (shared) and AUX (the sub’s AUX
input). When MAIN is in effect, the 1-2 and RX
icons show which antenna the sub is sharing with
the main receiver. When AUX is in effect, these
icons will all be off (if CONFIG:KRX3 is set for
AN T=BNC) or will show the non-transmit ATU
antenna, 1or 2 (if KRX3 is set for ANT=ATU).
The sub receiver’s AUX antenna must be well-
isolated from the main (transmit) antenna to avoid
activating the sub receiver’s carrier-operated relay.
Using the AUX input for the sub receiver
slightly improves sensitivity of both the main and
sub receivers because the splitter is not used.
Sub Receiver Band Independence
Using B SET, you can set the sub receiver to a
different bandfrom main (using B AN D ) if
CONFIG:VFO IND is set to YES.
If the two receivers are sharing an ATU
antenna, putting the sub receiver on a higher band
than the main receiver may result in signal loss in
the sub receiver due tothe shared low-passfilters.
To avoid this, use the sub receiver’s AUX input.
SPLIT Mode with the Sub Receiver
During split (SPLI T), VFO A is the receive
frequency and VFO B thetransmit frequency. If the
sub receiver is on, you can listen to both receive
and transmit frequencies, making DXing more
convenient. You can set up the sub receiver’s
filtering independently using B SET.
Diversity Receive
Diversity receive can improve signal copy during
fading (QSB). A separate antenna must be used for
the sub receiver (AUX; see above). You’ll also
need to link VFO B to VFO A by holding SU B .
For best results, use identical crystal filters and DSP
settings on thetwo receivers. (Elecraft can provide
5-pole crystal filters with matched offsets on
request. 8-pole filters are already matched.)