ELECRAFT KRX3 - Diversity Receive; Sub Receiver Crystal Filter Considerations; SPLIT Mode with the Sub Receiver

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receiver. To avoid sub receiver signal loss in this
case, use the AUX input.
When the main and sub receivers are used on
separate bands, some additional weak spurious
carriers may be heard in either receiver at certain
VFO A and B settings. (Both receivers have high
dynamic range, and use high-level signal sources
which cannot be perfectly shielded.) Such spurious
signals should be heard very rarely. If you
encounter one that is problematic, try using the
notch filter on the affected receiver."
Diversity Receive
Diversity receive can greatly improve signal copy
during fading (QSB). True diversity requires a pair
of identical receivers running from a common
frequency reference and using two different
antennas. The K3 is one of very few transceivers
that offer this capability. Most offer only a low-
performance sub receiver, or “dual watch” (split-
I.F.) circuitry, which doesn’t provide for separate
main/sub antennas.
An antenna with different polarization, or at least
different orientation, should be used for the sub
receiver (via its AUX input). This ensures that the
two receivers will not experience the same fading
characteristics.
To turn on diversity mode: Hold SUB to set the
sub receiver to the same frequency as main (VFO
A), match the sub receiver filter bandwidth to main,
and switch the sub receiver to its AUX antenna. The
kHz decimal point of the VFO A display flashes as
a reminder. VFO A sets the receive frequency for
both main and sub in diversity mode. This leaves
VFO B free for use as the transmit frequency in
SPLIT mode (see details at right).
Mode and filtering changes made to the main
receiver will immediately be made at the sub, as
well, to preserve diversity characteristics. However,
PRE, ATTN and other receive controls remain
independent for the sub. These must be changed
using BSET.
You can change the sub receiver antenna selection
by holding BSET, then tapping ANT. When you’re
not using BSET, holding RX ANT will accomplish
the same thing, providing a convenient shortcut.
The K3 saves the sub receiver MAIN/AUX
selection independently for diversity and non-
diversity. AUX should be used for diversity, as
explained above. You might use MAIN with
diversity when comparing main/sub receiver gain,
such as when adjusting crystal filter gain
compensation (
CONFIG:FLx GN). The built-in true-
RMS voltmeter is ideal for this purpose. Entering
diversity mode will allow you to tune both receivers
with VFO A, while VFO B displays the voltage (see
your K3 Owner’s Manual, VFO B Alternate
Displays).
Sub Receiver Crystal Filter Considerations
Like the main receiver, the sub has slots for up to
five crystal filters. For best dynamic range, we
strongly recommend the use of the narrowest filter
consistent with each operating mode. CW and
DATA operators should have at least one narrow
filter, e.g. 400 or 500 Hz, on each receiver.
For diversity receive, we recommend using
identical crystal filter configurations for the two
receivers. This will ensure that both receivers have
the same characteristics when strong QRM is
present.
You should also use crystal filters with closely
matched offsets (
CONFIG:FLx FRQ). Otherwise,
you may hear a slow phase modulation (similar to a
beat note) between the two receivers on some
signals. 8-pole filters are already matched (
FLx
FRQ = 0.00
). Elecraft can provide pairs of 5-pole
crystal filters with offsets within 40 Hz of each
other on request. When setting up
FLx FRQ, use the
average of the filters’ marked offsets as the value
entered for both filters (main and sub). If you enter
different offsets, you’ll hear phase modulation, even
if the offsets are very close.
SPLIT Mode with the Sub Receiver
During split (SPLIT), VFO A is always the receive
frequency and VFO B is the transmit frequency.
Holding REV allows you to temporarily listen to
your transmit frequency.
Non-Diversity with SPLIT: If the sub receiver is
on, but you’re not in diversity mode, you can listen
to both your receive and transmit frequencies at the
same time during SPLIT. You can set up the sub
receiver mode and filtering independently using
BSET in this case. Cross-mode SPLIT is possible
in supported modes, e.g. CW/SSB.
Diversity with SPLIT: In diversity mode you can
still use SPLIT, but both receivers will be set to the
frequency of VFO A. Both receivers will always be
in the same mode, and will use the same filter
settings.