Elecraft K3 Owner's Manual - Manual (Page 38)

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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 S U B for 2
seconds or longer. This sets the sub to the same
frequency as main (VFO A), matches the sub’s
filter bandwidth to main, and switches 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,
P R E , A T T N and other receive controls remain
independent for the sub. These must be changed
using
B S E T .
You can change the sub receiver’s antenna selection
by holding
B S E T , then tapping A N T . When you’re
not using BSET, holding R X A N T will accomplish
the same thing, providing a convenient shortcut.
The K3 saves the sub’s 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
AFV/dBV, pg. 36).
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
With the sub receiver installed, in a sense all
operation is “split,” since you listen on the sub’s
frequency (VFO B) and listen/transmit on the main
RX/TX frequency (VFO A). Cross-mode and even
cross-band operation is possible in this case. Cross-
band operation may require the use of the sub’s
AUX antenna source to avoid the low-pass filter
problem described on the previous page.
If you do turn on
S P L IT , the VFO’s roles are
reversed, with VFO B controlling the transmit
frequency, and VFO A used only for receive. The
advantage of this is that the receive controls are
always “visible” for VFO A, while receive controls
for VFO B must be accessed using
B S E T .
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.