Elecraft KRX3 User Manual download pdf (Page 47)

receiver signal loss in this case, use the sub

receiver’s 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 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,

PRE, ATTN and other receive controls remain

independent for the sub. These must be changed

using BSET.

You can change the sub receiver’s 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’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

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’s 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.

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Elecraft KRX3 User Manual Page 47

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