7-5
7
FUNCTIONS FOR RECEIVE
■
Twin PBT operation
In general, the PBT (Passband Tuning) electronically
narrows the IF passband width by shifting the IF fre-
quency to slightly outside of the IF filter passband, to
reject interference. The IC-7850 uses DSP for the PBT
function.
You can watch the nearby intended signal using the
spectrum scope.
Rotate [PBT1] (inner control) and [PBT2] (outer
q
control) to the opposite direction from each other to
narrow the IF passband width.
• Before rotating, the PBT settings of [PBT1] and [PBT2]
should be cleared.
• Rejects interference of both higher and lower pass
-
bands. If you rotate the control too much, the received
audio may not be heard because the passband width is
too narrow.
• Displays the passband width and shift frequency.
• The [PBT CLEAR] indicator lights.
• Hold down [PBT CLEAR] for 1 second to clear the PBT
setting. In that case, the [PBT CLEAR] indicator goes
OFF.
•
The variable range depends on the passband width and
the operating mode. The edge of the variable range is half
of the passband width. The PBT is adjustable in 25 Hz
steps in the SSB/CW/RTTY/PSK modes, and 100 Hz in
the AM mode.
• Moving both [TWIN PBT] controls to the same position
shifts the IF left or right.
Hold down [FILTER] for 1 second.
w
• The Filter screen is displayed. The current passband
width and shift frequency are displayed.
Push [EXIT/SET].
e
• Exits the Filter screen.
NOTE:
While rotating the [TWIN PBT] controls,
noise may be heard. This comes from the DSP unit
and does not indicate an equipment malfunction.
[EXIT/SET]
[PBT CLEAR]
[TWIN PBT] control
[FILTER]
[PBT CLEAR] indicator
• Filter screen when operating [TWIN PBT]
• About Passband width and Shift value on the
screen
PBT1
PBT2
IF center frequency
Passband’s center frequency
SFT: Shift value
BW: Passband width
• When operating [TWIN PBT]
Filter width Shifting value
Passband width
(Duplicated with PBT1 and PBT2)
Selected
IF filter
Passband
Passband
IF center frequency
Desired signal
Interference
Interference
Interference
Desired signal
PBT2
PBT1
PBT2
PBT1
PBT2
PBT1
PBT is OFF
Cutting a lower
passband
Cutting both higher and
lower passbands
• PBT operation example
