REF 0.0 dBm MKR 14.16 MHzDL −30.0 dBm
10 dB/
0dB
−8.73dBm*A_Write Norm B_Blank Norm
START 0 Hz STOP 30.00 MHz
RBW 300 kHz VBW 300 kHz SWP 200ms ATT 10 dB
MARKER
1 4 . 16 MHz
Premium components yield
premium performance
The IC-7851 continues the +40dBm, 3rd order
intercept point and 110dB receiver dynamic
range benchmark set by the IC-7800. To
achieve this superb receiver performance, the
entire analog circuitry and components have
been re-engineered to match the DSP units. A
newly designed LO amplifier generates high
output while keeping flat frequency characteris-
tics over a 60MHz wide range.
BPF unit
Triple DSP Power
Digi-Sel Preselector
The IC-7851 incorporates high-grade,
long-term reliable mechanical relays rather
than PIN diodes for switching the Band Pass
Filters (BPF). This deployment of relays re-
moves secondary
distortion products
from the primary
stage of signal
processing.
1. 2 k H z
Optimum Roofing Filter
3, 6, 15kHz
High-Spec 1st IF filters
Automatic Preselector
High Performance OCXO Unit
The IC-7851 uses the
OCXO (Oven Control
Crystal Oscillator) unit
which is stable to
within ±0.05ppm at
0°C to 50°C. This
specification means
that even on the 50MHz band, frequency error
is less than 2.5Hz! In addition, a 10MHz refer-
ence frequency can be input and output for
accurate tuning.
OCXO unit
PA unit and heat sink
The push-pull power
amplifiers using
power MOS-FETs
work on 48V DC.
They provide a pow-
erful 200W output
power at full duty
cycle and low transmit intermodulation. An
effective cooling system maintains internal
temperatures within a safe range and
prevents thermal runaway.
200W Output Power
at Full Duty Cycle
Solid Aluminum Main Dial Knob
Basic Functions
The main dial tuning
knob is pure functional
beauty. Machined
from a solid aluminum
block, the main dial
tuning knob gives you
a solid operational feel. The diamond engraved
accents are cosmetic perfection – expected
only from a radio of this caliber.
Dynamic Range (dB)
Spacing
Roofing
Filter
Bandwidth
IC-7851
1kHz
100
99
15kHz
1. 2 k H z
2kHz
101
105
5kHz
104
111
20 kHz
114
113
Dynamic Range Characteristics
Three separate 24-bit AD/DA converters and
dedicated DSP processors are at the heart of the
IC-7851. With one AD/DA and DSP dedicated to
the spectrum scope and two 24-bit AD/DA and
DSP chips for the receivers and transmit circuits,
there is plenty of DSP power for the most
demanding RF environment.
The IC-7851 has multiple AGC loops. The AGC voltages detected in front of and behind the digital IF filter
in the DSP unit. The first AGC loop prevents saturation of the 1st IF amplifier. The other AGC loop detects
the AGC voltage at the digital IF filter output which has only passed the intended signal and draws the full
potential from the digital IF filter.
Combining the digital IF filter,
manual notch, and the 1st IF stage,
these are all controlled by the DSP
unit. 110dB of ultra wide dynamic
range in the receiver means the IF
amplifier is distortion free from
strong signals.
Dual AGC Loops
Simple receiver system configuration is the
best way to eliminate sources of the spurious
signals and distortion from transceivers. The
IC-7851 uses a double conversion system com-
posed of a D-MOS FET 1st mixer and image
rejection mixer for the 2nd stage. The 1st mixer
stage is driven with a signal from the high-drive
Local Oscillator with excellent C/N. The image
rejection mixer for the 2nd stage reduces signal
distortion through IF processing and provides a
high-fidelity signal to the DSP unit. This system
provides wide dynamic range, reducing the dis-
tortion from strong signals and lower intermodu-
lation.
Image Rejection Mixer
BPF
AGC Loop line
A/D
D/A
AGC
DET
AGC
DET
AGC
DET
AGC
DET
2nd Mixer (Image Rejection Mixer) Receiver DSP Unit
AMP
AMP
IF
AMP
IF
AMP
IF
AMP
IF
AMP
IF
AMP
IF
AMP
90 degrees
Phase shifter
90 degrees
Phase shifter
Transmit/
Receiver DSP (left) and
Receiver DSP (right)
ADSP-21489
by Analog Devices
32-bit floating point DSP
2400 MFLOPS
393 MHz clock speed
The preselector
works between
1.5MHz and 30MHz
and rejects distortion
components derived
from out of band
interference such
as multi-multi operation or strong broadcast sta-
tions. It automatically tracks the intended signal
keeping the preselector’s bandwidth centered on
the operating frequency. The center frequency of
the preselector is manually adjustable from the
DIGI-SEL tuning knob on the front panel.
Intercept Point
+40dBm IP3
Dynamic range 110dB
Antenna Terminal input
Receiver output
Noise Floor
level
+40dBm IP3
(3rd Order Intercept Point)
BPF Switching:
Mechanical Relays
Three high-spec 1st IF “Roofing” filters plus
the new 1.2kHz Optimum Roofing Filter
allow only signals within the filter passband
to the 1st IF amplifier stage. You can select
the filter width from 15kHz, 6kHz, 3kHz and
1.2kHz, depending on your operating mode.
(FM mode is fixed at 15kHz)
Four 1st IF “Roofing” Filters
Dynamic Range (typical)
Automatic Preselector bandwidth characteristics
At 14 MHz band
4
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