background image

REF 0.0 dBm

MKR 14.16 MHz

DL −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 . 1 6 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

T h e   I C - 7 8 5 1   i n c o r p o r a t e s   h i g h - g r a d e ,  
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 
s t a g e   o f   s i g n a l  
processing.

1.2kHz
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 
w h i c h   i s   s t a b l e   t o  
within ±0.05ppm at 
0 ° C   t o   5 0 ° C .  T h i s  
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 
a m p l i f i e r s   u s i n g  
p o w e r   M O S - F E T s  
w o r k   o n   4 8 V   D C .  
They provide a pow-
e r f u l   2 0 0 W   o u t p u t  
p o w e r   a t   f u l l   d u t y  
cycle and low transmit intermodulation. An 
effective cooling system maintains internal 
t e m p e r a t u r e s   w i t h i n   a   s a f e   r a n g e   a n d  
prevents thermal runaway.

200W Output Power 
at Full Duty Cycle

Solid Aluminum Main Dial Knob

B a s i c   F u n c t i o n s

The main dial tuning 
knob is pure functional 
b e a u t y .   M a c h i n e d  
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

1.2kHz

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. 
Co m b i n i n g   t h e   d i g i ta l   I F   fi l te r,  
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 distor tion 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

AGC

DET

AGC

DET

2nd Mixer (Image Rejection Mixer)

Receiver DSP Unit

AMP

AMP

AMP

IF

AMP

IF

AMP

IF

AMP

IF

AMP

IF

AMP

IF

AMP

IF

AMP

IF

AMP

IF

AMP

90 degrees

Phase shifter

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

T h e   p r e s e l e c t o r  
w o r k s   b e t w e e n  
1.5MHz and 30MHz 
and rejects distortion 
components derived 
f r o m   o u t   o f   b a n d  
i n t e r f e r e n c e   s u c h  
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

R

e

ceiv

er

 output

Noise Floor 
level

+40dBm IP3 
(3rd Order Intercept Point) 

BPF Switching: 
Mechanical Relays 

Three high-spec 1st IF “Roofing” filters plus 
t h e   n e w   1 . 2 k H z   O p t i m u m   R o o f i n g   F i l t e r  
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

Summary of Contents for IC-7851

Page 1: ...THE TRANSCEIVER...

Page 2: ...the design of the IC 7851 Icom s engineers focused on a new Local Oscillator LO that drastically reduces the phase noise As a result of this design the purity of the LO achieves a Reciprocal Mixing D...

Page 3: ...ssive 20dB improvement is seen with the IC 7851 s 10 kHz measure ment and more than 30dB improvement at a 1 kHz measurement in com parison to the IC 7800 Phase Noise Characteristics Comparisons Receiv...

Page 4: ...r filtering by watching filtering adjustments take out interfering signals including filter width and notch filter placement The processing power in the IC 7851 allows for dual mini band scopes as wel...

Page 5: ...851 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 dete...

Page 6: ...eble The receive audio can be tailored with mode specific Bass Treble or audio passband settings Digital Twin PBT Passband Tuning Once the IF filters have been tweaked the op erator has additional con...

Page 7: ...synthesizer announces the operat ing frequency mode and S meter level Programmed scan memory scan select memory scan VSC scan and f scan Auto tuning step function Dial lock function Main dial tension...

Page 8: ...V 2 V 0 5 V 28 29 9MHz 50 54MHz 0 13 V 1 V 0 32 V SM 50 DESKTOP MICROPHONE IC PW1 IC PW1EURO HF 50MHz 1kW LINEAR AMPLIFIER SP 34 EXTERNAL SPEAKER Automatic antenna tuner and compact detach able contr...

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