ICOM IC-7851



Solid Design Basics and HF Expertise Raising the Bar

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Solid Design Basics and HF Expertise Raising the Bar

Competitive Advantage: Reciprocal Mixing Dynamic Range

RMDR: 110dB Raising the Bar

Design advances developed by the Icom HF engineers for the Local Oscillator (LO) enable the IC-7851 to set a new benchmark for amateur radio receivers. The goal was to dramatically reduce the phase noise that degrades the target signal due to the sum of the entire signal present. The result was a RMDR of 110dB*. Below is a comparison of the improvement over the IC-7800.

*At a 1kHz offset frequency
Receiving frequency: 14.2 MHz Mode: CW, IF BW: 500 Hz
Roofing Filter IC-7800 = 3 kHz, IC-7851 = 1.2 kHz

RMDR Comparison

RMDR (Reciprocal Mixing Dynamic Range) is the relative level of an undesired signal, offset “n” kHz from the RX passband, which will raise noise floor by 3 dB. The local oscillator phase noise will mix with strong unwanted signals and unavoidably generate noise which masks a wanted signal.

1.2kHz Optimum Roofing Filter

Optimum Roofing Filter

Despite the trend to switch to a down conversion or a hybrid conversion receive design, Icom bel ieves in the sol id per formance of the up-conversion design. In an up-conversion receiver, suppression of image interference and reduce distortion from electric components is easily overcome. A flat consistent performance is delivered over a wider frequency range.
The IC-7851 introduces a new 1.2kHz Optimum Roofing Filter, greatly improving the in-band adjacent signal performance. This newly developed filter overcomes the gap of a narrower roofing filter in an up-conversion receiver.

Optimum Roofing Filter Characteristic Diagram

Crystal Clear LO (Local Oscillator) Design

Breaking the boundaries of traditional designs, the IC-7851 employs a Direct Digital Synthesizer (DDS) along with a Phase Locked Oscillator for the LO. The C/N ratio excels beyond the IC-7800 and other similar class HF transceivers. This design significantly reduces noise components in both receive and transmit signals.

LO C/N Characteristics Comparisons

Receiving Frequency: 14.2 MHz Mode: CW 1st LO frequency: 78.655 MHz
SPAN = 20 kHz, RBW = 30 Hz, VBW = 10 Hz

Improved Phase Noise Characteristics

Phase noise is coherent in radio circuit design and the new LO design introduced
in the IC-7851 makes some major breakthroughs while utilizing the 64MHz, up-conversion receiver design introduced in the IC-7800.
An impressive 20dB improvement is seen with the IC-7851’s 10 kHz measurement
and more than 30dB improvement at a 1 kHz measurement in comparison to the IC-7800.

Phase Noise Characteristics Comparisons

Receiving Frequency: 14.2 MHz Mode: CW 1st LO frequency: 78.655 MHz

Twice the Speed, Sensitivity, Resolution and More Control

Improved Spectrum Scope

Following the design linage of the IC-7800, the IC-7851 uses a dedicated DSP unit for the Fast Fourier Transform (FFT) spectrum. The 2250 MFLOPS DSP processor enables a new dual scope function and significantly faster sweep speeds and better accuracy than in the IC-7800.

Scope Comparison

Audio Scope Function

The audio scope simultaneously shows an oscilloscope and FFT for receive and transmit audio. Adjust your transmit audio by watching your compressor level, equalization and mic gain settings to give you the audio you want for SSB. The oscilloscope shows the CW waveform. On receive, you can see the power of your 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 well as the audio scope.

Specifications for the audio scope

• Attenuator: 0 dB, –10 dB, –20 dB and –30 dB
• FFT scope with waterfall and FFT scope without waterfall
• Waveform color and drawing (outline or fill) settings for the FFT scope

Specifications for the oscilloscope

• Level: 0dB, –10 dB, –20 dB and –30 dB
• Sample rate: 1ms/Div, 3ms/Div, 10ms/Div, 30ms/Div 100ms/Div and 300ms/Div, 5 Div width
• Waveform color setting

Dual Scope Function

While you can watch both receivers on the scope of the IC-7800, within the limits of the scope bandwidth, the IC-7851 introduces the new dual scope – the ability of watching both receivers in separate spectrum scopes. Scroll mode automatically keeps the operating signal within the scope range. The dual scope function is vital for watching for multipliers or band openings in contests, or working all bands/modes on a DXpedition.

High Resolution Spectrum Waterfall Display

Spectrum scope with waterfall
(wide screen setting)

The waterfall display captures signal strengths over time. This allows you to see signals that may not be apparent on a normal scope. Additionally, the combination of the scope attenuator and the wide screen mode gives you a better view of weaker signals as band conditions change. For the ultimate scope enhancement, the IC-7851 has a digital video interface (DVI-I) for a larger display.

Click Control

• Left click to change operating frequency
• Click a button (either left or right) and move right or left side on the screen to increase or decrease the operating frequency (similar to rotating the main dial)
• Right click to temporarily change the receive frequency. Release the mouse button to return.

By connecting a human interface device (such as a USB mouse, trackball or touchpad) to the USB port on the rear panel, you gain control over the spectrum display pointer for “Click-and-Listen” receiver control. Fix/Center mode, sweep speed and other settings are controllable.

Premium components yield premium performance

+40dBm IP3 (3rd Order Intercept Point)

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 characteristics over a 60MHz wide range.

Dynamic Range Characteristics

Dynamic Range (typical)

BPF Switching:Mechanical Relays

BPF unit

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 removes secondary distortion products from the primary stage of signal processing.

Four 1st IF “Roofing” filters

1.2kHz Optimum Roofing Filter
3, 6, 15kHz High-Spec 1st IF filters

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)

Digi-Sel Preselector

Automatic Preselector

The preselector works between 1.5MHz and 30MHz and rejects distortion componentsderived from out of band interference such as multi-multi operation or strong broadcast stations. 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.

Automatic Preselector bandwidth characteristics

Triple DSP Power

Transmit/Receiver DSP (left) and Receiver DSP (right)
ADSP-21489 by Analog Devices
32-bit floating point DSP
393 MHz clock speed

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.

Premium components yield premium performance

Dual AGC Loops

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

Image Rejection Mixer

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 composed 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 highdrive 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 distortion from strong signals and lower intermodulation.

High Performance OCXO Unit

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 reference frequency can be input and output for accurate tuning.

200W Output Power at Full Duty Cycle

PA unit and heat sink

The push-pull power a m p l i f i e rs u s i n g power MOS-FETs work on 48V DC.
They provide a powerful 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.

Solid Aluminum Main Dial Knob

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.

Videos for IC-7851 performance

Transmit and Receive


Frequency coverage*1
U.S.A. Version Europe Version
Receiver 0.030–60.000MHz*2 0.030–60.000MHz*2
Transmit 1.800–1.999MHz
*1 Varies according to version.
*2 Some frequency bands are not guaranteed.
Mode USB, LSB, CW, RTTY, PSK31/63, AM, FM
No. of memory channels 101 (99 regular, 2 scan edges)
Antenna connector SO-239×4 and BNC×2 (50Ω unbalanced (Tuner off))
Operating temp. range 0°C to +50°C; +32°F to +122°F
Frequency stability Less than ±0.05ppm (0°C to +50°C @ 54MHz, after warm up)
Frequency resolution 1Hz (minimum)
Power supply requirement 85–265V AC
Current drain TX: 800VA (Max. power)
RX: 130VA/120VA typ. (Max. audio/standby)
Dimensions (W×H×D,
projections not included)
425×149×435 mm; 16.73×5.87×17.13 in
Weight (approximate) 23.5 kg; 51.8 lb


Output power SSB/CW/FM/RTTY/PSK: 5–200W
AM: 5–50W
Transverter connector (CW): More than –20dBm
Modulation system SSB : Digital P.S.N. modulation
AM : Digital low power modulation
FM : Digital phase modulation
Spurious emissions HF bands: More than 60dB,
50MHz band: More than 70dB
Carrier suppression More than 63dB
Unwanted sideband
More than 70dB
⊿TX variable range
Microphone impedance
Microphone impedance 600Ω (8-pin connector)


Receive system Double conversion super-heterodyne system
Intermediate frequencies Main receiver: 64.455MHz/36kHz (1st/2nd)
Sub receiver: 64.555MHz/36kHz (1st/2nd)
Sensitivity (typical)
(HF: Pre-amp 1 ON, 50MHz: Pre-amp 2 ON)
SSB, CW, RTTY, PSK (BW=2.4kHz, at 10dB S/N)
50MHz~54MHz   :0.13μVAM (BW=6kHz, at 10dB S/N)
50MHz~54MHz   :1μVFM (BW=15kHz, at 12dB SINAD)
1.8MHz~29.990MHz:0.5μV (28–29.9MHz)
Sensitivity for RED (Less than)
Preamp ON
SSB, AM, FM: at 12 dB SINAD
(EURO Version)
SSB (2.4 kHz):
1.8–2.999 MHz 10 dBμV emf
3.0–29.999 MHz 0 dBμV emf
50 MHz band –6 dBμV emfAM (4 kHz, 60% modulation):
1.8–2.999 MHz 16 dBμV emf
3.0–29.999 MHz 6 dBμV emf
50 MHz band 0 dBμV emfFM (7 kHz, 60% modulation):
28–29.700 MHz 0 dBμV emf
50 MHz band –6 dBμV emf
Squelch sensitivity SSB, CW, RTTY, PSK: Less than 5.6μV (Pre-amp: OFF)
FM: Less than 1μV (Pre-amp: OFF)
Selectivity SSB (BW=2.4kHz, sharp):2.4kHz/-3dB 3.6kHz/-60dB
CW/RTTY/PSK (BW=500Hz, sharp):500Hz/-3dB 700Hz/-60dB
AM(BW=6kHz):6.0kHz/-3dB 15kHz/-60dB
FM(BW=15kHz):12kHz/-6dB 20kHz/-60dB
Spurious and image rejection ratio More than 70dB
Audio output power More than 2.6W (10% distortion, 8Ω load)
RIT variable range ±9.999kHz

Antenna Tuner

Matching impedance
HF bands: 16.7Ω to 150Ω unbalanced (VSWR better than 3:1)
50MHz: 20Ω to 125Ω unbalanced (VSWR better than 2.5:1)
Minimum operating
HF bands: 8W,
50MHz band: 15W
Tuning accuracy VSWR 1.5:1 or less
Insertion loss Less than 1.0 dB (after tuning)

Supplied Accessories

● Rack mount handles
● SD card
● AC power cable
● Spare fuses
● Plugs

Panel View

Additional information

Additional information



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