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

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

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 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

 
IC-7851                                                                             IC-7800

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.

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.

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.
 
Mini spectrum scope and audio scope                    Mini dual spectrum scope and audio scope

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. The dual scope function is vital for watching for multipliers or band openings in contests, or working all bands/modes on a DXpedition
 
Dual scope example (Vertically aligned)                  Dual scope example (Horizontally aligned)

Click Control

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.

+40dBm IP3

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

BPF Switching

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

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

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.

Triple DSP Power

 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.

 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.

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 XCXO 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.

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 Aliminium 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

Dual Receivers

The IC-7851 incorporates two completely independent receivers, from the antenna inputs all the way through to the stereo headphone and individual external speaker outputs. All the performance of the first receiver is duplicated for a perfectly matched set of “Twins”. When connected to external stereo headphone, main and sub receiver audio can be mixed or separated to the right and left.

RTTY/PSK31 and PSK63

RTTY, PSK31 as well as the new PSK63 modes are available at your finger tips without the use of a computer. The built-in Modulator/Demodulators are activated by via the radio's functions buttons or an optional USB keyboard. TX memories make contacts a snap and communications logs can be stored on an SD memory card.

 Digital IF Filters.

“Build your own” IF filters by adjusting the IF filter width, 50-3600 Hz, as well as soft or sharp filter characteristics for your perfect sound. Save these settings in three userdefined filter presets, Wide/Mid/Narrow, by mode to give you full customization of your filters.

Digital Manual Notch

HF operators marvel at how well DSP reduces interfering signals and noise. Signals such as heterodynes and AM Carriers can be eliminated with automatic notch filter technology. Making interference from RF sources such as beat signals and RTTY signals is a thing
of the past. Additionally, the filter shape of the manual notch can be adjusted in three steps – with more than 70dB of attenuation!

Digital Twin Passband Filtering

Once the IF filters have been “tweaked,” the operator has additional control with the digital twin passband tuning (PBT). The digital twin PBT allows flexibility of both the IF shift and narrowing of the digital IF passband by moving the IF passband. With the digital IF filters, PBT performance allows you to cut away all the interference and noise to hear the actual signal.

Auto Digital Noise Blanker

While most noise blanker reduces pulse type noise, the IC-7851 introduces a new automatic digital noise blanker circuit. While using the 15/9/6kHz roofing filters, the digital noise blanker gives you full control. When the 1.2kHz Optimum Roofing Filter is activated, the best blanking level is automatically selected. Additional adjustments allow you to tweak the threshold level, blank time and attenuation level parameters.

Digital Transmit Bandwidth (TBW) and Audio Equalizer

With the flexibility of DSP-based waveform shaping, transmit and receive audio quality is adjustable to suit your preference. Three user-adjustable transmit filters, Wide/Mid/Narrow, allow you to set both the low and high cut-off frequency limits. (100, 200, 300, 500Hz for lower and 2500, 2700, 2800, 2900Hz for higher frequencies.) In addition to the TBW filter, the IC-7851 has an equalizer to digitally tweaks your transmit audio with separate bass and treble controls (11 steps each for bass and treble). The receive audio can be tailored with modespecific Bass/Treble or audio passband settings.

Digital RF Speech Compressor

The DSP controlled RF speech compressor provides additional punch while maintaining the original tone quality of the operator. The IC-7851 utilizes the 32-bit DSP for the RF speech compressor, providing the maximum punch without the fuzzy sound. It's great for breaking through the noise and hash to complete the QSO.

SD Memory Card Slot

Save operator profiles, digital voice keyer, CW memory keyer, RTTY/PSK logs, IC-7851 “Screen Shots” and various other operational settings to your SD Memory card

Digital Voice Recorder

The digital voice recorder captures both receive and transmit audio to your SD or USB storage devices. Up to 9 hours of continuous audio recording is possible with 2 GB of storage. Record your QSO with a rare entity or record your operating time in a contest. Operating frequency, mode, S-meter and output power are automatically captured.

 Memory Keyer

Whether operating phone, CW, RTTY or PSK31/63, the IC-7851 has a convenient
memory keyer to ease operations. Record your CQ, station information or other items in one of 8 keyer memories for the CW and digital modes; 4 memories for phone operation. For CW, the memory keyer has timesaving functions like auto repeat, contest serial number counter and short Morse number functions. For phone operation, you have a voice-saving auto repeat function.

Improved Automatic Antenna Tuner

The automatic antenna tuner utilizes tunesetting memories to record the best tuner configuration for the lowest SWR. This allows a faster response time when jumping bands or moving around in the same band.

Internal Antenna Switch

With six antenna ports – two receive-only and four receive/transmit – the IC-7851 enables the operator to have fingertip control over a vast array of antenna configurations. Switch to 80/160m and you want to use your beverage
antenna for receive, but transmit on your vertical. Not a problem: the antenna switch
memory will automatically switch antennas when you select the band you want to operate.
This is very convenient when using the RS-BA1 for remote base operation.

Enhanched PC Conectivity

The IC-7851 has various computer interfaces, giving you maximum connectivity between your computer and radio. Digital modes become a snap when controlling with the USB port. USB audio and some CI-V commands including USB send (DTR/RTS) and USB keying (CW and RTTY) are selectable. You can also interface your computer with the S/P DIF optical digital interface provides audio I/O.
The Ethernet jack allows you to connect the IC-7851 directly to your router and control your radio over your wireless Internet, or travel the globe and operate your station remotely over the Internet.

Other Features

Receiver

• General coverage receiver covers from 30Hz to 60MHz* (* Some frequency ranges are not guaranteed.)
• Two types of preamplifiers:
• Preamp 1: improves intermodulation characteristics
• Preamp 2: High gain preamp for high bands
• A seven step attenuator (3, 6, 9, 12, 18, 21dB and OFF)
• A dedicated 50MHz band mixer using a Quad FET
• Twin peak filters for better RTTY signal reception

Transmitter

• Speech compressor increases average talk power (SSB mode)
• TX monitor functions
• Fifty sub-audible tones (CTCSS) for repeater access
• VOX (Voice operated transmission) capability
• All mode power control

CW

• DSP controlled CW keying waveform shaping
• Multi-function electronic keyer with adjustable keying speed, dot/dash ratio, keyer type, rise time and paddle polarity
• Electronic keyer speed popup
• CW pitch control from 300 to 900Hz (5Hz pitch)
• CW reverse mode operation for receiving USB side signal
• Double key jacks for front and rear panels
• Full break-in and semi break-in functions
• CW/AM auto tuning function helps to zero in on intended signals within ±500Hz range
• Soft and sharp audio filter shapes for the Audio Peak Filter (APF)

Operation

• Set mode functions for flexible and speedy settings
• Memo pads stores up to 10 operating frequencies and modes
• Quick split function and split lock functions
• Quick Dualwatch function
• SSB/CW synchronous tuning
• RIT and ⊿TX variable up to 9.999kHz
• UTC/Local clock and timer function
• 1Hz pitch tuning and display
• 101 memory channels with 10-character channel name
• Built-in voice synthesizer announces the operating 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 control
• Programmable band edge beeps
• S/P DIF input/output connectors
• BNC type transverter connector
• External speaker connectors for Main/Sub receivers
• FFT scope waveform averaging function for PSK and RTTY decoder
• Screen saver function

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