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 (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.
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
- Icom IC-7851
Optimum Roofing Filter Characteristic Diagram
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
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
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.
*1 Number of dots shown at the 60 dB level, when receiving a signal.
*2 SPAN = More than 20 kHz, SPEED = Slow
*3 SPAN = Less than 20 kHz, SPEED = Fast
*4 SPAN = 500 kHz, SPEED = Slow
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
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
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)
- 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.
Spectrum scope with waterfall
(wide screen setting)
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.
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)
- 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.
- 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)
1.2kHz Optimum Roofing Filter
3, 6, 15kHz High-Spec 1st IF filters
- 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
- 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.
Transmit/Receiver DSP (left) and Receiver DSP (right)
ADSP-21489 by Analog Devices
32-bit floating point DSP
393 MHz clock speed
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 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.
- 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.
- 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.
PA unit and heat sink
- 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.
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 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.
RTTY mode display
“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.
Filter preset screen
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!
Manual Notch Filter Characteristics
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.
The digital noise reduction separates a target signal from noise components and noise suppression level is variable in 16 -steps, depending on the noise level. The low latency digital noise reduction is achieved by applying an adaptive filter using the high speed DSP computing power.
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.
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.
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.
- 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.
Recorded list display
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.
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.
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.
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.
The IC-7851 can grow as feature and function enhancements become available via the USB or your SD Card.
Remote base operation is made easy as the IC-7851 operating system incorporates
the remote base server software. A computer is not required in the shack for audio or rig control. Up to three, unique user log-in/password configurations are part of the internal server. As the rig control has a priority of service, the controls will feel like you are right in front of your rig.
Optional RS-BA1 main features
● Most functions of your transceiver, including interference rejection functions and IF filter settings, can be controlled. Also, received signal strength and SWR can be observed on the computer display.
● Received voice recording function.
● Optional RC-28 USB remote encoder provides a hardware dial/transmit functions for a realistic dial operation.
● The IC-7851 can wake-up from the standby mode through the RS-BA1 software.
Other Outstanding Features
● BNC type RX input/output connectors for receiver antennas or external attenuators
● 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
● 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
● 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)
● 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
|*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)
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
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|
|More than 70dB|
|⊿TX variable range
|Microphone impedance||600? (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)
(HF: Pre-amp 1 ON, 50MHz: Pre-amp 2 ON)
|SSB, CW, RTTY, PSK (BW=2.4kHz, at 10dB S/N)
50MHz?54MHz????0.13?VAM (BW=6kHz, at 10dB S/N)
50MHz?54MHz????1?VFM (BW=15kHz, at 12dB SINAD)
|Squelch sensitivity||SSB, CW, RTTY, PSK: Less than 5.6?V (Pre-amp: OFF)
FM: Less than 1?V (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
|Spurious and image rejection ratio||More than 70dB|
|Audio output power||More than 2.6W (10% distortion, 8? load)|
|RIT variable range||±9.999kHz|
|HF bands: 16.7? to 150? unbalanced (VSWR better than 3:1)
50MHz: 20? to 125? unbalanced (VSWR better than 2.5:1)
|HF bands: 8W,
50MHz band: 15W
|Tuning accuracy||VSWR 1.5:1 or less|
|Insertion loss||Less than 1.0 dB (after tuning)|
● Rack mount handles
● SD card
● AC power cable
● Spare fuses
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