Description
THE TRANSCEIVER
IC-7851
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
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
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.
Phase Noise Characteristics Comparisons
Receiving Frequency: 14.2 MHz Mode: CW 1st LO frequency: 78.655 MHz
IC-7851
IC-7800
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
*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
Scope DSP
TMS320C6745 by Texas Instruments
32-bit floating point
2250 MFLOPS
370 MHz clock speed
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
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.
Dual scope example (Vertically aligned)
Dual scope example (Horizontally aligned)
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
2400 MFLOPS
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
General
| Frequency coverage*1 |
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| *1 Varies according to version. *2 Some frequency bands are not guaranteed. |
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| 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) |
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| 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 | |||||||||
Transmitter
| 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 suppression |
More than 70dB |
| ⊿TX variable range Microphone impedance |
±9.999kHz |
| Microphone impedance | 600Ω (8-pin connector) |
Receiver
| 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) 0.1MHz～1.7999MHz：0.5μV 1.8MHz～29.990MHz：0.16μV 50MHz～54MHz ：0.13μVAM (BW=6kHz, at 10dB S/N) 0.1MHz～1.7999MHz：6.3μV 1.8MHz～29.990MHz：2μV 50MHz～54MHz ：1μVFM (BW=15kHz, at 12dB SINAD) 1.8MHz～29.990MHz：0.5μV (28–29.9MHz) 50MHz～54MHz：0.32μV |
| 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 range |
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 power |
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
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