Contesters and DXers are always looking for that competitive edge to magically pull out the weak signal that is either the rare country or multiplier they need to climb up the list.
Solid design basics and HF expertise raising the bar
Contesters and DXers are always looking for that competitive edge to magically pull out the weak signal that is either the rare country or multiplier they need to climb up the list. Larger antennas, higher gain pre-amps and other devices in line are great. However, what happens inside the radio with all those signals coming down your feedline can defeat all your efforts.
With 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 Dynamic Range (RMDR) of 110dB. In addition to the incredibly clean LO allowing you to hear the weak signals, the new spectrum scope design enables you to see the weak ones! Faster processors higher input gain, higher display resolution and a cleaner signal from the receiver's LO will give you a new window into the RF world. Adding this performance and functionality for both receivers give you a dual scope portal.
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 (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.
1.2 kHz Optimum roofing filter
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.
LO C/N 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.
TMS320C6745 by Texas Instruments
32-bit floating point
370 MHz clock speed
*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
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. 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 waterfall 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.
- 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.
0.030– 60.000 MHz*2
1.800– 1.999 MHz
3.500 – 3.999 MHz
5.255 – 5.405 MHz*2
7.000 – 7.300 MHz
14.000– 14.350 MHz
21.000– 21.450 MHz
28.000– 29.700 MHz
*1 Frequency ranges vary depending on version.
*2 Some frequency ranges are not guaranteed.
|Mode||USB, LSB, CW, RTTY, PSK31/63, AM, FM|
|Number of channels||101 (99 regular, 2 scan edges)|
|Antenna connector||SO-239×4 and BNC×2 (50Ω unbalanced (Tuner off))|
|Power supply requirement:||85–265V AC|
|Temperature range||0°C to +50°C; +32°F to +122°F|
Less than ±0.05ppm
(0°C to +50°C @ 54MHz, after warm up)
|Frequency resolution||1Hz (minimum)|
|Power supply requirement||85–265V AC|
|Power supply requirement||Tx Max. power: 800VA
Rx Stand-by: 200VA (typ.)
Max. audio: 210VA (typ.)
|Dimensions||425×149×435 mm; 16.73×5.87×17.13 in|
|Weight||23.5 kg; 51.8 lb|
SSB, CW, RTTY, PSK31, FM
Transverter Connector, CW
More than –20dBm
Digital P.S.N. modulation
Digital low power modulation
Digital phase modulation
|Spurious emission||More than 60dB (HF bands)
More than 70dB (50 MHz band)
|Carrier suppression||More than 63dB|
|Unwanted sidebandr suppression||More than 70dB|
|δTX variable range||±9.999 kHz|
|Microphone impedance||600Ω (8-pin connector)|
|Receive system||Double conversion super-heterodyne system|
SSB, CW, RTTY, PSK31, FM
(BW: 2.4 kHz at 10dB S/N)
(BW: 6 kHz at 10dB S/N)
(BW: 15 kHz at 12dB SINAD)
|Squelch sensitivity (Pre-amp: OFF)
SSB, CW, RTTY, PSK
Less than 5.6μV
Less than 1μV
|Selectivity (representative value)
SSB (BW: 2.4 kHz, sharp)
CW, RTTY, PSK (BW: 500 Hz, sharp)
FM (BW: 15 kHz)
More than 2.4 kHz/–3dB
Less than 3.6 kHz/–60dB
More than 500 Hz/–3dB
Less than 700 Hz/–60dB
More than 6.0 kHz/–3dB
Less than 15.0 kHz/–60dB
More than 12.0 kHz/–6dB
Less than 20.0 kHz/–60dB
|Spurious and image rejection ratio||More than 70dB|
|Audio output power||More than 2.6W at 10% distortion with an 8Ω load|
|RIT variable range||±9.999kHz|
|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)|
All stated specifications are subject to change without notice or obligation.
The LCD display may have cosmetic imperfections that appear as small or dark spots. This is not a malfunction or defect, but a normal characteristic of LCD displays.
- Rack mount handles
- SD card
- AC power cable
- Spare fuses