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ICOM
HF/50MHz Transceiver - The Pinnacle of HF Perfection
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 gives you a dual-scope portal.
Frequency coverage
Receiver:
0.030–60.000MHz
Transmit:
1.800–1.999MHz
3.500–3.999MHz
5.255–5.405MHz
7.000–7.300MHz
10.100–10.150MHz
14.000–14.350MHz
18.068–18.168MHz
21.000–21.450MHz
24.890–24.990MHz
28.000–29.700MHz
50.000–54.000MHz
Power Output:
5–200W
Mode:
SSB, CW, RTTY, AM, FM
Number of channels:
101 (99 regular, 2 scan edges)
Operating temperature
+32°F to +122°F
Dimensions W x H x D
16.73×5.87×17.13 in
Weight
51.8 lb
Display
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
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.
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.
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.
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
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
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 (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.
BPF Switching:Mechanical Relays
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 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
The push-pull power amplifiers using 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.
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