ICOM IC-7851 IC-
THE TRANSCEIVER
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 eorts.
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 spec-
trum 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.
THE TRANSCEIVER
1
Reciprocal Mixing Dynamic Range
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(dB)
1kHz
IC-7851
IC-7800
110
78
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.
2kHz
116
87
10kHz
121
106
20kHz
124
112
1.2kHz Optimum Roofing Filter
Despite the trend to switch to a down conversion
or a hybrid conversion receive design, Icom
believes in the solid performance of the
up-conversion design. In an up-conversion
receiver, suppression of image inter ference and
reduce distortion from electric components is
easily overcome. A flat consistent performance
is delivered over a wider frequency range.
Optimum Roofing Filter
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
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
IC-7851 IC-7800
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
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
-70 dBc/Hz
-80
-90
-100
-110
-120
-130
-140
-150
-160
1 kHz 10 kHz 100 kHz 1 MHz100 Hz 10 MHz
IC-7851 IC-7800
Frequency Offset
-70 dBc/Hz
-80
-90
-100
-110
-120
-130
-140
-150
-160
1 kHz 10 kHz 100 kHz 1 MHz100 Hz 10 MHz
Frequency Offset
2
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