Icom IC-7851, Quick Start Manual, Page: 3 / 8

Competitive Advantage: Reciprocal Mixing Dynamic Range
R e c i p r o c a l M i x i n g D y n a m i c R a n g e
RMDR: 110dB
Raising the Bar
IC-7851 IC-7800
IC-7851 IC-7800
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 pres-
ent. The result was a RMDR of 110dB*. Below is a comparison of the
improvement over the IC-7800.
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.
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 measure-
ment and more than 30dB improvement at a 1 kHz measurement in com-
parison to the IC-7800.
Phase Noise Characteristics Comparisons
Receiving Frequency: 14.2 MHz Mode: CW 1st LO frequency: 78.655 MHz
LO C/N Characteristics Comparisons
Crystal Clear LO (Local Oscillator) Design
1.2kHz Optimum Roofing Filter
Optimum Roofing Filter Characteristic Diagram
Optimum Roofing Filter
Despite the trend to switch to a down conversion
or a hybrid conversion receive design, Icom
b e l i eve s i n t h e s o l i d p e r f o r m a n c e o f t h e
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 devel-
oped filter overc omes the g ap of a narrower roofing filter in an
up-conversion receiver.
* 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
R M D R ( d B )
I C - 7 8 5 1
I C - 7 8 0 0
1 k H z
1 1 0
7 8
2 k H z
1 1 6
8 7
1 0 k H z
1 2 1
1 0 6
2 0 k H z
1 2 4
1 1 2
1 kHz 10 kHz 100 kHz 1 MHz 100 Hz 10 MHz
-160
-150
-140
-130
-120
-110
-100
-90
-80
Frequency Offset
-70 dBc/Hz -70 dBc/Hz
1 kHz 10 kHz 100 kHz 1 MHz 100 Hz 10 MHz
Frequency Offset
Receiving Frequency: 14.2 MHz Mode: CW 1st LO frequency: 78.655 MHz
SPAN = 20 kHz, RBW = 30 Hz, VBW = 10 Hz
-160
-150
-140
-130
-120
-110
-100
-90
-80
-10
0
-20
-30
-40
-50
-60
-70
-80
-90
-100
-10
0
-20
-30
-40
-50
-60
-70
-80
-90
-100
2