Icom IC-7851 Quick Start Manual page 3

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
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 pres-
ent. 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
RM DR(dB )
1kHz 2kHz
I C - 7851 110 1 16
I C - 7800 78 87
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 0kHz 2 0kHz
1 2 1 1 2 4
1 0 6 1 1 2
1.2kHz 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 fo 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 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
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
-70 dBc/Hz
-80
-90
-100
-110
-120
-130
-140
-150
-160
100 Hz 1 kHz 10 kHz 100 kHz 1 MHz 10 MHz
Frequency Offset
IC-7851
Optimum Roofing Filter
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
IC-7800
-70 dBc/Hz
-80
-90
-100
-110
-120
-130
-140
-150
-160
100 Hz 1 kHz 10 kHz 100 kHz 1 MHz 10 MHz
Frequency Offset
IC-7800
2