With the Icom 7610 using the new True Diversity Tracking Function, the Linrad program and by attaching separate antennas to the antenna ports in the Tracking receive mode, you have true "Diversity Receive". It is a fantastic Improvement in reduction of QSB/fading. If one antenna is experiencing a deep fade, it is likely that another has a sufficient signal. Pattern diversity consists of two or more co-located antennas with different radiation patterns. This type of diversity makes use of directional antennas that are physically separated by some distance. Spatial diversity employs multiple antennas, usually with the same characteristics, that are physically separated from one another. Phase Synchronous Diversity Reception uses two widely spaced antennas (500 to 1500+ feet) feeding two identical high performance SDR receivers. Depending upon the expected incidence of the incoming signal, on the order of a many wavelengths. Collectively they are capable of discriminating a large portion of angle space and can provide a higher gain versus a single omni-directional radiator. This is absolutely a major Improvement, with Diversity Receive my station uses over a mile of wire listening to signals coming in at different angles. Signal-to-noise ratio (S+N/N ratio, or SNR) is one technical aspect not too many amateurs give a second thought about, however if you can't hear them you can't work them. This is very apparent on audio reception, Diversity eliminates much of the audio amplitude fading. The RF signal is almost never in a stable phase relationship at both places at the same time. This means the signal will have random phase and amplitude differences. The arrival angle and polarization of incoming signals will change. This generally results in the fading, by having two antennas, the chances are that while one experiences a fade, the other will not. The power is in the diversity and what you can now hear with out QSB fading.
Icom did it right on the IC 7610.
Two separate DIGI-SEL preselectors, two separate Band Pass Filter networks, feed two separate A/D converters into the FPGA, not just two Receivers.
The IC7610 has synchronized ADCs using a single clock and customized VCXO used with the Master Clock for phase synchronous streams.
The 7610 has an input for a 10 MHz reference signal for higher precision.
Direct Sampling means incoming RF signals are digitized by the Analog-to-Digital Converter and immediately processed by the FPGA (Field-Programmable Gate Array). This process greatly reduces distortion that naturally occurs in the various mixer stages found in traditional superhetrodyne receivers.
RF Direct Sampling System in the IC-7610 is capable of 110 dB RMDR. This performance gives you the ability to pull weak signals out of the noise of strong adjacent signals.
The DIGI-SEL preselectors are RF filters with sharp, narrow passband characteristics preventing Analog-to-Digital Converter overflow from large out-of-band signals when sampling the RF signals. Additionally the third and higher order IMD components are reduced. This is ideal when strong signals are received in a contest pile-up or from broadcast stations on adjacent frequencies or bands.
The IC-7610 can output I/Q signals to a connected PC. Using the I/Q signals on the HDSDR (freeware), you can listen to received signals, or observe the spectrum scope on the PC to be used in combination with the LinRad software.
A few years ago I was very honored to have been personally invited by Icom's American President Hiro Nakaoka a few years ago, to meet with him and key staff members at their WA office to discuss a mutually interesting project. Later several key Icom executives also visited my office in Kansas.
Also K0UO uses the Linrad program which has routines to correct amplitude and phase for complex input signals These routines operate in the frequency domain and can absorb frequency dependent phase and amplitude errors that are introduced by differences in amplifiers and filters used between the I/Q mixers and the audio board. The only requirement is that amplitude and phase errors are independent of amplitude, time and temperature.
Linrad together with hardware that can bring RF signals into digital form, Linrad forms an SDR receiver (A Software Defined Radio receiver). There is also a transmit part inside Linrad that will form an SDR transmitter together with appropriate hardware. see http://sm5bsz.com/linuxdsp/videos.htm