Many thanks for your thorough and thoughtful comments on the IC-7300. As you are doubtless aware, I have tested a fair number of direct-sampling SDR's over the past few years as well as legacy (conventional) transceivers. I have learned from this test activity that a direct-sampling SDR receiver is a totally different "animal" than a legacy receiver, and requires a completely different approach to performance testing. The old "touchstone" metrics of DR3 (3rd-order IMD dynamic range), BDR (blocking dynamic range) and IP3 (3rd-order intercept point) are completely meaningless in the context of an ADC.
I have covered these matters in a paper I gave at our club, at APDXC 2014 and at several other venues. The paper is entitled "HF Receiver Testing: Issues and Advances." Here is the link:
BDR has no relevance to a direct-sampling SDR, as an ADC does not block until it clips (at which point the receiver crashes.) A DR3 test does not yield useful data when performed on an ADC, as DR3 is dependent on test-signal power and varies all over the map. IP3 is meaningless, as the transfer and IMD3 curves of an ADC diverge and never intersect (in contrast to a legacy receiver, where they converge and intersect at the IP3 point.)
On an SDR, I do not test BDR, DR3 or IP3. I measure the absolute power of IMD3 products over a range of test-signal levels (typically from just below clipping to the noise floor) and draw a chart with the ITU-R typical urban and rural band noise levels at the test frequency as datum lines. This test is termed IFSS (interference-free signal strength). If the IMD3 product is below the band noise level, it will not be heard.
RMDR (reciprocal-mixing dynamic range), a function of phase noise, is still highly relevant to an ADC. Unlike the case with IMD3, it takes only one interferer to create reciprocal mixing noise which will mask a weak signal. One big advantage of a direct-sampling SDR is that it gets rid of the analogue LO's, which are the source of phase noise in a legacy receiver. The major determinant of phase noise here is the ADC clock, which can be a high-grade, low-noise crystal oscillator. By the same token, a DUC (digital up-conversion) transmitter will generate a much cleaner signal than almost any legacy transmitter. I always measure RMDR.
Second-order dynamic range (DR2) is a measure of IMD2 products in an amateur created by two far-off interferers. Example: 6.1 and 8.1 MHz, whose IMD2 product is on 14.2 MHz. A good preselector ahead of the ADC will largely eliminate this problem. IMD2 can be an issue in areas with many high-power HFBC stations, e.g. Region 1. I also test DR2 by the classical method (product at the noise floor.)
The noise-power ratio (NPR) test is also useful for assessing the performance of a receiver on a crowded band. It is a great test for direct-sampling SDR's, as the NPR value for a given ADC can be predicted mathematically and the measured value compared to it. The NPR test will also reveal passive IMD (PIM) in preselector inductor cores and other passive components. I measure NPR on every radio I test.
I am really looking forward to getting an IC-7300 onto my lab bench. The test report will appear on my website in due course.
73, Adam VA7OJ/AB4OJ