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.
http://www.nsarc.ca/hf/npr.pdf
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
can we assume that this will mean full software operation as in Flex's "SmartSDR"? but produced by Icom?
ReplyDeletesince you're the Icom soothsayer, what has been the past lag time between a Toyko HamFair announcement and radios being offered for sale in the US? Dayton, Orlando, Two Daytons hence?
I don't see the dstar mode listed in the preliminary cut sheet. I suppose Icom could only afford to pack so many features into their entry level SDR machine.
ReplyDeleteI don't see why Icom would want to even think about D-Star on a radio that doesn't cover 2 meters and 70 cm. So far as I know, D-Star is exclusively above 144 MHz.
ReplyDeleteI have watched the video, and have downloaded the presentation. I stand corrected on the BDR, vs clipping range. I think that the clipping range of the direct samplers is still a bit less than the BDR of the best superhets, from what I see of the specs and dBm figures for the onset of clipping. Clipping onset will be a very important spec for the SDR, and will be I think determined by the ADC, with possibly some help coming from front end filtering.
ReplyDeleteIt will be interesting to see how the 7300 works. From the one 5+ minute video, it seems to have many features, and if the performance is anywhere near what I think it could be, and the price is in the $1200-$1300 range as speculated, it will be a game changer. I would think it may exceed the performance of a couple of conventional ICOM rigs higher up the line. It seems from looking at this that the feature set is what would be on a $2500-$3000 radio, but I would like to see more details on features, available controls, and more ergonomic details.
I currently have a Ten Tec Orion here in the shack as well as a QS1R SDR, which I purchased in 2008, so I am familiar with Direct Samplers. If the Receiver performance can get close to that (which I would think that it should as parts costs have come down). It should be a sweet rig, if it is as it looks and there are no bugs or upcoming surprises.
The closest stand alone xceiver is ADAT 200a, which I have. What it lacks is touch screen which will make a big difference especially in portable ops. I have my pre-order in and waiting for US approval!
ReplyDeleteAny one know the tentative release dates here in the U.S. or elsewhere?
ReplyDelete