For Rob’s receiver tests, he turns on Dither is the radio supports that option. The IC-7300, the Perseus, and other models support dither. However, there are radios that have a very high DR without dither. Look at Rob’s recent test on the Yaesu FTDX10.
It is my understand that the QST Product reviews use a 3rd signal to simulate noise. They measured a DR of about 70 for the Duo in their 2016 review.
73
Clint
W7KEC
If the two source signals are pure tones, then you'll get pretty terrible results as there is no dither signal injected into a DUO as far as I know. A proper test of a radio with a straightforward ADC at the front end needs a reasonably large unrelated signal or random noise to smother the artefacts. In any normal usage with an antenna, there will be enough wideband noise and signals to add sufficient random dither.
At very low levels, the receiver noise floor is probably sufficient to dither the signal, hence perhaps the better results measured close to MDS.
The Sherwood results are correct, but if I understand his methods, the results don't provide any useful information, he is just mapping out what a 16 bit ADC does with two pure signals.
I might be wildly wrong about this of course!
Neil G4DBN
On 12/01/2021 20:31, Clint Chron wrote:
I am not sure. I don’t have the ability to inject a signal from a 3rd signal generator.
A couple of things to keep in mind.
Putting a HF pre-selector on the front end of the Duo should improve the DR, but I have not made that test.
The NPR measurements on the DUO come out very good, when compared with other high end radios.
73
Clint
W7KEC
Hi Clint, does injecting a realistic level of wideband noise (or some additional non-harmonically-related signals to provide dithering) change the results at all?
Neil G4DBN
On 12/01/2021 19:54, Clint Chron wrote:
I just ran the same tests several times on my Duo. The results came out the same each time.
The challenge in testing the Dynamic Range of SDR receivers is that the DR bounces all over the board, depending upon the level of your two primary test tones (separated by 2 kHz).
So while the DR of the Duo may be low at the MDS measuring point, that does not mean that it is low for all measuring points.
Here is the IFSS graph for my Duo, the IC-7300, and the Perseus.
To get the dynamic range for a given primary signal level, subtract the IMD product signal level from the primary signal level.
Example:
The MDS on my Duo is -132 dbm. A -64 dbm primary signal produces an IMD product of -132 dbm. So the dynamic range is 68 db.
Now look at a primary signal of -40 dbm. This produces an IMD product of -126 dbm. So the dynamic range is 86 db.
Now look at a primary signal at -30 dbm. This produces an IMD product of -125 dbm. So the dynamic range is 95 db.
For a given primary signal level, the radio that has the lowest IMD product signal level has the best dynamic range for that particular measuring point.
Of the three radios that I tested, the Perseus receiver has the best overall dynamic range.
73
Clint
W7KEC
