[Elecraft] Sherwood's receiver performance table updated

[Rick WA6NHC]

This is interesting to follow but well above my full understanding...  
But how do we come up with a common standard between the two types of 
radios (although I expect direct sample to improve to a point to become 
common)?

Further from Rob (since we're off topic here):

-=-=-=-=-=-

How to rank direct-sampling SDR radios is a real can of worms.  If you 
look at the review in the May QST of the Elad DUO, you will see the only 
dynamic-range data is listed as “Best Case”.  There is no “typical case” 
or “worst case” data, and the “best case” dynamic range (DR3) of 99 dB 
was obtained with a third strong “incidental dither” signal.  That 
strong “incidental dither” signal may or may not be there when you need it.

In the case of the 7300, on the lower bands, 160 – 40 meters, the 
increased noise floor caused by enabling IP+ would not be an issue. 
Nighttime 40 meter band noise is about -100 dBm, and the noise floor of 
the 7300 with IP+ ON is about -122 dBm.  If 40-meter AM broadcast 
stations above 7200 are stressing the radio, IP+ will be a good 
solution.  On the other hand, if one is on 15, 12, 10 or 6 meters, the 
noise floor of the radio with IP+ ON may be about equal to band noise in 
a rural environment.  All bets are off in an urban environment, due to 
all the local RFI.  In some cases on the higher HF bands, receiver noise 
will be higher than band noise with IP+. That is why I made the caution 
to not just turn IP+ ON and leave it there.  Of course in a foot note I 
don’t have unlimited space to explain all this.

The dynamic-range data is all there, IP+ both ON and OFF.  It is similar 
to my KX3 data and footnotes.  The dynamic range is high, but because 
the opposite sideband rejection is limited to about 65 dB, in some cases 
that limitation will dominate.  Thus three values of dynamic range are 
in the table, explained by the foot notes.

The same concern can be lodged about the original K3 data where dynamic 
range (DR3) is listed as 101, 96 and 95 dB, with foot notes.  The DR3 
due to RMDR is higher with a 200-Hz bandwidth than with a 500-Hz 
bandwidth.  In effect the radio is ranked assuming one is operating the 
radio in its best configuration.

One other note, even though the close-in dynamic range data is mainly 
applicable to CW operation due to the narrower transmitted bandwidth of 
CW stations, an SSB only operator may assume that level of performance 
applies to him, too. In reality on SSB, transmitted IMD splatter of an 
adjacent channel signal (3 kHz away) is usually the limit in copy of a 
weak station.  The radio is rarely the limit in this case, as splatter 
is usually worse than the dynamic range of the radio.

-=-=-=-=-

And later...

-=-=-=-=-=-=-

No, IP+ is not an attenuator.  It enables “dither” and “random” on the 
ADC chip.  The Apache ANAN series also has dither and random as an 
option, but in the case of newer ANAN-200D transceivers, the noise floor 
is not degraded.  Older 100D and 200D units did have an 11 to 13 dB 
noise floor degradations.

Clarity is important, so thanks for the chance to expand on this issue.

73, Rob, NC0B

-=-=-=-
Rick nhc

On 4/25/2016 1:44 PM, Dave Hachadorian wrote:
> It's interesting that the 7300's ranking in the table is because of 
> its 94 dB Dynamic Range at 2 KHz spacing.  But the footnotes indicate 
> that this dynamic range is with AP+ turned ON. With AP+ ON, minimum 
> detectable signal is degraded by 11 dB.
>
> With AP+ OFF, as generally recommended in the footnotes, 2 KHz dynamic 
> range is only 81 dB, which would place the 7300 considerably lower in 
> the table, but still pretty good.
>
> Dave Hachadorian, K6LL
> Yuma, AZ