[hpsdr] NOISE FLOOR

[Scott Traurig]

Very little. Mostly just small details. Looking at the SDR boards
themselves, if you compare it to the original Hermes design there have been
no changes to key components or signal flow in the receiver. It's still the
same LPF, step attenuator, preamp and ADC, although in the 7000 and 8000
the preamp has been changed to 14dB gain instead of 20dB gain. This has
actually proven to provide superior performance. Along with some change to
clock generation (same clocks and clock rates, just different TCXO and
layouts) I see 3 or 4dB improvement in my noise floor and activating dither
and random in the ADC does not move the noise floor at all. Indeed I leave
those features enabled all the time.

The latest schematic freely available for you inspection is the Apache
Orion board, which is two revisions beyond the Hermes (Hermes, then
Angelia, then Orion):

https://apache-labs.com/community/viewtopic.php?f=35&t=2338

The PA/filter board schematics are there as well.

You can request from Apache a copy of the Orion MKII schematic, used on the
7000 and 8000, under the auspices of the derivative open source hardware
agreement, but Apache has not publicly posted those schematics yet. In
addition to the change to a 14dB preamp, the output drive mechanism has
also changed. On the Hermes, and all designs prior to the Orion MKII, the
DAC reference voltage was used to adjust drive. On the Orion MKII the
output of the DAC now goes to another step attenuator. This allows drive to
be adjusted in 1dB increments by the attenuator and now the DAC can remain
at almost full scale all of the time, with only slight adjustments
necessary to DAC reference level for fractional dB adjustments.

73,

Scott/w-u-2-o

On Fri, Jan 18, 2019 at 11:29 AM Helmut Oeller <dc6ny at gmx.de> wrote:

> What is the difference between Apache hardware and HPSDR hardware?
>
> DC6NY
>
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