Thanks Rob and Glenn for your comments.

I am doing tests with a pair of phased loops so good current balance and they are each coupled to their feedline through an isolation transformer at the amtenna end and each also have a feedline choke with good common mode isolation at the frequencies of interest as well to guard against common mode noise injection at least on the feedline end of things. I think for the ground loop issues I will try to simplify and eliminate CM noise sources and ground loops as follows.  I discovered a clone of the KiwiSDR called flydog which uses a Pi 3B or even 4B (but ships with a 3B).  If there are enough resources there to run the Kiwi host and WD concurrently it will help a lot with these issues.  I'm guessing I will need a 4B with some extra memory. Since the logging will be done without any internet whatsoever that's another noise source eliminated and I can use a substantial lithium battery which I already have with a linear regulator for the tests.  I don't know if this knock off SDR is any good, but I don't have any backup for my bonafide SEED KiwiSDR so this will serve as an exploration of the clone and possible backup for the good one as well and allow it to stay safely at home. I like it too much to leave it out in a field overnight!

Joe

Joe,

To be honest, though I have a portable system intended to approach the
propagated noise floor over LF-HF I continue to learn about impediments
to achieving this.  My current best method, subject to change, is to
only use a WiFi interface to the Kiwi. For a BBG/Kiwi I use the "YT"
attached via USB, as documented on the kiwiSDR forum.  For the BBG/AI I
use its built-in WiFi. These are colocated with a very symmetric 2 m
reference dipole active antenna of known characteristics and high common
mode rejection.Even so, the power management IC within the BB's as well
as other digital activity on those boards is still perhaps visible in
some situations.  For some measurements I have constructed a 3D printed
AzEl rotor, also interfaced by WiFi and without any connections which is
also used to learn about polarization and direction of signal and noise
sources.  I am leaning toward using only linear power supplies to
convert to the various voltages needed by the Kiwi, preamps and rotator.

Doing it this way, the RPI has no wired connection to the kiwi, either
by power supply or network conductors. This is important to reduce the
possibility for common-mode current injection which can degrade the
noise floor.  I'm tending to use an access point (but not the routing
function built into YT and similar wireless/routers) to communicate with
the stand-alone Kiwi/AxEl rotor system and either the RPI or monitoring
laptop which can be located at significant distance so don't contribute
to the measurement data.

Glenn n6gn


On 7/14/21 10:17 AM, VE3VXO wrote:
> Hi Glenn
>
> Thanks for the very quick and informative response.  Since I have no
> experience with the Pi, before I buy one do you have any other
> recommendations given that I intend to run this from a battery and am
> concerned about shielding emissions from the Pi while keeping it cool,
> the typical plastic cases they push at the Pi outlets are probably not
> what I want.  I see the Pi 4B requires 3.1A, I was initially
> envisioning running the Kiwi on one of those 1MHz buck converters
> which are relatively RF quiet but I guess that idea won't work for the
> Pi-4B as the SMPS is rated for 3A max.
>
> Joe