On 5/18/2020 3:15 PM, Paul F. Merrill wrote:
Hi Group -
Does anyone have any experience with a Tesla Powerwall installation at
their QTH? If you have, have you noticed any RFI from them?
Someone posted a link to this ham's blog, but now I can't find the post.
http://ka7oei.blogspot.com/2017/12/does-tesla-powerwall-2-produce-rfi.html
http://ka7oei.blogspot.com/2018/10/reducing-rfi-from-tesla-powerall-2.html
Anyhow, I went there and browsed it. There's a lot of good information
there, but the author doesn't seem to understand the concept of
saturation in the clamp-on ferrite parts that he places on individual
conductors, nor the concept of a common mode choke applied to all three
conductors, which eliminates saturation.
He observes that you've got to have an antenna right next to Powerwall
wiring to hear it on any band above 160M, and it still isn't bad there,
but that it gets increasingly problematic as you go down in frequency,
and is pretty bad by the bottom of the AM broadcast band.
The problem he faces is that he needs a pretty large i.d. clamp to
surround the three conductors (phase, phase, neutral), and #75 is the
material he's chosen to work with. The largest clamp-on has a
dimensional resonance around 750 kHz
https://www.fair-rite.com/product/round-cable-snap-its-475176451/
A possible solution would be to wind a suitable three-wire choke on one
or more 2.4-in o.d. #75 toroids using a wire diameter sufficient to
carry the current. In http://k9yc.com/630MTXChokes.pdf I showed the Z
plot for 18 turns of RG400, which provides about 2.5K on 630M and 160M.
Dimensional resonance is too high for #75 to be useful much below 300
kHz. Although I didn't publish measured data for a #12 Teflon pair, my
recommendation for 630M was 17 turns.
Another observation. Santa Claus brought us a Model 3 (delivered a bit
late on the afternoon of New Years Eve), and I sometimes charge it at
home on a 20A 120V circuit. It's slow, but it works, AND I hear nothing
from it on 160M when I probe along the short run of #10NM that feeds it.
It is also my understanding that the increasing noise in the AM band is
the reason there's no AM radio in Teslas. AND another observation -- the
interior of that vehicle is very carefully shielded at some frequencies
but not at others. My VHF/UHF talkie is useless inside the vehicle,
suggesting that the glass is providing shielding. BUT -- my cell phone
works fine inside, so that shielding is carefully tailored to couple
cell frequencies.
And finally, the FM radio with it's antenna(s) in the Model 3 has
excellent sensitivity. All of the stations I listen to are NPR stations,
and I'm not in the service contour of any of them, so I really notice
weak signal performance. The radio in my XYL's Prius is often hunting
between digital and analog streams; not the Tesla -- it nearly always
holds the digital streams as I drive up and down the mountain from home
into town(s).
Note also his observations with respect to the solar part of the system,
which I believe to be good advice. W6GJB has been doing some research of
his own in preparation to building his own custom installation with off
the shelf components.
73, Jim K9YC
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