The Starlink emissions are regular old spurious EMI from digital circuitry.
Odd as it may seem, spacecraft have no requirements for unintended emissions.
That is, there's no Part 15 or CISPR type rules on noise.
There are tons of requirements on spurious emissions related to intended
transmissions - there's spectrum masks and such.
This is because, historically, nobody cared - all you cared about is "self
compatibility" - that is, as long as your noise doesn't interfere with your
receivers (whcih tend to be at microwave frequencies), you're good to go. Only
the most exotic spacecraft with sensitive wideband receivers at low frequencies
pay attention to self generated noise. For instance, on Cassini, all the power
supply DC/DC converters are synchronized to a common reference, so the spurs
are all in the same place (and some of the instruments run their ADCs at
multiples of that rate, so they can just throw out 1 out of every N samples as
appropriate).
As an example, A typical RE102 (MIL-STD-461 radiated emissions) requirement for
a spacecraft might be "must be less than 60 dBuV/meter" (except for "notches"
in the receiver bands). For comparison, the standard level for airborne
equipment and a lot of other things is 24 dBuV/meter. That's at 1 meter
distance.
Part 15 subpart B&C is 100 microvolts/meter (40dBuV/m) at 3 meters.
WiFi in the 5 GHz band is -27dBm/MHz EIRP.
All those folks pitching radio astronomy on the Far Side of the Moon because
it's quiet are sort of ignoring that it's quiet *today* but probably not in
5-10 years. Gateway is based on a Maxar/Space Systems Loral GEO bus, which is
quite noisy.
One BIG source of noise is electric propulsion (EP) - basically a multi
kilowatt plasma discharge. The levels from that can be in the 100 dBuV/meter,
easily. And EP is very, very common these days. The Starlinks use Krypton EP,
I think.
[I'm manager of the SunRISE mission, and we are going to be flying receivers
for 100kHz to 23 MHz in GEO, and our noise floor is low enough that we are
"galactic noise limited" - about -20 or -40 dBuV/m, so MIL-STD-461 doesn't
even get close.
https://science.nasa.gov/blogs/sunrise/2025/09/30/nasas-sunrise-set-to-launch-in-2026/
]
On Thu, 2 Oct 2025 10:47:48 -0700, Steve Harrison <k0xp@k0xp.com> wrote:
On 10/2/2025 9:35 AM, Jim Brown wrote:
> On 10/2/2025 7:55 AM, Steve Harrison wrote:
>> However, it is a fact that connectors of the 1/2"-size (which
>> includes UHF, type N, and even type C with their extra-thick center
>> pin) do heat up when a kilowatt or more is passed through them,
>> particularly at V/UHF.
>
> Have you observed this issue with top quality connectors?
This was a commercial application, and our customer was a well-known
governmental agency; of course I used (and the company and power
combiner manufacturer paid for) the best available: silver-plated
Amphenol as well as some Suhners in several other places. And as I
mentioned, the agency's techs later showed me failed
formerly-silver-plated Amphenols (they burned up, so the silver-plating
was flaking off some of them). We did not, however, go as far as to spec
gold-plated: I don't know whether such was even available at the time,
unless you could specify space-qualified components.
That was not the issue: the real issue was the thermal expansion and
contraction of the connectors causing the connectors to loosen over
time. We are talking about connectors that passed a kilowatt at 450 MHz
heating up, then cooling off suddenly as they were near or within the
cool air-conditioned stream from the rack's environmental systems.
When I told my dad about the problem, he mentioned that at one time, TRW
was experiencing trouble with spurious radiation in satellites that was
eventually traced to some coaxial connectors in birds. As you know, most
commercially-available type SMA connectors are (or were, back then)
stainless steel. They had to quit using those and switch to
wholly-gold-plated coaxial connectors everywhere. That problem was due
to minute galvanic corrosion between dissimilar connector materials that
caused micro- diode junctions between connector interfaces, causing
microwatt-level spurious products even at very low transmit powers. The
present stories circulating about the spurious radiation from Starlink
birds that can be easily-heard on ground receivers makes me wonder
whether they made the same mistake. All over again 8-).
I have also heard of big multi-multis experiencing connector generation
of spurious products due to poor or loose coaxial connectors, which can
result from thermal expansion/contraction. Dissimilar-material coaxial
connectors can also cause problems; I remember reading of one in New
England that took the station operator SEVERAL YEARS before he
accidentally ran across (and cured) the real source of the spurious
products that had plagued his operators for years.
Steve, K0XP
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