Gerard, except that those transceivers that do the gigabit serial links 
have their own, fenced off circuitry and isolated regions  on the die.
They also have their own fenced off, isolated power supplies and ground
regions.
And, they require clocks with < a few hundred pS of jitter for their PLL
references  to work.

Jim : a few mW from your satellite with a -60dB spur is really bad if
you are a radio astronomer !
example frequency : 1000MHz, 1mW ERP
spurs at -60dBc  = -90dBW
distance from earth station : 5000km, signal = -245dBW/m2
say it was spread over 100 Hz, uniformly = -265dBW/m2/Hz or  0.3 Jy
(Attila, pls check) .
Detection threshold of of SKA   at this frequency :   micro Jys

so your -60dB spur will be like a jumbo je taking off overhead

so, satellite spurs do matter. Starlink is causing lots of problems
right now....

On 4/10/2025 20:38, Gerhard Hoffmann via time-nuts wrote:

Hello,

I wanted to thank you very much for these beautiful and very interesting
links. I learned so much. TWSTFT is amazing.

The prospect of using SDR and modern radio transmissions to distribute
accurate and stable time is very appealing to me, an amateur with a
rather limited budget.

I own several SDRs, including a second hand USRP B200. Which seems to be
supported by amaranth_twstft.

The prospect of an amateur radio based accurate clock distribution
network is extremely appealing.

GPSDOs work, but they have issues, like jitter sawtooth phase errors etc.

By knowing the position of emitting and receiving stations, can TWSTFT
be used in a kind of "receive only" mode?

I also believe that one could use it just for simpler frequency
transfer, without dealing with two way ranging?

Best regards,

Sebastien

On 10/4/25 06:42, jeanmichel.friedt--- via time-nuts wrote:

the issue is that "geostationary" satellites are not stationary, but precess around their
equilibrium position daily by +/-30 km or 200 ms excursion, see Fig 20 of
https://pubs.gnuradio.org/index.php/grcon/article/view/131/109 so much worse than the VLF
broadcasting stations discussed elsewhere on this list. Identifying and sharing the position
of the geostationnary satellite would be a fantastic feat that quite a few people would be
interested in or have demonstrated
https://www.ion.org/publications/abstract.cfm?articleID=15002
https://epapers2.org/eftf2024/ESR/paper_details.php?paper_id=2117
but there is no open, functional solution, while orbit determination is way beyond my skills
despite having collected passively the time of flight broadcast by European NMIs (see Fig 17
of the  above GRCon presentation) and spent quite some time investigating GMAT and Orekit.
If interested to pursue, all you need is a 60-cm satellite dish pointed to Telstar11N and
tuned according to e.g. https://webtai.bipm.org/ftp/pub/tai/data/2025/time_transfer/twstft/op/twop60.677
frequency settings.

On a side note, I learned yesterday that ACES was broadcasting the Ku microwave beam generated
from PHARAO constantly, a nice challenge as well, for the next ISS pass overhead. I have not searched
the web to find if the frequency is a publicly available information (but will be easier to find
with the solution now).

The satellite is moving at a few ns per seconds so a few 1e-9 accuracy, and we have no
control of the frequency offset introduced by the satellite transceiver from the 14 GHz
uplink to 11 GHz downlink, so unfortunately  I do not believe there is much use there.

Thanks for the interest, JM