4 ms·

The phase of the moon really can affect performance. A friend of mine worked on wireless links in Scotland and was struggling with loss at certain times of day

The phase of the moon really can affect performance. A friend of mine worked on wireless links in Scotland and was struggling with loss at certain times of day, but not exactly the same time every day. When they graphed loss against time, the pattern was really periodic over many days. The periodicity turned out to be 12 hours 25 minutes, which they eventually realized is exactly the time between low tides. The problem was at low tide the reflected path off the water interfered with the line-of-sight path causing signal fading, whereas at high tide it interfered much less. In particular, see figure 2 of their paper for the correlation between tide height and SNR: https://homepages.inf.ed.ac.uk/mmarina/papers/EDI-INF-RR-1365.pdf https://homepages.inf.ed.ac.uk/mmarina/papers/EDI-INF-RR-136... As tide height really does depend on the phase of the moon, presumably their loss did too, if they measured for long enough.

deleted 5y ago
[deleted]
pedrocr 5y ago
Cool result. That figure 2 is begging for a scatter plot of SNR and tide level to see how well correlated they are.
abkfenris 5y ago
I remember reading that paper when I was trying to figure out why we were having issues with a wireless link down in the Patagonia fjords. Unfortunately we didn't have the hardware or enough control over the link (it took negotiating access with armed forces to work on either end) to try to implement any of their ideas.
m4rtink 5y ago
I heard a story about an astronomer loosing the chance to be the first to report a commet one cold winter night - just as he wanted to send the email to report it, the Internet connection was dead! He ran from the observatory to the nearest place with Internet connectivity, but by the time he sent the email from there, there was already a report from another astronomer elsewhere, a few minutes ago. Reason for the mysterious network outage ? Thermal contraction! The observatory was connected to the Internet via an optical link to a highrise building in the city that contracted ever so slightly due to the very low temperature, moving the laser beam of the optical link out of alignment, shutting down the connection.
- bgirard 5y ago
  When I started dating my wife she lived in a shared student residence. She would tell me that her internet didn't work when her room was cold. She had to wait for her space heater to heat up the the room. I didn't believe her at first but it turned out be true. She lived there for a year so I observed it several times. Never did find out what the problem is. I don't know if thermal contraction could effect solders between ~10C -> 22C.
  - Animats 5y ago
    Yes. Not uncommon with bad soldering jobs. Problems like that can be diagnosed with freeze spray if necessary.[1] [1] https://www.techspray.com/using-freeze-spray-to-diagnose-faulty-electronics https://www.techspray.com/using-freeze-spray-to-diagnose-fau...
  - ethbr0 5y ago
    We had it on a copper cable line in university. The line was hung overly-tight without slack (old job). When it got just cold enough in the winter: no connection. Warmed up: connection. Finally realized it was the line, got Comcast to redrop from pole, and situation was resolved.
  - TheOtherHobbes 5y ago
    Yes, and not at all unusual. The gap between the ideal world of textbook circuits and the messy and random world of real circuits is a source of constant distraction and surprise. Thermal stresses, RF interference, issues caused by lighting, rain, and condensation, bad solder joints, other kinds of temperature sensitivity, designs with marginal component tolerances, component drift over time, vibration sensitivity, strange failure modes in damaged ICs, timing issues, power supply noise, coupling between circuit tracks and/or adjacent wiring, logic errors due to radiation (sometimes from surrounding metal), dust, insects, and animal damage - and on and on.
  - stephen_g 5y ago
    Some electronic parts are not rated to work below 0° C - for ‘commercial’ equipment the range is usually 0° to 50°C, and you often have to pay extra to get ‘industrial’ or extended range versions of parts that have ranges like -45° to 85°C (some fairly common parts you can even get to 105°C). It it’s failing at 10°, I’d suspect there is a crack in a PCB somewhere or a badly soldered joint that isn’t actually making proper contact until there’s some thermal expansion. We don’t do anything special with the PCBs or soldering specifically, and all the stuff we make is tested down to -35° and up to 55°C with no issues…
fragmede 5y ago
The moon is a nightime light source, and a pretty good one at that, every 30 days or so. Even after the invention of the light bulb it continues to light up the night. Thus it's not astrology to suggest that the phase of the Moon could affect things on Earth seeing as how it's what causes tides. (It is astrology to suggest the Moon is causing an effect based on magic though).
ColinWright 5y ago
For those who are interested, this is why you usually have two dishes/aerials, vertically displaced, so that when one has destructive interference between the direct and reflected signals, the other has constructive interference. I learned something about this when writing data compression and encryption software for radar surveillance systems, where there were multiple radars over a moderate coverage area, all sending data via microwave links over water back to the Command and Control Centre.
- walrus01 5y ago
  in modern point to microwave systems, unless the budget is really high, or the path is very long, it's rather unusual to have a vertical spatial diversity setup. much of the problem of losing link due to fade is accommodated by modern radios that have advanced variable modulation and FEC, which can operate anywhere between 4096QAM 5/6 and QPSK 1/2.
  - ColinWright 5y ago
    Interesting, thanks. My information is dated, but also it was a project with some specific requirements. It's possible that our client opted for the vertical spatial diversity setup because of that. I'd be interested to know what you think is a very long link ... 10km? 100km? I can't say too much more about where we were.
    - walrus01 5y ago
      Beyond 35-40 km is where you would start to see atmospheric ducting, temperature inversions and such really affect a link. In the bands where it pretty much has to be 6 GHz because anything 11 GHz or above (in the FCC licensed bands) would suffer extreme rain fade with the rain rate and amount of rain in the total length of the path. Generally things where you'd be looking at a pair of 6 ft high performance dual polarity dishes at minimum, and ideally a pair of 8 ft. The budget for just a couple of those and getting them properly mounted and aligned is a lot already before adding a spatial diversity second dish at each end.
walrus01 5y ago
point to point microwave link sounds like the bottom part of the fresnel zone was scraping the water - bad engineering design from the outset, tides or no tides. Not a good idea to do unless you have absolutely no economical way of getting one or both ends of the link higher.
eitland 5y ago
> When they graphed loss against time, the pattern was really periodic over many days. The periodicity turned out to be 12 hours 25 minutes, which they eventually realized is exactly the time between low tides. I've set up a couple of monitoring systems at a couple of different companies and one thing I've heard some people saying is that they don't care about "fancy graphs", they just want a dashboard of what is red and what is green. This might be a manager vs engineer perspective, because for me the graphs are the main point: it allows me to spot - patterns (each night, each weekend, some weekends, more-or-less-randomly-except) - and also trends: at this speed we are going to reach 80% utilization before November.
- rramadass 5y ago
  The key here is to describe and explain what/why to look for and how to do it. Don't leave it to the Client/Customer to struggle and figure it out on his own. I have often found it surprisingly difficult (in spite of being an Engineer myself) to read and interpret the various graphs in monitoring dashboards when i don't know what i am looking for. This is ten times harder for most "Manager" types.

deleted 5y ago

[deleted]

pedrocr 5y ago

Cool result. That figure 2 is begging for a scatter plot of SNR and tide level to see how well correlated they are.

abkfenris 5y ago

I remember reading that paper when I was trying to figure out why we were having issues with a wireless link down in the Patagonia fjords. Unfortunately we didn't have the hardware or enough control over the link (it took negotiating access with armed forces to work on either end) to try to implement any of their ideas.

m4rtink 5y ago

I heard a story about an astronomer loosing the chance to be the first to report a commet one cold winter night - just as he wanted to send the email to report it, the Internet connection was dead! He ran from the observatory to the nearest place with Internet connectivity, but by the time he sent the email from there, there was already a report from another astronomer elsewhere, a few minutes ago. Reason for the mysterious network outage ? Thermal contraction! The observatory was connected to the Internet via an optical link to a highrise building in the city that contracted ever so slightly due to the very low temperature, moving the laser beam of the optical link out of alignment, shutting down the connection.

bgirard 5y ago
When I started dating my wife she lived in a shared student residence. She would tell me that her internet didn't work when her room was cold. She had to wait for her space heater to heat up the the room. I didn't believe her at first but it turned out be true. She lived there for a year so I observed it several times. Never did find out what the problem is. I don't know if thermal contraction could effect solders between ~10C -> 22C.
- Animats 5y ago
  Yes. Not uncommon with bad soldering jobs. Problems like that can be diagnosed with freeze spray if necessary.[1] [1] https://www.techspray.com/using-freeze-spray-to-diagnose-faulty-electronics https://www.techspray.com/using-freeze-spray-to-diagnose-fau...
- ethbr0 5y ago
  We had it on a copper cable line in university. The line was hung overly-tight without slack (old job). When it got just cold enough in the winter: no connection. Warmed up: connection. Finally realized it was the line, got Comcast to redrop from pole, and situation was resolved.
- TheOtherHobbes 5y ago
  Yes, and not at all unusual. The gap between the ideal world of textbook circuits and the messy and random world of real circuits is a source of constant distraction and surprise. Thermal stresses, RF interference, issues caused by lighting, rain, and condensation, bad solder joints, other kinds of temperature sensitivity, designs with marginal component tolerances, component drift over time, vibration sensitivity, strange failure modes in damaged ICs, timing issues, power supply noise, coupling between circuit tracks and/or adjacent wiring, logic errors due to radiation (sometimes from surrounding metal), dust, insects, and animal damage - and on and on.
- stephen_g 5y ago
  Some electronic parts are not rated to work below 0° C - for ‘commercial’ equipment the range is usually 0° to 50°C, and you often have to pay extra to get ‘industrial’ or extended range versions of parts that have ranges like -45° to 85°C (some fairly common parts you can even get to 105°C). It it’s failing at 10°, I’d suspect there is a crack in a PCB somewhere or a badly soldered joint that isn’t actually making proper contact until there’s some thermal expansion. We don’t do anything special with the PCBs or soldering specifically, and all the stuff we make is tested down to -35° and up to 55°C with no issues…

fragmede 5y ago

The moon is a nightime light source, and a pretty good one at that, every 30 days or so. Even after the invention of the light bulb it continues to light up the night. Thus it's not astrology to suggest that the phase of the Moon could affect things on Earth seeing as how it's what causes tides. (It is astrology to suggest the Moon is causing an effect based on magic though).

ColinWright 5y ago

For those who are interested, this is why you usually have two dishes/aerials, vertically displaced, so that when one has destructive interference between the direct and reflected signals, the other has constructive interference. I learned something about this when writing data compression and encryption software for radar surveillance systems, where there were multiple radars over a moderate coverage area, all sending data via microwave links over water back to the Command and Control Centre.

walrus01 5y ago
in modern point to microwave systems, unless the budget is really high, or the path is very long, it's rather unusual to have a vertical spatial diversity setup. much of the problem of losing link due to fade is accommodated by modern radios that have advanced variable modulation and FEC, which can operate anywhere between 4096QAM 5/6 and QPSK 1/2.
- ColinWright 5y ago
  Interesting, thanks. My information is dated, but also it was a project with some specific requirements. It's possible that our client opted for the vertical spatial diversity setup because of that. I'd be interested to know what you think is a very long link ... 10km? 100km? I can't say too much more about where we were.
  - walrus01 5y ago
    Beyond 35-40 km is where you would start to see atmospheric ducting, temperature inversions and such really affect a link. In the bands where it pretty much has to be 6 GHz because anything 11 GHz or above (in the FCC licensed bands) would suffer extreme rain fade with the rain rate and amount of rain in the total length of the path. Generally things where you'd be looking at a pair of 6 ft high performance dual polarity dishes at minimum, and ideally a pair of 8 ft. The budget for just a couple of those and getting them properly mounted and aligned is a lot already before adding a spatial diversity second dish at each end.

walrus01 5y ago

point to point microwave link sounds like the bottom part of the fresnel zone was scraping the water - bad engineering design from the outset, tides or no tides. Not a good idea to do unless you have absolutely no economical way of getting one or both ends of the link higher.

eitland 5y ago

> When they graphed loss against time, the pattern was really periodic over many days. The periodicity turned out to be 12 hours 25 minutes, which they eventually realized is exactly the time between low tides. I've set up a couple of monitoring systems at a couple of different companies and one thing I've heard some people saying is that they don't care about "fancy graphs", they just want a dashboard of what is red and what is green. This might be a manager vs engineer perspective, because for me the graphs are the main point: it allows me to spot - patterns (each night, each weekend, some weekends, more-or-less-randomly-except) - and also trends: at this speed we are going to reach 80% utilization before November.

rramadass 5y ago
The key here is to describe and explain what/why to look for and how to do it. Don't leave it to the Client/Customer to struggle and figure it out on his own. I have often found it surprisingly difficult (in spite of being an Engineer myself) to read and interpret the various graphs in monitoring dashboards when i don't know what i am looking for. This is ten times harder for most "Manager" types.