Hi Paul

Just for interest what is the S/N margin with most commercial satellite
systems and how "strong" is the sun relative to those levels? I would
assume the margin for an end use TV viewer would be less than this?

Cheers Bob VK2YQA

KD7HB wrote:


Exactly right. Back in 1986, I worked for a bank data processing
service in Bellevue, WA. I set up a leased data line between our site
and two banks in Hawaii. The line went to San Francisco then via
satellite to Hawaii. Twice a year the service was stopped for about
1/2 hour while the sun passed through the focus of the satellite dish
in Hawaii. I don't think it affected the SF end of the link. AT&T
always called to warn of the disruption.

Paul

Bob Bob wrote in news:7kjom6-m74.ln1
@p400bob.personal.cox.net:

Hi Paul

Just for interest what is the S/N margin with most commercial satellite
systems and how "strong" is the sun relative to those levels? I would
assume the margin for an end use TV viewer would be less than this?

Bob, it is a few years since I did satellite path designs... but relying
on memory...

Most satellite TV here is digital, and the issue becomes a C/N ratio that
delivers acceptable error rates after FEC. The characteristic has a knee,
and error rates degrade rapidly at the knee. Satellite facilities are so
expensive, that operation is usually quite close to the knee... save a
margin for such things as weather, and that margin is usually no more
than necessary for most but not all such variables. You don't need much
Sun noise to ruin performance. (BTW, I think that the satellites used for
this purpose here are bent pipe technology (aka linear transponder), the
uplink is not regenerated on the bird.)

The issues discussed in the thread seem to mix up two distinct effects.
If the earth station sees the sun behind the satellite, C/N may be
degraded sufficiently to disrupt digital services. At equinoxes, the bird
rotates into the earth's shaddow and some times of day, and that means it
has to operate exclusively on battery, and if it uses the Sun for antenna
tracking, it will need to change reference. Using CO2 for a reference
(earth's atmosphere) is not reliable if the Moon appears from behind the
earth, the antennas could track the moon. I am not up to date on the
latest tracking references... but I am sure the Sun is still a good
reference, good contrast, visible most of the time.

Owen

"Dave" wrote in message
...

"Art Unwin" wrote in message
...
Aussiland television was turned off for a short while yesterday.
Statement made that there was a sunburst aproaching the satellites!
They were only off for a short while but it would appear the sunspot
cycle has become alive!

no solar activity... eclipse season maybe? for a short time each spring
and
fall geostationary satellites happen to line up with the sun's path,
stations that have no backup satellite may lose signal when their
satellite
lines up with the sun for a few minutes and the sun's noise blocks the
satellite signal.


Don't know if they still do it, but once upon a time HBO produced a program
guide for their home-sat subscribers. In the issues for April and October
(I think) they'd always advise us about sun outages and give us the
predicted dates, based on our latitude.

"Bob Bob" wrote in message
...
Hi Paul

Just for interest what is the S/N margin with most commercial satellite
systems and how "strong" is the sun relative to those levels? I would
assume the margin for an end use TV viewer would be less than this?

Cheers Bob VK2YQA

The Carrier-to-Noise ratio for analog TV was recommended to be 8db or better
for a noise-free picture (~50dB S/N after demodulation). With my 10-foot
dish, the peak of a solar outage would render the picture unrecognizable as
such for up to a minute. This means the sun had to be about 4 dB stronger,
since I recall 4 dB C/N was no picture at all. I hope this helps.

Sidelight: Analog degradation showed up as a type of video snow known as
"sparklies," usually in brightly colored areas. The beginning of a solar
outage would always be the appearance of sparklies.

I had the analog system for almost 20 years, so I was pretty conversant with
these periodic outages.

Digital, I don't know. I have a small dish setup but I haven't played with
it in years.

Sal