Can TP Power and Footprints be Dynamically Changed (or Why is AMC21 PBS So Tough)?

[cyberham]

I have been struggling to receive PBS from AMC 21 this week. You can read the blow-by-blow here. I have never before found an "80-cm dish required footprint" that I couldn't receive with my 1-metre Ku dish. There must be something I don't know.

I've always assumed that satellite tp output powers and footprints could be modified by their operators. Probably even in real-time by uplink commands. For such an expensive investment, this must be required. Assuming this is true, I have questions as follows:

• Can we trust footprint plots and tp output powers given to the general public if, at any time, the sat operator could change them?
• How often might an operator change tp / footprint and, if they do, why do they?
• Has the AMC 21 PBS tp output power been reduced, or footprint changed, from the information seen by the general public? I have this same question for MSNBC on 15W which used to be easy for me to receive but now is impossible using the same equipment at my end.
• Can anybody confirm using accurate info from a reliable source that PBS tps truly deliver 46~48 dBW to Atlantic Canada as indicated on satbeams.com and lyngsat?
• Any other information in this field would be devoured.

 

[northgeorgia]

The only thing I can answer is yes, from the beginning of the year I have noticed a TP output power decrease on some, but not all of the PBS TPs on AMC 21.

 

[cyberham]

Interesting. Wonder if it's atmospheric conditions or due to a change made by the operator.

 

[robosat]

This is the first post I read talking about possible power changes in TPs. I also noticed same problem from beginning of this year. I use a MicroHD with a 90cm dish aimed to AMC21. For many months I was receiving a strong signal with a Quality Signal of 60-70, and catched some 10 channels. But some months ago signal almost disapeared, and only channels PBS-E HD, PBS-W HD and another named HD04 (You see Japanese News there) are those that I can watch (sometimes none of them). I was thinking of possible terrestrial interference, but now that i read this post, old questions raised again : Changes in TP power? Changes in TP Footprint? I asked this as yo do, cyberham... and months ago some expert forum's guy answered me that he didn´t believed these changes can occur...
Anyway, I don't have an answer of what's going on ... Greetings...

 

[Conky]

could the age of a satellite come into play? ie slow degradation of the solar panels

 

[Mr Tony]

Can we trust footprint plots and tp output powers given to the general public

no

if, at any time, the sat operator could change them?

yes. A great example is the NBC news feeds on 103W. They operate them at 1/4 the normal power (per an uplinker who posted here a while ago) because "the networks have 15 foot dishes so low power doesnt affect them"
edit: found that
Power levels are kept VERY conservative since it's designed for big dish reception. We only run about 1/4 of the transponder's actual power capacity to save the batteries on the satellite, and to minimize interference.

 

[Mr Tony]

could the age of a satellite come into play? ie slow degradation of the solar panels

amc21 is newer..its only 5 years old

 

[cyberham]

no

yes. A great example is the NBC news feeds on 103W. They operate them at 1/4 the normal power (per an uplinker who posted here a while ago) because "the networks have 15 foot dishes so low power doesnt affect them"
edit: found that
Power levels are kept VERY conservative since it's designed for big dish reception. We only run about 1/4 of the transponder's actual power capacity to save the batteries on the satellite, and to minimize interference.

That's definitive! Interesting you mention NBC on 103W. Because this week's experience trying to catch PBS on 125W was exactly the same as NBC on 103W. Even when I skewed correctly for NBC, all I could ever receive was an SL 45% and SQ wiggling below 10%. I would propose that both NBC and PBS are using similar tp output powers and footprints in Atlantic Canada. On a 1-metre dish, neither are receivable here. That's my story until somebody else in this area convinces me otherwise.

 

[toucan-man]

That's my story until somebody else in this area convinces me otherwise.

Let's get you that bigger dish. You said 1.2M, but would you go 1.8M if one were available ? Even bigger ?

 

[Tron]

I'm getting ready to install a spare 1 meter Channel Master on 103W. I've had too many bad experiences with adjacent transponders.

 

[cyberham]

Let's get you that bigger dish. You said 1.2M, but would you go 1.8M if one were available ? Even bigger ?

No new procurements of anything. Sitting on edge of seat waiting to see if I am going to have a dramatic personal relocation.

 

[toucan-man]

No new procurements of anything. Sitting on edge of seat waiting to see if I am going to have a dramatic personal relocation.

Gaspésie ?

 

[cyberham]

Mon dieu...that's your dream...not mine!

 

[toucan-man]

Mon dieu...that's your dream...not mine!

You said dramatic, I give you dramatic.

 

[cyberham]

Dramatic is where even offset dishes truly point "up" and longitudes are measured east of Greenwich.

 

[Titanium]

Published EIRP and dish sizes for a given footprint are based on a full transponder that is saturated at full power. This rarely happens on FSS satellites.

Most transponders are SCPC (Single Channel Per Carrier) and/or only use a portion of bandwidth available on a transponder. The link budget is based on the signal strength required, priority, reliability and financial requirements.

Most modern satellites output: C-band 35 - 100watts and KU-band 20 - 130watts (DBS 250+ watts). The beam shaping also affects the required output power to provide required EIRP levels at the downlink locations.

Possibly over simplified.... Less popular satellites / lower wattage / less power consumption = decreased demand on the finite satellite resources = lower uplink $$$ One of the cost factors when an uplinker or satellite management is preparing the link budget for a broadcaster is the amount of power to provide the required signal and reliability in a given footprint.

The amount of amplification required on the satellite platform to meet the link budget will be affected by the uplink dish size and output. One broadcaster may uplink with a low gain dish and power for direct to home and require 85% uptime using a 90cm dish with average to poor performance characteristics. Another broadcaster may be distributing to commercial downlinks with 4 meter dishes with defined performance and require 98% uptime and another to 7 meter dishes with exceptional performance and 90% uptime.

Each link budget purchases the bandwidth and the signal gain and robustness needed to meet their distribution requirements.

 

[cyberham]

This explains why, in this case of AMC21 at least, the published "80-cm dish required spec" is of little value.

What is needed is for a cool programmer to create a website where satellite hobbyists could input their reception data including date/time/sat/tp/receive dish size. Once this data is collected, it could then be put in various output formats (in real time?) on graphs including dish size vs sat, dish size vs tp, etc. With a lot of data, it would be useful for hobbyists and maybe even for sat operators who want to understand their actual measured footprints for their purposes. This would be a parallel of amateur radio operators that report in real time stations they have communicated with around the world and then the whole community understands current propagation conditions.

 

[toucan-man]

This explains why, in this case of AMC21 at least, the published "80-cm dish required spec" is of little value.

Maybe the publisher is of little value.

 

[Jim S.]

I'm starting to wonder about a possible power reduction on PBS myself. I'm in Pennsylvania where I used to have strong signals, as I should. Last spring, I lost AMC21 due to a tree growing into LOS. Now, as the leaves are coming off (very, very slowly, since it's an oak), signals are starting to return, BUT, the national PBS feed is the LAST thing to come back! I get one (but only one) of the Claro transponders with maximum quality. All the PBS channels are still intermittent -- however, I get a more reliable signal on the notoriously-difficult Montana PBS than I do on the national feeds!

 

[cyberham]

Misery enjoys company.