Re: [Starlink] one dish per household is silly.

[Alexandre Petrescu <alexandre.petrescu@gmail.com>]

Le 13/11/2023 à 21:34, Ulrich Speidel via Starlink a écrit :
>
> Caution - 250 kW peak sounds more like a horror movie (around 500 W 
> average powers your average household) but there's an easy 
> explanation. It's also a good example for why Reddit isn't a good 
> source of information unless you know and can interpret what it is 
> that you're looking at. The figures you've seen are almost certainly 
> EIRP ones (effective isotropically radiated power). And EIRP ain't the 
> same as power consumption.
>
> Simple example: Take a 100 W light bulb that radiates more or less 
> isotropically (same amount of light power in all directions) without 
> any reflectors etc. When you look at that light bulb, you see 100 W 
> EIRP. Put a mirror behind the lightbulb, so you now see the bulb and 
> its reflection, which looks like two bulbs. Makes 200 W EIRP, but it 
> doesn't increase your power bill. A simple mirror like that has a gain 
> of 3 dBi.
>
> At a Ku band frequency of 18 GHz, a 1.5 m diameter parabolic dish has 
> a gain of over 48 dBi. Each 3 dBi step in there effectively doubles 
> the number of transmitters you see reflected to you if you're the 
> receiver. 48 dBi means 16 such steps. So you have to divide the EIRP 
> of something like this by the "2^16" reflections that this gives you. 
> If you're having 250 kW EIRP, then the actual transmit power is just a 
> few watts, and similarly your power consumption is a lot more modest.
>
> Another way of looking at this is that what goes up (to the satellite 
> in terms of bits) has to come down (to another ground station / 
> dishy). That happens via a similar path. So if you'd transmit to a 
> satellite with anything like even 25 kW actual transmitter power, 
> you'd also need a similar amount of transmit power at the satellite to 
> downlink. And you'd have to generate that power up there in orbit. Now 
> I have solar PV, and I know that generating a measly 5 kW peak takes 
> 20 panels of around 2 sqm size each. Generating the sort of power 
> you'd need to transmit at 25 kW would require solar arrays on the 
> satellite that are more like the size of a football field. Ballpark.
>
> Thankfully EIRP for a dish of fixed size goes up as a linear function 
> of dish diameter and transmit frequency as the antenna becomes more 
> "pointed" as you move from conventional C band to the Ku and Ka bands 
> used by Starlink.
>
Also, I'd check the label on the power supply unit of the dish box.  
That tells how many Ampers - at a maximum - it can draw.

Alex

> On 14/11/2023 5:22 am, Inemesit Affia via Starlink wrote:
>> You have to size power equipment for max power plus a percentage 
>> regardless of current traffic needs.
>>
>> Look for the ANATEL docs on Reddit you'll see it there(per dish at 
>> least). Or search the NASASpaceflight forum.
>>
>> I think it's 250kw peak. Could be 25kw instead can't remember right. 
>> But each dish is more than 5kw and there's other equipment than dishes
>>
>> Nov 13, 2023 5:10:27 PM J Pan <Pan@uvic.ca>:
>>
>>     is the power consumption related to traffic volume? currently the
>>     traffic is very light
>>     https://www.reddit.com/r/StarlinkEngineering/comments/17k3jas/intergs_ground_station_satellite_links_much/
>>
>>     -- 
>>     J Pan, UVic CSc, ECS566, 250-472-5796 (NO VM), Pan@UVic.CA,
>>     Web.UVic.CA/~pan <http://Web.UVic.CA/~pan>
>>
>>     On Sun, Nov 12, 2023 at 10:40 PM Inemesit Affia via Starlink
>>     <starlink@lists.bufferbloat.net> wrote:
>>
>>
>>         It's kinda expensive to run. Likely 75KW peak.
>>
>>         Check the power requirements for a regular gateway and divide
>>         by two.
>>
>>         Might be useful for Taiwanese Islands though
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> -- 
> ****************************************************************
> Dr. Ulrich Speidel
>
> School of Computer Science
>
> Room 303S.594 (City Campus)
>
> The University of Auckland
> u.speidel@auckland.ac.nz  
> http://www.cs.auckland.ac.nz/~ulrich/
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