Question on satellite uplink and downlink power budget?

[mngeow]

I have this question here which I'm not sure about:

**broken link removed**

I have no idea how they get the answers for part d and part c,is power received at transponder input the same as the power of the power transmitted from the earth station?I'm really unsure about this question.


I also want to know what would happen if the question wanted me to find the signal power and C/N ratio at the satellite transponder output instead

Thanks for the help!

 

[JimB]

The EIRP, Effective Isotropically Radiate Power, in other words the power we would need to put into an isotropic antenna to give the same field strength as this transmitter and antenna.

The transmitter power is stated as 2000 watts, calculate the equivalent dBw by using the formula 10.Log(2000/1).

As we are now working in db, add the antenna gain (which should be relative to an isotropic radiator, but that is not explicitly stated).
You should now have the answer 98dbw (I did).


To find the received signal power:

We already have the EIRP from the transmitter, from this we need to subtract the free space path loss, just off the top of my head I cant remember the formula for this, Google it.
That will give you the power at the antenna, so now add the satellite antenna gain and you will have the receiver power in dbw.
Use the db = 10.Log(P1/P2) formula to convert the dbw to (nano)Watts.

Does that help?

JimB

 

[RCinFLA]

https://en.wikipedia.org/wiki/Free-space_path_loss

Ku uplink freq is 14-14.5 GHz.

You have all info you need to calculate.

just comments:

Echo delay does not have any time delay for transponder which is unrealistic. (solution is showing two times round trip free space propagation delay for echo).

100 deg K for satellite receiver is a bit optimistic as antenna is pointing at hot earth (300 deg K). 100 deg K might be realistic for earth station receiver which points at sky.

 

[koolguy]

Good thread good replies.....

The transmitter power is stated as 2000 watts, calculate the equivalent dBw by using the formula 10.Log(2000/1).

2Kwatt isn't a big power from a transmitter ..
I mean that FM transmitter are generally of this rating in big cities....
Please explain , why it require less power...

 

[RCinFLA]

Good thread good replies.....

2Kwatt isn't a big power from a transmitter ..
I mean that FM transmitter are generally of this rating in big cities....
Please explain , why it require less power...

Commercial FM transmitting antenna (100 MHz) has much lower omni directional gain (maximum EIRP is 100kW) compared to the 65 db gain (at 14 GHz) highly directional satellite earth station dish. EIRP of Ku band earth station transmitter is 2kW times 65 db gain of antenna equals 6.3 E 9 watts.

Bandwidth of satellite uplink is 36 MHz compared to 150 kHz for commericial FM.

 

[koolguy]

Bandwidth of satellite up link is 36 MHz compared to 150 kHz for commercial FM.

why satellite has 36mhz bandwidth??

 

[trash]

One of the antennas at the earth station where I worked is 32m. For C Band it has a gain of about 65dB.
We use 2.5kW TWTA's on this antenna. So at full power on a single polarity this has an EIRP of about 8GW.
Double that if you consider the other polarity.

In reality, this antenna very rarely runs more than 12 watts.

On another 18m Ku Band dish I worked on has 12 x 2kW KPA amplifiers all running at saturation on Ku Band.
This can chuck about 152GW EIRP into the sky at full power, and there is room for expansion !

In terms of paying for the lease, less is better
Satellite transponders are linear devices. More power in = more power out.
If you're running on solar power with battery backup, then using as little power as possible allows for better power budgets and greater transponder use.

why satellite has 36mhz bandwidth??

It's a trade off. If a satellite has only one transponder, if that transponder fails then satellite is useless.
If the transponder is too small, then wide bandwidth signals like analog FM TV carrier or a high symbol rate digital signals will be too wide for the transponder.

I've seen commercial satellites with small ~24MHz transponders and others with large ~250MHz transponders.
On the ground the users do not notice that several assigned transponders are actually just one big one.
While the guard bands aren't used, they certainly could be. I've seen pirate stations sometimes use them itinerantly.

 

[koolguy]

One of the antennas at the earth station where I worked is 32m.

Yes, i have seen this antenna in my city...
and the gain you are talking about 65db is very high?? how??

I've seen pirate stations sometimes use them itinerantly.

If you know the terrorist and pirate are using these signal why don't you catch them and disable there signal...

 

[koolguy]

One of the antennas at the earth station where I worked is 32m.

Yes, i have seen this antenna in my city...
and the gain you are talking about 65db is very high?? how??

I've seen pirate stations sometimes use them itinerantly.

If you know the terrorist and pirate are using these signal why don't you catch them and disable there signal...

 

[RCinFLA]

Normal clear sky power is usually only about 12-20 watts from PA. You need the reserve power at Ku band because of the heavy attenuation due to rain. I was working with an uplink vendor in N. Carolina that had an 10 meter dish when their signal went out. When I called them to find out what happen the guy said they have the PA pushed to 3 kW and can't burn through the rain storm. I joking asked if they where turning the rain into steam.

For shared single carrier per subscriber dedicated transponders like used at branch banks, they are very strict about uplink power control. Too much power by a single user can put the transponder into saturation region and pinch out the other users.

A long time ago a renegade tech used an earth station in northern Florida to put HBO's C band transponder into saturation taking HBO off the air to all the cable TV companies across the U.S.. Now they use multiple Ku transponders with backup. There are still C band cable TV installations around. C band doesn't have the rain fade problem anything like Ku band.

 

[trash]

Yes, i have seen this antenna in my city...
and the gain you are talking about 65db is very high?? how??

It's a big antenna
I'm sure you can run the gain through any of the online calculators and they will give you the same result for 6GHz

If you know the terrorist and pirate are using these signal why don't you catch them and disable there signal...

What can I say, there's some bad people in the world.
As for catching them well it really isn't my problem. It's not my satellite and not my job to find them.
Though some of the data they send over the satellite it isn't too hard to work out who and where they are.

Even if the satellite owners wanted to prosecute them, they can't. They're often in another country where there are no laws offering protection or if there are, they are very difficult to exercise. I have my own transmitting gear and I have played around with satellite piracy. (ha, I'm one of those bad people)
My signals are very different from the other pirates that are usually companies with VSAT's who turn on their earth station and send a burst of data, usually emails etc and then they shut down. Mine are, well even harder to find and notice.

Generally there aren't that many people who have their own transmitting gear and the pirates do not want to attract attention to themselves so they usually do their homework and behave themselves. As far as the satellite owners are concerned, it's not so much a theft that will hurt them, but more rather like somebody picking the pennies from their pocket.

The effort to find, catch and prosecute them far outweighs the cost of just ignoring them.

 

[koolguy]

I have my own transmitting gear

What is transmitting gear..??

The effort to find, catch and prosecute them far outweighs the cost of just ignoring them.

Does every satellite is under pirates?? why govt. not take action??

 

[trash]

Transmitting gear = Equipment to transmit and uplink to a satellite. TWTA (traveling wave tube amplifier), Upconverters (and/or downconveters), and a modem or IF stage.
In some cases it is possible to modify an internet SSPA (Solid State Power Amplifier) from a two way internet unit, but they require a lot more effort to put them on a frequency of use.

No, not every satellite has pirate traffic. In fact it is quite rare. Individual hobbiests who might get their hands on equipment are not of any threat to the satellite owners.
Their signals a small and no commercial loss to the satellite owners. They really only do it to see if they can.
Most of the pirates are small commercial operators. They usually cannot warrant spending a large sum of money on the data link. The carriers often charge a premium price for their service and in some cases they will require some extensive quality testing on the equipment used. So it's easier for them to stow away a signal for short periods and 99% of the time nobody will notice.

Governments can't take action. If the pirate is located in a foreign country, then that country may not have any laws with respect to radio spectrum.
They also often have no will to take action because these small companies are often in remote areas providing income to local people.
Then of course the local government may have no method of finding them. It's hard enough to find a low power VSAT in a developed country let alone a remote village in a third world country.
Think of how you would find something like a signal that is 2MHz bandwidth, about 5 watts, on 14GHz on a very directional antenna pointed at the sky AND ... it could literally be located anywhere on your half of the planet.
There is very little anybody can do about it.

Even in a developed country like Australia where I live, there are laws against it. The problem is that the cost of prosecuting somebody is very expensive and it is very difficult to prove let alone find the company or person doing it.

However in cases like Captain Midnight where a major carrier is effected, a lot of money is involved and the number of people capable of doing it is small.
In the USA, the FCC has less restrictions and legal minefields than other countries so high profile examples are dealt with swiftly and harshly.

 

[bryan1]

G'day Trash,
You wouldn't be working with IPStar by any chance ???

Regards Bryan

 

[koolguy]

Think of how you would find something like a signal that is 2MHz bandwidth, about 5 watts, on 14GHz on a very directional antenna pointed at the sky AND ... it could literally be located anywhere on your half of the planet.

To receive signal from satellite will be a problem, but if i have a bus i can know how many people are there and what they have..so, why don't satellite charts like lyngsat don't provide information on that??
and if we talk about satellite mobile phone then why don't the satellite owners record the data..??

 

[trash]

You wouldn't be working with IPStar by any chance ???

No, I have done work (subcontracted) for them though. I haven't had much to do with them as other guys I worked worth picked up most of that work.

but if i have a bus i can know how many people are there and what they have..so,

In the real world the pick pocket is not going to tell you where he lives, when he strikes, even how much money he took or that he even exists.

why don't satellite charts like lyngsat don't provide information on that??

Because Lyngsat aren't a registry of satellite services, it is just a web page managed by one person and support from users who submit information to it.
They don't record uplinks, nor do they record narrowband data services.
Nobody has any interest in monitoring a 9600bps remote water logger etc, let alone have the LNC or modem to receive and decode the information.

and if we talk about satellite mobile phone then why don't the satellite owners record the data..??

Satellite phone services are itinerant and unpredictable both in their frequency and usage.
I don't see the need to 'record' data for a phone call. The only reason to do this is the service provider for billing purposes.

 

[koolguy]

In the real world the pick pocket is not going to tell you where he lives, when he strikes, even how much money he took or that he even exists

But in satellite communication, I can't up-link and down-link the signals without permission or some code ...( I think)

They don't record uplinks, nor do they record narrowband data services.
Nobody has any interest in monitoring a 9600bps remote water logger etc, let alone have the LNC or modem to receive and decode the information.

Is there any place where i can get this info.

 

[trash]

But in satellite communication, I can't up-link and down-link the signals without permission or some code ...( I think)

Downlink there is nothing anybody can do to stop you. Well not unless your government has some secret police that go around looking for dishes, but even they can be hidden. I heard that Malaysia is one country like this. I've not paid much attention to home satellite users whenever I've been there.

But in most of the free world, there is nothing stopping you receiving any signals you like. There may be laws that say that you cannot do it, but those laws are usually very difficult to enforce and prosecute. In reality satellite service providers are free to air because they want you to watch them. The various religious channels are like this. Or in the case of pay TV, the service providers protect their content by scrambling the signal. Even breaking those codes is quasi legal.

In Australia the law allows anything that is not mentioned. The only restriction is not to listen to telephone calls. So satellite traffic can be received by anybody (as long as it is not phone calls). Like most countries we have pay TV and those services were cracked and broken. Doing this and watching the services for free has never been illegal. What you do with the information you recover is your business. The emphasis is on the service provider to provide their security, not the taxpayers.
So if you cracked pay tv, then you could watch it for free. Even if there was a law against it, there is no way the authorities could catch or prove that you were doing it.
However, several people were caught because they were selling cracked cards. They were breaking the law because they were selling information and tools to enable other people to breach program content. Even then these cases were very marginal in this country and the penalties were minor compared to some of the money these people made selling cards.

Uplinking to satellites, well that's a different story. Generally the government will grant you a licence for an earth station enabling you to legally use the uplink bands.
Then you need the permission of the satellite owner to lease transponder space on their satellite.

In the case of two way satellite units used for internet etc. They come under a class licence system. The service provider (who may not even be the satellite owner)
leases the transponder space and ensures all the customer equipment meets a certain specification. They also control the two way equipment, like what frequency, power and when they transmit their data to the satellite. The customer does not need to worry about licences because the service provider takes care of it.

But if you're a pirate, then the government doesn't know you have the equipment and nor does the satellite owner. If you transmit to their satellite, there is very little they can do about it. They really only have two options. 1> Jam your signal or 2> shut down that transponder. But since it has paying customers on it, they can't do that.
The best they can hope for is to monitor the content of the signal and try to work out from this information who the pirate is.
A smart pirate will just encrypt the signal, and they will get no information from it.

Is there any place where i can get this info.

The satellite owners know who is (legally) using their satellites and they keep a record of that. But they're not going to share that information with you or anyone.
It's sensitive corporate information.
The only way for you to find these small services is to buy a good spectrum analyser (or borrow one) and a good dish and LNC and scan the entire downlink spectrum for even the smallest signals.
This is an example...
**broken link removed**

The symbol rates and encoding you'll have to guess or blind scan.

 

[koolguy]

If we talk about the reception some times the scramble channels act as FTA, why??
for short duration...

 

[trash]

For testing purposes. Sometimes also for publicity.