Transponder Power

[BigDutchStrikesBack]

So the meters that the sat. fitters use, these would be able to give a reading of each transponder ? Assuming the time and effort was applied to do it ? Personally, this would be good to know how each transponder differs.

 

[iceman]

So the meters that the sat. fitters use, these would be able to give a reading of each transponder ?

Thats correct....Digital satellite aligning meters have BER (Bit Error Rate) reading which can tell you number of bit errors in the data stream...

Bit Error Rate: A measure of transmission quality. It is generally shown as a negative exponent, (e.g., 10-7 which means 1 out of 107 bits are in error or 1 out of 10,000,000 bits are in error).

Bit Error Rate. Denotes the quality of a received demodulated digital signal. The lower the rate, the better the signal. Example: a BER of 10 -4 means one error in every 10,000 bits.

 

[dxsat]

So the meters that the sat. fitters use, these would be able to give a reading of each transponder ? Assuming the time and effort was applied to do it ? ..

It's a doddle to meter an individual transponder. Makes pointing a dish relatively easy, particularly Astra 2D.

 

[BigDutchStrikesBack]

i thought as much so suddenly its not a matter of "luck" to get channels, just a matter of understanding ;)

So attached is a list of all the Astra transponders at 28.2, it would interest me to know the signal level of each transponder when focused on each different satellite !

How long does each reading take - a minute maximum ?

 

[dxsat]

To take a reading from one transponder takes a small fraction of a second.
Signal strength on transponders varies with location.

I use a Lacuna/Wolsey Satmeter 3

 

[BigDutchStrikesBack]

if it takes such a short time and every 3 months from a "test" location ie the same place every time "someone" were to measure the signal strength of every transponder of each satellite whilst focused on each satellite then we'd all know what happened to Ch4 ;)

Focused on 2A
2A Transponders / 2B Transponders / 2D Transponders

Focused on 2B
2A Transponders / 2B Transponders / 2D Transponders

Focused on 2D
2A Transponders / 2B Transponders / 2D Transponders

If when a channel disappears it was clear that everything on 2A was slightly weaker when focused on the other dishes then it would suggest 2A was further away than previously to the other sats.

You get me .....

 

[dxsat]

Not really..
It's not practical to test every single transponder regularly, unless you have a great deal of time to kill. (currently, I'm doing regular readings on one 2D transponder, and that is time consuming enough)
The installers in Cyprus say that they can focus a large dish on one of the four Astra 2 satellites. (i.e. they are in slightly different positions) I've never found this, but I never work with dishes larger than 1.8 metres.

 

[Topper]

Added to all the previous especially

So the meters that the sat. fitters use, these would be able to give a reading of each transponder ? Assuming the time and effort was applied to do it ? Personally, this would be good to know how each transponder differs.

you must also take into account that re-positioning takes place at regular intervals as the satellites drift and they need to bring the sats back in within a pre-determined transmission position so that they appear from the earth to be from one source point when in fact they are hundreds even thousands of meters apart. This is bound to affect readings obtained by transponder and those readings would probably have to be grouped by satellite even begin to make any sense of it all.

 

[Zorba]

Most of the sky package we get over here usually works okay on a 2.4m dish.When someone wants a 3m or bigger its to get bbc/itv on 2D .So,because the dish is bigger I dont have to worry about 2A 2B etc because if the dish is slightly off those sats you wouldnt notice.Thats why I set my sat meter to a 2D frequency,and align the dish for maximum signal.Its only recently that ch4 sky three etc have gone weak,so now,after I have aligned the dish for ,say,bbc 1 frequency I can instantly switch my meter to the ch4 frequency and see the signal strength and then I know whats going on and what to do.
On a spectrum analyser each"spike" is a frequency which might have one channel or 10 or 20(radio included).and the spikes are not equal length some longer some shorter.This applies to all satellites.Obviously the longer the better and i can switch from high,low vertical and horizontal and see differences but theres much more involved in aligning and thats what seperates the cowboys and the professionals.
Now where did I park my horse?

 

[iceman]

theres much more involved in aligning and thats what seperates the cowboys and the professionals.

He he...too bloody true M8...couldn't agree more.

 

[Topper]

He he...too bloody true M8...couldn't agree more.

And I have nothing but respect for you guys on the fringe in some repects I am only jealous as I like a challenge:-worship :-worship

 

[BigDutchStrikesBack]

Hey ! I`m not belittling what you guys do, sorry if it came across that way.

I used to be involved with tuning audio in cars and part of that was with an AudioControl RTA ... visual representation of the audible sounds received by the mic ... sounds very similar to the analyser Zorba mentioned.

To me, a periodic measurement of each transponder from a set location would give a good idea on seasonal signal strength changes (if any) and if those measurements were done a couple of times during a day then it would really help to explain/understand to the interested customers what they will and won't receive and why .... before they order rather than after they have spent a small fortune on a large dish.

 

[dxsat]

If you can wait another month or so, I'm going to publish my 2D readings for a six-month period ending around April. I have been curious to see if there is a peak around December 21. If I can manage it, I'll keep the readings going all year, and to put them in graphic form to help to try to understand the seasonal goings- on that people complain about.

 

[Analoguesat]

Added to all the previous especially

you must also take into account that re-positioning takes place at regular intervals as the satellites drift and they need to bring the sats back in within a pre-determined transmission position so that they appear from the earth to be from one source point when in fact they are hundreds even thousands of meters apart. .

Try dozens of miles apart each sat sits in a box something likew 75 miles square.

 

[Zorba]

Hey ! I`m not belittling what you guys do, sorry if it came across that way.

I used to be involved with tuning audio in cars and part of that was with an AudioControl RTA ... visual representation of the audible sounds received by the mic ... sounds very similar to the analyser Zorba mentioned.

To me, a periodic measurement of each transponder from a set location would give a good idea on seasonal signal strength changes (if any) and if those measurements were done a couple of times during a day then it would really help to explain/understand to the interested customers what they will and won't receive and why .... before they order rather than after they have spent a small fortune on a large dish.

I suppose its like the sound in cars,you might get more bass in one car and more treble in another.So,doing tests on my roof would give me different results from another roof,be it up a mountain,down in a valley ,top of a seven storey block,near mobile phone transmitters etc.
I could test on a clear,dry day and the same time next day we might have 75% humidity.
Not that I have time to take multi readings everyday,but I welcome Snaps commitments and look forward to his findings.Then you can come to Cyprus and take measurements all day long :-beer
We learn from experience,Paphos good,Larnaca bad.I am honest to customers and I tell them expect break up early evening in the summer when its humid or go for a bigger dish,where apropriate.

 

[BigDutchStrikesBack]

Snap - i`d be interested in your results and hope to check back into this forum in a few months to see them

Zorba - any analysis will need "control" conditions so same location, same time(s), same weather conditions .... the more data recorded the more accurate any results will be.

I was just focusing initially on why desptie getting one transponder/frequency very well, another from the same satellite is not being received, and the difference in power of said transponders.

 

[OldShep]

Hi

I’ve been following the “loss of Ch 4” thread on this forum for a while, and then saw this thread last week. I thought I might have a valuable input to the transponder power debate…

Several contributors seem to have accepted as fact that satellite transponder power output is fixed when the transponder is manufactured, and can not be altered once the satellite is in orbit. This is possibly causing some confusion. It is the GAIN of a transponder which is fixed; notwithstanding that this tends to deteriorate with spacecraft age. Power output can be (and routinely is) varied throughout the life of a spacecraft (and often on a daily basis), by altering the power of the uplink for a specific transponder. The over-riding factor which determines how much power is allocated to each transponder channel is the power available to the overall comm’s payload of the satellite (i.e. from the solar cells, less platform overheads such as inertial stabilization {e.g. three-axis stabilisation as found on Astra 2A and 2B} ), and often more importantly, the amount of power which can be “eclipse protected” (i.e. the battery back-up the spacecraft has to rely on whenever it is in the shadow of the earth and away from the sun).

One of the main functions of a satellite control centre is to “power-balance” the spacecraft. The only power which is available comes from the solar-cells (or batteries during an eclipse). No spare power can be stored; you can’t add an extra battery or two. Conversely, there is no source of extra power available. I believe that SES (Astra) actively monitor the radiated power from every channel on every transponder on their fleet of satellites at several (?? around 6??, need confirmation) sites throughout Europe. The output power of each channel (note, each channel, not each transponder) is constantly modified in attempt to maintain a specific signal-to-noise ratio at each receiving site. For DTH television these “receiving sites” could potentially be every home within the target area, e.g. for most BBC channels this is the whole of the UK, assuming that each home had a correctly installed dish of the appropriate size… but that is a discussion for another thread.

I personally believe that the problems we have seen here “on the fringe” over the last few weeks/months have more to do with the fundamentals of satellite communication. Personally I’ve been keeping an “eye” on the orbital positions of Astra 2A, B and D since I started loosing Ch 4 at the end of last year (wot! no ER !! no Big Brother !!!). The positions of all the Astra satellites (and many, many others) are published daily by NORAD (try a google search for “NORAD two line elements”). To translate these figures into something a bit more useable I use some free software called “Satscape” (again a google search will find this).

The upshot of all this is that Astra 2D seems to have been moving significantly eastwards since the back-end of last year {2006} (see 2 attached jpgs, which are taken from satscape “3D” screen-shots, Dec 06 and Feb 07). My theory (for what it’s worth), is that here in the fringes of the footprints, many of us with large enough dishes to recieve UK terrestrial TV have been “tweaking” alignment to follow 2D (to maintain BBC) for some time, but we may have inadvertently lost some 2A verticals (including Ch 4). Sooner-or-later (I believe…) there will have to be a station-keeping burn on 2D. That is that SES will fire its rocket motors to move 2D significantly westwards (and shoten its in-service life at the same time).

A good test for this theory would be if there were a significant number of Astra 2 “users” in fringe areas who hadn’t enough antenna gain to receive 2D (couldn’t receive BBC/ITV etc.), and so hadn’t gone “2D” chasing , who hadn’t noticed any significant change over the last couple of months. I’m sure there are plenty of suitable contributors on this forum.

I realise that I’m possibly asking to be shot down in flames with this posting )(-red (please be gentle..) but I at least hope that readers will realise that there is still a bit of “rocket science” involved with satellite communications.

 

[geoffreys]

Thanks for that, but I not sure you have the true explanation. I cannot receive 2D so have NOT been "2D chasing", but Ch4 4 reception has got
worse. Just that transponder NO others. In fact I know others in Cyprus
wh CAN receive 2D, some have "2D chased", some have not (did not need
to as they have bigger dishes so 2D was still OK); both of these categories
have also had a reduced Ch4 transponder signal. The other explanation
given, that seems perhaps more plausible (?), is that an ARABSAT transponder
on the same frequency is causing some desense (what we used to call
the capture effect when 2 FM transmissions were on the same freq,).
Unfortunately for most of us the ARABSAT signal is stronger so we lose
out on Ch4 at times of day when Ch4 gets weaker anyway. Before we still
got a picture, now we don't as the Ch4 signal is being pushed down enough
to be below the necessary threshold. The only cure would appear to be
either (a) to get ARABSAT to change freq OR ( buy bigger dishes.
Geoff
Cyprus

 

[iceman]

Geoff
In the light of my personal experiences,i have to disagree with you on both points..

1-Channel 4 signal has not been reduced,i can still pick it up on even 1.8m offset dish...Ok,it is unwatchable between 1-4pm but it has always been like that..(even before this signal loss was reported)
No problems whatsoever on my 3.0m dish 24/7 :-righton ..

2-If Arabsat was the reason for this problem why do we not get effected in North Cyprus?

OldShep's post confirms my theory that the problem is caused by the movement of Astra satellites from eachother...
If the dish is peaked on any one of the satellites,you will notice that the signal strenght is there but when the whole group is targetted the problem starts (if the dish is not large enough to compensate for the loss)

 

[Zorba]

My turn again.
1)its not just ch4 ,its also sky two and three.and sometimes eurosport.
2)offset dishes not affected.
3)I'm not sure its 2d drifting east,because the problem is "ch4" getting worse so the "ch4" satellite is drifting.
4)Adjusting the elevation downwards gets ch4 back,but makes 2D weaker.
Also,I installed a 3m last saturday and looking in the direction of the satellite the 2 storey house next door was to the left and we feared that it might interfere but not only was 2D excellent but the signal from the ch4 sat was also high,so no "compromise"adjustments were required.
So the other theory is the Arabsat 3 at 30e might be the problem and kyrenia might be just outside of the footprint of the offending frequencies.
to Oldshep and geoffreys or anybody else,if your ch4 is there but weak,why not try adjusting your dish down a bit and see if ch4 improves ?just to prove me wrong?