A good spectrum analyser or field strength meter or both.
A nice steady, sturdy and precise vertical post.
A good compass for N-S alignment.
A lot of time for setup. ;)
Posts by Ignax68
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I know by direct experience too, many reasons on how and why this can happen.
I name a few:
_weather conditions, all tastes, tx side, rx side, control side and all relevant combinations.
_direct feedhorn sunlight collimation, especially in the winter, last few minutes.
_line-up errors and mistakes.
_thermal gain shift, the warmer the equipment, the lower the gain.
_sng operator needs, too low or too high signal.
_destinatiin needs, too low or too high signal.
_transponder density.
_equipment failure.
_modulation changes.
This can happen in various levels and different combinations and on both sides.
As per the destination of the signal, any dish below 3m diameter is considered not broadcast :eye-tongue:
Have a nice day!
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Meanwhile, I'll attach some pics of latest nice job I did at end of september.
KA-band 13.2m dish:54_002::bravo: i have got to get me on of those...... as an added bonus the wife would deffo leave me !!
My misses was happy I was away for a while :rasta2bigsmoke0gf1::rasta2bigsmoke0gf1:
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What I mean, I could continue putting sources there - but the proof of the pudding is in eating: a number of us saw the same phenomenon and we started talking (I think some feed chasing board) and this was the conclusion, that three different types of wobble (that clearly exist), combined with whatever dance of the satellites up there and who knows what other phenomenon, gave us a headache for a good chunk of the year... Then, good quality would return for the other part of the year...
Various people, various countries, usually noticing slightly weaker TPs but one could see it in the signal, generally... We are talking a normal weather, nowt to do with clouds!
But go on, I am all ears, how can you explain it better?
Difficult to explain a phenomenon which is only described as a slightly better or worse.
I'm used to make measurement with dBm and calculate a link budget, no data available equals to just a guessing.As first I should know the size of the dish, the level measured and few other conditions, any datas available?
In earlier post I was describing that the variation can be on the transmit side too not only on receive, more details of the transponder affected would be useful, at least to check if they were excited with SNGs or Teleports, TWT, Klystrons or solid state, manned or unmanned stations, dozens of factors come into play.There are entire transponders affected by average temp and having a variable gain due to heat, many, many factors to take account of.
Keeping the TX station gain constant (and is not, belive me) my best attempt to explain the phenomenon, is that with small home TVRO dishes the orbit variations could only be seen during they extreme position path on long term variation.
The bird, kept in the position with on board truster is not just steady, it is in costant movement and what has been seen buy feed hunters, has been probably only a long path variation of the orbit, not connected with any precession movement aka known as Earth wobble.
Meanwhile a couple of pics of the BT era... :wink: I was much younger LOL -
I could go on but...
Good evening!
Please do, I'm interested to find how the precession movement is affecting the sat pointing technique.
According to NASA: https://www.nasa.gov/feature/n…ries-about-wobbling-earth it has rised a lot in the last years. From 8 to 17 cm per year.
I would like to understand how this tiny movement can affect the bird position @36K km circa from the Equator and how the precession is affecting the user pointing a small dish on earth. The precession little movement, as far as I know, is corrected easily during regular orbit maintenance of each geostationary bird, I can change my mind easily after some explanation ;):redface:
Meanwhile, I'll attach some pics of latest nice job I did at end of september.
KA-band 13.2m dish
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Well,
I've been sat engineer in BT, followed BBC courses pointing dishes as I wrote in my introduction since 1990 and Earth wobble is a total new thing.
I've transmitted hundreds of feeds over the years but the Earth has always been at the same place LOL.
The sat to be seen as a geostationary has to orbit in a cube of about 3km side (look at Eutelsat for info)
It can't stay steady still, its orbit moves with a 8 shape within the cube. During the movement, the antenna on Earth has to follow, end of the story.With a small 1m dish with only 1.2° angle beam, it is impossible to see the difference. Bigger antennas can see the differences.
Cherry on top of the cake is the weather, any weather variation makles a difference in levels.
Not only where you receive. Transmission site has the same implication.The level correction works constantly as weather change. The rtransponders are normally linear so input power variations affect the output at the same level.
You can have a beautiful sunshine or clear sky on the reception side but a bounch of clouds moving on transmission side and you can see many level variations.
In two occasions during my BT work I had a complete loss of my transmission due to bad weather. Once in Italy and the Bird was Eutelsat 2F2 @16E. I had 70Watts on the antenna and despite I rised the power up to 700W, yes seven hundred, I lost complitely the tx, it was a serie A football match for "TELEPIU'"
The second time, I was in Spain, same story, can't remember the bird, customer was BBC and they had to interrupt the broadcast as per my transmission lost... Athletyic games, 2002 circa.Good memories!
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Btw, when it comes to Gibertini with 2 polarmount motors...
I presume some positions are only C-Band and might need a different inclination - am I correct in assuming that?
So, one moves the dish to that position with the bigger motor and then, using the other, smaller polarmount motor, one moves the dish up and down to get the C-Band signal, right?!?
I mean, 1,5m dish is not that big, so this correction with the second motor might be required. right?
I presume that with bigger dishes there is no need for that, they can get just about anything as is?Any ideas?
Well a little bit of incorrect assumptions...
Will try to explain.The two motors polarmount are for 2 possible reasons.
1st, the person setting the dish, is not performing a correct Clarke belt alignement and is correcting inperfections with second motor.
2nd if the arc is just as it has to be, the second motor is very good at pointing those satellite with inclined orbit, standing just below the Clarke belt to save fuel.
C-band birds act like KU or X, no difference, same inclination and declination. Clarke belt doesn't change because the frequency.
The smaller the dish, the less precise is the pointing.
A few days ago, one of my customer was surprised to see that with a 2.4m was able to see difference in the pointing of co-located satellites, he could easily discriminate the difference in position.
Bigger the dish, higher accuracy required in pointing., and that is the reason of double motor on dishes above 4m even on stationary satellite. The tracking of the bird is required to keep the pointing at top level. -
Very pleased to help!
Well not a teen-ager here too, going 53 next year ;)
As you may know already (forgive me if I do talk about things you are perfectly aware of) the bigger the dish, the narrower the pointing angle.
it may be useful for others reading the post.
A good 1.5m dish is probably on the 0.7° range and pointing not precisely at geographical south, it makes a unprecise E-W setup.
As per the Gibertini,I recall something, if I have more info, will let you know.
I haven't seen the double polarmount but I'll have a look around.
I'm very used to broadcast SNG systems. I was BT staff a while ago...Cheers!
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Just a little advice.
Your antenna can't be on any "central satellite".
Your in London, hence o°Az. Except a meteosat, which is not a DTH bird you wil not have anything.
Make sure that your alignement East-West is correct and declination arc of the correct type.Do not focus too much on little details like the bracketing, any will suffice.
I don't know if I can post external link, will have a few, mostly UK based to advice for shopping.
Happy to help for any question or setup instructions. ;)Cheers!
