The Aero Thread..

[s-band]

1.4m Steel Satellite Dish

1.4m vs. 1.2m is only about 1.3dB improvement, theoretically. Also, that dish is 1.4 longest dimension, what's the Gib? Are you getting ground noise from the wall in front (or behind if over-illuminating)?

 

[Vipersan]

So ...
amyone able to calculate the extra gain on the surface are increase ..
My gibby 1.2 measures 1300mm x 1200mm
This unknown claimed 1.4 measures 1400mm x 1270mm

if true ..
what will this yield gain wise in db ??
anyone ?

 

[Vipersan]

1.4m vs. 1.2m is only about 1.3dB improvement, theoretically. Also, that dish is 1.4 longest dimension, what's the Gib? Are you getting ground noise from the wall in front (or behind if over-illuminating)?

Didn't quite expect such a speedy reply ..
Thanks SB ...
guess you answered the question I was typing at the time ..

Over illumination was certainly a possibility ..but tried altering the lnbs position in and out ..to little effect ..

I'll measure the dimensions of my fortec star ...and add to this post ..
back in a mo ..

Fortec star 1.5 measures..
1650 x 1510

Assuming you are correct about the 1.3db increase in gain ...would that be sufficient ?
Hard to say ...
Jaero is clocking up a long list of Bad RT packets and no actual 'hits' so I guess is borderline on the 1.2 ...no idea if and extra db and a bit would help ..

I might try temporarily mounting the C1PLL on Carl at the focus ..
just to see if there are any hits ..
rgds
VS

 

[Vipersan]

Well ..I guess that at least saved me from wasting more money ..
Exactly the same with the C1PLL rough mounted at the focus of the 1.5 ..
Long strings of bad RT packets ..and no acyual data hits..
So ...25E is looking like no go at my QTH ..
Local interference ?
Dish too small ?
Dead spot in the footprint ?

My money is on the first ..on account I've _always_ had trouble with C band to the East ..
Ask Nelson ..
We've often debated by I could never receive Yamal ..and had problems with signals from Turksat ...which he could receive on a 1.8m dish ...but I could not with a slightly bigger dish ...yet we were only 70 miles apart ?
This problem might fall under the same banner..
Nuked

 

[spacedish]

Hi All

Sorry I havn't been around for a couple of weeks, after the dodgy ticker do I then got hit by a flu like virus which is only just clearing....still hav,n't had chance to do any work outside :O(

I posted the image below to the PP group yesterday which might help explain some of the routes used.You can see the great circle tracks emerge almost like satellite orbits , plus tracks heading North/South which are the polar tracks.

Notice also the distinct cut off points , which are where the satcoms disconnect on establishing contact with ADS-B ground stations.

 

[Vipersan]

And just to make me a liar ..
Just got a single hit of data ..

 

[Vipersan]

Hi All

Sorry I havn't been around for a couple of weeks, after the dodgy ticker do I then got hit by a flu like virus which is only just clearing....still hav,n't had chance to do any work outside :O(

I posted the image below to the PP group yesterday which might help explain some of the routes used.You can see the great circle tracks emerge almost like satellite orbits , plus tracks heading North/South which are the polar tracks.

Notice also the distinct cut off points , which are where the satcoms disconnect on establishing contact with ADS-B ground stations.

The 'Like' was for your picture submission ...not for liking the fact that you have been so ill ..
Hope your recovery continues at a pace ..
;)

 

[spacedish]

The 'Like' was for your picture submission ...not for liking the fact that you have been so ill ..
Hope your recovery continues at a pace ..
;)

He he...realised that :O)

Its really frustrating as I had plans for all sorts including tests on an upside down offset for C band ....all now on the back burner til [well ] after the op

Sorry to see you are having probs with 25 east.
Interference might well be the answer. I can maintain the signals constantly , however from time to time a heavy carrier pops up , nothing to do with Inmarsat , its local I think . Damn annoying.

 

[Vipersan]

He he...realised that :O)

Its really frustrating as I had plans for all sorts including tests on an upside down offset for C band ....all now on the back burner til [well ] after the op

Sorry to see you are having probs with 25 east.
Interference might well be the answer. I can maintain the signals constantly , however from time to time a heavy carrier pops up , nothing to do with Inmarsat , its local I think . Damn annoying.

What size dish are you using at 25E S D ?

 

[spacedish]

What size dish are you using at 25E S D ?

1.8 prime focus.....I have inclined tracking but don't use it as signals are good through the orbit.....just set the dish slightly above the arc.
I do get freq drift from the lnb , but that varies with temp.

 

[Vipersan]

1.8 prime focus.....I have inclined tracking but don't use it as signals are good through the orbit.....just set the dish slightly above the arc.
I do get freq drift from the lnb , but that varies with temp.

All my lnbs have been modded with TCXOs ...so lnb drift is eliminated 99% ...but I am limited to dish size at my QTH ..so 1.8 isn'y practical ..though might well solve my problems at 25E .
cest la vie

 

[Vipersan]

So ...there were a total of 15 flight positions logged whilst I was out at work today ..
Granted that isn't a huge number ...but it does look as though a 1.5mtr will at least catch some activity from 25E.
but now I'm wondering how well one of those cheap 1.4 mtr dishes would do ..
??
Is it worth a gamble ?
Price and availability being a crucial factor ..
Hmmm

 

[s-band]

Have you tried using the opposite polarisation and flipping the dielectric plate? If you are scratching around for the last 1/2 dB perhaps the other half of the LNBF is better.
1.5m vs 1.2m ~+1.9dB
Work out exactly how much more signal you need by turning the 15W dish until you degrade the signal (EbNo) on 15W to the level that you had on 25E, measure the SNR on the SDR(=SNR1). Turn the 15W dish until you get your desired EbNo (still on 15W), measure the SNR (=SNR2). Improvement needed = SNR2-SNR1. That should tell you what you need to do.

 

[Vipersan]

Have you tried using the opposite polarisation and flipping the dielectric plate? If you are scratching around for the last 1/2 dB perhaps the other half of the LNBF is better.
1.5m vs 1.2m ~+1.9dB
Work out exactly how much more signal you need by turning the 15W dish until you degrade the signal (EbNo) on 15W to the level that you had on 25E, measure the SNR on the SDR(=SNR1). Turn the 15W dish until you get your desired EbNo (still on 15W), measure the SNR (=SNR2). Improvement needed = SNR2-SNR1. That should tell you what you need to do.

Good suggestions SB ...
a job for tomorrow weather permitting ..
Thick cloud and occasional showers here ...which does nothing to improve the situation ...
Plus the fact I am now gonna have to chase the satellite ..on account of its wobble..
rgds
VS

 

[Vipersan]

Just to give some idea of the variation here are 2 screen grabs ..
of 54W and 25E
54W is on the 1.1m maxx dish with homebrew lnb support arm ..(guestimated)

25E is at the focus of my 1.5 m dish ..

rgds
VS


upper is 25E
lower is 54W

Looking at that 25E data pulse ..
tricky to catch ..
looks to be enough ...but rarely will jaero decode it ..
odd eh ?

 

[Vipersan]

A couple of important questions about inmar at 25E ...
Having probs finding tracking info on this bird which I believe is Inmarsat 4AF4 ...or is it ?
Has this bird been re-named Alphasat ?
Also ..
how accurate are inclination trackers ?
As ..Im sure this bird is more inclined than is claimed ..
All I know is that on a 1.2m dish set to get the most signal in the morning is seeing next to nothing by evening ..
Yes it can be found again by declination adjustment or re-tracking ...but if the numbers are to be belived the signal shouldn't totally disappear over a 12 hour period ??
So it looks like the inclination is actually greater than that claimed ?

Does anyone have accurate data ?

Here is what I think is accurate ..but then is this even the correct bird ..?
Track ALPHASAT at 24.9°E and view detailed satellite position data
rgds
VS

 

[Analoguesat]

Inmarsat 4AF4 is indeed also known as Alphasat. Shes officially 1.4 degrees inclined and atm is virtually at the bottom of the arc according to n2yo

Technical details for satellite ALPHASAT (INMARSAT 4A-F4)

The inclination is a lot considering she was launched in 2013!

 

[Vipersan]

Inmarsat 4AF4 is indeed also known as Alphasat. Shes officially 1.4 degrees inclined and atm is virtually at the bottom of the arc according to n2yo

Technical details for satellite ALPHASAT (INMARSAT 4A-F4)

The inclination is a lot considering she was launched in 2013!

I guess my best hope is to average out the wobble and try aligning as Alphasat/4AF4 crosses the equator ...
But here is the dilema ...a larger dish is definately needed on this one ...which of course has a narrower beamwidth ..thus more affected by the inclination changes ..
Sods law I guess ..
cheers for the confirmation AS

Last question ..
scuse my ignorance ..but does a 1.4 degree inclination mean that the variance is 0.7 degree either side of the mid point ..or 1.4 degrees each side ..making a total of 2.8 degrees ???

 

[Vipersan]

...Currently crossing the equator viewed from my QTH approx 4:00 pm (descending) and 4:00 am (ascending) approx.

Not today ..but I'll be trying to catch the crossing point for optimum postioning of the dish.
rgds
VS
...and looking at those figure sort of answers my earlier question ...
unless I'm not understanding those numbers..
quite possible ..
there is almost a 3 degree swing on this bird N to S ..
that's a lot ...and the bigger the dish the greater the gain ...and the worse for catching signals without mechanical tracking..

Which begs the question ...
How are you guys with 1.8m dishes coping ??

...all I can say is ...thank higgs we are working in C band ..which is forgiving of about 2 degrees -max-

..perhaps it would be better to choose max N or max S deviation ..
cos theoretically the bird would spend a longer period of time in virtual focus during these periods of the oscillation ...but this introduces another problem ...the maximum E-W deviations close to these points ??
-comments welcomed -

 

[Vipersan]

Well ...
in fer a penny etc ...
Took a chance and ordered one of those cheap 1.4m Mix dishes which arrived this morning ..
Spent the evening making the parts fit ..
lol
Now I know why they are so cheap ..
The rear dish brace which attaches to the AZ/EL mount ...
..attaches with 6 bolts ..
The holes through from reflector to rear brace dont quite line up ...so required a bit of work with a round file on the rear brace ..
This wasn't too bad a job...but worse to come ..
The blind bolts with flat domed heads that mount through from the reflector side have shallow squares to stop them rotating when located ..thus you can tighten up the nut side without them rotating in the hole ...there is no other way as they have blind domed heads..
our survey says ...nahh Ahhh ...
The reflector has 6 round holes but not pierced for squares ...thus you cannot fit the domed head bolts flush ...nor stop them rotating ...
AND you would distort the dish should you try and tighten them ..
So ..out came the small square file ...and spent an couple of hourse making those round holes ...square ..

Where is Quality Control when you need it ????
Anyway ..this being the second cheap ebay dish I've bought recently ...I wasn't going through the hassle of arguing for return ...
..No parts missing this time so made the damned thing fit together ..

Already worked out how I'm gonna fit a C band LNB to the offset tripod ...which is only really designed for ku ..
...and the mod wont destroy the ku mount so ...this being my last attempt at getting 25E with an extra 1.3 db ..
If all else fails it should be useful in its current location for Newsfeeds in ka from 19E ..
So there's the plus..
rgds
VS
photos to follow once its up and mounted..
;)