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uk.tech.tv.sky (Sky Television) (uk.tech.tv.sky ) Technical issues of Sky television.

why does it fade



 
 
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  #1  
Old July 26th 03, 12:30 PM posted to uk.tech.tv.sky
mike james
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Posts: 3
Default why does it fade

We are on the edge of reception and I'm just curious as to why
the signal is worse in the morning and gets better towards evening?
I can be more specific if needs be but I thought I'd see if some one had any
general ideas of what is going on.
mikej


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  #2  
Old July 26th 03, 05:02 PM posted to uk.tech.tv.sky
HJK
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Posts: 20
Default why does it fade


"mike james" wrote in message
...
We are on the edge of reception and I'm just curious as to why
the signal is worse in the morning and gets better towards evening?
I can be more specific if needs be but I thought I'd see if some one had

any
general ideas of what is going on.


There are a few possibilities:
- You could be outside the footprint (ie outside UK).
- Your LNB localoscillator have too large variation during the day.
- Antenna is not peaked wery well.

When outside UK and in fringe areas the signal varies and thats quite normal
as a tiny satellite
movement will cause big variations to the signal outside footprint. If the
uplink does not track the satellite
movement it can also give quality (not EIRP) variation during the day which
is much more easier to detect on the
edge of the footprint or inside the footprint with wery small antennas.



  #3  
Old July 27th 03, 05:50 AM posted to uk.tech.tv.sky
Jomtien
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Posts: 6,814
Default why does it fade

mike james wrote:

We are on the edge of reception and I'm just curious as to why
the signal is worse in the morning and gets better towards evening?


I suspect that your LNB is just getting tired. Your headers don't put
you on the "edge of reception" as far as I can see.

Test your box on a friend's dish and vice-versa to be sure.

--
Digibox problem? : A reboot solves 90% of these.
The Sky Digital FAQ: http://tinyurl.com/guiv
How to get UK TV overseas: http://tinyurl.com/6p73
Fed up with logos / red buttons? : http://logofreetv.org/
BBC gone? : http://www.astra2d.cjb.net/
----
Only the truth as I see it.
No monies return'd. ;-)
  #4  
Old July 27th 03, 09:00 AM posted to uk.tech.tv.sky
HJK
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Posts: 20
Default why does it fade


"Jomtien" wrote in message
...
mike james wrote:

We are on the edge of reception and I'm just curious as to why
the signal is worse in the morning and gets better towards evening?


I suspect that your LNB is just getting tired. Your headers don't put
you on the "edge of reception" as far as I can see.


I did not notice that he's on the edge of reception. Then its quite clearly
the footprint
24H movement that causes the problem but it could be in combination with no
tracking
at the uplink.

If the uplink does not constantly track the satellite the received C/N in
the satellite could
vary. Downlink C/N cant be better than what the satellite receives from the
uplink.
The EIRP is always kept stable by automatic level control (ALC) in the
satellite but EIRP
and C/N is two different things and in the end it is the resulting C/N that
counts.

Inside the footprint the variations caused by no uplink tracking does not
make any
difference but outside the target area where the signal is much weaker the
result of no
tracking at the uplink and footprint movement will add up and make the
variation even
greater.

Having said that my signal (50km North of Oslo) is at the worst when the
satellite is inclined
-0.03 deg. If the variation was only caused by no tracking at uplink one
should expect it to
be at the worst at +0.03 and -0.03 if the uplink antenna is peaked when the
satellite is at 0.00.
A normal error is to point a fixed uplinkantenna when the satellite is not
at "center of box" (ie.
current inclination=0.00) which will result in huge variation. There is a
possibility that the uplink
is carried out at 18GHz and then the beamwidth of the is even smaller.

It should also be noted that SES let Astra 2D be more and more inclined (
still not anyway near whats
called inclined orbit). At the moment it is inclined +/-0.06 degrees (
according to Lyngsat tracker ).
I think I remember it was +/-0.02 deg. or even less some months ago and the
last two line parameters from Celestrak showed +/-0.03 so it will be
interessting to see how much
more SES let the satellite drift. More drift will cause even more problems
on the edge of the footprint
but will probably not be noticed inside so there is no point in keeping it
extremely low.

At this site the inclination can be found
http://celestrak.com/NORAD/elements/geo.txt
It is the second parameter on the second line which is the inclination at
the start of the
twoline of parameters start date.

Example (Astra 2D inclination +/-0.0340deg):
ASTRA 2D
1 26638U 00081A 03207.00000000 .00000159 00000-0 10000-3 0 2550
2 26638 0.0340 271.3776 0004463 313.6080 106.5319 1.00269938 9591


Example (Astra 2B inclination +/-0.0178deg):
ASTRA 2B
1 26494U 00054A 03207.00000000 .00000159 00000-0 00000+0 0 2757
2 26494 0.0178 354.5658 0005000 302.8402 34.0704 1.00276704 10492

Example (Eurobird inclination +/-0.0086deg):
EUROBIRD
1 26719U 01011A 03205.91543983 .00000160 00000-0 10000-3 0 3760
2 26719 0.0086 328.9683 0002827 137.8617 193.4102 1.00272837 8729


One thing I notice is that the parameters used in the Lyngsat tracker and on
the Celestrak site does not
match evewn though the Lyngsat tracker should be feed by data from the
Celestrak site. The inclination
might be lower than the Lyngsat tracker suggests.
http://www.lyngsat.com/tracker/astra2d.shtml


  #5  
Old July 27th 03, 10:46 AM posted to uk.tech.tv.sky
mike james
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Posts: 3
Default why does it fade

So much info - thanks everyone.

I am on the edge of reception of the North beams of 1D and its the reception
pattern
of this that I noticed.

I follow the arguments about the position but I didn't know I could get
obital elements for
Astra sats - so thanks.

The only argument against sat positioning being the cause is that it's not
quite like
clockwork but almost.

10am - no signal.
11-12 - occational picture and sound
by 2 pm no problem

I've noticed that 1-2 pm is about the time the sun goes off the dish.
Could it be solar heating of the LNB?
mikej




  #6  
Old July 27th 03, 09:43 PM posted to uk.tech.tv.sky
HJK
external usenet poster
 
Posts: 20
Default why does it fade


"mike james" wrote in message
...
So much info - thanks everyone.

I am on the edge of reception of the North beams of 1D and its the

reception
pattern
of this that I noticed.

I follow the arguments about the position but I didn't know I could get
obital elements for
Astra sats - so thanks.

The only argument against sat positioning being the cause is that it's not
quite like
clockwork but almost.

10am - no signal.
11-12 - occational picture and sound
by 2 pm no problem

I've noticed that 1-2 pm is about the time the sun goes off the dish.
Could it be solar heating of the LNB?


LNBs could have temperatur instability problems but if you are on the edge
of the
Astra 2D footprint I believe its not the LNB which causes the problem. Its
most likely
the footprint 24H cycle movement.

In Scandinavia the 2D is best early moring and until evening around 21 CET.

You are south ? Spain ?
Its interessting if you are far south and have best signal in the evening
cause that makes it
even more likely that its caused by fooprint movement. To get signal all
day you will
need a larger antenna. The time when signal is gone slowly changes. 12
months ago
the Astra 2D signal in Oslo was at the best in the evening prime time. Now
its best in
the early moring hours until a few hours after noon.


  #7  
Old July 28th 03, 08:50 AM posted to uk.tech.tv.sky
mike james
external usenet poster
 
Posts: 3
Default why does it fade


"HJK" wrote in message news:PHXUa.9200

LNBs could have temperatur instability problems but if you are on the edge
of the
Astra 2D footprint I believe its not the LNB which causes the problem.

Its
most likely
the footprint 24H cycle movement.
In Scandinavia the 2D is best early moring and until evening around 21

CET.

Haven't checked early morning because...

You are south ? Spain ?


we're in southern spain where everything starts later and we are 1 or is it
2 hours ahead of GMT.

Its interessting if you are far south and have best signal in the evening
cause that makes it
even more likely that its caused by fooprint movement. To get signal

all
day you will
need a larger antenna. The time when signal is gone slowly changes. 12
months ago
the Astra 2D signal in Oslo was at the best in the evening prime time.

Now
its best in
the early moring hours until a few hours after noon.


If I'm following what you are suggesting is that Oslo is at the northern
edge of the
beam and Southern Spain (Vera if you want to be exact) is on the southern
edge.
So if the beam moves north you get it and I don't and vice versa.
Interesting.
I'm going to try for heating effects by changing the LNB (two identical LNBs
one in place and heated by the sun for an identical model that's cool).
mikej


  #8  
Old July 28th 03, 09:22 AM posted to uk.tech.tv.sky
HJK
external usenet poster
 
Posts: 20
Default why does it fade


"mike james" wrote in message
...


If I'm following what you are suggesting is that Oslo is at the northern
edge of the
beam and Southern Spain (Vera if you want to be exact) is on the southern
edge.
So if the beam moves north you get it and I don't and vice versa.
Interesting.
I'm going to try for heating effects by changing the LNB (two identical

LNBs
one in place and heated by the sun for an identical model that's cool).


It is perhaps possible to get ice on box - such as electricians use to test
components
for temperature drift. It might be a useful test if it is possible to cool
the LNB enough.
....but I think variation is not cause by temperature

What LNB are you using ? MTI seems to be wery good on 2D frequencies.
I went from reception 20% a day to 80% a day by changing from Digistar
0.7dB to
MTI Ap8-TW 0.5dB. The MTI Blueline is even better with nf=0.4dB.



  #9  
Old July 28th 03, 06:07 PM posted to uk.tech.tv.sky
HJK
external usenet poster
 
Posts: 20
Default why does it fade


"mike james" wrote in message
...

"HJK" wrote in message news:SX5Va.16178
What LNB are you using ? MTI seems to be wery good on 2D frequencies.
I went from reception 20% a day to 80% a day by changing from Digistar
0.7dB to
MTI Ap8-TW 0.5dB. The MTI Blueline is even better with nf=0.4dB.


I can't remember the make etc. (I'm not in Spain at the moment).
but it is a low noise unit and it was an improvement over the replacement
but until
BBC moved reception of 2D north beam wasn't an issue so I didn't do any
tests.

I will find out what I fitted and take your recomendations seriously.


Might be worth it :-)

About 2D there is only one beam. No north or south beam just one beam
covering the British isles.


 




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