SatSig topic:

IMPACT OF FEC ON SATELITE SETTING

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Oct 6^th, 2010 at 2:47am

Hi
I located in Melbourne Australia and was given by a friend a satelite dish and receiver as well as the information to set up as follows:
Sattracker: 122E
Transponder ID: k3v
Carrier Type: Ku Band
Downlink Freq: 12428.5MHz
Polarization: V
Symbol rate: 20MS/s
FEC: 3/4
And the information for azimuth and Elevation as well.

I tuned the dish accordingly. Yet the signal level the most I could only reach = "26%" while Quality = 0.

I encountered the following queries and would appreciate some advise and help:

1. I found the receiver setting could only allow the following setting:
a) Satelite: I failed to set exactly to 122E as it always has 1 decimal behind
b) For Downlink: there is Lo and Hi, and it does not accept decimal entry like 12428.5MHz
c) I couldn't find the setting for FEC? What is this for?

Can someone give me some advise?

Regards

Oct 6^th, 2010 at 10:03am

Quote:

a) Satelite: I failed to set exactly to 122E as it always has 1 decimal behind

If this is a motorised polar mount system that has already been installed and aligned correctly, setting the satellite selection on the receiver to 122 will make the motor turn the antenna to the correct satellite. Don't worry about 0.1 deg on the display. If you have a motorised system that has not been installed you may have a week or two of work ahead of you setting it up.

If you have a simple fixed pointing dish system then a menu selection of a satellite may simply be to pick up a list of possible TV programs from an old database in the receiver. This list may be out of date and the receiver may be able to scan the satellite to record the actual carriers now - takes several minutes.

From what you say you are looking for a specific TV carrier, which you should enter manually (frequency, symbol rate, polarisation). Then move the dish till the carrier is found. Set the elevation and polarisation accurately and then swing the dish boldly sideways. See Satellite dish pointing Australia and New Zealand for pointing and polarisation angles.

Quote:

b) For Downlink: there is Lo and Hi, and it does not accept decimal entry like 12428.5MHz

Assuming you have a universal LNB, capable of operating in Ku low band and Ku high band your receiver will need to send 22kHz tone ON to the LNB to switch the LNB to high band in order to receive a carrier as high as 12428.5 MHz. A universal LNB also has switchable polarisation - controlled by DC volts, 13 or 19 volts, and set by V or H selection in the menu.

The receiver synthesiser probably only works in 1 MHz steps so choose either 12428 or 12429. When the tuner tries to lock onto the carrier it will sweep possibly as much as +/-2 MHz either way searching for it.

Quote:

c) I couldn't find the setting for FEC? What is this for?

The receiver looks for a carrier with the 20 Msps symbol rate. Having found that it will probably then try alternative FEC ratios till it finds one that works. Having found out what is the FEC rate the receiver may then display this value. If you can't preset the FEC rate don't worry.
wxw
Best regards, Eric

Oct 7^th, 2010 at 12:27am

Hi Eric

Thanks a lot for your great explanation. I will try it out again.

Yes, the dish I got is a non-motorised small dsh and will point to one specific carrier.

Mean time, I would appreciate your clarification with regards to azimuth and elevation.

This TV supplied me the following data for Melbourne area:
Azimuth: 325.89
Elevation: 40.64

While I used the facility in this web site to do calculation from my house address, and have thus arrived the following data:

Satellite az-el Calculator
Satellite: 122 Asiasat 4
Lat: S37.8
Lon: E145.23
Dish azimuth: deg 324.39 True N
deg 311.75 MagN
Elevation: deg 40.42
Polarisation: deg -27.66
Polar mount Main: deg 37.82
Polar mount tilt: deg 5.23
Polar mount axis rotation: deg -26.46

My queries are:
1. Which azimuth data should I used? The one by TV provider or the az-el Calculator?
2. If data from az-el Calculator to be used, shall I use trueN or magN data?
3. For LNB polarisation. I thought I should use only deg -27.66, right?
4. Then what is the purpose of the other polar data like "mount Main', "mount tilt" and "mount axis rotation"? Are these for motorised dish?

Once again, I thank you in advance for your guidance.

Oct 7^th, 2010 at 9:32am

Quote:

1. Which azimuth data should I used? The one by TV provider or the az-el Calculator?

It does not matter, they are both about the same. If you have the elevation accurate then just swing the dish boldly sideways till you find the satellite.

Quote:

2. If data from az-el Calculator to be used, shall I use trueN or magN data?

If you use a magnetic compass use the magnetic bearing as a guide but even that is approximate (+/- 5 deg or so), especially in your area..

Quote:

3. For LNB polarisation. I thought I should use only deg -27.66, right?

Yes, turn the LNB anticlockwise by that amount, while facing forwards towards the satellite in the sky.

Quote:

4. Then what is the purpose of the other polar data like "mount Main', "mount tilt" and "mount axis rotation"? Are these for motorised dish?

Yes. That data is for setting up a motorised polar mount.

Best regards, Eric.

Oct 7^th, 2010 at 10:55pm

Eric,
Heaps thanks to you.

Regards
Ming