Post by Eric Johnston on May 1st, 2012 at 9:45am
Your polarisation setting may be slightly wrong.
What is your polarisation scale reading ?
A polarisation error, like 10 deg, would have little effect on your receive SQF, provided there is no one using the opposite polarisation. This may have been the case for your first six months operation and, recently, during the night 9pm - 9am. Maybe some new, part time, daytime only, satellite service started 2 months ago. Any error in your polarisation makes you vulnerable to cross-pol interference. Check your polarisation angle. An error of 8 deg would definitely cause your symptom (SQF drops from 80 to 60 between 9am and 9pm) if someone else transmits during this period.
According to my calculations using https://www.satsig.net/maps/lat-long-finder.htm
your polarisation adjustment angle amount should be +82 deg clockwise, as viewed facing towards the satellite in the sky.
If you look at the circular white scales on the two yokes that hold the transmit/receive radio assembly you will see scales like this below:
Setting the polarisation is a two step process.
First set to nominal. Rotate until the tick mark is either at the centre bottom (zero) or at the side (90 deg). Which of these two options depends on the name of the polarisation you have been told to use. Sideways = Vertical name receive polarisation.
Second apply the adjustment amount. Consider the view in the direction towards the satellite in the sky. Then apply the adjustment amount; positive is clockwise. Note that the scale reading numbers may be misleading, going forwards or backwards from 0 or 90, so simply count the amount of adjustment required along the scale, ignoring the numbers.
In the example scale above the initial setting was sideways (vertical name receive polarisation) amount and the adjustment was +34 deg clockwise.
In your case, once +82 deg clockwise is applied you will end up with the tick mark at either +8 or -82 on the scale. If you look at the scale at the other end, near the feed horn, the signs will the the other way round.
Whatever, the adjustment amount is +82 deg clockwise, as viewed while facing towards the satellite and starting at either 0 or 90. One option will be correct.
In your case you are already about right so all you need to do is loosen the clamps and make a small adjustment.
Best regards, Eric.
What is your polarisation scale reading ?
A polarisation error, like 10 deg, would have little effect on your receive SQF, provided there is no one using the opposite polarisation. This may have been the case for your first six months operation and, recently, during the night 9pm - 9am. Maybe some new, part time, daytime only, satellite service started 2 months ago. Any error in your polarisation makes you vulnerable to cross-pol interference. Check your polarisation angle. An error of 8 deg would definitely cause your symptom (SQF drops from 80 to 60 between 9am and 9pm) if someone else transmits during this period.
According to my calculations using https://www.satsig.net/maps/lat-long-finder.htm
your polarisation adjustment angle amount should be +82 deg clockwise, as viewed facing towards the satellite in the sky.
If you look at the circular white scales on the two yokes that hold the transmit/receive radio assembly you will see scales like this below:
Setting the polarisation is a two step process.
First set to nominal. Rotate until the tick mark is either at the centre bottom (zero) or at the side (90 deg). Which of these two options depends on the name of the polarisation you have been told to use. Sideways = Vertical name receive polarisation.
Second apply the adjustment amount. Consider the view in the direction towards the satellite in the sky. Then apply the adjustment amount; positive is clockwise. Note that the scale reading numbers may be misleading, going forwards or backwards from 0 or 90, so simply count the amount of adjustment required along the scale, ignoring the numbers.
In the example scale above the initial setting was sideways (vertical name receive polarisation) amount and the adjustment was +34 deg clockwise.
In your case, once +82 deg clockwise is applied you will end up with the tick mark at either +8 or -82 on the scale. If you look at the scale at the other end, near the feed horn, the signs will the the other way round.
Whatever, the adjustment amount is +82 deg clockwise, as viewed while facing towards the satellite and starting at either 0 or 90. One option will be correct.
In your case you are already about right so all you need to do is loosen the clamps and make a small adjustment.
Best regards, Eric.