Dish Setting

[atabo40]

Found I hope this help to some
C/P


The principle to follow is: Set the elevation angle really accurately and then swing the dish around
boldly, but slowly, till you find the satellite.

To recognise that you are on the correct satellite you need to have some kind of detector.

Inexpensive power detectors will give an indication as you pass each satellite, but don't tell you which
one you are looking at. This is adequate if you can recognise some significant satellite which will provide
you with a known reference satellite. You can then count along the orbit till you come to your wanted satellite.

Satellite identifiers comprise a satellite carrier receiver (normally for digital DVB-S TV type carriers)
pre-programmed to detect a particular carrier with a specific symbol rate and frequency.
If the pre-programming of your identifier is correct and the expected carrier is present then you will
see on a screen verification that you are on your chosen satellite. This is attractive if you are regularly
installing dishes to work to TV broadcasting satellites. Beware that carriers with identical or very similar
symbol rate and frequency may occur on nearby satellites. LNBs have frequency stabilities in the
order of +/- 1 MHz so a satellite identifier may be unable to distinguish between two satellite carriers
of the same symbol rate but with frequencies within 1 or 2 MHz of each other. You must have preset your
polarisation correctly first. You must also have an LNB with the same local oscillator frequency as used when
the satellite indentifier was programmed and understand how the local oscillator frequency of the LNB may be
changed, by 22kHz tone, by voltage or external dongle.

Spectrum analysers are similar to power meters in that they clearly show when you pass a satellite but they do
not tell you the satellite identity unless you can recognise some of the carriers.
You really need a set of pre-recorded satellite spectrum views that are easy to recognise.
Some care is required as large TV carriers may occur at the same frequencies on several nearby
satellites so you need to have distinctive patterns of carriers to look for. Satellites with very little
traffic or with narrow band carriers not detectable with satellite identifiers can best be identified with
a spectrum analyser. Note that satellite carriers come and go, so the signals visible last week may not be
still there today ! Ideally pre-record the spectrum of that satellite that you will be seeking.
You will need a supply of DC voltage and possibly 22kHz tone. A coupler is useful with one side power pass.
Used the DC block side to the analyser. Note that many $1000's damage may occur if you apply DC volts to
some spectrum analysers.

Satellite TV receiver: Often the receiver that you are using for the service can prove to be a fully acceptable,
but rather inconvenient, detector. If you have set the polarisation and elevation angle all you need to do is
swing the dish boldly, and very slowly, while waiting for the receiver to lock on. This assumes that you can
confidently pre-tune the receiver to the wanted carrier and set the polarisation approximately correctly.
Also, you need to be patient enough to move the dish very slowly as the receiver may take several seconds
to lock onto the carrier. One azimuth sweep of the dish will be sufficient if you have pre-set the elevation angle
with sufficient accuracy, otherwise change the elevation angle in 0.5 deg steps and try again. Find out how to
display the bit error rate on your TV screen. Aim to minimise this figure. You either need the received outdoors
at the dish or very good communications and cooperation with someone.

It may take you 10 minutes to 10 days to find the satellite.

Start with the azimuth direction and try swinging the dish either side of the satellite till
you lose the signal. You need to identify two points on either side where the signals are
down by exactly the same amount (on your meter) and then put the dish in the exact centre.
If you have a screw with 2 nuts, one way is to unscrew both nuts by perhaps 2 to 3 turns and
then, while adjusting the nut positions, repeatedly swing the dish against each nut in turn until
the same, low, quality is at both sides. Then tighten the nuts inwards equally counting the turns
and flats. If you use only one nut to drive the dish and see the signal increase and then decrease
you need the repeat the whole process in the same direction and aim to just stop at the top.
This avoids backlash.

After setting the azimuth, tighten any big bolt holding the head down. This locks the azimuth
setting but will often simultaneously increase the elevation angle, so you may temporarily lose the signal.
Elevation adjustment is best done with one nut while allowing the weight to keep tight contact (no backlash).
Count the turns while moving from one low measurement to the same low measurement.
Then turn the nut accurately back to the middle position. Do it accurately to 1/6th of a turn by counting
the flats. Marking one flat with a felt tip pen helps

Polarisation adjustment normally needs assistance from the network hub. The hub can switch your
transmitter on and make it transmit a continuous wave (CW) un-modulated clean carrier on a frequency
where it is unlikely to cause interference to other satellite services. The hub uses a spectrum analyser to
look on the opposite polarisation transponder and tries to detect this carrier. This is quite easy, but slow,
using a narrow resolution bandwidth. If you turn the feed (while not getting yourself or your arm in the beam)
the hub sees the carrier go down to a sharp null around -30 dB when you are rotated correctly.
The null is really important and you need to rotate very slowly when near the null.
About 1 deg feed rotation accuracy is expected. Make movements very slowly as the people at the
hub may only be able to take accurate readings once every 15 seconds or so. If you have a spectrum
analyser yourself, you can often see cross polar interference rising up if you misadjust the feed rotation.
By finding two equally misadjusted points at equal angles either side of the null you can determine the centre
of the null yourself, prior to tests with the hub.