How to point satellite dish.
Focal length of parabolic dish
How to make inclinometer
Sub reflector adjustment
Use rear side struts
VSAT antenna anti-icing
Dish interference: Site shielding
Correcting VSAT dish distortion
Antenna panel alignment
How to point a satellite dish and use a spectrum analyser
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Prior to attempting to point the dish at the satellite you need to pre-set the polarisation. The polarisation refers the axial rotation of the feed horn/LNB/BUC assembly at the front of the dish. There will be some kind of clamp around the feed throat which may be loosened sufficiently to allow the feed assembly to be rotated. The may be a tiny scale, possibly marked + and - either side of central. Ignore the + and - signs and concentrate just on the scale steps, try to determine how many degrees between each tick mark, perhaps 10 or 15 deg ? Quarter of a turn = 90 deg. In some cases the entire dish needs to be rotated to set the polarisation. There will be a large circular scale behind the dish.
Polarisation setting is a two step process:
1. Start by setting the polarisation to nominal. If you are trying to receive a polarisation called "Horizontal" then you need to set the feed so that the broad faces of the LNB input waveguide are on either side. If "Vertical " then set the LNB waveguide so that the broad faces are on top and underneath.
2. Now, based on calculation, ( Antenna angle pointing calculator ) make the required polarisation adjustment. Face towards the satellite. A positive + rotation adjustment means turn the feed clockwise. A negative - adjustment requires an anti-clockwise adjustment. Ignore any +/- on the scale. it may be the wrong way round. Numbers like 0, +45, -45, -90, +90 may also be back to front. Think: + means clockwise.
More useful links:
For the elevation angle: use http://www.satsig.net/ssazelm.htm or http://www.satsig.net/ssazelm-palmos.htm or new experimental Satellite Finder - V5 to calculate the required angle. Set the dish elevation angle on the scale on the bracket behind the dish.
You need to know where your are located (latitude and longitude). I have two pages to help you do this. The first helps you find your latitude longitude in decimal degrees, the second which also shows satellite photos on a larger size gives latitude and longitude in degrees and minutes format as well.
If you have your location is decimal degrees and
know the satellite orbit position then use the main
Satellite Angle Calculator
If you have your location in degrees and minutes format and the satellite name use my satellite angle calculator at Satellite Finder-V5.htm This calculator contains a look up table of satellite names like Astra, DirecTV, Hotbird etc.
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.
Peaking up is the second phase of pointing the dish. It normally takes 20 minutes. If you do it in 5 minutes you have not done it sufficiently carefully.
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.
When searching for the satellite, chose settings that will give a fast sweep rate under 250mS so you can move the dish at a reasonable speed without missing the satellite. Wide spans like 40 to 500 MHz to 1 GHz work well for me, but much depends on what satellite spectrum picture pattern you can remember for the satellite you want. You may experiment with on-line satellite spectrum measurements.
Make sure video averaging is OFF. Max hold must be OFF also.
Possible problems: The LNB may be off frequency by up to 1 MHz; the LNBs has a local oscillator frequency different from what is expected (9.75 GHz, 10 GHz, 10.5 GHz, 10.6 GHz, 11.3 GHz etc); you are using the wrong polarisation.
Note for Cambridge universal Ku band LNBs:
13 volts = vertical linear polarisation, 19 volts = horizontal linear polarisation ( assumes you have the LNB 'upright' )
22 kHz OFF = low band LO at 9.75 GHz 22 kHz ON = high band LO at 10.6 GHz.
When peaking up, the zero span mode with sweep set to 30 seconds or more and a vertical amplitude scale set to 1 dB per division, can be very helpful. If you do this using a beacon use a resolution bandwidth wide enough to accommodate any frequency drift that may occur in an hour or so - otherwise the signal might mysteriously fall slowly.
Other link: Antenna sub reflector adjustment
Page created 23 May 2004, amended 20 June 2008