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VSAT technology and installation >> Dish pointing and alignment >> Satlook Digital NIT or Mark III suitable for VSAT

Message started by lorryboys on Aug 3rd, 2007 at 4:31pm

Title: Satlook Digital NIT or Mark III suitable for VSAT
Post by lorryboys on Aug 3rd, 2007 at 4:31pm
I'm not a technicion, however my company has started to install VSAT systems here in South Sudan.  I am looking for a technologically and cost effective spectrum analyser and am wondering if either of the above units would fit the bill.  Any other recommendations are appreciated.  Am looking to purchase right away, so please try to give a quick response.


Title: Re: Satlook Digital NIT or Mark III suitable for V
Post by Eric Johnston on Aug 8th, 2007 at 5:45pm
The SATLOOK DIGITAL NIT and SATLOOK MARK III are both detailed here:

I have used the MARK III and my comment would be that there is no indication of the frequency and span in use and as a result it is difficult to identify satellites.  You must have a set of spectrums, at full span, on paper for comparison purposes.  I don't recommend it unless you have made your own paper charts.   If you work with the same satellite all the time then it is easier, you need to make a chart for that one satellite - or remember well what it looks like.

The SATLOOK DIGITAL NIT by comparison has a digital TV demodulator built in and is able to identify the TV programmes on a carrier.
Download the user manual here:

For VSAT installation work you should know that a spectrum analyser is not really essential.  It is quite feasible to configure the VSAT modem first, using a PC, so that is set to receive the specific outlink carrier from the service provider hub.   You set the symbol rate and frequency of the downlink carrier into the VSAT modem.

Regarding the dish.  Set the feed polarisation angle to nominal, then turn the feed by the calculated adjustment angle.  Set the elevation angle on the back of the dish.  Swing the dish boldly sideways and you will find the satellite on the first swing.  A receive LED will go green on the modem.  Then spend half an hour peaking up using your PC to measure the carrier Eb/No to 0.1 dB accuracy or the BER.  Linkstar VSAT systems must be lined up using the modem BER readout to get at least 4 zeros like 0.00005   iDirect systems are set up using iSite PC screen and a red/yellow/green graph.

It is obviously necessary to have the PC and the modem close to the antenna during alignment and this inconvenience must be balanced with the use of the spectrum analyser alternative. If you use the spectrum analyser to peak up do check with the modem that you are on the correct satellite and polarisation before spending 30 minutes on fine adjustments (possibly on the wrong satellite).  The SATLOOK DIGITAL NIT spectrum analyser appears to show only 1 dB resolution steps for C/N measurements but does give finer resolution in the BER (Bit error rate mode).  The SATLOOK DIGITAL NIT is obviouly designed for traditional DVB-S TV carriers using QPSK. If any of your VSAT sites use the new DVB-S2 outlink carrier (which incorporates 8PSK etc) then the BER display will not work.   The 1 dB C/N resolution is poor compared with a professional HP type spectrum analyser where 0.1 dB resolution is the norm.   I have such an analyser, HP8560A, and would say that it is as good as using the VSAT modem and a PC display of Eb/No and BER for alignment.

A spectrum analyser is the only way of diagnosing interference and some antenna assembly errors and cross polarisation problems.  I would recommend you have a 3 dB 2-way splitter (one side power pass) to insert into the LNB cable so that the LNB power comes from the modem and you tap off the signal to the analyser near the dish, using a local 10 ft length of coax cable properly terminated with F and BNC plugs.  The SATLOOK analysers are able to provider DC power 13v or 19v and also 22 KHz tone, but using this does not prove the VSAT modem is supplying a voltage.  

Best regards, Eric.  

Title: Re: Satlook Digital NIT or Mark III suitable for V
Post by Oasis Networks on Aug 9th, 2007 at 11:52am
satlook is indeed the cheapest option, as far as i know, but in this case you really get what you pay for..

as mentioned, you can not get any readings such as freq, span, rbw and such.

bigger problem i think is that the f-type connector is not properly attacheched to the chassis, and after a while you will find that the satlook doesnt work properly as the central pin inside the unit is starting to get torn, as a result of connecting and disconnecting cables to the unit.

another problem is that the battery does not last too much time, and when the dc is running low the device starts to behave kind of strange.

however, it is a cheap device, and if you dont mind paying for it just for couple of installations and have it around its fine.

i think that it makes dish pointing not only much easier and comfortable, but it also allows you to do some troublshooting and not to be so blind when you are having hard time finding the satellite.

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