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VSAT technology and installation >> Dish pointing and alignment >> Cannot Get Receive Lock

Message started by mmabinge on Nov 16th, 2007 at 11:02am

Title: Cannot Get Receive Lock
Post by mmabinge on Nov 16th, 2007 at 11:02am
I havea 2.4 m Patriot dish and am pointing to IS901. I am in Sudan and have several 1.8m installations already working. I searched for the satellite and got a signal using Unaohm of -33dBm.

However when I connect my Idirect 5150 Modem I do not get treceive lock. Even when I open my Isite i do not get any receive Voltage.

I tried changing the polarization but it  dot help me.
I took my feed assembly to a nearby 1.8m Patriot dish and got receive lock immediatley.

I thought probably I c ould be getting a wrong signal and set my elevation and swung my dish but could not get any other signal. I tried to set the azimuth and adjusted my elevation but nothing still .

Can someone help please, this is a new one for me!


Title: Re: Cannot Get Receive Lock
Post by nera_installer on Nov 18th, 2007 at 5:29pm
Dear sir ;
you said that you have another systems nearby this dish .
when you changed the feed horn to another dish , did you lock by using this modem ?
did you check one of the old modems with this new dish ?
you should check the modem and see if there is problem with it or not .
Best regards

Title: Re: Cannot Get Receive Lock
Post by mmabinge on Nov 18th, 2007 at 6:44pm
Yes when I took the feed assembly to the other dish I used the same modem. I also tried two other modems but cannot get them to lock on my 2.4m dish

I even went further and tried the TV channels on IS901 but could not get them. I tried another Satellite IS1002 with same results.

I have never come across a dish that can be said to be faulty but in this case I am inclined to think so! Your views



Title: Re: Cannot Get Receive Lock
Post by Eric Johnston on Nov 18th, 2007 at 7:44pm
If your 2.4m antenna is one of the Patriot "Bat Wing" designs then this 2.4m Patriot antenna manual may be appropriate.   Warning 1.04 Mbytes pdf file.

The beam direction should be the same as the feed support boom so put your inclinometer there. Set the elevation angle accurately and then swing the dish sideways to find the satellite.  Try up and down in 2 deg (C band) or 1 deg (Ku band) increments is you miss the first time.  Sight along the boom.  Is the direction to the satellite obstructed by trees, wall etc ?

If no luck, suspect an assembly anomaly.  Read all the instructions again and check every detail.  Was it difficult to make anything fit ?  Was anything 'forced' to make it fit ?   Did all screws go in easily ?   Are there any gaps ?   Do the part numbers match the documentation?.  Assembly of the ribs to the hub must be exact and the assembly of the panels requires a sympathetic mechanical approach where all is very gently assembled and then carefully and progressively tightened from the middle outwards, without stressing anything.  If anything becomes a tight fit suspect that some screw elsewhere has accidentallybeen tightened too early.

Best regards, Eric.

Title: Re: Cannot Get Receive Lock
Post by mmabinge on Nov 19th, 2007 at 5:18am
Thanks Eric. You are right in 2 respects.

We did force a few panels to fit and the Part numbers do not match all what is in the manual. See below. I have written to Patriot and wait for their response but meanwhile I will try to disassemble the dish and try to fit it without forcing anything.

Radial beams per manual                                                             What we have

224109                                                                                               No number

224106                                                                                               224108

224103                                                                                               224105

224106                                                                                               224108

224109                                                                                               224111

Panels as per manual                                                                    What we have

B-right  224102                                                                                 224102

A-Right 224101                                                                                224100

A-Left 224100                                                                                  No number

B Left  224099                                                                                  224099


Title: Re: Cannot Get Receive Lock
Post by mmabinge on Nov 19th, 2007 at 6:23am
Further to Eric's contribution I would like to emphasise that I am getting a signal but not able to lock, so I would appreciate knowing what the wrong part numbers for the dish and the tight fitting forced on it would do the signal for it not to lock


Title: Re: Cannot Get Receive Lock
Post by Eric Johnston on Nov 19th, 2007 at 10:08am
Good.  Get Patriot involved. They will know which part numbers make up a proper matching set.

Dish distortion and panel or subreflector alignment problems cause lower gain and wider beams.  The effect can be very serious with gain reduced by many dB.

A combination of low gain and more interference from adjacent satellites will cause loss of lock if the margin above lock was already small.

Even on single piece dishes such as 1.8m or 1.2m plastic the sides can get pulled forwards a few mm and make the gain low by several dB at Ku band.  Fortunately on such dishes the front rim is (often) supposed to be flat and you can do the crossed fishing line test and check and correct any distortion.  Putting a length of girder across the back and pulling the sides back with steel cored cable ties is my favourite trick when you have a heavy ORU pulling the sides forward.  Anyone installing an Andrew Class II or III antenna should note the short side struts that go at the back.  These have slots at one end so you can pull (or push) the sides of the dish back or forwards to make the dish flat in its operational angle - use up/down and across fishing lines and adjust any gap to zero.  
Useful links:  
Large dish panel alignment with fishing line
Small VSAT dish distortion correction, with fishing line test
Sorry, but none of this works on Bat Wing antennas :(

Best regards, Eric.

Title: Re: Cannot Get Receive Lock
Post by Oasis Networks on Nov 19th, 2007 at 4:55pm
Hi, another point worth to be considered (especially if the dish is new and looks like she is in a good state), is to make sure the feedhorn is located at the right distance from the reflector.
Try to ask Patriot for the ABCD distances of the dish model and then mesure what parameters you have on your dish.

Title: Re: Cannot Get Receive Lock
Post by mmabinge on Nov 19th, 2007 at 9:03pm
Dear All,

I have rsolved this problem with assistance fro Patriot. For some reason though this is an Offset Antenna you must set the elevation on the feed supports to the actual angle you want (Angle of Elevation!). This is what was making me failt to lock to the satellite. So for all you guys out there when you install a Patriot Batwing dish don't try to copensate for the offset angle.

Thank you all


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