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  Satellite Internet forum › Satellite Connection in Africa › Re: IS904 circular polarisation feed problem
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Re: IS904 circular polarisation feed problem

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Admin1
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Jan 26th, 2008 at 1:52pm  
I have no experience with iDirect but suggest checking the following:

The two F connectors on the BUC cable must be good. The centre pin must stick out 2mm beyond the rim of the plug. When inserted, the pin must actually go in properly and not push back the cable. The braid must also make good contact.  No fragments of braid wire etc must be left short-circuiting the cable.

The BUC DC power supply must be ON (possibly a software configuration option).

The 10 MHz reference to the BUC must be ON (possibly a software configuration option). If the 10MHz is switched OFF, the BUC output will probably go to automatic inhibit.

Your modem transmit power level must be sufficient to make the BUC transmit at least a few mW. It is normal to start with the power setting very low and go up in steps of say 3dB until the hub starts to see your CW carrier and then go up cautiously in 2 dB or 1 dB steps. If you have an exceptionally long cross site cable you will need a few dB more power.

Check the transmit frequency is correct.

Your dish needs to be pointed accurately so the satellite is at the centre of the beam. The transmit beam is narrower than the receive beam. On receive it is no good just getting a "good enough" signal as this will be possible for quite a wide range of pointing movement. You need to get to the exact centre, even though this makes little or no detectable improvement to the receive quality. Do this by measuring the receive quality and moving the antenna either side of the satellite and then winding back so many turns and flats to get back to the exact centre.

Are you sure the hub has control of your modem ? Have you seen the modem change in response to commands from the hub ? If the BUC is not transmitting, I can't see how the hub know they are communicating with your modem. Are you pointed at the correct satellite/polarisation? It is not impossible to lock to a similar, but wrong, carrier but it should be possible for you to verify the wanted carrier this by examining the carrier ID code send by the hub and detected in the modem. Talk to the hub and see if thay can send commands to your modem and can you see this happen ?

Best regards, Eric.
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Oasis Networks
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Reply #1 - Jan 26th, 2008 at 5:12pm  
my friend,

If your hub operator can access the idirect (i assume they manage to do so by the sat link and not via external connection); and they can not see your CW, my advice is to ask them to either change their spectrum, change their glasses or change the hub operator..

The CW is a very narrow signal, and it is possible (though I hardly believe it) that your hub operator can not detect it.
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« Last Edit: Apr 24th, 2009 at 11:50am by Admin1 »  
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maxfire2020
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Reply #2 - Jan 27th, 2008 at 12:03pm  
about the cable i get the cables from working satellite its 15 meter and i double check it
the joke in the story im getting from 10 to 11 SNR is that passable im in wrong satellite ????!!!

over that my 2 lights the RX and TX green and i make in the test the CW reach 10- dbm and they can not see the signal also they get stack whit the sat operator ????

also this provider charge 250 USD for each 3 test is that true ?
they saying the intellsat operator charging them for the test
is that true ???

also i note there is anther plorizer between the BUC and the OMT i can make it cross or parallel
so any one have idea about that ????
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« Last Edit: Jun 3rd, 2023 at 3:51pm by Admin1 »  
 
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Eric Johnston
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Reply #3 - Jan 27th, 2008 at 1:43pm  
I suggest power off and disconnect your BUC cable and do not connect it again until you can verify:

a) that your modem receives and responds to commands sent by the hub. You need to talk to the hub while they send commands. You need to observe your modem via local PC and note if any changes are caused as commanded by the hub. This will verify if you are on the correct satellite and that the hub is really communicating to your modem. You must be pointed at the correct satellite, on the correct polarisation and all your receive parameters must be correct.

b) that your feed assembly is correct. Clarify with your hub what receive and transmit polarisations you are supposed to be using. If they tell you use cross-pol then your feed must be configured like that. A typical C band, cross-pol, circular polarisation feed looks like this:
...
It may help if you take some photos of your feed and the extra "polariser" you have between the BUC and OMT. Send them to eric@satsig.net and to your service provider.

Do not transmit unless told by the hub and then start at the very lowest drive levels. The hub must be monitoring on a spectrum analyser when you first attempt to transmit.

When a new site is activated only a very low level CW is necessary as the hub can easily detect this, provided the frequency is correct. If you are on the wrong satellite, wrong frequency or wrong polarisation they see nothing and the interference you cause while transmitting such low levels is minimal. If you ever see nothing your immediate reaction must be to turn off the transmitter and think.

An observed C/N of 10 or 11 does suggest that you may be on the correct satellite but until you verify in the modem that you are receiving the correct ID, PID or whatever sent by the hub you cannot be certain. Ask the hub to send commands to your modem and you look to see if they are received.

Best regards, Eric.
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« Last Edit: Jun 3rd, 2023 at 3:52pm by Admin1 »  
 
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nigelgoboom
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Reply #4 - Jan 29th, 2008 at 12:50pm  
hey max, i've worked with iDirect a bit.

1- never heard of a charge simply for the isolation test to access. afterall this is to help ensure that the rest of their space is clear.

2- i have seen some modems that would modulate but not put up a cw(and vice versa), although there are a number of other reason why they may not be able to see it.

3- make sure youre using the same idirect version for isite as you are for the modem software. also if it is just a software issue you can verify by putting up the cw via a console session in telnet.

applicable commands:

tx freq "lband freq here but not with quote marks" example "tx freq 1370.00000"

tx power "desired power here" example "tx power -25"

tx cw on

tx cw off

you said they could access the modem. if you meant that they could reset it then youre definitely on the right bird since your reading your recv carrier

if you meant that you can actually access the network then you are putting up a modulated carrier(so your buc works), then it's your modem just not putting up a cw. if neither then check your xmit chain. if you don't a multimeter you can verify your tx cable by checking your rx level and then swapping the cabling out and checking rx again.

and of course there's no substitute like spare parts! Smiley

nigel
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« Last Edit: Apr 24th, 2009 at 11:51am by Admin1 »  
 
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maxfire2020
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Reply #5 - Jan 30th, 2008 at 7:27pm  
Hello, really I get tired from this story even the provider telling me don't remove the RX cable when I making the CW and in the iDirect manual they note clearly to remove the RX cable
I do everything I think they trying to fraud the people
also they ask me to but this command in the telnet :-

#cd /proc/board_info
#cat model_number

and I'm getting bad commend
what I have to do .
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« Last Edit: Jun 3rd, 2023 at 3:53pm by Admin1 »  
 
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Eric Johnston
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Reply #6 - Jan 30th, 2008 at 11:53pm  
Please send a picture of the feed assembly and the "polariser" between the BUC and the OMT. Send to eric@satsig.net and I will put it here.

I've no idea why the rx cable needs disconnecting to make a CW transmit test. The hub should be able to command this by remote control via the receive path. A site transmitting CW while the rx is disconnected is out of control. Most VSAT regulations say that you must have rx lock before transmit can be enabled.  If you disconnect the rx cable it will almost certainly cause the tx to go to inhibit - this is a test that all VSAT modems must pass.

Best regards, Eric.
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« Last Edit: Jun 3rd, 2023 at 3:53pm by Admin1 »  
 
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Eric Johnston
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Reply #7 - Jan 31st, 2008 at 11:58am  
Thanks for your pictures. This helps a lot.

...
The first image above shows the LNB and the BUC with their rectangular waveguides the same way round, with the broad faces of both uppermost. This is a co-pol arrangement. Both receive and transmit are vertical polarisation when they merge in the OMT.

When the polariser is attached, the vertical polarisation will change to a circular polarisation at the feed horn.

There is a further complication. The polariser may be attached to the OMT at two alternative positions, at 90 deg to each other. As shown the polariser is at one of its positions. I don't know which.

If you are told to use co-pol operation try the above arrangement. If you can receive the outlink carrier you have everything correct. You will transmit and receive on the same circular polarisation. If you cannot receive the outlink then rotate the polariser 90 deg to its other position. It goes to +45 deg or -45 deg either way. Now you will see the outlink on the other circular polarisation and transmit on the same.

The device between the OMT and the BUC appears to be a square to rectangular adaptor, incorporating a receive reject filter. This makes sure that all the wanted receive signal goes to the LNB, rather than half to the LNB and half to the BUC. The two filters, on the LNB and BUC form a diplexer.



...
The second image, above, shows the LNB and the BUC with their rectangular waveguides the opposite way round, so the LNB is vertical and the BUC horizontal. This is a cross-pol arrangement and like most Ku band linear systems. The receive is vertical and the transmit horizontal polarisation when they merge in the OMT.

When the polariser is attached, the vertical and horizontal polarisations will change to two opposite circular polarisations at the feed horn.

There is a further complication. The polariser may be attached to the OMT at two alternative positions, at 90 deg to each other. As shown the polariser is at one of its positions. I don't know which.

If you are told to use cross-pol operation try the above arrangement. If you can receive the outlink carrier you have everything correct. You will transmit and receive on opposite circular polarisations. If you cannot receive the outlink then rotate the polariser 90 deg to its other position. It goes to +45 deg or -45 deg either way. Now you will see the outlink on the other circular polarisation and transmit on the opposite.

Sorry it sounds so complicted, but it will work in the end !

Best regards, Eric.
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« Last Edit: Jun 3rd, 2023 at 3:53pm by Admin1 »  
 
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maxfire2020
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Reply #8 - Jan 31st, 2008 at 7:27pm  
hi eric

i make every thing as you say since two weeks
i can receive their signalvery good  but no transmiting  they can not see the BUC signal in the CW test
i think maybe the BUC damge i change it 4 times and im getting the same problem
did you think i need to upgrade the BUC power ??
and im getting 11 SNR
i check the modem it ok and working
some people say some times you receive the signal very well and you can not trancmit tell you get more watt

Thank you for the value information Smiley
                                    
                                   
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Eric Johnston
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Reply #9 - Jan 31st, 2008 at 8:34pm  
If you are receiving the outlink carrier OK then the relationship of the LNB, OMT and polariser must be correct.

There may be misunderstanding as to whether you are supposed to be transmitting co-pol or cross-pol, in which case be prepared to reattach the BUC in two different positions (at right angles) Use just two screws at opposite corners till you get it right.

More power is not the answer to the detection of a CW carrier. If the hub have a spectrum analyser and know how to use it then they can easily see 0.1 watts of CW power. There is no need to transmit whole watts of CW power to verify that it is you. Watts are needed once the signal is modulated and spread out.

Check you have DC power at the BUC cable connector. Do this carefully so you don't short circuit the pin.

Try to verify what frequency you are supposed to transmit CW. C band BUCs have a conversion frequency and the L band modem tx frequency needs to the difference between the BUC local oscillator and the wanted transmit frequency (usually in range 5.625 - 6.4 GHz).

Your service provider should be helping you. Can they send a command to your modem to reset it and can you see this happen ? Can you see them trying to activate your transmitter ? Proving you are receiving the correct carrier from the correct satellite and polarisation is a critical first step.

Maybe someone else can explain how or why an iDirect may be unable to send a CW carrier. Why not try with a normal modulated carrier and see if the system works as it should for operational service ?

Best regards, Eric.
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mhaut
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Reply #10 - Feb 4th, 2008 at 11:16am  
Dear Eric,

thanks for your comments. We as hub operator rely on Intelsat capacity and also let them perform our cross pole tests to obtain Site ids. During all times do have access to the screnplots measured. So far this customer was unable to rise any CW with the equipment he is using. We certainly can exclude communication problems as we run this process 25 times a day.

From our impression this setup is causing quite some difficulties, as the customer uses unknown 3rd party equipment which he lost any manuals and not knows any more how to configure his feed.

Antenna Feed needs for our capacity on IS904 must be comissioned for RHCP CROSS POLAR and not like the customer has set CO-POLAR (PARALLEL) !

This problem us quite common in the area of North Somalia, as many guys there use satellites comissioned to Dubai Hubs and those like PAS4 do require indeed a CO-POLAR setup. So they do not understand what they must do in order to change their orthagonal feed configuration.

We think that this is the ONLY problem causing the problem that the customer cannot transmit a CW signal.

We asked him to send us new pictures with the changed setup as you suggested - but so far the customer not has replied to us.

In the meantime we keep growing our customer base on IS904, as we can operate with small 1.8 meter C-Band antennas all over Africa thanks to our 12 meter uplink facilitiy.

Greetings

Markus
Level421
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Eric Johnston
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Reply #11 - Feb 4th, 2008 at 3:01pm  
If the operation is in the IS904 up in hemi beam and down in hemi beam then it is cross-pol, the uplink is LHCP and downlink RHCP.

I am working on the images etc you sent me by email. Is this the correct configuration below ?

...
Best regards, Eric.
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mhaut
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Reply #12 - Feb 5th, 2008 at 1:32am  
Dear Eric,

the picture shows a feed of an prodelin antenna. Although we are not using these any more due to the quite bad isolation values and the terrible export policy of Vertex, its assembled correctly - yes.

Feeds of other suppliers might of course look different.

Greetings

Markus
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maxfire2020
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Reply #13 - Feb 6th, 2008 at 9:21am  
Now bingoo.net saying we are LEVEL 421 before 4 days I make the configuration as they tell me and NO Transmitting in same time we connect spectrum analyzer in our site and we don't see anything whats that mean !!!!!!!
I don't like to say that but its the true over that we migrate our system to PAS 4 and we make the feed linear and every thing works good in the TEST also we make another test in Telestar 10 and everything goes well when we back TO bengoo.net and configure the feed and SEND THE Picture to them the say its quite good"like every time its good till Eric get the source of the problem when I post my problem here"
and over that no signal !!!!
when we ask them about the cancellation we found they don't have any policies and just the wiret in there site "you can cancel any time "
when we email them for the cancellation they say we will detect 50%+200Eur as test fee from your total !!!!
and asking us to check there site after they add the New police to it and email it to me.

what ever i will send all the emails and every thing to be published here

and I hope you stop this kind of work if you don't have experience on it and always say when you see any pictures whit out responsibility it assembled correct !!!!

Thank you Eric because you clear to me many things when this provider playing on my budget

and

Thanks for satsig forums.

= amended by forum admin =
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Eric Johnston
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Reply #14 - Feb 6th, 2008 at 10:37am  
It hard to keep up with all this.

I've put together a page based on information sent in by Level 421. See Circular polarisation feed for IS904 hemi beam

If you want to operate on PAS-4 or Telstar 10 other polarisation arrangements will probably apply.

If you have a good circular polarisation feed assembly and want to change it to linear, just remove the polariser or rotate the polariser 45 deg so its pins/slots line up with either of the linear polarisation planes.

Regards, Eric
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maxfire2020
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Reply #15 - Feb 6th, 2008 at 12:29pm  
Hello Eric

i rely get upset and west my time whit this company even they don't have a company forum  once they saying we are bongoo.net and we are devision from Level421 and when you go deep whit them they start saying we are LEVEL421
believe me Eric the time i wested whit them i make 4 site up

and till now they still saying i assembled it wrong and they didn't even tell me about the circular or cross when i post  her and i give them the link the stat post *****
any way the subcontractor is the subcontractor he don't own the equipment wither they are bongoo or level 421 

Thank you
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Eric Johnston
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Reply #16 - Feb 6th, 2008 at 2:33pm  
Please obtain clarification about your service by direct email communication with mhaut@level421.com

They provide the same service to many other Africa sites without any problem.

See my explanation page here C band Africa service from Level 421

bongoo.net appears to be a trading name for service from Level 421 GmbH, I quote "bongoo.net is a label of Level 421 GmbH" from their web site:
https://www.bongoo.net/

See also:  https://www.level421.com/

Regards, Eric.
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Reply #17 - Feb 25th, 2008 at 11:28am  
unfortunatly i know a few people who have had the same problem with this bongoo thing. Infact one of them told me that they clain to be cheap yet they  sell you lower bandwidth inaddition to an internet accelerator ie if you buy 256/512 you actually recieve 128/256 unless you use the internet accelarator. and their equipment bumdles are actualy more expensive than the unlocked lot even if they tell you of the virtual discount, beware , i almost subscribed to them and if it were not for my freinds...i would have been a goner.
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mhaut
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Reply #18 - Dec 7th, 2008 at 7:41pm  
Dear forum members dear Eric,

Please let me clarify that bongoo.net is since 1.7.2008 not any longer a level421 owned operation. It was sold to an outside investor which continues to operate services with on site installers in Sub Sahara Africa.

level421 continues to be the technical partner and operates the platform.

Such bongoo.net has developed to the biggest reseller for level421.

Coming back to Maxfire who tried to activate equipement not supplied by bongoo.net - I am aware that I saw several feed assemblies who show a CO polar and not a Cross Polar feed. Such it will be quite impossible ever to track a CROSS CIRCULAR requiring satellite.

In addition IS904 requires RX = RHCP polarisation setup.

We have seen some customers trying with a linear polarized feed to shoot on IS904. Driving Intelsat mad - and us as well. Of course all this operation with little success and quite frustration on the customer side.

It also has shown to be difficult in the past - like maybe as well in future, to point at a satellite while in front of a "high wall" or "next to a tree". Smiley A quite common problem I heared about ....

I can confirm that several hundreds of happy customers use today IS904. The satellite definitely is "there" and our carriers "exist".

bongoo.net offers by the way all over Africa installation services by V-SAT professionals.

Of course customers who operate on very low budget and decide not to book this option - do find it sometimes quite difficult in particular when they are not keen in V-Sat to get a system going. This process can take between 2 days and basically 2 months.

Generally V-SAT installations are nothing for beginners. I personally always recommend everybody to book an installation service from an professional installer.

I do not know mr "bigeye" - but I can confirm that the SG (Second Generation) software bongoo.net uses which compresses the link over the satellite is working quite well. Compression rates reached can be with standard internet traffic 200 % and more. And customer may use it - or may not use it. As they like.

So far all I personally know use it as the enhancement is quite surprising.

I can confirm that such rubbish like: "if you buy 256/512 you actually recieve 128/256 unless you use the internet accelarator" is absolute nonsense and quite unqualified.


Greetings

Markus
level421
Germany
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