HELP! Signal loss after TX enabled (ViaSat)

We have installed a 2.4 Meters Ku-Band dish in Ghana (close to Sunyani) and recently tried to set up the system. After pointing our dish we received a good signal (QPSKBER constantly below 0,0000x) and were looking forward to the lineup. When our Provider switched on the TX of our Transceiver (SkyWare 2 Watts model) and established the link we could not believe what we saw: BER sank down to 0.00x and the RSCorrected and UnCorrected ErrorCount started rising. At the end we had a packet-loss of about 50% - too bad for any connection. We don't have any clou where this problem is originating from. Some guesses: Feedhorn issues? Interference or Sidelob reflecting into our own RX? What's your guess? Ay, we're trying to set up this system for a small community in Ghana to supply facilities and a hospital with internet-connections. So our project is really endangered if we cannot solve this packet-loss issue.

Mmh, all right, but checking my cross-pole (is Eutelsat W3a) is kind of difficult without having having someone on the hub to test it nor a spectrum analyzer - is it possible to contact the hub people before you choose a provider? or are there some tricks to check for the right polarization? Can't I just transmit a carrier and realign my dish until i get a good BER again?

So let's post some tech details of my equipment:

Modem: ViaSat RCST Modem - I think it's Rev. D
Tranceiver (Integrated RX/TX): Skyware 2 Watts Cross-Pole Ku-Band (see www.skywareradio.com)
Antenna: 2,4 x 2,6m Offset (ND-Satcom)
Provider: still about to choose - could be Level421 (Germany)

But if the only possibility is to check with the Hub on the phone - how to reach these people? W3a Hub is in Turin/Italy right? Can i just call there and ask for assistance?

PS: Found out, that my KU-Feedhorn is not the one originally supplied with the antenna. Could this be the origin of my problems? But if RX is fine, how should it affect TX?

So here's the whole story for you:

Indeed, we had a german provider and supplier doing the test with us - but because we really needed a long time (one year) for getting our equipment he was a litte fed up and told us to solve our problems bevore he will try to reconnect - this means, actually were free to choose again, but i don't want to do this without having my equipment working. From our primary Provider we also received the modem and transceiver and the access information - only our dish and feedhorn is supplied by another company - but still all the components are KU-band so I don't see why they should be troublesome.

For the Feedhorn (It's KU-Band from an Prodelin antenna) - I hope i got right that for every VSAT you use just ONE Feedhorn for RX and TX, and because we use a Transceiver and not a detached BUC/LNC there's no Waveguide splitting the Signals.

Let's come back to my most beloved question   Any way to contact the hub directly?

Ahh. got that. I always thought that you can troubleshoot with the satellite operator directly -  but in this case i'll have to ask my provider (It is or has been "Level 421") again for tech support or choose a new one to support me. Do you think just realigment whilst online with the provider will do the trick?

I am just back from cycling around Hungary - again !

A few thoughts:

If the receive BER went down badly when DC power was applied to the BUC then you probably have a bad connection at one or more of the F connectors.  If the outer and inner conductors are not perfectly connected then the current via the BUC comes back via the LNB cable and drops the DC volts for the LNB.

If the receive BER went down slightly when the BUC power was turned and goes down further whenever a transmit burst occurs then this is probably a version of the above problem.  Many BUCs take more DC current when the unit is transmitting.

If the receive BER went down badly when the BUC transmitted its first burst and HAS STAYED DOWN EVER SINCE, you have probably damaged the LNB by allowing excessive RF power into the LNB input.  This may happen if the transmit reject filter is missing in the waveguide to the LNB.   Temporary mild overload of the LNB will produce error bursts in the receive continuous signal every time the BUC transmits a burst.  If the LNB is not damaged it will operate normally when the BUC is not transmitting.

If the BUC cable has a faulty connector that is short circuiting the cable, then when the BUC power is switched on the power supply unit in the Linkstar will be damaged.  The damage may well affect the LNB supply. There must be no fragments of braid wire scattered inside the F connector.

Please say if you can get back to the original high quality receive signal with just the LNB, and LNB cable connected.

The disconnection and connection of cables must be done with the indoor unit switched off.   Take great care not to cross over the cables.

Best regards, Eric.

Checking the connectors means making sure that the outer braid is properly connecting to the F type outer shell.  I would suspect that the BUC cable outer is not connected.

Does a waveguide transmit reject filter (band stop to the transmit frequency band and band pass to the receive frequency band) exist between the OMT junction and the LNB ?    

Such a transmit reject filter will be a length of waveguide, perhaps 2-3 inches long, with either an array of pins across it, some set of cavities attached alongside or with rows of slots along the opposing broad walls.   An example is shown at the TOP of the figure on this page https://www.satsig.net/feed1.htm The straight through waveguide filter on the left is a transmit band pass filter. This is often omitted.    

During commissioning, transmit is enabled by the hub.

During normal operation transmit is enabled every time you press the return key or upload a file or email for example.  

Transmit operation is not shown by the LEDs.   It occurs at exactly timed brief instants, lasting a fraction of a second, so that your streams of transmit bursts arrive at the satellite interleaved in time with bursts from all the other sites sharing the same uplink transmit frequency.

Best regards, Eric

The integrated ORU unit should have adequate transmit reject filtering incorporated.   Ideally, it should take stable, steady DC supply currents via each cable.

The good electrical connection between the outer of the two sockets at the ORU makes it all the more important that the transmit cable outer braid is well connected and of low DC resistance.  

You might consider an additional really thick earth cable from the ORU to the indoor unit.  You do not want the BUC DC current or transmit burst induced or switch mode converter induced variations of BUC current superimposed on the LNB DC current.  

( There is the possibility that the BUC uses a switch mode DC-DC converter and tries to pull short pulses of very high current from the cable. )

If you still have problems contact your supplier or the manufacturer.  Has this kit ever successfully worked before with a LinkStar modem at an operational site with the types and lengths of cable that you are using ?

Best regards, Eric.

Please say what your transmit power setting is.

use command: pconf

Note that  -t -30 is the normal starting value which means attenuator set to 15 dB   

The hub will adjust this remotely to set your level correct into the hub.

If you have an excessively high value setting (like -t  -6) then this could cause your symptoms and also damage the transmitter.  High values like this are only needed on exceptionally long, high loss, transmit cables.

Best regards, Eric.