SatSig topic:

Newbie member with limited tech knowledge!

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Apr 11^th, 2015 at 8:35pm

Hi, I'm Paul and I found this site looking for advice on the internet about my satellite system which is fitted to my motorhome. It is an Oyster 85cm dish with a Newtec MDM2200 modem, the system has automatic skew etc. My ISP is Satelliteinternet.co.uk (formerly BeyonDSL I believe). I have had the system for a year or so and always managed to get a signal as far as Sicily and the Algarve, although understandibly weak at times. Recently I have had trouble getting a signal at all (in Northern Sicily at the moment) and started looking into the system not knowing what I was doing really. Using the diagnostic software supplied by the ISP I have verified that the TX and cross-polarisation readings are good but the RX reading is below what it should be, which according to the ISP should be between 14db and 15db. Using the autosearch on the satdish usually gives me a signal beyween 11db and 12db, manually adjusting it can get it up to 13.6 if I am lucky, but more often around 12.7db to 13db.
This seems to make quite a difference to my download speed and I have emailed the ISP who are looking into it. I don't know if the amount of people using the service affects the RX signal but obviously the more people using the internet the more congestion and slower speeds are to be expected. Would fitting better coaxial RX/TX cables help at all or has anybody else had this problem and have any advice? One other thing, sometimes I get an error when I do a diagnostic test on the Newtec modem via their software, which is a hardware test 'ODU current measurement test'. Sometimes it comes back ok, twice is has come back 'no current' and once it stated 'wrong current detected on RX', giving readings of 64mA for the RX and 334mA for the TX. I have no idea what that means but have tested all the connectors to make sure they are ok.Thanks in advance for any help or advice

Apr 12^th, 2015 at 7:23pm

The outdoor equipment comprises a receive low noise block downconverter LNB and a transmit block upconverter BUC.

The coaxial cables carry signals: RX usually in the range 950-2150 MHz plus DC power, typically 13 - 19 volts. TX signals usually 10 MHz reference plus signals 950-1450 MHz for the BUC and perhaps 24 - 48 volts DC supply for the BUC.

Your indoor unit is monitoring the DC supply currents, 64 mA, for example. What voltages and currents you have will relate to your particular configuration. I suggest writing down the values when the system is working normally. The BUC current may increase significantly for a moment when a burst is transmitted. The BUC current value displayed will generally be the baseline value unless you are transmitting a very big file which takes some time and even then such a long transmission will probably comprise a series of bursts with gaps.

The most common faults on VSAT equipment are the F type cable connections and corrosion within the cables. A example I have seen, after 1 month in seaside location, are blackened and burned centre pins and the cable braid sheath turned to white dust over lengths of many feet down the cable. The combination of DC power and even the slightest moisture is a disaster. The cure is new cables and very carefully prepared F connectors. The solid copper centre pin (wire) needs to be bright and the tip slightly rounded so it pushes smoothly into the socket. The pin should be long enough so that it is about 1.5mm proud of the rim of the plug. A smear of electronic grade silicone grease is suggested. Wrap the entire plug in self amalgamating tape. Professionals use axial crimp F connectors which incorporate a moisture seal but the cost of the crimp tool is high.

Your symptoms of "no current" or "wrong current" are probably due to bad connections. Both the inner centre pin and the outer braid must make perfect connections.

Always power off at the mains before working on the cables.

A receive signal quality, when peaked up of between 11 and 15 dB will probably work fine. The lower values are to be expected near the beam edge and will leave little or no margin for any rain. Get yourself a beam coverage map with contour lines for your satellite. Note that your transmit beam is narrower than your receive beam and if you are not peaked up on receive (e.g. 12 when you could get 14 dB) the transmit signal can be really bad and this will affect your service. The dB figure relates to the power of the carrier and your dish size. It is not affected at all by the number of customers on-line.

Service problems, particularly during early evening, could be due to congestion with other customers sharing.

Apr 13^th, 2015 at 9:18pm

Thanks for that, it is a very detailed reply. I will work through your suggestions and let you know how I get on