Troubleshooting a DVB-S Problem in Auckland

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BlakJak

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#82445 29-Apr-2011 10:00

G'day folks.
I moved into a new place and the TV Solutions available were basically not working for me:
- UHF antenna has fallen off the roof
- No VHF
- Sky Dish when plugged into my (old, legacy) DVB-S receiver doesn't have enough signal to be useful.

Steps taken so far include:
- Mate with signal strength meter tested signal at the dish as OK (established Dish is aligned and such)
- Same meter at the end of the coax run said it was 'borderline'.
- Shortened the run by removing a coupla extension lengths connected with F Barrell Connectors - Still no joy.
- Replaced the coax run complete with new RG6. Still no joy.

I'm left with either a receiver problem, or a Dish/LNB problem, near as I can tell.
I think the next step would be to borrow a receiver and eliminate mine as a potential issue. Anyone got a DVB-S receiver in Auickland I can borrow for a day or so? :-) (or any other suggestions) ?

Screenie of my TV.

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Oblivian

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#463637 29-Apr-2011 10:06

I could be wrong.. but doesnt look like the LNB has been set to be powered? use to hang off back of a sky box powering it?)

Shouldn't your 12v switch be set to active. Sat finders have batteries that provide a bit of juice to liven LNB up.

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Brunzy

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#463692 29-Apr-2011 12:29

I'd suggest you signal is not 'ok' at the dish.
What kind of meter did he have ?
What is the BER?

BlakJak

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#463706 29-Apr-2011 13:06

Not sure about feeding power up to the Dish, some googling suggested I shouldn't but then again, wasn't an exact science.

The guy who checked the dish is a professional Sky Installation Contractor so I hope he's got some cloo. He said the BER was fine but I didn't get the actual numbers from him.

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kiwirock

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#463713 29-Apr-2011 13:33

I'm inclined to double check the LNB power is turned on in the satellite receiver as mentioned by another poster. LNB power must be set to ON, unless another receiver is supplying power to the LNB.

Horizontal though should be putting out 18V not 12V.

The question is whether that 12V off setting in your screenshot is LNB power in general 12 or 18V, or whether it just refers to the point that it's set to 18V so therefore 12V is off.

You should have had him check the cable at the receiver as well. If it's not an LNB power problem of the receivers (not the LNB its self) then there could be the rear chance of a stray mains voltage between your mains power and whatever the roof is earthed to. Although I think LNB holders are plastic for that reason to prevent any earth problems.

You appear to be getting a reasonable signal strength though from the LNB, 63% is not that bad on a really long coax run.

Make sure LNB power is turned on int he receivers settings, or try another receiver or have someone check the quality with a meter at the end of the coax run.

BlakJak

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#463728 29-Apr-2011 14:06

Coax is about 20m end to end.
Before I replaced it my mate checked signal strength at the TV and he said it was 'borderline ok' which I gather is around 60%. Having replaced the coax myself the numbers on the OSD are the same which suggests the coax wasnt the problem, but I don't have hard data for how much loss is occuring in the cable.

I'll look closer into the power-back options when I am next home...
I would like to see if I can find someone who'll loan me a receiver to try as a sanity check...

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kiwisat

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#463753 29-Apr-2011 15:18

Hi Blakjak. Call me, Paul. You are welcome to borrow a receiver and satfinder from me. Satfinder will at least tell you if the power is getting to the dish. Bring the receiver to me and I will test that for you at the same time. 021 681371 Paul

BlakJak

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#464039 30-Apr-2011 22:26

Hi Paul, and others, thanks everyone for the advice.
I borrowed a DVB-S receiver from a friend and established that I need to send 18V up to the LNB. My decoder doesn't seem to do more than 12V and that wasn't enough to cut it.
With 18V I have 98% signal. :-)

So now I have his decoder on loan and my old one ... well i'm not sure how useful it is (are Dishes that require 12V common?) anymore.

Still amused that I don't recall ever adjusting the settings, which implies that the last time I used the decoder I didn't have to feed any power to it....

The next challenge is to see if I can put a splitter in and acquire a second decoder for the bedroom...

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LennonNZ

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#464051 1-May-2011 00:05

About Splitters.. There are a couple of different kinds...

- Ones which have power pass on 1 leg only so 1 BOX powers the LNB always
- Ones which have power pass on both legs so you have to make sure you don't power the LNB from both (or you _might_ break it).

mm1352000

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#464156 1-May-2011 13:12

BlakJak: I borrowed a DVB-S receiver from a friend and established that I need to send 18V up to the LNB. My decoder doesn't seem to do more than 12V and that wasn't enough to cut it.
With 18V I have 98% signal. :-)

This is strange. Have you measured the voltage on the cable (between the inner conductor and the outer shield/connector)? I could be completely wrong, but it is my understanding that 12 V is used for inline aerial amplifiers and dish moving motors that require that specific voltage (why they couldn't just downconvert 13/18V is anyone's guess). I suppose the voltage in that case would be measured between the cable's outer shield and ground. In any case, in my understanding it is something separate to the 13/18V used to select the LNB polarity. It is a pretty useless STB that can't send 13/18V...

BlakJak

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#464226 1-May-2011 18:09

LennonNZ: About Splitters.. There are a couple of different kinds...

- Ones which have power pass on 1 leg only so 1 BOX powers the LNB always
- Ones which have power pass on both legs so you have to make sure you don't power the LNB from both (or you _might_ break it).

Cheers for the headsup, was aware of that one. There was a splitter in the line when I moved in (I removed it and shortcircuited that entire leg when I reran the coax) but there's no pressing need to do this yet as I need to buy a decoder first (well two, as the one I now have is on loan).

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BlakJak

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#464227 1-May-2011 18:12

mm1352000:
BlakJak: I borrowed a DVB-S receiver from a friend and established that I need to send 18V up to the LNB. My decoder doesn't seem to do more than 12V and that wasn't enough to cut it.
With 18V I have 98% signal. :-)

This is strange. Have you measured the voltage on the cable (between the inner conductor and the outer shield/connector)? I could be completely wrong, but it is my understanding that 12 V is used for inline aerial amplifiers and dish moving motors that require that specific voltage (why they couldn't just downconvert 13/18V is anyone's guess). I suppose the voltage in that case would be measured between the cable's outer shield and ground. In any case, in my understanding it is something separate to the 13/18V used to select the LNB polarity. It is a pretty useless STB that can't send 13/18V...

The receiver I have was passed down by a friend, I'll harrass him for feedback. ;-)
Actually it occurs to me that if I run the second link, I can use this receiver where I don't need to feed power back... A plan is forming...

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kiwirock

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#464337 2-May-2011 00:13

BlakJak: Hi Paul, and others, thanks everyone for the advice.
So now I have his decoder on loan and my old one ... well i'm not sure how useful it is (are Dishes that require 12V common?) anymore.

Dishes or LNB's? If you meant LNB's, most of them are all 12/18V in order to switch between horizontal and vertical polarised transmissions. Freeview uses 18V (horizontal) but there is a lot of channels available in NZ on various satellites that also use vertical.

If your dish is only being used for Freeview (horizontal polarised), you can work with 12V on a dual polarised LNB the cheats way... just rotate the LNB manually exactly 45 degrees clockwise, send it 12V and see if it works. If it doesn't, rotate it another 45 degrees clockwise (same directino important) and it should definately work then. You're effectively polarising it the same way with 12V all the time, so manually rotating and re-polarising the LNB physically will work, but at the sacrifice of vertical polarised reception on a 12V only LNB power output receiver. If you try this cheat, make sure before you start rotating the LNB, you mark on the LNB and the LNB holder it's current possition so if everything turns to custard you can start again. When you rotate it 45 degrees you need to make it as accurate as possible.

I would strongly suggest just getting a new receiver, it's easier than mucking up the LNB alignment if you don't have a meter to re-align the LNB.

kiwirock

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#464338 2-May-2011 00:17

BTW for those with Strong SRT4620's which are a good older receiver, their later firmware versions have a bug that also doesn't output 18V. I had to re-flash one recently to older more buggy firmware to get it to output 18V.