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Nebula Reception questions


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Hi All,

I have recently installed a nebula PCI card and am having a few reception issues.

I have a Strong srt 5290 STB which gives a perfect picture on all channels except SBS which breaks up a fair bit.

On the nebula card I get a perfect reception on SBS and everything else breaks ups to varying degrees, ABC and 10 being worst.

The signal strength being reported by DIGITV is about 78% for most channels and 73% for TEN (this is Sydney by the way)

The strong box reports 100% for all channels except SBS which is at about 66%.

The antenna is brand new, the cable run is all quad shield RG6 and the patch leads from the wall are all RG6 as well. The cable from the antenna feeds only one wall outlet at which point it is split 3 ways to a VCR strong STB and the nebula.

The cable run to the antenna is 15 meters and there is a GME Kingray masthead amplifier on the line.

Any sugestions as to why would the nebula cards reception would be so much poorer than the strong box. By the way, I have tried each device on its own using the same patch lead on each device individually and the results are the same.

Cheeers

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This is all normal. There has been a lot of debate about the tuner performance on DVB-T PCI cards and it has never really been definitively answered. Whether the problem lies with the tuner's used, limitations due to form factor, the environmental issues inside the PC both in terms of radiated RF and perhaps via the DC power rails from the PCI Bus. There are a lot of clocked circuits operating in the 100's MHz to GHz's range. Generating who knows what ?

It would appear that the tuner's used on some of the newer cards like the Dvico Fusion are a couple of dB more sensitive and perform more in line with good STB tuners. But apparently some STB Tuners are just as bad ~

I used to have some problems with the Nebula on some channels until I put a GME Kingray 4 way distribution amp at the wall socket and then 4way passive splitters at the back of the computers.

Can you crank the output from the masthead amp up a bit at all ?

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What you are seeing is a bit odd

Given you say you have 78% signal strength, what are the other parameters for S/N and BER. You already have a masthead amplifier which in most cases should be more than adequate for excellent reception

Also where are you in Sydney and what frequencies are you seeing for the channels

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Its possible other devices in your PC such as a cheap Power supply or mainboard components are interfereing with the Nebula Card - which is why the Nebula USB has a better signal.

Some people have actually wrapped the card in metal + plastic insulation to avoid this problem, but average joe shouldnt attempt it since they could short/damage something.

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Hi Joeybloggs

Getting to the masthead amp is a bit problematic, not becasue its in a bad location but because its at the site that I work and for OH&S reasons I am not allowed near a ladder under fear of execution.

I might come in one weekend anf give that a try.

By the way thanks for the EPG program it works a treat.

Murrayt

The figures for SNR and BER are as follows

SBS signal 78 SNR 22 BER 0.051 (average)

ABC signal 78 SNR 22 BER 0.060 (average)

TEN signal 74 SNR 22 BER 0.058 (average)

We are in the north west of Sydney (Kenthurst) and all frequencies are set to Sydney Frequencies.

Thanks

Stephen

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Stephen

Looking at the figures you are quoting it's no surprise you have a lousy picture !

a BER of less that 0.01 is a good measure. On my best channel 0.004/5 is about the standard. 22 SNR is a bit lower than I would expect given the strong signal measure of 78%

I get the impression this is a shared installation. All I can guess is that there is a source of interference from somewhere.

...and by the way even if on the weekend they'll probably execute you !

also what about Seven and Nine, and also the frequencies ? VHF/UHF

Maybe the antenna installation while new has not been set up properly etc

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Bit Error Rate is usually expressed in errors per million so 0.02 would be 1 error in every 50 million bits or 1 error every 2.5 seconds at a 20 Mbit signalling rate.

BER is not necessarily going to follow signal strength. You may have a very strong multi path signal that interfers with itself or atmospheric or local interference that affects the BER regardless of signal strength ~

The 'best' solution is standard RF engineering. Best antenna correctly orientated, amplify as close to the source as possible and use quad shielded cabling to minimise local interference.

my readings today

Channel  Strength  SNR    BER  
-------------------------------
     2       81%  24 dB  0.010
     7       78%  23 dB  0.015
     9       76%  22 dB  0.015
    10       72%  23 dB  0.012
   SBS       82%  23 dB  0.013

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Hi All

Thaught I would post a follow up for anyone interested.

I am now getting great picture on all sydney channels with only the very occasional glitch on ABC.

The sollution turned out to bit a bit of antenuation in the form of a longer rf lead from the wall to the puter. An extra pre made rf lead was added to the existing rf lead from the wall. The additional lead is not rg6 but a thin flexible lead, the type that comes startard with a VCR etc.

Maybe the gain of the masthead AMP is too high, but I'm not allowed on the roof to check it.

Also for editing and burning to DVD I have found the following working great.

Generally I can dump the recorded MPEG direclty into Pinnacle studio 9 and burn straight to DVD no conversion or other software required.

On occasion I have found the files wont import into pinnacle. When this happens I play the file through once in DIGItv (fast forward will do) and then the file will import into pinnacle. Yes I know this sounds a little odd but it works repeatedly and without fail.

Cheers

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On occasion I have found the files wont import into pinnacle. When this happens I play the file through once in DIGItv (fast forward will do) and then the file will import into pinnacle. Yes I know this sounds a little odd but it works repeatedly and without fail.

Stephen, glad to hear that you have had some improvement. Sometimes too much signal can be as bad as not enough! :blink:

The failure to import problem sounds like it may be caused by the file locking problem that people have had. Maybe the current version of DigiTV is releasing the lock on the file once playback is complete.

You might want to try fully exiting DigiTV (including from the systray) next time you cant import into Pinnacle, and see if you can then import the file without the need to play through it first.

Anyway, Nebula's site says they've cured the problem for the next update.

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I'm getting a bit lower strength, and a bit better BER than joeybloggs.

On SBS its totally different. Very Good strength, OK SNR, very poor BER <0.1

However, moving my antenna a little I can bring down the BER to 0.05-0.08 and its very watchable, maybe a small glitch every 10-15 minutes.

A bit OT but bringing up "Technical Information..." causes the network PC's viewing to drop out the picture/audio almost totally. Anyway to fix this?

And a little hint: If you're like me and use a simple indoor antenna, after moving it around to get the best signal, restart DigiTV (right click - Exit). The strength, SNR and BER will be a little higher. I dont know why but all the loss of signals permanently lowers the quality when you finally do get the 'sweet spot'.

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