Signal problem?

Darby OGill

Since the BBC went over to the 2D satellite, I've been having some problems. About half the time I try to tune BBC1/2 in particular, and sometimes some of the others, I get the dreaded "no signal being received " message. If I go to another channel, and then try again, I get the signal fine. I've checked the signal quality for both 10773 and 10447, and it's 90%.

Any ideas? This NEVER happened before the changeover.

watty

Sounds like the "LNB 22Khz tone switch too sensitive/ Digibox PSU noisy" combo that affects channels below 11.7GHz intermittently when you change from above 11.7 to below 11.7.

www.satcure.co.uk has addon filter now to cure this. Other options are to swap the LNB with someone who has different model Digibox and different model LNB.

Darby OGill

Thanks Watty, had a look at that, but my box is a Pace. What I'm really wondering is why this has happened now, and did not occur with ITV., C4 etc?
All my neighbours are Sky subscribers, so no swapping LNB's alas.
Mine is an MTI.

watty

Or perhaps your dish is slightly out and you are getting interference from 26E etc.

I actually get a better signal from new BBC frequencies than old ones.

There seems to have been quite a few unrelated reasons for BBC / 2D problems.

Where about are you? If newbridge (Kildare?) then "footprint" is not problem.
o alignment
o Noisy digibox PSU (aging PSU electrolitic capacitors dry out in heat)
o LNB 22Khz switch too sensitive
o Damaged or faulty cable (even a sharp kink) can affect just some transponders
o Damp in cable or corroded connections
o Badly fitted F connector at LNB or Digibox
o One place had Satellite coax "extended" with TV coax.
o Overhanging leafy trees (usually blocks everything)


Try your Pace box in someone elses house. If it still bad it *might* be a PSU or tuner problem.

Darby OGill

Thanks Watty. The box is about 4 years old, so that could be an issue. My parents have a Sky sub, with Panasonic box (only six months), I'll try a swop and see what happens.

Regarding alignment, what should I be looking for? On the default transponder, signal quality is 80%. I've moved the dish/LNB about in the past, but never got higher than this. How is this figure related to proper alignment, or would I meed a meter to get things 100% spot on?

Cabling is less than a year old, and I'm satisfied it's not a problem. I installed it myself- no sharp bends atc. In any case, if this was the problem, would it not happen on all channels?

watty

The explaination of why a cable fault in Coax can affect some frequecies and not others is a bit technical.

1) At higher frequencies (greater than 30 MHz) the coax is progressively more like a "pipe" or waveguide for the signal much like a optical fibre or a microwave waveguide. Esp at UHF and Higher as used by satellite I.F. signal from LNB to box (750MHz to 2150MHz band), the signal does not flow in the wires the way it would for say an audio signal in the same wire.

2) because the signal is like a wave down a pipe any sudden change wil cause reflections ( join from 75 Ohm to 50 Ohm can do it when wrong connector or cable is used. Even a crush due to cable clip).

3) A reflected wave can either add or subtract the forward wave depending on position in the cable or wavelength.

Though speed of RF in air or vacuum is like speed of light about 300 Million metres per sec, so wavelength in centimeteres is (300 *100) /frequency where frequency is in MHz so 3000 MHz = 10cm, 1500Mhz = 20cm, 750MHz = 40cm.

But RF is slower in coax. perhaps as slow as 200M metre/sec so 20cm becomes about 14cm (this is opposite to behaviour of sound which is about 300metre/s in air but faster in a solid rod etc).


So cancellation depends on frequency (which transponder) AND distance of "damage" along cable. It is worst at multiples of 1/4 wavelength, if memory serves me.

A special instrument called a Time Domain Reflectometer puts high frequency pulses down a cable and can identify how far away the open end (or cut) or a short (or bad crush).

A very sharp kink may well act like a short circuit at some frequencies.

carrolls

had a look at that, but my box is a Pace

Is your LNB a Grundig? If yes, get a Cambridge or Similar LNB. Grundig lnb's and Pace boxes don't mix.

aersat

Here is the procedure to test wheither you are receiving all four Sky Digital wavebands correctly.
Enter the installers menu:services,4,0,1,select manual tuning and enter the following information.

Frequency 10.862H,symbol rate 22000,fec 5/6 and press select.This is the low band horizontal channels.
Now try 10.906v,22000,2/3 and press select.This is the low band vertical channels.
Now try 11.914H,27500,2/3 and select.High band horizontal channels.
Finally try 11.934V,27500,2/3.High band vertical channels.

This test will ensure that all four wavebands from the Sky Digital satellite are being received ok.Note the network id remains the same (currently 0002),yet the transport stream will vary as alternative transponders are being selected from the satellite.The lock indicator should be on OK for all four signals.

aersat

Please note the FEC should be 5/6 for frequency 10.906v,22000 above and not 2/3 as stated.
My apologies,
Peter.

Darby OGill

Carrolls, LNB is an MTI.
Aersat, will try those tests tonight.

Thanks for all the replies guys- will let you know the outcome. Has anyone else had similar problems?

Darby OGill

What exactly is the default transponder?

watty

Originally posted by carrolls
Is your LNB a Grundig? If yes, get a Cambridge or Similar LNB. Grundig lnb's and Pace boxes don't mix.

My "sky" LNB is grundig. I also have a "regular" Universal LNB that is Grundig too (very simlar units inside two different plastic boxes, one for neck mount the other the plastic spike for minidish.

Both these work perfectly on all Sky channels on my Pace Digibox (faster cpu, one earliest subsidy ROI boxes) and on my later purchased S/H Grundig Digibox (€60, but old slow cpu).

Certinally some LNBs and some Digiboxes together don't seem happy at selecting low band sometimes. Often a different model does cure the problem, yet the alleged "faulty" LNB (or Digibox)works fine on a different Digibox (or LNB).


In the old days when the VHF 405 worked and the UHF 625 BBC 2 didn't I just had to replace the two valves in the TV tuner... Or solder the 405/625 switch in the 625 UHF position.

Darby OGill

Aersat, ran the tests on those frequencies as suggested. Got 80% and 90% signal quality on high and low band (or vice versa- can't remember ). How does this rate?

Watty, do I have to tune in my box on another system or is it just a matter of connecting my box to the cables? My father looked very doubtful when I suggested swopping boxes for a few minutes

ShaneOC

Originally posted by Darby O'Gill
do I have to tune in my box on another system or is it just a matter of connecting my box to the cables? My father looked very doubtful when I suggested swopping boxes for a few minutes

You do not have to tune in any channels. That all happens automatically. It is as simple as just swapping all the leads from your father's digibox to yours.

watty

Well unless the RF out is the same any RF channel on a TV might need tuned (1 channel, add it on TV, leave existing RF channel alone and digibox settings alone and then easy swop back). But watching the Digibox via SCART lead nothing needs changed at all.

You do have SCART cable connected?

JimG

I live in the Northwest. I have the standard Sky minidish. I always get signsl strength of 50 percent, rarely 60 percent. Should I be getting better than this?

Mike 1972

If by "standard minidish" you mean a 45 or 60cm one then yes you should really use an 80cm or greater (especially in the West)

If however you dont have any problems with pixellation/breakup/freezing/loss of signal (check during heavy rain) then you may be experiencing a "lucky fluke"

aersat

Darby.... Try the above procedure using 10.773H,SR 22000,Fec5/6 which is the BBC Northern Ireland Transponder.
Repeat the process several times,which may show up an intermittent fault.
I would be almost certain that the problem is with the Digibox Tuner,the Pace boxes are renowned for it.

Aersat.

Darby OGill

Aersat, before I try this, I'm not subbed. Just FTA and FTV. Will this matter?