Does anyone know what happens when a Sky box displays "Searching for
listings please wait"? I understand that it gets the EPG from the default
transponder, and that it contains channel numbers and names, their
corresponding stream IDs, and information about which transponder carries
the required stream. But how does it know which transponder is which?

Does the EPG contain preset frequencies that the box must tune in to
accurately, for example "go to 1023 MHz for BBC1" (having already done the
high/low band and H/V switching), or does the box use search tuning like a
general purpose non-Sky satellite receiver does?

If it is the latter then I assume each video stream must contain data on the
name of the transponder and the box uses that instead of a preset frequency.
Could this explain why when resetting my Sky box recently, it was able to
get the full up to the minute EPG listings but it continued to display "no
satellite signal is being received" on all channels until I pulled the mains
out and in again? I wonder if the search tuning failed because in my haste I
hadn't waited long enough for it to finish "searching for listings"? Or
maybe it had just updated the actual channel listings, as it must do every 5
minutes or so, but the channel tuning data had got corrupted and doesn't
normally get updated until you pull the mains out and in? The lock indicator
was going on and off initially because the box was cold. I think it needs
new capacitors. Channels that break up come good if I point my fan heater at
the box.

It's funny how the only visibly bulging electrolytic capacitor is adjacent
to the dish input can. Do these run hot? Could it be drifting off frequency?
All the power supply capacitors that are supposed to be the ones in danger
of frying look ok.

I am so disappointed that no one has been able to answer this - I would love to know how it works.

Best

Fred F.

On 2010-02-20, Stephen wrote:
Does anyone know what happens when a Sky box displays "Searching for
listings please wait"? I understand that it gets the EPG from the default
transponder, and that it contains channel numbers and names, their
corresponding stream IDs, and information about which transponder carries
the required stream. But how does it know which transponder is which?

It goes to the default transponder frequency. I think the info is in
fact on all transponders, so it could start anywhere that it finds a
signal.

It reads the "Network Information Table" to find the frequencies etc of
all the transponders in this "Bouquet".

Here's part of a dump of the NIT (from when I was experimenting in 2006):

NtwkInfoActual tabid=40p seclen=03FB value=0020 ver=12 c sec=00/01 iend=03FD
| NwkInfo.Actual NtwkNm(ASTRA) MlngNetw(eng,ASTRA) nilen=03DC
| TsId=07D1 OrigNwk=0002 SatDelSys(011.71950,028.2E,H,QPSK,027.5000,2/3)
| TsId=07D5 OrigNwk=0002 SatDelSys(011.69750,028.2E,H,QPSK,027.5000,2/3)
| TsId=07D2 OrigNwk=0002 SatDelSys(011.73900,028.2E,V,QPSK,027.5000,2/3)
| TsId=07D9 OrigNwk=0002 SatDelSys(011.87550,028.2E,H,QPSK,027.5000,2/3)
| TsId=07DB OrigNwk=0002 SatDelSys(011.91450,028.2E,H,QPSK,027.5000,2/3)
| TsId=07D7 OrigNwk=0002 SatDelSys(011.83650,028.2E,H,QPSK,027.5000,2/3)
| TsId=07D4 OrigNwk=0002 SatDelSys(011.77800,028.2E,V,QPSK,027.5000,2/3)
| TsId=07E5 OrigNwk=0002 SatDelSys(012.10950,028.2E,H,QPSK,027.5000,2/3)
| TsId=07DC OrigNwk=0002 SatDelSys(011.93400,028.2E,V,QPSK,027.5000,2/3)
| TsId=0807 OrigNwk=0002 SatDelSys(010.92075,028.2E,H,QPSK,022.0000,5/6)
...
| TsId=07F6 OrigNwk=0002 SatDelSys(012.44100,028.2E,V,QPSK,027.5000,2/3)
| TsId=0009 OrigNwk=0002 SatDelSys(099.89994,028.2E,H,QPSK,027.5000,2/3)
| TsId=096B OrigNwk=0002 SatDelSys(011.66154,028.2E,H,QPSK,027.5000,2/3)
| TsId=270E OrigNwk=0002 SatDelSys(999.89999,028.2E,H,QPSK,027.5000,2/3)
| TsId=0801 OrigNwk=0002 SatDelSys(010.83225,028.2E,H,QPSK,022.0000,5/6)
| TsId=0805 OrigNwk=0002 SatDelSys(010.79125,028.2E,H,QPSK,022.0000,5/6)
| TsId=0806 OrigNwk=0002 SatDelSys(010.90600,028.2E,V,QPSK,022.0000,5/6)
| TsId=0961 OrigNwk=0002 SatDelSys(011.46923,028.2E,H,QPSK,027.5000,2/3)
| TsId=0965 OrigNwk=0002 SatDelSys(011.54615,028.2E,H,QPSK,027.5000,2/3)
| TsId=0964 OrigNwk=0002 SatDelSys(011.52692,028.2E,V,QPSK,027.5000,2/3)
| TsId=07F7 OrigNwk=0002 SatDelSys(012.46050,028.2E,H,QPSK,027.5000,2/3)

It's interesting that there are a few bogus entries in this table!

It also reads the "Bouquet Association Table". This lists all the
services which exist across all the satellites in the bouquet.

Here's an extract from the BAT (decoded by a program of mine):

BouqAssoc tabid=4Ap seclen=03FA value=100C ver=1E c sec=08/0B
BqName(BSkyB Bouquet 12 - Commercial Other)
PriDatSpec(00000002)
Lkg(07D4,0002,105D,90)
Lkg(07F3,0002,138C,91)
...
| TsID=0807 OrigNtwk=0002 SvcL()
PriDatSpec(00000002)
[B1](FFFF,101B:04:044F:4095:4095,
139D:01:071D:543:543)
...

The parts after "PriDatSpec(00000002)" are "private data" which in this
case is BSkyB specific data. Their B1 descriptor contains the type (01=TV)
Epg Service ID, and the sky number (e.g. 543). So it says these services
can be found on the specified transport stream (0807) which from above we
already know is at "10.92075GHz 28.2E H QPSK 22.0000 5/6".

In addition, there is the Service Description Table, which on each
transponder gives more details of services on that transponder:

SvcDescOther tabid=46p seclen=03CE TsId=0807 ver=08 c sec=00/02
| SvcDescr.Other OrigNtwkId=0002
| SvcId=05E6 EIT: nvod PriDatSpec(00000002) Svc(82,,) [B2](000000,)
| SvcId=101A EIT:Sc nvod CA Svc(NVODr,BSkyB,Sky Box Office)
Nvod(07E4:0002:133E,07E4:0002:133F,07E4:0002:1340, 07E4:0002:1341,
0961:0002:1342,0807:0002:13A2,0968:0002:1215,0968: 0002:1216,
07DC:0002:1276,07DC:0002:1277,07E4:0002:12DA,07DC: 0002:1278,
07E4:0002:12DB,07E4:0002:12DC,07DC:0002:1279,07E4: 0002:12DD,
07DC:0002
PriDatSpec(00000002)
[B2](1D01D0,Sky Box Office brings you up to 25 widescreen movies every
day, starting as often as every 15 minutes. You only pay for what you
watch - each movie costs just œ3.75)

Does the EPG contain preset frequencies that the box must tune in to
accurately, for example "go to 1023 MHz for BBC1" (having already done the
high/low band and H/V switching), or does the box use search tuning like a
general purpose non-Sky satellite receiver does?

It aims exactly at the frequency. If there's no signal, it searches a few
times slightly to each side in case your LNB frequency is slightly off.
(My box has a readout of frequency on it, and one can watch it doing
this!)

If it is the latter then I assume each video stream must contain data on the
name of the transponder and the box uses that instead of a preset frequency.
Could this explain why when resetting my Sky box recently, it was able to
get the full up to the minute EPG listings but it continued to display "no
satellite signal is being received" on all channels until I pulled the mains
out and in again?

I think the box software just got confused. I've seen mine fail to try
to adjust the tuning frequency when switching channels. As always, a power
cycle gets it sorted out again. The EPG data is cached to some extent
which I guess is why it appeared still to work for you.

I wonder if the search tuning failed because in my haste I
hadn't waited long enough for it to finish "searching for listings"? Or
maybe it had just updated the actual channel listings, as it must do every 5
minutes or so, but the channel tuning data had got corrupted and doesn't
normally get updated until you pull the mains out and in? The lock indicator
was going on and off initially because the box was cold. I think it needs
new capacitors. Channels that break up come good if I point my fan heater at
the box.

If lock is going on/off then there is certainly a problem somewhere.

It's funny how the only visibly bulging electrolytic capacitor is adjacent
to the dish input can. Do these run hot? Could it be drifting off frequency?
All the power supply capacitors that are supposed to be the ones in danger
of frying look ok.

If it gets better when warm, I'd definitely suspect dead capacitors,
even if they look visually ok.

Regards,
Mike.

P.S. more of my technical info at http://u1061771158.freehostia.com/pvr.html