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Freesat PVRs - can I check my understanding of the technology



 
 
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  #1  
Old October 28th 18, 12:54 PM posted to uk.tech.digital-tv
NY
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Posts: 1,518
Default Freesat PVRs - can I check my understanding of the technology

I know about DVB-T terrestrial and the fact that channels are grouped into
multiplexes. A single receiver (in a PVR or as a USB DVB-T decoder attached
to a PC with suitable software) can simultaneously record several channels
providing they are all in the same multiplex; to record simultaneously two
channels which are in different multiplexes, you need two decoders, each
with its own aerial feed.

What is the situation with satellite? Is the following correct...

1. Is a dish that was installed for Sky going to work for Freesat, subject
to the fact that it won't receive Sky-specific channels because they are
encrypted?

2. Satellite transmissions are grouped into four "groups" (roughly
equivalent to DVB-T multiplexes), and the LNB at the dish needs to be
instructed which "group" to tune to.

3. If a satellite dish has two downleads to the TV, it can receive two
"groups" simultaneously and hence record two channels or record one and
display the other on the TV.

4. Can a PVR (dedicated hardware or DVB-S decoder to PC) record more that
one channel on the same "group", in the same way that a DVB-T decoder can
record multiple channels on the same mux?

5. If a dish currently has two LNBs, can it usually be upgraded to more, to
allow an extra downlead - eg to allow two recordings from different "groups"
and also a channel to be watched live? Or does that usually require a
completely new dish?

6. Satellite cables can't be fed fed through a splitter in the way that a TV
aerial can be (subject to suitable signal level to compensate for splitter
losses) because any receiver needs to instruct the LNB which "group" to tune
to, and two receivers (TV or PVR) on the same cable could end up sending
conflicting tuning commands (I presume these are sent up the cable in the
opposite direction to the signal), so to feed two TVs in different parts of
the house separate cables and LNBs are needed.


I'm asking because when we move house, one house that we are looking at is
in a satellite-only area, where (according to JavaJive's site) there is no
terrestrial reception - or if there is, it may be very marginal, and may
require a very high-gain aerial on a very tall mast from the chimney (*). I
want to be able to continue recording to a computer (for archiving) and to
be able to watch a channel live (which may or may not also be being
recorded). I currently use TVHeadend on a Raspberry Pi using two USB
DVB-T/T2 decoders.

Alternatively, are there any dedicated PVRs which can export their
recordings to a computer as opposed to them having to remain on the PVR's
disk and only exported by copying to an analogue recorder?



(*) This house has no aerial, just a dish on the chimney; other houses in
the streets have very large aerials with many X-shaped dipoles, on very tall
masts. The vendor was not available to ask whether he had tried terrestrial
and failed to get a good signal. The problem is a road which slopes
downwards away from the transmitter and so the top of the street blocks line
of sight, and there is no other transmitter which covers that area.

  #2  
Old October 28th 18, 02:38 PM posted to uk.tech.digital-tv
Michael Chare[_5_]
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Posts: 85
Default Freesat PVRs - can I check my understanding of the technology

On 28/10/2018 11:54, NY wrote:
I know about DVB-T terrestrial and the fact that channels are grouped
into multiplexes. A single receiver (in a PVR or as a USB DVB-T decoder
attached to a PC with suitable software) can simultaneously record
several channels providing they are all in the same multiplex; to record
simultaneously two channels which are in different multiplexes, you need
two decoders, each with its own aerial feed.

What is the situation with satellite? Is the following correct...

1. Is a dish that was installed for Sky going to work for Freesat,
subject to the fact that it won't receive Sky-specific channels because
they are encrypted?


A Sky dish will work for Freesat, the dish and the LNB don't care about
the encryption.


2. Satellite transmissions are grouped into four "groups" (roughly
equivalent to DVB-T multiplexes), and the LNB at the dish needs to be
instructed which "group" to tune to.


Transponders are the equivalent of terrestrial multipleses.

Universal LNBs can only download one of those for groups at a time High
Low, Horizontal and Vertical. See Wikipedia for more detail

See
https://en.kingofsat.net/freqs.php?&...filtr e=Clear

3. If a satellite dish has two downleads to the TV, it can receive two
"groups" simultaneously and hence record two channels or record one and
display the other on the TV.


That is generally a function of a satellite PVR


4. Can a PVR (dedicated hardware or DVB-S decoder to PC) record more
that one channel on the same "group", in the same way that a DVB-T
decoder can record multiple channels on the same mux?


Yes, though it will need to have a free LNB port if a channel to be
recorded is in a different one of the above 4 groups.


5. If a dish currently has two LNBs, can it usually be upgraded to more,
to allow an extra downlead - eg to allow two recordings from different
"groups" and also a channel to be watched live? Or does that usually
require a completely new dish?


I think you mean a twin LNB, i.e. one with two cables coming from it.
You can get quad and 'bigger' LNBs. An alternative to a 'bigger' LNB is
to use a multiplex switch

6. Satellite cables can't be fed fed through a splitter in the way that
a TV aerial can be (subject to suitable signal level to compensate for
splitter losses) because any receiver needs to instruct the LNB which
"group" to tune to, and two receivers (TV or PVR) on the same cable
could end up sending conflicting tuning commands (I presume these are
sent up the cable in the opposite direction to the signal), so to feed
two TVs in different parts of the house separate cables and LNBs are
needed.

In general correct.



I'm asking because when we move house, one house that we are looking at
is in a satellite-only area, where (according to JavaJive's site) there
is no terrestrial reception - or if there is, it may be very marginal,
and may require a very high-gain aerial on a very tall mast from the
chimney (*). I want to be able to continue recording to a computer (for
archiving) and to be able to watch a channel live (which may or may not
also be being recorded). I currently use TVHeadend on a Raspberry Pi
using two USB DVB-T/T2 decoders.

Alternatively, are there any dedicated PVRs which can export their
recordings to a computer as opposed to them having to remain on the
PVR's disk and only exported by copying to an analogue recorder?



There are Linux PVRs which will record to any network drive and Freesat
channels are not encrypted.


(*) This house has no aerial, just a dish on the chimney; other houses
in the streets have very large aerials with many X-shaped dipoles, on
very tall masts. The vendor was not available to ask whether he had
tried terrestrial and failed to get a good signal. The problem is a road
which slopes downwards away from the transmitter and so the top of the
street blocks line of sight, and there is no other transmitter which
covers that area.


There is a new technology. There are FBC Tuners and Unicable SCR LNBs
which are all different and could be a good idea for a new installation!:-)


--
Michael Chare
  #3  
Old October 28th 18, 04:14 PM posted to uk.tech.digital-tv
Angus Robertson - Magenta Systems Ltd
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Posts: 73
Default Freesat PVRs - can I check my understanding of the technology

2. Satellite transmissions are grouped into four "groups"
(roughly equivalent to DVB-T multiplexes), and the LNB at the
dish needs to be instructed which "group" to tune to.

3. If a satellite dish has two downleads to the TV, it can
receive two "groups" simultaneously and hence record two channels
or record one and display the other on the TV.

4. Can a PVR (dedicated hardware or DVB-S decoder to PC) record
more that one channel on the same "group", in the same way that a
DVB-T decoder can record multiple channels on the same mux?

5. If a dish currently has two LNBs, can it usually be upgraded
to more, to allow an extra downlead - eg to allow two recordings
from different "groups" and also a channel to be watched live? Or
does that usually require a completely new dish?


This was correct until two years ago when Sky Q was launched with new
technology. Instead of four 'groups' there are now only two wideband 'groups',
and no reason to limit the number of tuners in the receiver. Older LNBs were
switched between to different bands.

So Sky Q has 11 (maybe 12) tuners fed with two coax downleads from the new
wideband LNB, and can record six channels simultaneously while viewing four
more live using wifi connected devices around the house.

There is no reason Humax or other Freesat receivers could not use the new
wideband receivers and more tuners, but I've yet to see any such products.

The Sky Q boxes can also record six channels from a single coax when fed from a
dSCR Multiswitch designed for multi dwellings.

Angus


  #4  
Old October 28th 18, 07:53 PM posted to uk.tech.digital-tv
David Woolley[_2_]
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Posts: 557
Default Freesat PVRs - can I check my understanding of the technology

On 28/10/18 11:54, NY wrote:
2. Satellite transmissions are grouped into four "groups" (roughly
equivalent to DVB-T multiplexes), and the LNB at the dish needs to be
instructed which "group" to tune to.


They are not really equivalent to multiplexes. They are more equivalent
to a complete television band.

Processing speeds of software defined radios are getting higher and
higher, so it might, one day, be economical capture a whole band at
once, rather than the 8MHz slice used by DVB-T, but I don't think that
consumer products with that capability currently exist.

I'd always assumed that digital satellite has a direct equivalent of
multiplexes, but, not having satellite myself, I haven't looked in detail.

As already noted, the high low band distinction is artificial resulting
from engineering constraints. There is real significance in the
polarisations, though.
  #5  
Old October 28th 18, 08:08 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 3,025
Default Freesat PVRs - can I check my understanding of the technology

On 28/10/2018 11:54, NY wrote:
I know about DVB-T terrestrial and the fact that channels are grouped
into multiplexes. A single receiver (in a PVR or as a USB DVB-T decoder
attached to a PC with suitable software) can simultaneously record
several channels providing they are all in the same multiplex; to record
simultaneously two channels which are in different multiplexes, you need
two decoders, each with its own aerial feed.


No the receiver will have a number of independent tuners.

Bill
  #6  
Old October 28th 18, 08:16 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 3,025
Default Freesat PVRs - can I check my understanding of the technology

On 28/10/2018 13:38, Michael Chare wrote:

I'm asking because when we move house, one house that we are looking
at is in a satellite-only area, where (according to JavaJive's site)
there is no terrestrial reception - or if there is, it may be very
marginal, and may require a very high-gain aerial on a very tall mast
from the chimney (*).


What's the postcode?

Bill
  #7  
Old October 28th 18, 08:16 PM posted to uk.tech.digital-tv
NY
external usenet poster
 
Posts: 1,518
Default Freesat PVRs - can I check my understanding of the technology

"Bill Wright" wrote in message
news
On 28/10/2018 11:54, NY wrote:
I know about DVB-T terrestrial and the fact that channels are grouped
into multiplexes. A single receiver (in a PVR or as a USB DVB-T decoder
attached to a PC with suitable software) can simultaneously record
several channels providing they are all in the same multiplex; to record
simultaneously two channels which are in different multiplexes, you need
two decoders, each with its own aerial feed.


No the receiver will have a number of independent tuners.


You mean I'd need one tuner per recording (even if all the channels being
recorded are in the same high/low band and the same polarisation), rather
than (as for terrestrial) one tuner which produces a data stream that is
split into separate recordings from the same multiplex.

  #8  
Old October 28th 18, 08:25 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 3,025
Default Freesat PVRs - can I check my understanding of the technology

On 28/10/2018 18:53, David Woolley wrote:

As already noted, the high low band distinction is artificial resulting
from engineering constraints.* There is real significance in the
polarisations, though.


The short-lived British Satellite Broadcasting was laughably unambitious
about the number of channels so used one band and one polarisation. Thus
the signal could be distributed to blocks of flats by simply adding it
to the terrestrial feed and adjusting the equalisation.

Bill
  #9  
Old October 28th 18, 08:27 PM posted to uk.tech.digital-tv
NY
external usenet poster
 
Posts: 1,518
Default Freesat PVRs - can I check my understanding of the technology

"Bill Wright" wrote in message
news
On 28/10/2018 13:38, Michael Chare wrote:

I'm asking because when we move house, one house that we are looking at
is in a satellite-only area, where (according to JavaJive's site) there
is no terrestrial reception - or if there is, it may be very marginal,
and may require a very high-gain aerial on a very tall mast from the
chimney (*).


What's the postcode?


LS8 2QN, towards the top (south) end of the road.

From other postings, it seems as if the people who do use aerials are split
between those who use Emley Moor and those who use Belmont, even though the
profile for Belmont shows obstructions for all the 60% Fresnel zone and one
half of the 100% Fresnel zone.

Even with an aerial 50 m high (being silly, for the hell of it!) JavaJive
recommends Bilsdale for fringe reception but not Belmont. But people have
aerials in that direction, so presumably it must work for them :-)

  #10  
Old October 28th 18, 08:36 PM posted to uk.tech.digital-tv
NY
external usenet poster
 
Posts: 1,518
Default Freesat PVRs - can I check my understanding of the technology

"Bill Wright" wrote in message
news
On 28/10/2018 18:53, David Woolley wrote:

As already noted, the high low band distinction is artificial resulting
from engineering constraints. There is real significance in the
polarisations, though.


The short-lived British Satellite Broadcasting was laughably unambitious
about the number of channels so used one band and one polarisation. Thus
the signal could be distributed to blocks of flats by simply adding it to
the terrestrial feed and adjusting the equalisation.


Were amplifiers and cables of a distribution system (presumably designed for
terrestrial at 400-850 MHz) up to the job of also passing a usable level of
satellite signal at a much higher frequency (10-15 GHz)? Evidently they
were!

 




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