Confusing configuration conundrum

Hi folks.

A couple of weeks ago I bought one of those sattelite dishes - mail
order from the subscription service provider - with one of those
tuners
where you can watch one channel at the same time you are recording
another.

It turned out that the whole system was a bit of a mess:

- One sattelite dish
- One or more reciever heads
- Each head had four cable connectors
- The tuner had two cable inputs

In my world, the dish needs to be outside the outer wall of the
house,
while the tuner is most conveniently kept inside. So to connect the
two,
one needs to make holes in the wall. I had the installer make *one*
hole
(this posh tuner arrived a few days after the rest of the set, which
contained
a simpler tuner), and everything was fine.

Until I opened the instructions for the posh tuner: "The tuner
contains two
independent tuners. Make sure to connect the tuner to the dish by
*two*
cables. No splitters."

Needless to say, I was a bit PO'd by the fact that I might need to
find a
way to get another cable between the inside and outside of the house -
which
I don't really want to have to do.

Why would one need to use *two* cables between two outputs of the
same reciever head? Why no splitter? Why not use one external
connector on the tuner, and split the signal internally?

Is this just to ensure that stupid users don't get any choises,
evaluations
or decisions they can mess up? Or is there a technical reason, e.g.
like
there will be too much cross talk between channels if the two tuners
are
electrically connected? (The tuner cost me some $400 as an add-on to
my
channel subscription, so I suspect it is not awfully sophisticated
from a
purely technical POV...)

Rune

On Oct 4, 12:13&#4294967295;am, Rune Allnor <all...@tele.ntnu.no> wrote:
> Hi folks.
>
> A couple of weeks ago I bought one of those sattelite dishes - mail
> order from the subscription service provider - with one of those
> tuners
> where you can watch one channel at the same time you are recording
> another.
>
> It turned out that the whole system was a bit of a mess:
>
> - One sattelite dish
> - One or more reciever heads
> - Each head had four cable connectors
> - The tuner had two cable inputs
>
> In my world, the dish needs to be outside the outer wall of the
> house,
> while the tuner is most conveniently kept inside. So to connect the
> two,
> one needs to make holes in the wall. I had the installer make *one*
> hole
> (this posh tuner arrived a few days after the rest of the set, which
> contained
> a simpler tuner), and everything was fine.
>
> Until I opened the instructions for the posh tuner: "The tuner
> contains two
> independent tuners. Make sure to connect the tuner to the dish by
> *two*
> cables. No splitters."
>
> Needless to say, I was a bit PO'd by the fact that I might need to
> find a
> way to get another cable between the inside and outside of the house -
> which
> I don't really want to have to do.
>
> Why would one need to use *two* cables between two outputs of the
> same reciever head? Why no splitter? Why not use one external
> connector on the tuner, and split the signal internally?
>
> Is this just to ensure that stupid users don't get any choises,
> evaluations
> or decisions they can mess up? Or is there a technical reason, e.g.
> like
> there will be too much cross talk between channels if the two tuners
> are
> electrically connected? (The tuner cost me some $400 as an add-on to
> my
> channel subscription, so I suspect it is not awfully sophisticated
> from a
> purely technical POV...)
>
> Rune

Basically your dish contains LNBs - i.e., these are Low Noise Block
Convertors. So what they do is both amplify and down convert the sat
signal (in the several GHz range) down to say 1 GHz. Cables are very
lossy at these freqs, so a 3.5dB hit with a splitter (they can't get
good enough to achieve 3 dB) will harm your signal. The multiple LNB
approach is puirely to maintain S/N. Sat signals undergoe a trememdous
loss and most users have small dishes so you don't want to take a hit
on the S/N. Also the DC supply for the LNB is fed up the cable and
sometimes the local osc is feed up the cable from the tuner.

IHTH,

Clay

p.s. I have three holes in my wall.

On Oct 4, 11:40&#4294967295;am, Clay <c...@claysturner.com> wrote:
> On Oct 4, 12:13&#4294967295;am, Rune Allnor <all...@tele.ntnu.no> wrote:
>
>
>
>
>
> > Hi folks.
>
> > A couple of weeks ago I bought one of those sattelite dishes - mail
> > order from the subscription service provider - with one of those
> > tuners
> > where you can watch one channel at the same time you are recording
> > another.
>
> > It turned out that the whole system was a bit of a mess:
>
> > - One sattelite dish
> > - One or more reciever heads
> > - Each head had four cable connectors
> > - The tuner had two cable inputs
>
> > In my world, the dish needs to be outside the outer wall of the
> > house,
> > while the tuner is most conveniently kept inside. So to connect the
> > two,
> > one needs to make holes in the wall. I had the installer make *one*
> > hole
> > (this posh tuner arrived a few days after the rest of the set, which
> > contained
> > a simpler tuner), and everything was fine.
>
> > Until I opened the instructions for the posh tuner: "The tuner
> > contains two
> > independent tuners. Make sure to connect the tuner to the dish by
> > *two*
> > cables. No splitters."
>
> > Needless to say, I was a bit PO'd by the fact that I might need to
> > find a
> > way to get another cable between the inside and outside of the house -
> > which
> > I don't really want to have to do.
>
> > Why would one need to use *two* cables between two outputs of the
> > same reciever head? Why no splitter? Why not use one external
> > connector on the tuner, and split the signal internally?
>
> > Is this just to ensure that stupid users don't get any choises,
> > evaluations
> > or decisions they can mess up? Or is there a technical reason, e.g.
> > like
> > there will be too much cross talk between channels if the two tuners
> > are
> > electrically connected? (The tuner cost me some $400 as an add-on to
> > my
> > channel subscription, so I suspect it is not awfully sophisticated
> > from a
> > purely technical POV...)
>
> > Rune
>
> Basically your dish contains LNBs - i.e., these are Low Noise Block
> Convertors. So what they do is both amplify and down convert the sat
> signal (in the several GHz range) down to say 1 GHz. Cables are very
> lossy at these freqs, so a 3.5dB hit with a splitter (they can't get
> good enough to achieve 3 dB) will harm your signal. The multiple LNB
> approach is puirely to maintain S/N. Sat signals undergoe a trememdous
> loss and most users have small dishes so you don't want to take a hit
> on the S/N. Also the DC supply for the LNB is fed up the cable and
> sometimes the local osc is feed up the cable from the tuner.
>
> IHTH,
>
> Clay
>
> p.s. I have three holes in my wall.- Hide quoted text -
>
> - Show quoted text -

I think the reaosn for the multiple cables is to support the watch and
record feature.   In order to have ALL channels avaiable
SIMULTANEOUSLY, you need 4 cables...  each feed has 2 polarizations
and you have 2 feeds so there are 4 streams of signals that each
receiver can choose from...  That means there are actually 4 LNBs at
the dish. If you didn't need the watch and record feature, you might
be able to get away with fewer cables... but you would need a
different dish that had some switching arrangment.

enjoy...
Mark

On Oct 4, 12:08&#4294967295;pm, Mark <makol...@yahoo.com> wrote:
> On Oct 4, 11:40&#4294967295;am, Clay <c...@claysturner.com> wrote:
>
>
>
>
>
> > On Oct 4, 12:13&#4294967295;am, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > > Hi folks.
>
> > > A couple of weeks ago I bought one of those sattelite dishes - mail
> > > order from the subscription service provider - with one of those
> > > tuners
> > > where you can watch one channel at the same time you are recording
> > > another.
>
> > > It turned out that the whole system was a bit of a mess:
>
> > > - One sattelite dish
> > > - One or more reciever heads
> > > - Each head had four cable connectors
> > > - The tuner had two cable inputs
>
> > > In my world, the dish needs to be outside the outer wall of the
> > > house,
> > > while the tuner is most conveniently kept inside. So to connect the
> > > two,
> > > one needs to make holes in the wall. I had the installer make *one*
> > > hole
> > > (this posh tuner arrived a few days after the rest of the set, which
> > > contained
> > > a simpler tuner), and everything was fine.
>
> > > Until I opened the instructions for the posh tuner: "The tuner
> > > contains two
> > > independent tuners. Make sure to connect the tuner to the dish by
> > > *two*
> > > cables. No splitters."
>
> > > Needless to say, I was a bit PO'd by the fact that I might need to
> > > find a
> > > way to get another cable between the inside and outside of the house -
> > > which
> > > I don't really want to have to do.
>
> > > Why would one need to use *two* cables between two outputs of the
> > > same reciever head? Why no splitter? Why not use one external
> > > connector on the tuner, and split the signal internally?
>
> > > Is this just to ensure that stupid users don't get any choises,
> > > evaluations
> > > or decisions they can mess up? Or is there a technical reason, e.g.
> > > like
> > > there will be too much cross talk between channels if the two tuners
> > > are
> > > electrically connected? (The tuner cost me some $400 as an add-on to
> > > my
> > > channel subscription, so I suspect it is not awfully sophisticated
> > > from a
> > > purely technical POV...)
>
> > > Rune
>
> > Basically your dish contains LNBs - i.e., these are Low Noise Block
> > Convertors. So what they do is both amplify and down convert the sat
> > signal (in the several GHz range) down to say 1 GHz. Cables are very
> > lossy at these freqs, so a 3.5dB hit with a splitter (they can't get
> > good enough to achieve 3 dB) will harm your signal. The multiple LNB
> > approach is puirely to maintain S/N. Sat signals undergoe a trememdous
> > loss and most users have small dishes so you don't want to take a hit
> > on the S/N. Also the DC supply for the LNB is fed up the cable and
> > sometimes the local osc is feed up the cable from the tuner.
>
> > IHTH,
>
> > Clay
>
> > p.s. I have three holes in my wall.- Hide quoted text -
>
> > - Show quoted text -
>
> I think the reaosn for the multiple cables is to support the watch and
> record feature. &#4294967295; In order to have ALL channels avaiable
> SIMULTANEOUSLY, you need 4 cables... &#4294967295;each feed has 2 polarizations
> and you have 2 feeds so there are 4 streams of signals that each
> receiver can choose from... &#4294967295;That means there are actually 4 LNBs at
> the dish. If you didn't need the watch and record feature, you might
> be able to get away with fewer cables... but you would need a
> different dish that had some switching arrangment.
>
> enjoy...
> Mark- Hide quoted text -
>
> - Show quoted text -

whoops, you have 1 feed with 2 polarizations (LH and RH) andd 2 LNBs
therefore you need 2 cables..

The other 2  connectors are probably to support a second receiver..

Some systems actually have multiple feeds to look" at multiple birds
without moving the dish and they need more cables.

Mark

On Oct 4, 12:08&#4294967295;pm, Mark <makol...@yahoo.com> wrote:
> On Oct 4, 11:40&#4294967295;am, Clay <c...@claysturner.com> wrote:
>
>
>
>
>
> > On Oct 4, 12:13&#4294967295;am, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > > Hi folks.
>
> > > A couple of weeks ago I bought one of those sattelite dishes - mail
> > > order from the subscription service provider - with one of those
> > > tuners
> > > where you can watch one channel at the same time you are recording
> > > another.
>
> > > It turned out that the whole system was a bit of a mess:
>
> > > - One sattelite dish
> > > - One or more reciever heads
> > > - Each head had four cable connectors
> > > - The tuner had two cable inputs
>
> > > In my world, the dish needs to be outside the outer wall of the
> > > house,
> > > while the tuner is most conveniently kept inside. So to connect the
> > > two,
> > > one needs to make holes in the wall. I had the installer make *one*
> > > hole
> > > (this posh tuner arrived a few days after the rest of the set, which
> > > contained
> > > a simpler tuner), and everything was fine.
>
> > > Until I opened the instructions for the posh tuner: "The tuner
> > > contains two
> > > independent tuners. Make sure to connect the tuner to the dish by
> > > *two*
> > > cables. No splitters."
>
> > > Needless to say, I was a bit PO'd by the fact that I might need to
> > > find a
> > > way to get another cable between the inside and outside of the house -
> > > which
> > > I don't really want to have to do.
>
> > > Why would one need to use *two* cables between two outputs of the
> > > same reciever head? Why no splitter? Why not use one external
> > > connector on the tuner, and split the signal internally?
>
> > > Is this just to ensure that stupid users don't get any choises,
> > > evaluations
> > > or decisions they can mess up? Or is there a technical reason, e.g.
> > > like
> > > there will be too much cross talk between channels if the two tuners
> > > are
> > > electrically connected? (The tuner cost me some $400 as an add-on to
> > > my
> > > channel subscription, so I suspect it is not awfully sophisticated
> > > from a
> > > purely technical POV...)
>
> > > Rune
>
> > Basically your dish contains LNBs - i.e., these are Low Noise Block
> > Convertors. So what they do is both amplify and down convert the sat
> > signal (in the several GHz range) down to say 1 GHz. Cables are very
> > lossy at these freqs, so a 3.5dB hit with a splitter (they can't get
> > good enough to achieve 3 dB) will harm your signal. The multiple LNB
> > approach is puirely to maintain S/N. Sat signals undergoe a trememdous
> > loss and most users have small dishes so you don't want to take a hit
> > on the S/N. Also the DC supply for the LNB is fed up the cable and
> > sometimes the local osc is feed up the cable from the tuner.
>
> > IHTH,
>
> > Clay
>
> > p.s. I have three holes in my wall.- Hide quoted text -
>
> > - Show quoted text -
>
> I think the reaosn for the multiple cables is to support the watch and
> record feature. &#4294967295; In order to have ALL channels avaiable
> SIMULTANEOUSLY, you need 4 cables... &#4294967295;each feed has 2 polarizations
> and you have 2 feeds so there are 4 streams of signals that each
> receiver can choose from... &#4294967295;That means there are actually 4 LNBs at
> the dish. If you didn't need the watch and record feature, you might
> be able to get away with fewer cables... but you would need a
> different dish that had some switching arrangment.
>
> enjoy...
> Mark- Hide quoted text -
>
> - Show quoted text -

For example with Direct TV, you have 4 LNBs in the dish's feed horn
assembly. If you have a unit that has record and simultaneous viewing
(a different channel), then you have 2 cables. If you have just a
tuner, then you only need one cable. Since the LNB is an amplify and
mix unit with the LO being sent up from the tuner, a splitter will
change the LO's level thus destroying your mix capability. The dish's
monitoring of different satellites uses different feeds, but they are
combined into a single LNB's output. Also in a case of a single
satellite, only a single polarization is observed at the dish. This is
very different from the old days where you had a steerable dish and
needed a feed horn rotator.

Clay

Rune Allnor wrote:
> Hi folks.
>
> A couple of weeks ago I bought one of those sattelite dishes
>   [snip]

And people wonder why I stay with rabbit ears ;>

[PS with advent of DTV it gives me a good crosscheck on local 
weather forecast.]

>On Oct 4, 12:13=A0am, Rune Allnor <all...@tele.ntnu.no> wrote:
>> Hi folks.
>>
>> A couple of weeks ago I bought one of those sattelite dishes - mail
>> order from the subscription service provider - with one of those
>> tuners
>> where you can watch one channel at the same time you are recording
>> another.
>>
>> It turned out that the whole system was a bit of a mess:
>>
>> - One sattelite dish
>> - One or more reciever heads
>> - Each head had four cable connectors
>> - The tuner had two cable inputs
>>
>> In my world, the dish needs to be outside the outer wall of the
>> house,
>> while the tuner is most conveniently kept inside. So to connect the
>> two,
>> one needs to make holes in the wall. I had the installer make *one*
>> hole
>> (this posh tuner arrived a few days after the rest of the set, which
>> contained
>> a simpler tuner), and everything was fine.
>>
>> Until I opened the instructions for the posh tuner: "The tuner
>> contains two
>> independent tuners. Make sure to connect the tuner to the dish by
>> *two*
>> cables. No splitters."
>>
>> Needless to say, I was a bit PO'd by the fact that I might need to
>> find a
>> way to get another cable between the inside and outside of the house -
>> which
>> I don't really want to have to do.
>>
>> Why would one need to use *two* cables between two outputs of the
>> same reciever head? Why no splitter? Why not use one external
>> connector on the tuner, and split the signal internally?
>>
>> Is this just to ensure that stupid users don't get any choises,
>> evaluations
>> or decisions they can mess up? Or is there a technical reason, e.g.
>> like
>> there will be too much cross talk between channels if the two tuners
>> are
>> electrically connected? (The tuner cost me some $400 as an add-on to
>> my
>> channel subscription, so I suspect it is not awfully sophisticated
>> from a
>> purely technical POV...)
>>
>> Rune
>
>Basically your dish contains LNBs - i.e., these are Low Noise Block
>Convertors. So what they do is both amplify and down convert the sat
>signal (in the several GHz range) down to say 1 GHz. Cables are very
>lossy at these freqs, so a 3.5dB hit with a splitter (they can't get
>good enough to achieve 3 dB) will harm your signal. The multiple LNB
>approach is puirely to maintain S/N. Sat signals undergoe a trememdous
>loss and most users have small dishes so you don't want to take a hit
>on the S/N. Also the DC supply for the LNB is fed up the cable and
>sometimes the local osc is feed up the cable from the tuner.
>
>IHTH,
>
>Clay
>
>p.s. I have three holes in my wall.
>
>

You can get a multiswitch to replace your splitter. I think it's just a
fancy splitter - but the funny thing is that it needs both LNB signals from
your dish. So basically, this will allow you to have more than 2 receivers,
but won't fix your holes drilling problem!

Just google for: multiswitch lnb

On Oct 4, 5:40&#4294967295;pm, Clay <c...@claysturner.com> wrote:
> On Oct 4, 12:13&#4294967295;am, Rune Allnor <all...@tele.ntnu.no> wrote:
>
>
>
>
>
> > Hi folks.
>
> > A couple of weeks ago I bought one of those sattelite dishes - mail
> > order from the subscription service provider - with one of those
> > tuners
> > where you can watch one channel at the same time you are recording
> > another.
>
> > It turned out that the whole system was a bit of a mess:
>
> > - One sattelite dish
> > - One or more reciever heads
> > - Each head had four cable connectors
> > - The tuner had two cable inputs
>
> > In my world, the dish needs to be outside the outer wall of the
> > house,
> > while the tuner is most conveniently kept inside. So to connect the
> > two,
> > one needs to make holes in the wall. I had the installer make *one*
> > hole
> > (this posh tuner arrived a few days after the rest of the set, which
> > contained
> > a simpler tuner), and everything was fine.
>
> > Until I opened the instructions for the posh tuner: "The tuner
> > contains two
> > independent tuners. Make sure to connect the tuner to the dish by
> > *two*
> > cables. No splitters."
>
> > Needless to say, I was a bit PO'd by the fact that I might need to
> > find a
> > way to get another cable between the inside and outside of the house -
> > which
> > I don't really want to have to do.
>
> > Why would one need to use *two* cables between two outputs of the
> > same reciever head? Why no splitter? Why not use one external
> > connector on the tuner, and split the signal internally?
>
> > Is this just to ensure that stupid users don't get any choises,
> > evaluations
> > or decisions they can mess up? Or is there a technical reason, e.g.
> > like
> > there will be too much cross talk between channels if the two tuners
> > are
> > electrically connected? (The tuner cost me some $400 as an add-on to
> > my
> > channel subscription, so I suspect it is not awfully sophisticated
> > from a
> > purely technical POV...)
>
> > Rune
>
> Basically your dish contains LNBs - i.e., these are Low Noise Block
> Convertors. So what they do is both amplify and down convert the sat
> signal (in the several GHz range) down to say 1 GHz. Cables are very
> lossy at these freqs, so a 3.5dB hit with a splitter (they can't get
> good enough to achieve 3 dB) will harm your signal. The multiple LNB
> approach is puirely to maintain S/N. Sat signals undergoe a trememdous
> loss and most users have small dishes so you don't want to take a hit
> on the S/N. Also the DC supply for the LNB is fed up the cable and
> sometimes the local osc is feed up the cable from the tuner.

I understand the technical aspects of getting the signal from the
LNB down to the tuner.

What I don't understand is why you need *two* cables: Since there
are no instructions on how to connect the head to the tuner inputs,
one must assume that the wiring is interchangeable, right?

If so, the signal that one amp recieves through one cable must
necessarily equal the signal it recieves through the other cable,
right?

In that case, what would be wrong with

1) Feeding the signal from the LNB to the reciever unit through
   *one* cable
2) Amplify it first thing at the reciever
3) *Then* split the signal and feed it to the two tuners?

I just can't see why this should be any problem at all.

Rune

On Thu, 7 Oct 2010 22:39:18 -0700 (PDT), Rune Allnor
<allnor@tele.ntnu.no> wrote:

>On Oct 4, 5:40=A0pm, Clay <c...@claysturner.com> wrote:
>> On Oct 4, 12:13=A0am, Rune Allnor <all...@tele.ntnu.no> wrote:
>>
>>
>>
>>
>>
>> > Hi folks.
>>
>> > A couple of weeks ago I bought one of those sattelite dishes - mail
>> > order from the subscription service provider - with one of those
>> > tuners
>> > where you can watch one channel at the same time you are recording
>> > another.
>>
>> > It turned out that the whole system was a bit of a mess:
>>
>> > - One sattelite dish
>> > - One or more reciever heads
>> > - Each head had four cable connectors
>> > - The tuner had two cable inputs
>>
>> > In my world, the dish needs to be outside the outer wall of the
>> > house,
>> > while the tuner is most conveniently kept inside. So to connect the
>> > two,
>> > one needs to make holes in the wall. I had the installer make *one*
>> > hole
>> > (this posh tuner arrived a few days after the rest of the set, which
>> > contained
>> > a simpler tuner), and everything was fine.
>>
>> > Until I opened the instructions for the posh tuner: "The tuner
>> > contains two
>> > independent tuners. Make sure to connect the tuner to the dish by
>> > *two*
>> > cables. No splitters."
>>
>> > Needless to say, I was a bit PO'd by the fact that I might need to
>> > find a
>> > way to get another cable between the inside and outside of the house -
>> > which
>> > I don't really want to have to do.
>>
>> > Why would one need to use *two* cables between two outputs of the
>> > same reciever head? Why no splitter? Why not use one external
>> > connector on the tuner, and split the signal internally?
>>
>> > Is this just to ensure that stupid users don't get any choises,
>> > evaluations
>> > or decisions they can mess up? Or is there a technical reason, e.g.
>> > like
>> > there will be too much cross talk between channels if the two tuners
>> > are
>> > electrically connected? (The tuner cost me some $400 as an add-on to
>> > my
>> > channel subscription, so I suspect it is not awfully sophisticated
>> > from a
>> > purely technical POV...)
>>
>> > Rune
>>
>> Basically your dish contains LNBs - i.e., these are Low Noise Block
>> Convertors. So what they do is both amplify and down convert the sat
>> signal (in the several GHz range) down to say 1 GHz. Cables are very
>> lossy at these freqs, so a 3.5dB hit with a splitter (they can't get
>> good enough to achieve 3 dB) will harm your signal. The multiple LNB
>> approach is puirely to maintain S/N. Sat signals undergoe a trememdous
>> loss and most users have small dishes so you don't want to take a hit
>> on the S/N. Also the DC supply for the LNB is fed up the cable and
>> sometimes the local osc is feed up the cable from the tuner.
>
>I understand the technical aspects of getting the signal from the
>LNB down to the tuner.
>
>What I don't understand is why you need *two* cables: Since there
>are no instructions on how to connect the head to the tuner inputs,
>one must assume that the wiring is interchangeable, right?
>
>If so, the signal that one amp recieves through one cable must
>necessarily equal the signal it recieves through the other cable,
>right?
>
>In that case, what would be wrong with
>
>1) Feeding the signal from the LNB to the reciever unit through
>   *one* cable
>2) Amplify it first thing at the reciever
>3) *Then* split the signal and feed it to the two tuners?
>
>I just can't see why this should be any problem at all.
>
>Rune

I think it's actually an LNB in the outdoor unit, and the cable feeds
power and the coarse tuning LO up the cable and gets block-tuned
signal back.    Since the indoor device has the capability to handle
multiple signals, i.e., one being viewed and one being recorded,
unless they're in the same tuning block you can't get them down in the
same cable.

Of course it's possible to do it another way, but that's not how these
systems are architected.   With the cost constraints and the available
RF hardware that's a pretty traditional way of doing it.

In the future the indoor-outdoor cable could be a POE
(power-over-ethernet) cable and the outdoor unit has not only the RF
but the demods, too.   You could then get as much demodulated content
as you wanted in as many channels as you had ethernet bandwidth to
handle.

But that type of architecture is not yet in common deployment.


Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com

Rune Allnor <allnor@tele.ntnu.no> wrote:
(snip)

>> > It turned out that the whole system was a bit of a mess:
>>
>> > - One sattelite dish
>> > - One or more reciever heads
>> > - Each head had four cable connectors
>> > - The tuner had two cable inputs
(snip)

> I understand the technical aspects of getting the signal from the
> LNB down to the tuner.
 
> What I don't understand is why you need *two* cables: Since there
> are no instructions on how to connect the head to the tuner inputs,
> one must assume that the wiring is interchangeable, right?

I am not sure about the specific system, but I have known systems
to supply a DC tuning voltage on the cable, or other control voltages
or signals.  In that case, it is possible that the two cables, with
different control signals, woult have different signals coming back.

That would only matter if you had two tuners to demodulate the
two separate signals.
 
> If so, the signal that one amp recieves through one cable must
> necessarily equal the signal it recieves through the other cable,
> right?

-- glen