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Old 04-23-2002, 01:44 PM   #1
unixadm
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Exclamation LNB and MULTISWITCH FAQ's

1. What is an LNB? LNB stands for "Low Noise Block Converter" (thanks toolbox ). It is the part of your Satellite dish that hangs off of the arm and looks like a flashlight. It is what captures the digital signal from the satellite.

2. How does an LNB work? There are 32 transponders on the 101 degree satellite (main satellite) that send channels. They are numbered 1-32. Each transponder sends a group of channels. An LNB on a satellite dish can look at either odd or even transponders at any given time. It cannot see both at the same time. If you change the channel to one that is on an odd transponder, then the LNB switches to look at the odd...if you change to a channel on an even transponder, then the LNB switches to look at the even.

3. How does the LNB know which side (even or odd transponders) to look at? This is done by voltage changes that your DirectTV receiver sends.

4. What is a Dual LNB? A Dual LNB is just two LNB's...each connection can operate independently of each other so you can have two receivers each looking at different stations on different transponders. They both look at the same satellite (101 Degree satellite). A single LNB only has one coax connection and cannot be used with more than 1 DirectTV receiver.

5. What is the difference between the "Round" 18" dishes and the "Elliptical" 18"x24" dishes? The 18" dish had a Dual LNB that looks at one satellite. The satellite is positioned at 101 degrees and sends all the main programming that is offered in the DirectTV packages. The 18x24" dish has TWO Dual LNBs and is set up to see two satellites...the 101 degree and the 119. The 119 degree satellite sends additional programming such as the NASA channel, ParaTodos Spanish programming, other foreign language programming and HDTV channels. You could also use two Round 18" dishes, one pointed at the 101 degree satellite and the other pointed at the 119 satellite to do the same as the Elliptical dish. You would connect the four cables from the two dishes to a multiswitch explained below.

6. Can I use a splitter to add more receivers or add dual Tuners to my DirectTiVo? NO....this is where multiswitches come into play. You cannot use regular splitters. From the explaination of LNBs above, you should understand that if I split an LNB with a regular splitter, then I will have two receivers using the same LNB and fighting over looking at odd or even transponders. One or both receivers will only be able to see half of the channels.

7. What is a multiswitch? A multiswitch takes the input from both of the LNB's (both cables from a dual LNB dish HAVE to be connected to the multiswitch)...it then locks one of the LNB's to always look at the even transponders and the other LNB to always look at the odd transponders. This is why a multiswitch only works with Dual LNBs and not single LNB's. The switch then has multiple outputs to receivers (4,8,etc). When you connect the receiver to the multiswitch, the switch determines which of the two LNB's the receiver needs to look at depending if it needs to view odd or even transponders. When you change the channel, the switch then swaps your connection to the other LNB when needed. With a multiswitch, the LNB's never change which side they are looking at.

8. What about multiswitches with Elliptical dishes? If you have the oval dish with two "dual LNBs" (4 cables), each of the Dual LNB's look at different satellites (101 degree and 119 degree satellites). A multiswitch is needed to see the second satellite. A multiswitch comes with the dish and is usually have 4 outputs. Multiswitches for elliptical dishes need to have 4 inputs so it can switch between the 4 LNBs rather than the 2 in the explaination in #7 above.

9. If my receiver sends voltage changes to switch between odd and even transponders on the 101 satellite, how does it tell the multiswitch that it wants to see the 119 satellite? The receiver sends a 22khz tone over the cable along with the voltage change so it tells the multiswitch that it wants either odd or even transponders by the voltage and that it wants the 119 by sending the tone.

10. What is the 2x4, 2x8, 3x4, 3x8, 4x4, 4x8, 5x4 & 5x8 designations mean when referring to a multiswitch? The first number in the number of inputs from the dish (or antenna) the switch has. The second number is the number of outputs the switch has.

A 5x8 multiswitch would handle 4 DTV inputs (Two Dual LNBs looking at the two satellites) and a Cable TV or antenna input if you wanted. It would have 8 outputs that could go to 8 DirectTV receivers, 4 Dual Tuner DirectTivos or any combo in between.

11. Can I connect two Multiswitches together (cascade one to another) to add more connections? Well, that really depends. If you are using an 18" Dual LNB dish, then you could "cascade" two switches together....so you could take a 2x4 switch and have 2 of the outputs feed the inputs of another 2x4 switch to give you a total of 6 outputs. There are many issues that you have to be aware of though....length of cable, quality of multiswitches and whether they are powered or non-powered may affect whether or not this will work. If you have an 18x24" elliptical dish, it is a little more complex, but can be accomplished. As mentioned above, the receiver will send a 22khz tone to tell the multiswitch that it wants the 119 degree satellite. This tone is only used by the multiswitch and is not sent back up to the LNB's....if you have two 4xn switches connected or a 4xn multiswitch connected to the built in multiswitch on a dish, the "2nd" one will never tell the "1st" one that it needs to see the 119 so the receivers connected to the "2nd" one would ONLY see the 101 satellite. There are switches designated as "cascadable" that WILL send that 22khz tone upstream, thereby allowing you to connect it in series with another multiswitch (such as a built in one on the dish). These are more expensive than non-cascading models. The other way is to get "tone generators" which go on the two cables designated for the 119 satellite. They go inline between the two multiswitches (or between dish and multiswitch if you have the built in multiswitch on the dish). These tone generators are about $10-$15 each and they put the 22khz tone on the line so that the 1st multiswitch (or built in one) sees the tone and puts that line over to the 119 satelllite.

12. There are SO many different multiswitches with a wide range of price...which one is for me?

Lets start with the Differences Between Multiswitches .
There are 3 main types of multiswitches:

a. Non-Powered mechanical multiswitch - Cheapest in price
Has mechanical switching mechananism that is controlled by the power coming off of the DirectTV receiver. The DirectTV receiver changes voltages on the line depending on which transponder group it wants to look at. This multiswitch uses that voltage to move the switch.
Examples of these are the cheap Recotron or any non-powered switch you find on Ebay or in CC or BB.

b. Powered mechanical multiswitch - Mid range in price
Has a mechanical switching mechanism. It uses the voltage changes from the DTV receiver to determine what it should look at, but uses it's own external power to control the switch.
Example of these are Channel Master.

c. Powered solid state multiswitch - Most expensive
Completely solid state-no moving parts. Reads the voltage changes from the DirectTV receiver and electronically routes the signal to the correct LNB.
Example of these are Spauns, Trunkline, JVI

There are variations of #b & c which include signal amplification.

13. How many inputs do I need?

If you have an 18" dual LNB dish, you have 2 outputs from the dish, therefore only need a "2 x n" switch meaning 2 inputs from dish and "n" output (to be determined at next step.

If you have an Elliptical dish (or 2 18" dishes looking at different satellites), you will need a "4 x n" switch meaning 4 inputs (from dish) and "n" outputs.

You will also see switches listed as "3 x n" or "5 x n"...This just means that there is an extra input for Antenna or CableTV. These switches allow you to combine an Antenna/CableTV signal onto the same RG6 cables as your DirectTV signal and split it out at the TV end. This saves you valuable cabling issues since you will only have to run 1 cable to a receiver instead of 2 (or 2 cables instead of 3 in the case of DirectTiVos)

14. How many outputs do I need? This all depends on how many DirectTV receivers you have. You need 1 output for each receiver. In the case of the DirectTiVo, you need 2 outputs for each receiver. If you have two DirectTiVos, it would max out a 2x4 or 4x4 switch. Once you max out a switch, you cannot split to any other receiver and must get a new switch if you need to expand.

15. Non-powered, Powered/Mechanical, Powered Solid state, Amplified......which one do I need?

Well, that depends on your budget and your setup. If you have very long cable runs (greater than 100 feet), you should definitely get a powered switch and better yet, a powered/amplified switch. A non-powered switch may work, but since it depends soley on the voltage of the receiver to move the switch, the voltage loss in long cable runs could make the switch unreliable. In the case of long cable runs, I recommend a switch like the Channel Master or Spaun. The Spauns are the most expensive and probably overkill for most people. A lot of people have them here on the forum since I had gotten a great deal on a batch of used ones. Prior to that, I used Channel Masters and they were very reliable. I originally had a Recotron Non-powered and with some of my long cable runs, I would get "Searching for Satellite" at times. I would not recommend non-powered cheap switches unless your cable runs are very short and you got for a really cheap price (under $30).

16. Where should I buy a multiswitch?
Well, I wouldn't recommend the Brick and Mortar stores....they are WAY too expensive....They want $79 for a cheap 2x4, non-powered switch.

a. hometech.com I had relied on hometech for a long time because I have had good experiences with them in the past and their website is very informative. For a while, they did have some of the best prices on the net for Channel Masters and Spauns. They still have discount prices, but other .coms have beat some of their prices.

To check out their products, go here: http://www.hometech.com/video/dssmulti.html
Price for Spaun SMS5801 5x8 switch: $459.00
Price for Channel Master 6314IFD 3X4 $55.00


b. futurehomesystems.com
http://www.futurehomesystems.com/v503.shtml
Price for Spaun SMS5801 5X8 switch: $355.00
Price for Channel MAster 6314IFD 3X4 $110.00
Notice that this company has the spaun for over $100 cheaper, but the Channel Master for DOUBLE the price!

c. Suburban Electronics http://www.suburban-elect.com/
Their website is horrible and you can't find prices or products there.
I have been told that the SpaunSMS5801 switch is $350.00 but you have to call them to get the price.


See the post reference in my sig about Which Multiswitch and Where to Buy for more information.

17. How to I wire up a multiswitch? feldon23 has some GREAT diagrams on how to wire everything up. Do a search on feldon23. (Feldon...if you see this, could you post a couple of your diagrams?)

18. What if I need an outdoor switch?
For those who need an outdoor switch but also need a 5x8 switch, JVI has a powered, outdoor 5x8 switch. I found it at hometech.com for $159.95. I haven't searched other places, but you may find it cheaper.....the model number is TRDS8.

http://www.hometech.com/video/dssmulti.html#JV-TRDS8

Here are the specs:

Waterproof! Safe for outdoor use.
External power supply (included) connects via separate coax cable.
Now includes built-in VHF/UHF/CATV amplifier!
Combines a cable carrying VHF/UHF signals (from an antenna or CATV) with all four cables from a dual-satellite, dual LNB, DSS satellite dish.
Outputs for up to eight runs to satellite receivers. (Requires TSDM2150 or SAT-D2 below at locations where both satellite and VHF/UHF/CATV signals are desired.)
Sealed aluminum housing with self-sealing F connectors.
Satellite Frequency (950-2150 MHz) Gain/-Loss: -2dB
VHF/UHF/CATV Frequency (54-806 MHz) Gain/-Loss: 3dB

Even though I recommend that you put the multiswitch indoors, there are times where that is just not possible, or not convenient. This is a quality switch that should solve that problem.
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Last edited by unixadm : 09-18-2003 at 11:30 AM.
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Old 04-28-2002, 11:23 PM   #2
Otto
 
Join Date: Mar 2000
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DTV Signal FAQs

How DTV works: What you need to know about DTV signals.

Okay, so way, way up high in the sky are these satellites. They send out signals and somehow your box gets them. This is the stuff you need to know to answer some of the more frequently asked questions.

101W and other numbers
----------------------
DirecTV satellites are in a geostationary orbit. This basically means that they go around the earth in exactly 24 hour periods, and therefore stay in the same place in the sky all the time. The only place they can do both of those is above the equator (physics.. you can't escape it). So, generally, positions are referred to by the longitude of the place they are above. Longitude, on the globe, are the lines that run from pole to pole. 101 West is the orbital position directly above, you guessed it, 101 West longitude. At 24,000 miles above the planet, this is a bit of a wide area, a couple hundred miles or so across. So, there's not one satellite there, but several. But to your dish, it's all the same. In order for your dish to see them, it has to point at them. That's why aiming is so critical. Less than a degree off and you see a completely different section of the sky. DirecTV also maintains satellites at 119 West.

Round vs. oval dishes
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Round dishes are the simplest. They point at one place in the sky. For DTV, this is 101W, of course. All the main DTV channels are sent from here. Quite a lot of local channels are sent from here as well. So, what's the oval dish for? The oval dish actually see a range of positions.

See, the signal coming from the sky looks almost like a point source. Imagine a bunch of lines drawn from a point in space to your round dish. The lines are all paralell, so when they hit your dish, they bounce in different directions. Your round dish is a curve, so all those lines bounce to come together. The point where they all come to is where the LNB is. It's at the focal point.

The oval dish, however, doesn't focus in one place, but several. You don't point the oval dish at 101W or at 119W (DirecTV's two major orbital locations). Actually, you point it at 110W, a point directly in between. Now, imagine the lines coming from 101W. The dish isn't pointing at 101W, but the lines still hit it. But, they reflect a bit to the side. You might notice that that is where the LNB on your oval dish is placed, off to one side. The other LNB is placed to the other side (119W is on the other side of the dish). Actually, if you look at the dish at a 9 degree angle (from the front of the dish) you'll see that it looks round. So actually, the oval dish is really round, when you consider it from those angles. Neat, huh? Depending on where the LNB is located in front of the dish, it's looking at a different point in the sky.

I hear I can use two round dishes? What up wif dat?
---------------------------------------------------
Yep. Remember the only thing special about the oval dish is that it has two LNB's looking at different places. So, if you have two round dishes, one pointed at 101W, the other at 119W, and you use the same kind of multiswitch that comes with the oval dish, then you see the exact same thing. There's nothing inherently special about the oval dish except that it's pointing at two places in the sky. A lot of people use two round dishes to get a minor signal improvement, or more frequently because getting a couple of round dishes can be cheap/free. All you really need is a 4xN or 5xN multiswitch and to aim the things the right way.

Okay, so what the hell is a spot beam?
--------------------------------------
A spot beam is a often used term now, and it affects what local stations you can possibly receive. The normal satellites send out a signal pretty indiscriminately. It simply is a microwave transmitter beaming data across the US. The spot beam is the same thing, but it points at a reflector that has a narrower focus. The upshot of this is that depending on where you are in the country, you won't see the beams pointing away from you. That is, the satellite sends a beam similar to a flashlight beam at one spot of the country. A 100-200 mile wide spot.

Why use spot beams? Because there's only a limited amount of space up there. They can't broadcast anything they want, the FCC would kill them. They only have so much bandwidth/frequency space. To make the most use out of it all, they rebroadcast on the same frequencies in different spots. This is *perfect* for sending local channels. So on frequency "3" they might send locals to Birmingham, Atlanta, and Denver and so forth. All on that same frequency. This reuse can be done because they're not sending Denver's channels to Atlanta (it would be a waste since they can't legally sell them there anyway). Because each spot on the ground only sees what's being sent to them, the other spots using the same frequency doesn't get interfered with by the other spots. Any spot map you look at will have overlapping spots. Any spots that overlap must use two different frequencies, but any spots that don't overlap can use the same frequencies.

119W spot beams?
----------------
They're planning on putting spot beams up in 119W too (DirecTV 7S). Right now they're only in 101W. These will be local channels for more/new markets. To get these, you will need to have an oval dish (or the equivalent, two rounds).

What about 110W?
----------------
110W is not used for much. A few local markets in the Carolinas used to require it. Now it's used mainly for HDTV programs. But mainly this is to keep their space on those satellites in usage while they figure out what to do with it. To get 110W channels, you need an oval dish with a third satellite adapter. This adapter hooks into the 119W LNB and uses some of the unused 119W frequency signals. You could also put a round dish pointing at 110W and use the same kind of adapter/signal combiner, but generally this isn't done because it's a pain in the arse.

The adapter is available as a kit, called the "Sat C kit". It's $40 or so and comes with everything to need to hook it up to the oval dish. It goes inbetween the other LNB's. It's also a special LNB, don't try to use it for something else, and don't try to use other LNB's on it either. Here's an image made by feldon 23 to show how it connects:



Anything else?
--------------
I dunno. Did I miss something? Message me, and I'll add it.

Last edited by Otto : 05-09-2002 at 10:21 AM.
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