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Cruzer · 03-29-2004, 03:20 AM

I have a KVH L3 in-motion dome on the roof. For times when trees block the signal I ran a new RG-6 coax from the basement to the receiver so that I can use a portable dish. I then have to remove the "dome" cable from the back of the receiver and plug in the "portable" cable feed when doing this. I would like this to be more automatic if possible.

My question is - can a splitter, combiner, or multiswitch work for this? I believe a splitter won't because I need to pass power back up to the LNB to power the dish. I'm not sure what a combiner does and I'm thinking that a multiswitch may do it but it seems that they are set up for dual LNB input whereas I'm only going from two inputs to one output.

Also, if that is the case, can you stack two multiswitches? I have a 2x4 multiswitch on my home systems and I run one line out to my pedestal at home so I can watch TV in the driveway if I'm out there. If they are in series like this would I still be able to get SATV in the RV while parked in the driveway (lots of trees)?

Cruzer · 03-29-2004, 03:20 AM

I have a KVH L3 in-motion dome on the roof. For times when trees block the signal I ran a new RG-6 coax from the basement to the receiver so that I can use a portable dish. I then have to remove the "dome" cable from the back of the receiver and plug in the "portable" cable feed when doing this. I would like this to be more automatic if possible.

My question is - can a splitter, combiner, or multiswitch work for this? I believe a splitter won't because I need to pass power back up to the LNB to power the dish. I'm not sure what a combiner does and I'm thinking that a multiswitch may do it but it seems that they are set up for dual LNB input whereas I'm only going from two inputs to one output.

Also, if that is the case, can you stack two multiswitches? I have a 2x4 multiswitch on my home systems and I run one line out to my pedestal at home so I can watch TV in the driveway if I'm out there. If they are in series like this would I still be able to get SATV in the RV while parked in the driveway (lots of trees)?

BagoBob · 03-29-2004, 04:49 AM

A combiner is a special kind of high-pass/low-pass filter/splitter designed for special applications. A Sat C combiner for DirecTV is made to filter out certain freqencies so that the Sat C signal can be combined with the Sat B signal on one specific multiswitch input. You can't use anything else for that purpose, and the combiner can't really be used in any other situation.

A multiswitch won't work for you because it's designed for both LNB ports to be connected to the same LNB, so it fixes one port at 13V and the other port at 18V. That means you'd receive even transponders only from one dish, and odd transponders only from the other dish.

Most multiswitches don't support cascading (not "stacking" -- don't even start talking about stacked systems...). You might work out a way to cascade two 2x4 or 3x4 multiswitches, and they may work for a while. But soon one or the other will fry a transistor because they aren't designed to see fixed voltages on their output ports.

You're right that a normal splitter won't work because it can't pass the DC voltage from the receiver to the LNB. There are power-passing splitters available from the satellite supply vendors. You can find them online, but you may have trouble finding them in a brick-and-mortar store. I think a power-passing, broadband digital splitter will do the trick for you.

Here is a URL to an example:
Audio Outfitter
(This is not an endorsement; I don't know anything aout this company.)

Hope this helps.

-Bob

Cruzer · 03-29-2004, 05:26 AM

Wow, thanks Bob! I knew I'd find the info from someone on IRV2. Now a know what the combiner does and how multiswitches work (or don't work - in my case). The high tech splitter you mentioned sounds like the way to go. I will check it out. I'm no expert on SATV stuff but do get around electrics in general so I can kind of pick this stuff up. I didn't get the part about 13V and 18V though. It appears that each LNB has a different voltage and that every other transponder frequency is 13V, while the others are 18V?

Mr_Bill · 03-29-2004, 06:47 AM

Another question along this line.... Would a good A/B switct work with SAT? I don't know if they would cause a signal problem or if they would pass the 13v correctly.

BagoBob · 03-29-2004, 12:14 PM

Cruzer,
I don't want to get into a long, drawn-out primer on how DBS systems work. There are many online resources for every kind of system. For instance, check out DBSForums.com.

The LNB switches between receiving odd- and even-numbered transponders according to a DC control voltage from the receiver (the IRD): 13V for odd, 18V for even. If there is only one IRD connected to one LNB, the IRD flips the voltage back and forth to control which polarity the LNB should use for the transponder the IRD needs. If there are two IRDs connected to one LNB, the receivers both sense that and one IRD may stabilize on 13V and the other IRD on 18V.

If there are more than 2 IRDs, a multiswitch is needed. The multiswitch fixes the voltage on one LNB input at 13V and fixes the other at 18V. It synthesizes the fixed voltages from the power supplied by the connected IRDs. The IRDs, in turn, may continue to flip their output voltages to the multiswitch outputs, but the switch's LNB inputs don't change.

GliderGuy,
It's hard to know what a "good" A/B switch is. Most of the stuff that's out there was designed for RF frequencies in either the VHF/UHF ranges or the CATV range. Almost none of them can pass the DC power cleanly. And most of them don't have the bandwidth for either digital cable or satellite. They'll either cause interference or dropouts, or not work at all (or for long).

There may be some power-passing, broadband A/B switches which might work for this, but generally trying to switch dishes in Cruzer's example is not something these little systems expect to do. Remember, DBS is a strictly-defined closed system and has developed just enough hardware and software to do its one specific task. This ain't C-band anymore....

Hope this helps.

-Bob

chasfm11 · 03-29-2004, 12:32 PM

Bagobob: Thanks for all of your information. It is much appreciated. I don't want to highjack Cruzer's thread but I have a question related to the voltages going to the LNB that you might help me answer.

I picked up an old Magnavox dish with a single LNB that was headed for the trash and stuck it on a tripod. I discovered that it has a LED on the LNB that goes out when the dish is properly aimed. I get my azmith and elevation from the zip code feature on the receiver, roughly aim the dish with those coordinates and use the LED to fine tune the adjustments. I've noticed, however, the the LED only comes on when I first plug in the reciever. Is there a explanation for what is happening? I sure love it - it takes the guesswork and time out of dish aiming.

Thanks,

Charlie

Cruzer · 03-29-2004, 02:51 PM

Thanks Bob, I understand enough about it now to meet my needs. I'll check on the link to the DBS forum later to learn more. Now I'll go check out that power passing splitter.

Thanks again,

BagoBob · 03-30-2004, 06:34 AM

chasfm11,
I don't recall if the LED flashed on when the signal peaked, or off. I've aligned dozens of old Sony dishes but always with an external alignment meter or beeper. I believe the LED indicates a signal presence above a certain threshhold, more than the achievement of maximum signal strength.

The SignalSeeker LED was a feature on the old Sony dishes (your Magnavox is a re-branded Sony) that was helpful when it worked. They don't last forever, and you can't get a new one. If it works at all and you find it helpful, good. If it stops working, you *might* find a used Sony LNB on eBay. Otherwise, you'll be looking for more modern dish and getting a SatFinder meter to aim it.

-Bob

chasfm11 · 03-30-2004, 02:12 PM

Thanks for your response, Bagobob. I'll just keep my fingers crossed that the LED continues to work. I have access (free) to a more modern dish, still in the box if I need it.

There are a couple of meters in the market. If I do need one, do you have a recommendation? Unlike the Hughs/RCA receivers that I have, the Sony receiver that I carry in the MH doesn't have the tone feature for aiming so I'll surely need something else.

THanks,

Charlie

P.S. Once the LED goes out, I just swing the dish back and forth and up and down until I find the limits and then set it in the middle of both movements. It might not be optimium but I seem to consistently get 95% on the signal strength meter on the receiver when I'm finished.

CAD-Man · 03-31-2004, 07:10 AM

I use a standard 2 in 1 out switchbox from radio shack to do the same function for my Directv. It is a standard cable A/B switch, just push a single button and you have your second dish input. It will pass the 16vdc required for the Dish.

cad_man

Ken Lenger · 03-31-2004, 09:53 AM

I use a Radio Shack A/B coax switch also to switch the SAT receiver from rooftop dish to portable antenna. Since I installed the rooftop dish, I've never needed the portable one.

MojaveJoe · 03-26-2005, 07:57 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I use a standard 2 in 1 out switchbox from radio shack to do the same function for my Directv. It is a standard cable A/B switch, just push a single button and you have your second dish input. It will pass the 16vdc required for the Dish.

cad_man </div></BLOCKQUOTE>

Hey Cad-Man and Ken, how is that radio shack AB switch working out? Fried a receiver yet? Asking because I want to switch my portable dish and fixed dome inputs to one sat receiver on board.

Thanks,
Joe