Picking up C-band transmissions with a 100cm dish?

[mgandalf]

I've been pooring over all the C-band channels available out there still but I have a 90cm dish (on a STAB100 motor). I don't have the room for a BUD (and my neighbors would kill me anyway). Does anyone have experience with picking up digital (DVB) or NTSC channels with a 90/100/120cm dish and a C-band LNBF?

Also, is there anyway to mount both a C-band and Invacom quad on the same dish? I really don't want to give up KU-band transmissions in favor of C-band assuming a 120cm or smaller dish would work.

One more question. Since I have a STAB100, if I were to elect to setup a 120cm dish, do I really need a STAB120 for this?

Thanks, Mark.

[rainman]

some of the guys are getting c band signals on the 120cm. will need to upgrade to the stab 120 motor or the motec sg 2100 motor. use the
bsc 621-2 c/ku lnbf.

[elgemcdlf]

Originally Posted by mgandalf

I've been pooring over all the C-band channels available out there still but I have a 90cm dish (on a STAB100 motor). I don't have the room for a BUD (and my neighbors would kill me anyway). Does anyone have experience with picking up digital (DVB) or NTSC channels with a 90/100/120cm dish and a C-band LNBF?

Also, is there anyway to mount both a C-band and Invacom quad on the same dish? I really don't want to give up KU-band transmissions in favor of C-band assuming a 120cm or smaller dish would work.

One more question. Since I have a STAB100, if I were to elect to setup a 120cm dish, do I really need a STAB120 for this?

Thanks, Mark.

What you can or can not pick up with a small dish for C Band will greatly depend on the sats footprint in relation to your location. As I understand it Rainman is in a great location signal strength wise so he probably stands a fair chance of doing what you are talking about with some success. Note some. If you are in CA and want some of the eastern sats probably can not do with a small dish. I would start by deciding/outlining what channels you are wanting to receive and then check footprint/signal strength for your location on each of these sats. That will let you know what your chances are of receiving what it is you desire.

[mgandalf]

Originally Posted by rainman

some of the guys are getting c band signals on the 120cm. will need to upgrade to the stab 120 motor or the motec sg 2100 motor. use the
bsc 621-2 c/ku lnbf.

The bsc 621-2 LNB is for a prime focus dish, however, the 120cm Fortec is an offset dish. Will that LNB work?

- Mark.

[rainman]

Location, Location,Location. thats what it's all about Steve now if we could only shave off a few of these mountain tops we could get a better line of site at the eastern sats.LOL

[rainman]

Originally Posted by mgandalf

The bsc 621-2 LNB is for a prime focus dish, however, the 120cm Fortec is an offset dish. Will that LNB work?

- Mark.

yeah alot of guys are using it on off set dishes. see the post on the bsc621-2.

[mgandalf]

Originally Posted by rainman

Location, Location,Location. thats what it's all about Steve now if we could only shave off a few of these mountain tops we could get a better line of site at the eastern sats.LOL

I'm located just south of lake Ontario. Would that preclude me from picking up more westerly sats like AMC 11 @ 131w?

- Mark.

[rainman]

you should be able to get amc11 the problem would be dish size. may need 8.5 dish or larger for this sat.

[elgemcdlf]

Originally Posted by mgandalf

I'm located just south of lake Ontario. Would that preclude me from picking up more westerly sats like AMC 11 @ 131w?

- Mark.

As memory serves me there is not a whole lot on 131 in the way of DVB MPEG2 C Band. I did not look yet though. It is all in the signal strength available to you from that sat. East/west is not the important factor but usually the farther away the sat is the weaker the signal.

As I thought. There are only two channels avauilable to you on a DVB MPEG2 receiver. Almost everything on that sat is encrypted of some form and it is primarily a DCII sat. Now you are talking a 4DTV receiver which will not work with the lnbf discussed in this thread. Not to mention I bet that 922 would get cranky about that tiny dish

Big receivers deserve big dishes By the way if you are looking at the movie channels there and have thoughts of subbing to them it will not happen with a small dish. I currently use a 8.5' mesh dish as my primary dish and those channels are touchy with it. HBO has a high FEC which translates into need to capture more signal on a very well aligned dish. Most likely can not be done with a dish the size you are talking about. Starz/Encore is also a bit touchy concerning alignment.

[mgandalf]

Take Anik2 @ 111w. It looks like I'm right on the edge of the 42db band. That said, I shouldn't have any problem picking up Movie Central HD on it?

Sorry for all the stupid questions. I don't want to spend another $200 just to find it won't work.

- Mark.

[wejones]

Originally Posted by elgemcdlf

......It is all in the signal strength available to you from that sat. East/west is not the important factor but usually the farther away the sat is the weaker the signal.

I've always thought it had more to do with the footprint than how far, like from Maine, G10r is one of my strongest sats, stronger than some of the sats directly south of me. However distance IS a factor in terms of getting down close to the horizon. Not quite sure why, but when you start getting close to the horizon, things get harder. I think it's more a case of picking up ground noise, and I think the angular separation between sats gets a bit smaller as well, plus I've read that having the signal pass close to the earth through more atmosphere results in some rotation of one of the polaritys, all of which don't help.
From my location, I have to look through trees to see that sat, but I can get it in the winter with my 10' dish, but I wouldn't have a chance with a 4' dish. However lake Ontario is quite a bit further west, and the further west, the easier it should be. It used to be a fairly easy sat for me when I lived near Baltimore.
I used to watch a DVB feed of Fox Sports on that sat, whenever it wasn't encrypted, but they moved that a year or two ago, so I'm not sure what of value is on that sat now. But I would sure recommend bigger than a 4 foot dish. They used to sell 5 or 6 foot dishes to get the analog subscription channels on what was G5, but that was when there weren't any nearby sats. Now there are sats nearby in that range, and you just don't have the resolution with a small dish. If you don't have any sats within 4 degrees, it can work, but with 2 deg spacing, it's very hard. A 4' dish has a resolution of approximately 4 degrees on C band, so it just can't keep out the signals from the nearby sats.

[rainman]

Originally Posted by mgandalf

Take Anik2 @ 111w. It looks like I'm right on the edge of the 42db band. That said, I shouldn't have any problem picking up Movie Central HD on it?

Sorry for all the stupid questions. I don't want to spend another $200 just to find it won't work.

- Mark.

you will have to have a receiver that will do HD for that channel most computer cards will do HD not to many set top boxes that will do HD.

[mgandalf]

Originally Posted by rainman

you will have to have a receiver that will do HD for that channel most computer cards will do HD not to many set top boxes that will do HD.

I'm using a DVB card configured in Linux so my options there are as limited.

- Mark.

[mgandalf]

Ok, here's something really whacky but sounds like an interesting experiment. Radio astronomers use a little hack of using two dishes together to create a virtual dish the size of the distance between them. Could that work for satellite transmissions? I mean, setup something simular to the following:

1. Two 90cm+ dishes at least 12 foot apart on rotors.
2. Move both dishes to the same angular position using two receivers/DVB cards.
3. Using a combiner, tune one of the receivers/cards to a C-band transponder using both dish's LNBFs.

I know, sounds crazy.. but is it just crazy enough to work?

- Mark.

[wejones]

Originally Posted by mgandalf

Ok, here's something really whacky but sounds like an interesting experiment. Radio astronomers use a little hack of using two dishes together to create a virtual dish the size of the distance between them. Could that work for satellite transmissions? I mean, setup something simular to the following:

1. Two 90cm+ dishes at least 12 foot apart on rotors.
2. Move both dishes to the same angular position using two receivers/DVB cards.
3. Using a combiner, tune one of the receivers/cards to a C-band transponder using both dish's LNBFs.

I know, sounds crazy.. but is it just crazy enough to work?

- Mark.

Are you sure the astronomers do that with only 2 dishes? I've heard of matrixes of many dishes, but never heard of using just 2 dishes. I would think that would be very complicated with next to no benefit, at least little benefit with respect to the amount of signal collected.

But relative to your TVRO idea, there are 2 different reasons for needing a big dish for C-band, and there are a couple problems with your idea, but it's interesting, and I had thought of doing that myself at one time.
Re why you need a big dish, I said 2 reasons, but it's really one reason, and that is gain. Basically, you need to collect a lot of signal to receive a sat signal, and you need a high gain antenna. The gain of an antenna is usually expressed as a function of the dishes diameter, but it is really more related to the surface area, ie collecting signal over a bigger area. A 12' dish is about 16 times more surface area than a 90 cm dish. Two 90 cm dishes are only 2 times the surface area, so there is little additional gain.
The second reason you need a big dish is resolution, because you have to be able to separate sats that are only 2 degrees apart. A 12 foot dish has about 1.4 degrees resolution at C-band freqs, whereas a 90 cm dish is nearly 6 degrees resolution. I am not positive how to estimate the resolution of TWO 90 cm dishes, but according to the equations, it is related to the GAIN, not to the separation of the dishes, so I think the improvement of resolution wouldn't be significant. Intuitively though, it seems to me, that this is a case where separation of 2 small dishes might help, but apparently not.
However there are a couple problems. One big problem, is that when you combine signals from 2 different antennas, you have to be very accurate with respect to the length of feed line between the antennas and where you join the signals. If you imagine the signal as being a wave, where the signals from the two dishes join, the signals need to be in phase, ie the peaks of the waves have to get there at the same time, or else you'll get destructive interferrence. The wave length at c band freqs is about 3 inches, so you'd have to do a lot of experimenting with changing the length of your feed line to get the signals to add together.
Also, almost as important as the total signal strength is the signal to noise ratio. Since a lot of your noise is coming from the lnbfs and feed lines, you are going to be adding almost as much additional noise as you are adding signal. This is something like trying to amplify a weak signal, ie you end up amplifying the noise more than the signal.
Another problem, is that the stock Ku lnbfs that you get on your 90 cm dishes only receive Ku band, not C_band, so you'd have to figure out a way to attach a BIG C-band feedhorn or lnbf to the little dish, and this bigger lnbf will most likely block some of the signal, reducing the gain of the dish. Plus, you would probably not be able to use a motorized system, because the motors that drive these little dishes are weight limited, and the C-band lnbfs are going to add a lot of extra weight to the system.

Anyway, the short answer is that you would get only a small amount of benefit from doing this, and it may end up being worse, and to get the equivalent amount of gain, it would end up costing MUCH more than just getting a bigger dish. Interesting idea though, and if you lived in a community that didn't allow dishes bigger than 1 meter, it's an interesting way to get the benefits of a big dish while staying within the legal limits by having 16 1 meter dishes.