Why wont 18 inch dish work for FTA?

[mikha_99]

Hi,
I have a 76cm dish with motor, and a Traxis receiver. I have no problems receiving FTA, but I have tried to get FTA channels with an 18 inch dish. A friend of mine is interested in GolTV, and I know I was able to get that with a Direct TV 18", using the originally supplied LNB, and a Traxis receiver. Now that GolTV is off the air, I only get the NASA channel and whatever info cards are on the sat (which is Echostar 8, I think).

My question is, why an 18 inch does not work for regular FTA (like the stuff on Galaxy 25). I have acquired a linear LNB that fits the 18 inch dish, but I have no luck getting anything.

I have been told the dish is too small. I can accept that, but want to know why it is not too small for the NASA channel, or why it worked for GolTV? Is it because of the LNB? Is circular somehow better than linear? If so, why does linear exist at all, if circular is better.

Just wanting to learn more about Satellite reception. I really don't know much about it, but have managed to get my system working.

Thanks,
Mike H

 

[voomvoom]

The DBS channels used by Directv and Dish Network are on very high powered satellites and they use Circular lnb's for most of their channels, while the normal ku satellites are a lot lower powered and use Linear lnb's for those channels. The main reason you don't get a signal is because the dish is to small for the power used. Hope this helps !

Al

 

[mikha_99]

Yes, this helps a great deal. It was never explained why the little dish wont work. So, my follow up question is what is the minimum to get some FTA? Would a 24 inch work?

I only ask because my friend is dish size sensitive. He could live with a 24 inch, but probably would not go all the way to the 30 inch.

Thanks,
Mike H

 

[Mr Tony]

You may get some of the very strong signals with a 24" dish but as soon as it clouds over or the signal isnt the best, say "bye bye" to the signal.

I have been able to get the very strong signals with a 18" dish and a linear LNB but they were near my true south satellites (the satellites near your longitude). Also, linear LNB's need to be skewed properly. Circular polarity needs no skewing

30" is really the minimum for reliable reception. Sure a 24" is great for tinkering but not the best for reliable reception

 

[alebowgm]

Well AMC4 is the exception to the rule, and that is only on some TPs (thankfully, the one that has KUIL)

 

[Morbius]

As well as SBS6 (G17) for ONN. I have a fixed 18" dish at my cottage and it will creep into the low 40's when raining, but most of the time its in the 60's.

 

[kymics]

The DBS channels used by Directv and Dish Network are on very high powered satellites and they use Circular lnb's for most of their channels

I'd like to rehash Mike's question a bit. Is a satellite high-powered by design (e.g. more expensive to build), or is because they burn more energy (solar only?) and therefore have a shorter lifespan? Obviously what I'm getting at here is, what's to stop non-subscriber satellites from being as powerful.

Also the question of circular vs. linear wasn't exactly answered. Is circular a more efficient wave type to receive on a dish. I think once I read about circular being used on C-band somewhere else in the world.

 

[lumpkin666]

... I think once I read about circular being used on C-band somewhere else in the world.

There is definitely such as beast as circular c-band. I think one of the Atlantic sats uses it. That dieletric slab that sometimes comes with c-band lnbfs is what is used to transform the lnb into a circular lnbf.

 

[Woofle]

Circular vs. horizontal

I'd like to rehash Mike's question a bit. Is a satellite high-powered by design (e.g. more expensive to build), or is because they burn more energy (solar only?) and therefore have a shorter lifespan? Obviously what I'm getting at here is, what's to stop non-subscriber satellites from being as powerful.

Also the question of circular vs. linear wasn't exactly answered. Is circular a more efficient wave type to receive on a dish. I think once I read about circular being used on C-band somewhere else in the world.

Hi there!

The reason for circular polarization is the problem of cross-polarization. Almost ALL earth-to-earth (terrestrial) communications, whether broadcast or two-way radio, are linearly polarized (either horizontal or vertical). If the transmitter is vertically polarized, you can lose up to 20 dB of signal strength if the receiver is horizontally polarized, and vice-versa, so matching antenna orientation is important. (On earth, that's not a problem as gravity makes "up" and "down" completely unambigous). By the way, a vertically polarized signal means a signal where the electrical field is vertical and at right angles with the earth, and is generated by an antenna which sticks up in the air. This is what almost all mobile radio reception/transmission is done with.)

A satellite doesn't share a common earth reference with all its receivers, which are looking at it from different "angles" depending on where the receiver is located. So the geometry of the situation is that a vertical or horizontal signal is really only truly vertical or horizontal for some locations, and is "skewed" or kinda "diagonal" in others. That's why you have to rotate your LNB to compensate or use a motorized dish which by virtue of its mount automatically compensates for this. (I think).

Circular polarization is symmetrical around 360 degrees so there is no problem of "skew". (You still have to match right-hand or left-hand rotation sense, but this is electronic and handled by the LNB).

So there's no inherent advantage of Linear vs. Circular in terms of power or range, BUT it's (very slightly) less complicated to set up a circularly polarized LNB because orientation is completely unimportant.

As for power, you're right -- it's economic. More power means more solar panels and bigger transmitters, both of which add weight and cost. Launching a heavier satellite costs a *lot* more.

For DISH or DirecTV, with a few transmitters and millions of receivers, it makes sense to spend a lot more on the few transmitters to allow for millions of cheaper, smaller dishes at the receiver. For point-to-point links, though, the situation is reversed. Remember, it costs a small fortune to boost each kilogram to orbit, and honestly, a 90cm dish isn't much by comparison to what most ground stations use.

Hope this helps. Please, any experienced users, feel free to correct anything I missed. I know radio and broadcast more than the specifics of satellite, and may have been a bit off in some areas.




To the very best of my knowledge, there's no inherent signal strength advantage between circular (left-hand and right-hand) or linear (horizontal and vertical) polarization *if* your LNA is properly oriented.



Horizontal and vertical polarization dominate in terrestrial communications. An antenna which goes up and down radiates a vertically polarized electric field and is vertically polarized.

 

[kymics]

Wow, great response. Welcome to SatelliteGuys!

It's a wonder that the DTH companies can take a multi-million dollar satellites, spend millions to launch them into orbit and then charge a similar price as other providers (cable company, etc) to make up their ROI.

Any thoughts on why some transponders on a linear satellite are so much stronger than others? I'm assuming it's distribution of total power to that specific transponder. Some channels within the same bird are just night-and-day when it comes to signal strength.

 

[Woofle]

Follow-up

Say DirecTV has one million subscribers per satellite. That means if they can shave $1 off the cost of each dish, that frees up $1 million more to spend on the satellite.

I'm sure the cost of launching one of those truly porky ultra-high-power DSS satellites is mind-boggling.

That's the real reason why small dishes only work well for DSS services and not the more general-purpose communications satellites. It's just too damn expensive. Not just for the satellite company, but for those who want to rent a piece of a transponder. I imagine that renting space on a DISH or DirecTV transponder would be *much much* more expensive than renting the same bandwidth on, say, Galaxy 25.

-- ross

 

[lumpkin666]

I'm sure the cost of launching one of those truly porky ultra-high-power DSS satellites is mind-boggling.

Shoot, you're only talking $250 - $300+ million dollars to launch one of them. Chump change.. that's all

 

[Corrado]

According to a program on PBS 2 weeks ago, not only the cost to build and launch. But, they have to pay an annual fee for the orbital position as well.

 

[Anole]

...But, they have to pay an annual fee for the orbital position as well.

Don't forget to pay the parking meter...
...or they'll tow you away and impound your craft!

Man, what's this planet come to?
Remind me not to park there next time I come for the holidays!

 

[hiker]

Anyone thought about using a DirecTV Slimline dish? In case you don't know, it's an elliptical dish about 32" x 23" and available cheap. I have a spare and would like to try but as a complete novice, I'm not even sure how to mount a suitable LNB.

 

[Mr Tony]

It might work for the stronger signals but for the weaker signals probably not. I have used an old DirecPC dish which is 32x20 and it worked for strong stuff but signal dropped on the weaker stuff

 

[hiker]

It might work for the stronger signals but for the weaker signals probably not. I have used an old DirecPC dish which is 32x20 and it worked for strong stuff but signal dropped on the weaker stuff

What dish/LNB would you recommend for a newb like me who will be asking Santa for a Traxis DBS-3500 and wants to experiment with sats G25, G10R, AMC3 to start?

 

[Anole]

Hiker -

I've recommended this set of hardware a few times.
Probably suit you quite well, too.