Why not simultaneous circular and linear?

[RedSavina]

Even though this question uses DBS as part of the example, I am posting to the FTA section since it is in the spirit of the FTA mad scientist / experimenter.

Why don't the mini dish guys use something like the QPH-031 from Invacom to double their capacity by transmitting vertical, left hand, right hand, and horizontal for each frequency? I know they would need to have the transponders up there to drive each polarity, but wouldn't this allow them to instantly double capacity for each frequency?

Does anybody offer this in the FTA world - as in all four from a single provider?

 

[qwert1515]

Even though this question uses DBS as part of the example, I am posting to the FTA section since it is in the spirit of the FTA mad scientist / experimenter.

Why don't the mini dish guys use something like the QPH-031 from Invacom to double their capacity by transmitting vertical, left hand, right hand, and horizontal for each frequency? I know they would need to have the transponders up there to drive each polarity, but wouldn't this allow them to instantly double capacity for each frequency?

Does anybody offer this in the FTA world - as in all four from a single provider?

Linear signals are usually broadcasted with lower power which requires a large dish. Even though providers use L/R they do not use the same center frequencies, they shift the transponders center frequencies so there is less chance for interference. The satellites would need to have more power (More solar cell arrays) and finally they would need the FCC to give them the license to do this.

Also my guess is that L and H would interfere with each other and R and V would interfere with each other at the same frequency. (My reasoning is that the signal will overlap and cause constructive or destructive interference)

(BLSA Pictures in a few minutes to show the shifted center frequencies for a DBS provider)

 

[Anole]

The vertical and horizontal polarization do interfere with each other to some extent.
I think in early C-band days, one bird might be all vert, and the next all horiz.
Now, the frequencies are chosen to lessen that interference and we run V & H on single birds.
Plus, the receiving LNBs can discriminate between V & H or RH & LH pretty well.
Read the specs for any LNB and note the spec on suppression of the non-selected polarity.

Problem is, circular RH and LH polarization while they don't interfere so much with each other, WILL interfere with V & H on the same bird.
And vice versa.
So, pick one pair:
- V & H, or
- R & L
but not both.

 

[qwert1515]

Here is my screenshot from my BLSA aligned to show the center frequencies shifted (Does not look nice since I used paint and I am watching the BCS Championship game at the same time ) (Also because I have not calibrated the BLSA for circular signals since I don't use the circular LNB often)

I picked the 119 DBS satellite to show the shift(I labeled the polarities H and V when it should be L and R)

 

[RedSavina]

As always, SatGuys comes through! Thanks for the responses - I appreciate your patience as I continue to learn more.

 

[updatelee]

Ive uploaded two pics from my spectrum analyzer, first is 91.0w circular second is 91.0w linear.

my lnb has a lof/h of 10750 for linear and 11250 for circular. so lets do some math

12224 is expressvu's first tp

12224 - 11250 = 974 and you'll see that on the lband on my spectrum,its right on the first tp, with the rest to follow.

now 12224-10750 = 1478 and even on the linear side, you'll see that, 1478 and all the tp's follow that. you'll also notice that not only are they on the spectrum, but they are a complete mess, lol. anything in there would be totaly fubard and unlockable.

ignore the rouge blip tp down at the bottom of the screen, its not a hidden unkown tp, its a birdy on my satlook, its been there since they day I bought it.

 

[Tron]

Circular is used by the pizza dish companies for a couple of good reasons... It allows for a smaller dish and eliminates the need for skew adjustments. While most pizza dishes require skew anyway (due to the fact that they're hitting more than one bird at a time), there is no need for fine adjustments of the LNBFs. Of course, with Ka band coming into the picture, it seems they are slowly sneaking larger dishes onto homes anyway.

UUUGGGHHH! What a HORRIBLE looking thing! What will the neighbors say

 

[updatelee]

just as an interesting note, the two KA sats in the sky right now are both circular.

 

[N4ST]

The same thing has been said several different ways (all correct!), but mathematically, linear and circular polarizations are not orthogonal. There is only a 3-dB separation between the two methods. The isolation we need between cross-polarizations isn't there to permit simultaneous use without interference.

 

[Mr Tony]

119 has both KU Band circular and DBS circular...sure the satellite is technically at 118.7 but it has frequencies from 11.7-12.2 for 118.7 and 12.2-12.75 on 119.

 

[updatelee]

119 has both KU Band circular and DBS circular...sure the satellite is technically at 118.7 but it has frequencies from 11.7-12.2 for 118.7 and 12.2-12.75 on 119.

exactly, if the providers wanted more bandwidth all they would have todo is use more of the spectrum, there is still ALOT left in the L band, problem is dishpro bandstacked lnb's, they would have to get rid of these as they eat almost all the lband.

if they switched to a non-bandstacked 10750 circular lnb, like 118.7 they would have tons of avalible room. most likley they would have allready done this though if their satellites supported it, as we see with 119, they launched a new sat anik F3 and parked it behind 119. so obv 119 doesnt have the support, their other sats prob dont either.