Newbie Here Combine two motorised antennas

[Matthias]

Hello there,

As mentionned above, newbie here, I'll do my best to stick to the mood of the forum and I know that the subject I'm throwing here has been discussed before. But for what I've read, never really resolved. Neither here nor wherever Google could get me!

Here's the thing: my install is on a boat, where I have two Seatel motorized antennas, both 1,20m. we have two of them to be able to cover 360° while the boat is moving, considering that a mast placed between them both creates a shadow. A very basic selector (relays) based only on the ship's heading selects one or the other antenna to avoid the shadow and feed a network of Dreamboxes through the ship.

The system works quite well as it is, but...

But we'd like to extend the coverage of our system. She's a ship, she's moving. And as we go further away we are loosing channels and all, as you could expect. In some cases, both antennas can point the same satellite, with no shadowing from our mast; in those cases, I was wondering if we would be able to combine both signals in order to improve the reception. I know that the first argument to dismiss that option is the price vs. technicality. But when you consider that an antenna like ours is in the 20-30k€ range, changing them both for bigger is not an option. But throwing a few k in good quality electronic is.

In theory, working in arrays is possible, right? Phasing signal is too? The fact that the relative position of antennas toward the sat will not be constant will be an extra food-for-the-brain, but could probably be resolve? In fact, I am looking for something to start with, dig up a solution and see how much it would cost, even if it is a prototype? What kind of equipment are we looking for? If anyone want to give me a lead, I'll be more than happy to follow the trail myself and let you know!

So, any volunteer?

Cheers!

Bonus track: now that we will have top-of-the-pop spectrum analyses in the racks, a semi-educated guess would be that we could use it as an antenna selector in order to strenghten the system (imagine a seagull is resting against one of the radome!)?

 

[Topper]

As this kind of array is already in use for radio telescopes it would seem reasonable to take a look at combining the signals as you describe however, as you would be the first to attempt such a set up for Ku band signals I would set aside £1 or £2 million for research and development before expecting a working prototype. It really is not feasible IMHO, indeed even in the analogue days it was not feasible and now that everything is digital and has to have pinpoint accuracy, I believe it is a total no no, but somebody on here may be willing to take on the challenge if you give them a significant budget

 

[Analoguesat]

Theoretically its possible - phased arrays and the like are exactly what are used in military antennas, radio astronomy telescopes etc.

Almost certainly not possible on any sensible budget for home or ship tv use, unless you budget stretches to the equivalent of the military spending of a small African nation.

Which satellites are giving problems & how far out are you when you start losing signal?

 

[Vipersan]

Phased arrays at these frequencies are not really practical ...but by all means prove me wrong..
If you acheive this mammoth endeavour at an affordable price ..you'd have the undying admiration of everyone on this and every other satellite forum.
A clue of how to begin ..
Custom made external reference PLL lnbs ..super cooled to improve stability ..and complex computer controlled phase analysis and control.
and that's just the easy part..
lol

 

[Matthias]

>Topper:
I would have thought that phasing digital signal would actually be easier than with analog? Isn't it the whole point of digital: giving a signal that is easy to identify (thus in my mind, easy to phase?)
>Analoguesat:
We are mostly tracking 28E for Sky and use 19E for Canalsat as a back-up. We do have good cover in the north of western med but loose the signal sailing south from Sardinia or east from Greece. We already have pretty good reception considering the size of the antennas if you ask me! But request went from "improve the antennas change-over" to "why not combining them to get a boost" in no time. That's where it gets beyond my qualification!
>Vipersan:
Actually, one of the lead I was following was this dutch company, Recore. They were said to have developed microchips (there for the computer controlled part? ;) to use simple antennas (not even dishes) in arrays... It seems that the technology has been leaning more toward the flat antennas they are now fitting on planes and probably soon on ships as well. But, he, who can do more, can do less, can't he?

Anyway, thanks for your thoughts already! Even though I feel like trying to fly a rocket with a steam engine in the times of nuclear fission!

 

[Topper]

>Topper:
I would have thought that phasing digital signal would actually be easier than with analog? Isn't it the whole point of digital: giving a signal that is easy to identify (thus in my mind, easy to phase?)

The reason what you are proposing is harder with digital, certainly from my understanding is that digital suffers from the cliff face drop off effect. In other words it is either there or it is not, hence it is no good trying to phase array two signals when one or both are not there in the first place or have little or no quality therefore how is this supposed to work? IMHO the only way to improve your current situation is a bigger dish or to super cool the lnb. which is again unknown territory for most on here on this hobby forum

 

[Analoguesat]

We are mostly tracking 28E for Sky and use 19E for Canalsat as a back-up. We do have good cover in the north of western med but loose the signal sailing south from Sardinia or east from Greece. We already have pretty good reception considering the size of the antennas if you ask me! But request went from "improve the antennas change-over" to "why not combining them to get a boost" in no time. That's where it gets beyond my qualification!

Things are only going to get worse for the eastern Med over the next year as Astras 2E & 2G come into service.

To be honest for English programming its going to be far far easier & cheaper if you look at something like Badr - theres loads of English language services on there.

 

[Huevos]

This isn't a passive aerial system so it's not just a case of getting the received signals in phase. The first thing you are going to have to work on is getting the LOs in the 2 LNBs to run at the same rate.

 

[Analoguesat]

If your ship owner is rich enough you could of course get the main desired channels uplinked onto another satellite on a private circuit and bounced back down across the eastern Med

It would need to be securely encrypted otherwise the sat hobbyists will find it in no time flat

 

[trigger]

I think going forward you have three choices.
1) Either increase your antenna size(s) but given new satellite launches and the massive costs for you then probably impractical/ impossible.
2) Look at getting services from other satellites with friendlier mediteranian footprints (7W or 26E etc)
Or (your best bet in my opinion)
3) Get a good quality Internet service supplied by satellite and then look around at IPTV service providers. There are loads that have appeared over the last year providing mainly a good quality of service. The one I use, uses about 360meg per hour and is a pretty decent quality picture. You will have to ensure you get sufficient download speed (1.8 meg minimum) and enough download per month. Quantis offer an unlimited connection but I have a customer that reached 90gb and they capped him at 1meg and his TV became unwatchable.
Hope this helps

 

[Huevos]

3) Get a good quality Internet service supplied by satellite and then look around at IPTV service providers. There are loads that have appeared over the last year providing mainly a good quality of service.

That is only a practical solution for 1 or 2 tv's. If it is a large boat with multiple tv's running on different channels only a satellite system would cut it.

 

[trigger]

That is only a practical solution for 1 or 2 tv's. If it is a large boat with multiple tv's running on different channels only a satellite system would cut it.

True. Didn't think of that one

 

[Analoguesat]

I think going forward you have three choices.
1) Either increase your antenna size(s) but given new satellite launches and the massive costs for you then probably impractical/ impossible.
2) Look at getting services from other satellites with friendlier mediteranian footprints (7W or 26E etc)
Or (your best bet in my opinion)
3) Get a good quality Internet service supplied by satellite and then look around at IPTV service providers. There are loads that have appeared over the last year providing mainly a good quality of service. The one I use, uses about 360meg per hour and is a pretty decent quality picture.

Or 4) Restrict your cruising to going round the Isle Of Wight and within the North Sea

;)

 

[Matthias]

>Topper : supercooling, huh. I think I won’t go any further than installing aircon into the radomes ^^ (couldn’t hurt anyway)(and as much as I would like to have fun flooding the thing with liquid nitrogen, I fear that any system added onto the moving part would be a nightmare to deal with… )

But let me come back to the phasing part (now i am more trying to cultivate myself ;) I think I get what misled me there.

When we talk about cliff effect, we talk about a raw signal we would phase straight from the dish , right? Where I was more considering a computer driven phasing of an already decoded signal (using header and synchro bits). I was thinking one step up in an OSI-like model (you, talking about a physical layer, while I was thinking about a data link layer). But then I realised I was steping in too late on my transmission, right ? considering that if I have my signal that much cleared of error I do not need that amplification I am asking for ! Now, is it completely insane to think about (in theory) feeding-back the phasing information one level up? Like : we have a signal, even poor, manage to clear it enough to set a zero once in while, feed-back that zero to correct the phasing of the raw signal ? Is this science fiction ? (if it is, then sorry, i am not a train telecom engineer ^^)


>Analoguesat : yes I know, I already brace myself. I’ll have a look about badr’s bouquets. It seems pretty interesting. Now I’ll have to manage a paid « scouting trip » to harvest some sim-cards for these bouquets ! (would be a cheaper request than private broadcast ^^)


>Huevos : you lost me here. What are the LOs ?


>Trigger : 1) is what we try to avoid in the first place : no fun ;)

2) we already do that, but i am not the one missing Sky Sports ^^

3) we do have an internet access, but prices with the types of providers we require (worldwide coverage) are already crazy high (a dedicated link with a guaranteed downspeed of 1024kbps would cost you some US$14k per month !) and, yet, I am far from having enough downlink for even one good permanent HDTV stream (although I push for a new VSat antenna . Let alone the few stream I can get with satTV and my dreamboxes, as Huevos noted.


>Analoguesat : 4) we do like warm water. Although I wouldn’t mind being up north sometimes !

 

[Analoguesat]

LO = local oscillator.

Its an electronic bit in the lnb.

 

[Matthias]

LO = local oscillator.

Its an electronic bit in the lnb.

Ah yes! I could have googled that one!

But then, about the LOs. Aren't they suppose to be particularly stable in frequency? Isn't it the whole point of a good quality LO? And if there is a slight shift in frequency, I'd expect it to be in a range admissible by the receiver, or?... Now if it is about the LOs of every antenna to be phased: I would guess that the frequently produced by the LO is ultimately based on the frequency of the grid powering the receiver that powers the LNB? If the grid is common and both install have pretty much the same characteristic (down to the length of cable to the LN, do we risk introducing such distortion, somewhere, that the signal would not be worth mixing? Hehe, I am not afraid of sounding too naive tonight, so I might as well ask all the questions that pop up in my head!

Cheers people!

 

[Matthias]

I would guess that the frequently produced by the LO is ultimately based on the frequency of the grid powering the receiver that powers the LNB?

Humph! LNBs are powered up in DC? Yeah, no need to slap me in the face, i'll do it myself before going to bed! With fresh posidonia ;)

 

[Analoguesat]

Stable to a degree - but they will vary in frequency by a few khz, and they will drift as the temperature changes, especially as they age.

 

[hairybadger]

If I were rich enough to be able to buy and staff such a vessel, I wouldn't be too worried about not being able to watch TV when the boat sails out of footprint. I doubt if I'd be watching TV at all while aboard (well, unless there were a test match on ).

 

[Huevos]

Aren't they suppose to be particularly stable in frequency? Isn't it the whole point of a good quality LO?

How stable an oscillator can you build for less than a fiver? The 2 local oscillators would have to be absolutely locked in synchronization for this to work. Those oscillators are beating at 9.75 billion times per second. If they were running at a different rate of just 1 beat per second the signals from the 2 dishes would go from completely in phase to completely out of phase to completely in phase again once every second. The reality though is an LO can easily be 1 MHz off frequency and still be considered to be working properly. So that would mean going in and out of phase a million times a second.

TBH, even if you did manage to get these dishes working together you would only improve SNR by about 2dB. That might just about get you 100km further out of the footprint, but not more.