Fringe reception - best to avoid Quattro/multiswitch?

[OldBen]

Figured fringe reception may be best place to ask this... if your on the edge of reception, is it wise to avoid a quattro and multiswitch versus a single/dual/quad LNB direct connected?

I think the loss is in the switch right, and the quattro LNB's will output the same as a quad or single in general?

Forum search seems to return mixed opinions on the topic.

(already planning on using a Inverto Black Ultra based on reading the forum to try and maximise signal either way).

 

[Lazarus]

For "normal" use with a quattro/multiswitch, it's conventional to use a slightly bigger dish than one would otherwise do, in order to overcome the losses you mention - but at the fringes those losses will of course have a potentially greater detrimental effect and so an even bigger dish might be needed.

Please remind us, in the absence of a link to any related Threads, what you consider yourself on the fringe for?

 

[PaulR]

Yes, converntional wisdom says that a Quattro/multiswitch combination has a higher noise floor and needs a dish one size karger than normal to compensate.

BUT

I've been thinking about this. If a Quad or Octo is basically a Quattro with built-in multiswitch (four out or eight out respectively) why should this be? Admittedly the multiswitch doesn't have to cope with mixing in terrestrial TV and radio frequencies but why should this affect the combination. Maybe it's very close proximity of the combined components that is important.

Opinions anyone?

 

[OldBen]

Please remind us, in the absence of a link to any related Threads, what you consider yourself on the fringe for?

Sorry, CSLink on Astra 3A at 23.5e (see comment in sticky earlier today), reading up I probably need a 120cm dish from my location about 20 miles west of (central) London. At the moment on my 85cm motorised I can't get 12525 V or 12070 H. Planning needed over 100cm right? Don't really want to go bigger than 120cm... it might not look like a 100cm!

PaulR - its confusing me as well and I assume the loss is in the switch. The switch I have my eye on (emp-centauri) also supports 22Khz tone, so if it was just the Quattro that has more noise due to its construction than a quad, I could use a quad with this switch. I think its the switch part where the loses occur, although the spec sheets usually say 0db insertion for the sat path (-db for terrestrial).

 

[PaulR]

PaulR - its confusing me as well and I assume the loss is in the switch. The switch I have my eye on (emp-centauri) also supports 22Khz tone, so if it was just the Quattro that has more noise due to its construction than a quad, I could use a quad with this switch. I think its the switch part where the loses occur, although the spec sheets usually say 0db insertion for the sat path (-db for terrestrial).

It may be that Quattro LNBs are built with higher noise figures than Quads. There's less electronic gubbins inside a Quattro - the price is cheaper for a start - so why should this be?

It seems really perverse that a Quad could end up wih a lower noise figure than a Quattro.

 

[BombedOne]

For fringe reception, everything matters, even the length of the cable!

Practical example -while sitting on roof, next to dish, cable length is only 2 meters, I can get quite stable picture from astra 1H (1.5m primefocus). If I move indoors, cable length about 15 meters, picture becomes heavily pixellated. If diseqc is used, no reception of 1H at all.

As I've read, quattro LNBs are best for fringe reception, when used directly, without multiswitch, because, since it's always only one sub-band is active, total noise generated by LNB circuitry and added to output signal is less. In practice, I've found no difference between single and quattro LNBs.

Another way to seriously boost fringe signal, without the dish size increase, is to use cryogenic cooling for LNB. While it's non practical in real life, it's quite interesting to do just for test. In certain cases, signal boost can be about 3db. In terms of dish size, this means upgrading from 1.2m dish to 2.4m dish. So, if you have weak signal, you can try to pour liquid nitrogen on LNB (form a kind of jar around the LNB body using some foamy insulator, and pour nitrogen into it). For a relatively short time (minute or so), you'll notice significant signal increase. After that, LNB will be dead.

 

[Llew]

After that, LNB will be dead.

I do like that closing sentence, almost mentioned as an afterthought

 

[Robbo]

. At the moment on my 85cm motorised I can't get 12525 V or 12070 H. Planning needed over 100cm right? Don't really want to go bigger than 120cm... it might not look like a 100cm!

You should be able to get 12070H easily, are you sure all your settings are correct?, as I'm getting that one very strongly, 12525V on the other hand, as you say is weak, I seem to be get roughly what I get from Nilesat V, for that TP.

You may be able to get those TPs from an actual 1m dish, as your 85cm, may be a little smaller than advertised.

 

[PaulR]

In terms of dish size, this means upgrading from 1.2m dish to 2.4m dish.

Surface area increases according to the square of the radius. The surface area of a 1.2m is approximately 1.13 sq metres. Doubling to 2.26 sq metres and working backwards gives a diameter of 1.7m - in practice a 1.8m dish.

 

[Huevos]

Yes, converntional wisdom says that a Quattro/multiswitch combination has a higher noise floor and needs a dish one size karger than normal to compensate.

I going to stick my neck out and say this is just another urban myth, a bit like cable runs must never have any connectors. If you check with a decent digital meter gross signal loss is negligable and MER is identical.

 

[OldBen]

Ok so my further reading and calculations deduced the following points:

- Difference between say a Andrews 1.2 (the forum darling it seems) and a 1M dish say a Triax TD110 (ok its 105cm if your being picky) is approx 2dB. The Andrews is 42dB to the Triax at 40dB (or .2 either way depending on freq).

- Even though we are talking about a logarithmic measurement, you can loose or not loose 2dB in a lot of places in a set-up.

- The LNB obviously uses a local oscillator to create an intermediate frequency somewhere between 950MHz-2150MHz for the receiver. So looking at cable WF 100 at 1000Mhz attenuates 19.9dB/100m, and at 2150Mhz 30.3dB/100m. If you look at WF125 though its 16.2dB/24.8dB for the same distances, or 13.6dB/20.9dB if you went extreme with WF165. So say I have 15m cable from dish to switch to receiver, WF100 attenuates 2.985dB/4.545dB but using WF125 would mean 2.43dB/3.72dB. So that's a saving of 0.55dB/0.825dB to possibly be made.

- A launch amp may preserve the weak signal better if mounted near the dish, or even before multiswitch if fed with nice strong signal from heavy cable, but probably introduce more problems than it solves with too high levels on other transponders.

- LNB seems to be easily able to loose/gain a few dB. My invacom is 5-6 years old now, new Inverto Black Ultra may give the missing strength.

- Investing in something like a Satlook Lite to maximise signal/BER for alignment would be wise.

At the moment my plan of action is going to be to wait until I move (6 weeks I hope), and try it with a Triax TD110 or Gibertini 1M on a temporary mount in the garden. If that works add some loss (longer cable run, or 3dB attenuator for example) and see the difference made. Will then try with a multiswitch as well. Will then try with some attenuation and switch. If that all works in test will chuck it all up and see how it goes fully installed. I can always changes the WF100 for some WF165 just for that LNB if its that marginal. I am thinking with the right well aligned setup it may be possible on a 1M. Rolf had some successes with some transponders on an 85cm as I recall in the Astra 3b sticky thread. Will report my findings ;)

 

[BombedOne]

Surface area increases according to the square of the radius. The surface area of a 1.2m is approximately 1.13 sq metres. Doubling to 2.26 sq metres and working backwards gives a diameter of 1.7m - in practice a 1.8m dish.

Yes I know that. But do you ever seen any dish sales point, which sells dishes by their surface area, not diameter?

 

[PaulR]

Very true.

But we try to educate on this forum and stop bad information. :-thumbup

 

[dovercat]

Ok so my further reading and calculations deduced the following points:

- Difference between say a Andrews 1.2 (the forum darling it seems) and a 1M dish say a Triax TD110 (ok its 105cm if your being picky) is approx 2dB. The Andrews is 42dB to the Triax at 40dB (or .2 either way depending on freq).

It is more than .2dB either way depending on freq if you are referring to the entire frequency range.
Triax TD110 11.7GHz 40.2dB
Using _http://www.satcom.co.uk/article.asp?article=22 Antenna Diameter, Efficiency, Gain or Frequency Calculator
That gives 10.7GHz 39.4dB, 11.7GHz 40.2dB, 12.7GHz 40.9dB

If you go with the Triax TD110 then you might like to try the Inverto Black Ultra 0.1dB Lnb with it as some people seem to like that combination.

- The LNB obviously uses a local oscillator to create an intermediate frequency somewhere between 950MHz-2150MHz for the receiver. So looking at cable WF 100 at 1000Mhz attenuates 19.9dB/100m, and at 2150Mhz 30.3dB/100m. If you look at WF125 though its 16.2dB/24.8dB for the same distances, or 13.6dB/20.9dB if you went extreme with WF165. So say I have 15m cable from dish to switch to receiver, WF100 attenuates 2.985dB/4.545dB but using WF125 would mean 2.43dB/3.72dB. So that's a saving of 0.55dB/0.825dB to possibly be made.

The Lnb is amplifying the signal and noise by about 100,000.
The Lnb will have a gain spec, mine for example say 57dB that is how loud it is shouting down the cable. As long as the receiver is getting 45+dB preferably 50+dB at the receiver end it should work fine. I am using 21mtrs of CT100 Cable (attenuation 1GHz -22.5dB per 100mtrs, 2GHz -29dB per 100mtrs) so -4.75dB to -6.09dB, that leaves me with 50+dB and my receiver shows no loss in signal quality attached by a couple of meter fly lead to the diseqc motor or at the the end of the 21mtr cable.

Attaching the cable directly to the lnb rather than via the diseqc motor does show a difference. Looping via the motor reduces signal quality on some channels by a few points. I have also tried a splitter and that reduces the signal quality more.

You definitely want a meter or to be able to see the TV screen displaying signal strength and quality readings to be able to peak alignment of the dish. Being 1 degree out on a 1mtr dish is about -1dB, on a 2" pole that is only rotating the dish 0.4mm around the pole.

It also helps after you finish lining up the dish. When optimizing the alignment of the lnb with the dish.
I found not just how far forward/back it is in the Lnb holder and how far turned skew, but also slightly adjusting the lnb arm bracket on the back of the dish helped peak the reception. Some people using Triax dishes and 55mm feedhorn Lnbs ( not the inverto black ultra which has a smaller feedhorn) add a couple of metal washers between the top lnb arm bracket attached to the back of the dish and the dish so the arm is at a slightly different angle. With my Televes dish and Televes Lnb I found adding one washer between the bottom arm bracket and tightening the bolt while watching the signal quality enabled me to better peak the signal better.

Moderation Note - Please do not post live links to outside sites.

 

[Huevos]

Ok so my further reading and calculations deduced the following points:

- Difference between say a Andrews 1.2 (the forum darling it seems) and a 1M dish say a Triax TD110 (ok its 105cm if your being picky) is approx 2dB. The Andrews is 42dB to the Triax at 40dB (or .2 either way depending on freq).

- Even though we are talking about a logarithmic measurement, you can loose or not loose 2dB in a lot of places in a set-up.

- The LNB obviously uses a local oscillator to create an intermediate frequency somewhere between 950MHz-2150MHz for the receiver. So looking at cable WF 100 at 1000Mhz attenuates 19.9dB/100m, and at 2150Mhz 30.3dB/100m. If you look at WF125 though its 16.2dB/24.8dB for the same distances, or 13.6dB/20.9dB if you went extreme with WF165. So say I have 15m cable from dish to switch to receiver, WF100 attenuates 2.985dB/4.545dB but using WF125 would mean 2.43dB/3.72dB. So that's a saving of 0.55dB/0.825dB to possibly be made.

These figures have no relevance for RX in the real world. When you increase the dish size you are increasing the desired signal in relation to the noise floor, i.e. you are being more selective about the direction that signal is being received from. When you increase the coax length both signal and noise are attenuated by the same amount. The only time the coax length is relevant is when the run is so long that the noise produced internally in the receiver becomes an issue.

 

[OldBen]

It is more than .2dB either way depending on freq if you are referring to the entire frequency range.

That's a typo, it should be 2dB either way depending on frequency. I made a small table of the dishes I was looking at and their bottom/mid/top band responses, what I meant to say was its about 2dB more gain at any given frequency with a 1.2m Andrews over the 1.05 Triax.

If you go with the Triax TD110 then you might like to try the Inverto Black Ultra 0.1dB Lnb with it as some people seem to like that combination.

Already thought of that, see post you replied to ;)

new Inverto Black Ultra may give the missing strength.

As long as the receiver is getting 45+dB preferably 50+dB at the receiver end it should work fine.

This is the challenge, that the missing 2dB can be the difference between being above or below the receiver's ability to tune the signal at an acceptable error rate. What I was trying to say is with a 1.2m dish it seems clear I will be above the threshold, with a 1m thrown in any old how below what the receiver can use, but with a careful setup the 1m may just do it, maybe, just.

These figures have no relevance for RX in the real world. When you increase the dish size you are increasing the desired signal in relation to the noise floor, i.e. you are being more selective about the direction that signal is being received from. When you increase the coax length both signal and noise are attenuated by the same amount. The only time the coax length is relevant is when the run is so long that the noise produced internally in the receiver becomes an issue.

Not sure I agree. If the coax has so much loss the signal you want to receive is at a level the receiver cannot filter and tune the signal at then you cannot receive the signal. The receiver has a minimum level of signal it requires to receive the transponder error free, so if you are outside the footprint, the signal is weak when received, and you loose a lot in the conversion (LN and transmission (coax) then the relation to the noise is immaterial if the signal is below the level the receiver can work with.

If you point a dish at the strongest satellite and transponder for your location you would have a large signal/noise ration, but if your run it through 2000m of cable for example... its below what the receiver can work.

 

[Huevos]

Not sure I agree. If the coax has so much loss the signal you want to receive is at a level the receiver cannot filter and tune the signal at then you cannot receive the signal.

You cannot compensate for an undersize dish by using a short (or fat) cable run. Collecting sufficient signal in relation to the noise floor is something that is done at the dish before the signal arrives at the LNB or any of the electronics.

Imagine the signal is rain and the dish is a funnel. If you want to capture a certain amount of rainwater you either need heavy rain (lots of signal) or a big funnel (dish). If the rain isn't heavy enough (weak signal) you will need a bigger funnel or you will never collect enough. The coax is just the pipe that carries the rainwater away after the funnel has collected it. It doesn't matter how big or free flowing that pipe is, if the funnel hasn't collected sufficient rain in the first place.

 

[OldBen]

What I am saying though is 1M is big enough I think, as long as most of the signal gets to the receiver... will be trying it soon anyway and the proof as they say will be in the pudding.

 

[OldBen]

Soon is always a relative term when a builder is involved!

TD110 Dish and possibly patio mount should arrive tomorrow, as should Inverto black Ultra single on way from eBay for testing, and I think I have somewhere to hide dish at ground level at the side of the house as well which is a Brucey bonus. I invested in a satlook lite (in post from Germany) to get best possible alignment and setup, so that should keep me busy one weekend soon! Will do some testing, then invest in a switch if the TD110 works ok with a single LNB.

Slight complication is my technomate has stopped listening to its remote, I suspected the remote, but I think its the box itself that's not receiving IR properly after some testing, so need to find spare cash for that VU+ I have been lusting after as well ;-)

 

[moonbase]

...The switch I have my eye on (emp-centauri)...................

OldBen,

Did you ever get round to installing the EMP-Centauri multiswitch with a Quattro LNB?

I am thinking about replacing a C120 Quad LNB with a C120 Quattro LNB and multiswitch and the EMP-Centauri is one of the options I am looking at for the multiswitch.



Regards
moonbase