Monoblock LNB + diseqc switch + Zone 1 dish

ant_thomas

Active Member
Hello (again)

For a while I've been trying to get 19.2e and 13.0e on a modern Zone 1 dish (larger type).

Tried a multi LNB setup using 2 quad Sky LNBs and a multi LNB bracket. This had previously worked quite well on a 60cm dish. No such luck on the Zone 1. I was focusing on 19.2 and trying to add the 13.0e as the extra LNB.

Anyway, my patience ran out and I gave up. Now I have bought a Twin Monoblock LNB 6 deg (Inverto IDLB-TWNM20-MNOO6-8PP).

I have a separate dish providing 28.2e, this will stay as a single LNB dish. Because of this I have some diseqc switches.

Previously it was simple:
Diseqc 2.0 switch
1 - 28.2
2 - 19.2
3 - 13.0 (which I couldn't get aligned)

A bit of reading lead me to buying a couple of splitters with DC pass which looked like they would be what I needed to make a monoblock + diseqc switch setup work (I bought these - 2 Way Satellite F-Type F Splitter for Satellite TV and SKY).

Setup is now:
Diseqc 2.0 switch
1 - 28.2
2 - empty
3 - splitter
4 - splitter
Splitter - monoblock

To look at the dish now (looking at the back of the LNB) I have the left feed horn as the main one (is that B?) on 19.2e, with the right one (A?) to provide 13.0e. Unfortunately 13.0e isn't working.

First question, assuming the dish is big enough, aligned etc, should this setup work? (from a cabling/technical point-of-view)
Second, I realise the monoblock LNB is designed for 6 deg on an 80cm dish, therefore is the my dish just too small for it to work?

I can tune to 19.2e very well (good signal etc) using BB (port 4) as the switch setting.
I assume then 13.0e is BA (port 3), but there's nothing there. I've tried changing the LNB skew with no luck.

Any suggestions would be great.
 

grahamlthompson

Distinguished Member
You do know the Monoblock has a built in diseqc switch ?
 

ant_thomas

Active Member
Yes, isn't that why you need a splitter to run it with another diseqc switch? (so I can have 28.2 on a separate dish/LNB and 19.2e/13.0e on the monoblock)

It's very possible I'm not understanding it, but if I have the monoblock attached without a splitter there's no way for me to send the correct command to switch between A/B?
 

grahamlthompson

Distinguished Member
Yes, isn't that why you need a splitter to run it with another diseqc switch? (so I can have 28.2 on a separate dish/LNB and 19.2e/13.0e on the monoblock)

It's very possible I'm not understanding it, but if I have the monoblock attached without a splitter there's no way for me to send the correct command to switch between A/B?

I cannot see how a splitter can possibly work.

I doubt you can easily combine a monoblock and a standard universal lnb on a single tuner.

Monoblock LNB in conjunction with separate switch?

You would need to set up one dish with a pair of offset universal lnbs and the other with one and use a standard diseqc switch.
 
You cannot cascade standard DiSEqC switches (known as "committed" switches) - the monoblock has a committed switch built in). The control data sent will act on both switches. You need to find an "uncommitted" switch (which are not easy to find and cost at least 4 times as much). See here for more info - all about DISEQC switches.

Another alternative solution is to replace the lnb with the adjustable separation type which usually do not have built in switches.
 
I cannot see how a splitter can possibly work.
It will not work

I doubt you can easily combine a monoblock and a standard universal lnb on a single tuner.
It can be done see the link in my previous post
You would need to set up one dish with a pair of offset universal lnbs and the other with one and use a standard diseqc switch.
That is another solution
 

grahamlthompson

Distinguished Member

ant_thomas

Active Member
Just moved the dish and 13.0e is now being picked up on the "A" device. Looks like technically it does work just the dish is too small for the monoblock LNB.
 
If that is the case then 19.2e shouldn't be working for me?
No all that says is that the default position of the monobloc DiSEQc switch is 19.2. Without any signals being received/recognised a DiSEQc switch uses its default option - usually port 1 or A. So your 4 way switch is switching to the monoblock but the monobloc cannot then receive the signals to switch to 13E because the 4 way switch receives the signal first and switches itself to port 2 which is empty. You could try connecting port 2 (instead of 3) on the 4 way switch to the splitter on the monobloc - it may work.
 

ant_thomas

Active Member
I can see why you think that, but...

13E is on A, which would be the default passthrough setting
19.2E is on B, which would require switching and works

After moving the dish a bit 13E works and 19.2E drops off.

I've even covered the 19.2E feedhorn to make sure that's not picking up the 13E.

So to conclude, technically it does work but the dish isn't big enough, shame.

A 3 or 4.3 deg monoblock may be an option.
 

logiciel

Moderator
With one slightly larger dish and three LNBs on a bracket this should be simplicity itself!
 

ant_thomas

Active Member
With one slightly larger dish and three LNBs on a bracket this should be simplicity itself!

You're right, and I've done it before on a larger dish and have all the brackets and LNBs.

But currently I only want to use a smaller more attractive minidish.

I'll probably give a 3 deg monoblock a go, if that can't get both then I'll concede defeat.
 

logiciel

Moderator
A 3 degree monoblock will only get you satellites 3 degrees apart!
 
I'll probably give a 3 deg monoblock a go, if that can't get both then I'll concede defeat.
An adjustable 4 to 12 monoblock would be a far better idea and also get rid of the splitter with its signal loss. With a zone 1 dish and splitter you are going to have little if any "rain fade" signal.
 

ant_thomas

Active Member
That's based on an 80cm dish, the focal point of the reflection is different on a smaller dish.

With a smaller dish the 3/4.3/6 deg separation isn't accurate. Hence why the 6 deg monoblock I currently have won't receive signal from 13e and 19.2e. A lower degree monoblock designed for an 80cm dish may work.
 

ant_thomas

Active Member
An adjustable 4 to 12 monoblock would be a far better idea and also get rid of the splitter with its signal loss. With a zone 1 dish and splitter you are going to have little if any "rain fade" signal.

I stayed away from the adjustable monoblocks because I wanted a twin output and I initially couldn't find one I fancied. Definitely worth considering as another option though.
 

logiciel

Moderator

logiciel

Moderator
Smaller - I think it's 65 cm.
 

ant_thomas

Active Member
Smaller - I think it's 65 cm.

The datasheet quotes 75-85 cm. The distance between the feedhorns is determined by the dish size (and arm length) and degrees required.

I'm sure you've seen plenty of multi LNB setups and it's clear to see that the distance between the LNBs needs to be smaller with a smaller dish.

So a "6 degree" monoblock designed for an 80 cm dish won't offer 6 degrees of separation on a minidish (unfortunately).

But a 4.3 degree or 3 degree designed for 80cm monoblock may offer close to 6 degrees on a minidish.

As an example Inverto make some monoblocks specifically designed for 60cm dishes. They are smaller.

Inverto 4.3 deg for 60cm - width of feedhorns - 9.8cm
Inverto 4.3 deg for 80cm - width of feedhorn - 10.75cm
 

TJT1

Member
The focal length of a zone 1 sky dish is about 240mm. The angular separation of 19.2E and 13 E is not 6.2 degrees, it depends on your location. At my location of about 50N 0E 19.2 is at an az of 156.4° and 13E is at an az of 164.0 degrees, a separation of 7.6 degrees. Separation of LNBs is approx Tan(sat az separation) x focal length (FL) of the dish and produces Tan7.6 x 240 = 32mm, so unless you can get the LNBs as close together as that, your'e on a hiding to nothing regardless of DiSEqC switching etc.
The 6 degrees that are referred to on monoblocks does depend quite a lot on dish size, or more strictly speaking, its FL. For instance the LNB separation calculations of a dish with 500mm focal length for 19.2 and 13E at my locatuion are about Tan7.6 x 500 = 66mm. So you can see that a monoblock designed for 19.2 and 13 with a 500mm focal length dish will have the LNBs spaced twice as far apart as that which is needed on a 240mm FL dish.
How far apart are the LNB centres on the monobloc and work backwards, bearing in mind that it's the focal length of the dish that is the important factor, not its diameter. Loads of stuff on 'tInternet to show how to calculate FL from diameter and depth.

EDIT: Strictly speaking, as the triangle is an isosceles triangle, not a right triangle, the correct calculation is (Tan(az diff / 2) x FL) x2. but at these small angles it makes hardly any difference to the result (about 0.08mm on a 240FL dish).
 
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ant_thomas

Active Member
Thanks for the great info.

In my case it is 7.3 degrees which comes to 30.7 mm (so pretty much the same as you).

A 3 degree at 80cm monoblock might even be too large, worth a try though (next step, slim LNBs)
 

logiciel

Moderator
All OK - all I know is that mine works on the small dish.:)
 

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