Advice needed please

[Trust]

Ok will do and thanks

Right, I think this could be the problem, with the C band LNB sitting above your Ku LNB you will need to lift up the dish to bring the C Band into focus, so go to 19E ku then nudge the dish a little to the east, then lift the dish upwards with you elevation jack which will then bring the C Band LNB into focus. i had the same arrangement on my Channel Master 1.8 before I had the changer.

To see howmuch the elevation must rise , tried that once with 2 Ku lnb's with 10 cm centerline difference at my 1.2 CM
Have to adjust the dish elevation ± 7º higher

 

[John]

Waited untill late afternoon before posting my findings just incase @gap30 had managed to solve his Cband problem.
I don't live too far away from gap30 so share pretty much the same of the footprint from 20°E & 5°W so thought i would put my spare Zinwell on my 1.2m CM test rig. After removing the top half of the Ku lnb holder the Zinwell sits in it and ty-rapped - - carry on to bottom of pics to pick up the sentance again ?? but is about 20mm higher than true focus.
The two samples shown were easily locked. The conical scalar was tried on and off just for reference and needs to be on for maximum performance and is fairly critical to within +/- 5mm to it's positioning depending on type and dish size.
As others have said, 5°W is the easiest catch.
A few pics of results attached.
* I would seriously recommend a £5 sat meter with an analogue type needle display as this will get you into the ball park far quicker.
.............................................................................................................................................................................................................................................................................................................................................................................................

 

[RimaNTSS]

@John To get C-band LNB in focus you have to make something like this- height adjustable LNB-holder.

 

[gap30]

Nice work John!! might go back up tomorrow, have not bothered the last few days

Thinking about putting the rail back on and having the lnb side on again

 

[John]

Nice work John!! might go back up tomorrow, have not bothered the last few days

Thinking about putting the rail back on and having the lnb side on again

Ok, good luck with it. Although it's still very cold, at least the rain has stopped and it's been very sunny down here today BUT- still very cold.
I thought i would share the pics and info for you just to show that even on a temp lash-up with a 1.2m and a ty-rapped on Zinwell that the signals are there so with your 1.5Gibby the same signals should be available and a bit stronger.

 

[gap30]

Cheers trying not to be annoying now, this has dragged on far too long need some nice pics to post up of findings....

 

[moonbase]

...Thinking about putting the rail back on and having the lnb side on again

Have you tried for C band signals with the C band LNB at the main focal point rather than to the side or above the Ku band LNB?
Having the LNB at the main focal point of the dish might increase the chance of locking some signals?

 

[gap30]

Waited untill late afternoon before posting my findings just incase @gap30 had managed to solve his Cband problem.
I don't live too far away from gap30 so share pretty much the same of the footprint from 20°E & 5°W so thought i would put my spare Zinwell on my 1.2m CM test rig. After removing the top half of the Ku lnb holder the Zinwell sits in it and ty-rapped - - carry on to bottom of pics to pick up the sentance again ??View attachment 113575View attachment 113578View attachment 113582View attachment 113583 but is about 20mm higher than true focus.
The two samples shown were easily locked. The conical scalar was tried on and off just for reference and needs to be on for maximum performance and is fairly critical to within +/- 5mm to it's positioning depending on type and dish size.
As others have said, 5°W is the easiest catch.
A few pics of results attached.
* I would seriously recommend a £5 sat meter with an analogue type needle display as this will get you into the ball park far quicker.
.............................................................................................................................................................................................................................................................................................................................................................................................

Just tried this method on my old 1.2m channel master which my father in law is now using

20e 3975 - 40% signal quality
5e 3173 - 70% signal quality

This was tie wrapped and in the pi$$ing down rain and the lnb was in main focal position

I did not realise just how much the scaler ring could affect it ie move it a couple of mm's and signal lost

Bear in mind this dish is low level and very easy to work on - not on a roof

Ok so I am not going to jump off the roof now, some progress made

 

[nelson_b]

Pleased you got a result - gap30 -
Getting the best out of C band can be quite fickle with smaller dishes ...
forward/back position of the - l.n.b. body - scalar position - and in/out positioning of the plate all need to be at the best spot ..
And that spot may be somewhat different on your other dish ........ it can take ages to get maximum signal sometimes ... and experimentation with non standard plates can bring more improvement too ....
All very time consuming mind

 

[Channel Hopper]

Pleased you got a result - gap30 -
Getting the best out of C band can be quite fickle with smaller dishes ...
forward/back position of the - l.n.b. body - scalar position - and in/out positioning of the plate all need to be at the best spot ..

With an offset dish you are always at the mercy of the manufacturer and /or the 'official' importer to give true figures on the geometry. With a prime focus dish all measurements are to hand to work out the sweet spot.

 

[moonbase]

gap30,

Well done, your preseverance has paid off.

Its just my own obeservation, with a 1.5m prime focus dish I found that the scalar position was not that critical when testing signals on 40.5W. Also, the absence of the scalar only reduced the signal level by a few percent or fractions of a db. It might be the case that a smaller offset focus dish needs more accuracy with the scalar.

When you get back to trying for C band on your Gibertini 1.5m dish you might find the location of the scalar to be less critical, however, that is just a guess? Personally, I would try for a C band signal on youe Gibertini 1.5m dish with the LNB at the main focal point first, rather than above or to the side of the main focal point.


Rgds

 

[a33]

With an offset dish you are always at the mercy of the manufacturer and /or the 'official' importer to give true figures on the geometry. With a prime focus dish all measurements are to hand to work out the sweet spot.

Well, it is true that the calculations for an offset dish are more complicated (needing goniometrics!) than for a prime focus dish, but you can also do them yourself.
I'm working on a calculator needing only three distances: hight of dish, distance from top of dish to deepest point of the dish, and distance from deepest point to bottom of dish (thus forming a triangle with distances).
You can calculate everything from that, thanks to the special characteristics of parabolics: offset angle, f/D, focal point position, G-spot, effective focal distance, etc...

The (russian/ukrainian?) program Parabola6 by Strannik does the same, using also only three distances, but 2 different ones as compared to my method: height and width of the dish, and depth at precisely the middle of the dish.
I think the measuring error of measuring depth is relatively greater than measuring the longer distances. That is why I prefer my method. :-)
Stranniks method could easily be modified to using two measurements instead of depth, though, with the same effect.

Don't trust the Parabola2 programm (wifi-part for offset dishes) however!
It (pre-)assumes bottom of dish at vertex of mother-PFdish, so if a dish doesn't have the bottom at exactly vertex (and I haven't seen a dish where that was proven to be exactly the case) a calculating error is baked in. The programm doesn't mention this assumption anywhere; on the contrary, it states the assumption as a (highly incorrect) conclusion... :-((

greetz,
A33

 

[Channel Hopper]

Well, it is true that the calculations for an offset dish are more complicated (needing goniometrics!) than for a prime focus dish, but you can also do them yourself.
I'm working on a calculator needing only three distances: hight of dish, distance from top of dish to deepest point of the dish, and distance from deepest point to bottom of dish (thus forming a triangle with distances).
You can calculate everything from that, thanks to the special characteristics of parabolics: offset angle, f/D, focal point position, G-spot, effective focal distance, etc...

The (russian/ukrainian?) program Parabola6 by Strannik does the same, using also only three distances, but 2 different ones as compared to my method: height and width of the dish, and depth at precisely the middle of the dish.
I think the measuring error of measuring depth is relatively greater than measuring the longer distances. That is why I prefer my method. :-)
Stranniks method could easily be modified to using two measurements instead of depth, though, with the same effect.

Don't trust the Parabola2 programm (wifi-part for offset dishes) however!
It (pre-)assumes bottom of dish at vertex of mother-PFdish, so if a dish doesn't have the bottom at exactly vertex (and I haven't seen a dish where that was proven to be exactly the case) a calculating error is baked in. The programm doesn't mention this assumption anywhere; on the contrary, it states the assumption as a (highly incorrect) conclusion... :-((

greetz,
A33

Good luck trying that on a Zone 1/2 dish

 

[a33]

Good luck trying that on a Zone 1/2 dish

Goofd luck trying what?

Trying this? :

only three distances: hight of dish, distance from top of dish to deepest point of the dish, and distance from deepest point to bottom of dish

The advantage of this method being it works also with non-flat-rim dishes and even with multifeed dishes (though these aren't totally paraboloid, but parabolical/circular).
If it weren't for that problem, Parabola6 would suffice, and another calculator wasn't usefull...

Greetz,
A33

 

[RimaNTSS]

This is another program for calculating of the offset dishes. It has more or less same principle as @a33 said. There are many measurements should be done after 10cm on the surface of the dish, but all of the along the vertical line.

 

[a33]

I'm working on a calculator needing only three distances: hight of dish, distance from top of dish to deepest point of the dish, and distance from deepest point to bottom of dish (thus forming a triangle with distances).
You can calculate everything from that, thanks to the special characteristics of parabolics: offset angle, f/D, focal point position, G-spot, effective focal distance, etc...

BTW I've got the mathematics of this calculator as good as finished now.

So if anyone with a zone1/2 dish wants to know these other specs of the dish, I can do the calculations.

Just post the three mentioned distances as precise as possible: hight of dish, distance from top of dish to deepest point of the dish, and distance from deepest point to bottom of dish; and I'll post the results.

Greetz,
A33

Edit, @Mods: Why don't the posts of this thread show in the "your content" part of my profile? Has this thread been banned from that database?

 

[RimaNTSS]

@a33 Finding the exact position of the deepest point of the dish is also not so easy task..... IMHO from my experience.

 

[a33]

No it's not. But what easy alternative do you have with non-flat-face dishes, to do the calculations?

You can use the marble, in a lying dish. Or a drop of water.

greetz,
A33

 

[RimaNTSS]

Not easy task does not mean impossible . Measuring precise depth at the very middle of the dish is also not so easy, but possible. Show your program, so users can try it.

 

[a33]

In due time!
I'm still working on some parts...

Greet,
A33