Tests of 120cm antennas

[jase1]

Where's the lnb pointing now?

 

[RimaNTSS]

Where's the lnb pointing now?

Where to point is very important, but also not less important from where to point . So, for CM120 LNB's Phase center should be located exactly in antenna's Focal point. And antenna's Focal point is 1220mm from upper point of the working area and 720mm from lover part of the working area of the dish. From that Focal point LNB should be aiming 791mm down from upper point of the working area.

 

[RimaNTSS]

In addition. angle between direction of LNB and "face" of the dish should be 72,3* (I did not checked it yet). Also "face" leaning, depending on the chosen satellite should be equal to "Direction to satellite" - "Antenna's offset angle". Direction towards chosen satellite could be taken from different sources like lyngsat.com and antenna's offset angle we all know from "books" and also calculations, and it is 22,6*.
For example, if at your location 7*W has elevation 30,6* than the leaning of dish face should be (30,6*-22,6*), yes, exactly 8*!

 

[samoloko]

thank you for test
I have said months ago that CM performance compared to triax Is not Impressive
would you please try with other lnb point - for example take down the mount lnb point with 5 - 12 mm and slightly to decrease 72 angle to compensate pointing to G spot

 

[RimaNTSS]

with other lnb point - for example take down the mount lnb point with 5 - 12 mm

That is exactly what has been done on original CM LNB holder- it holds LNB some 15-20mm lower than needed.
I do not have possibility (yet) to measure angle FG-AB, but will be able to do it by the end of month, with the precision up to 0,1*.

 

[samoloko]

ok
If you want you can try to go In other direction - slightly lower In height and with other lnb angle as I said
If you said why - because many offset dishes visually have that lnb point to name Gibby Is one like that

 

[RimaNTSS]

If I correctly understand, you want me to put LNB's Phase center approximately where red dot is? In fact, that was position of LNB 2 days ago, when I made first test and got results slightly better than with original LNB holder. Of course, when LNB is positioned not in antenna's focus, performance will be worse, do we really need more experiments to prove that? It is like to put LNB in multifeed position, but in this case multifeed is vertical not horizontal as we usually do. After making vertical multifeed antenna's elevation should be adjusted to get maximum possible signal levels, and that is why CM 120 with offset angle 22,6* leaning not enough. And all this is result from LNB placement not in antenna's focus.

 

[samoloko]

yes - red dot
Is red dot lower In vertical than original position
we don't know practical antenna focus just theoretical

 

[RimaNTSS]

Is red dot lower In vertical than original position ?

I think original CM LNB holder keeps LNB even more down than i marked by red dot. And, in addition it keeps LNB pointed to the wrong place on antenna's surface - to the very middle of it, which is very wrong .

we don't know practical antenna focus just theoretical

Practical antenna focus should be = to theoretical one. Otherwise we will not get best performance possible.

 

[samoloko]

Rima
do you plan to add subreflector

 

[RimaNTSS]

do you plan to add subreflector

Of course I am. It is well known that gregory-systems work better than simple offset ones, why should we hesitate to make our systems work better?!

 

[samoloko]

where would you find a subreflector to match CM dish

 

[RimaNTSS]

where would you find a subreflector to match CM dish

I do not think i will be able to manufacture one, so will take original from Fibo antenna.

 

[samoloko]

are fibo 90 and 120 subreflectors same

 

[RimaNTSS]

Nope, there are several variations. And do not forget about Fibo 55.

 

[RimaNTSS]

Seems that my tests (post #260) not fully valid. I mean results are not the best possible, as I have LNB placed in horizontal multifeed position. Yesterday, when it was Sun outage I took picture of antenna tuned to 4,8*E. At that time distance from bottom part of shadow (small red) to bottom feedarm was ~14cm, but, at the same time distance from another shadow (small green) to central feedarm was only ~13cm. And then I measured distances from antenna's sides to the LNB (long red and green lines) and one of them was longer than other one for about 1cm. Of course, that happened because of mine self-made LNB holder, which is apparently not perfect and therefore does not hold LNB in proper position but in multifeed position. That also means that I should work little bit more to get LNB in antenna's focus. And somehow I feel that after doing so, results should be even better. We'll see.

 

[Trust]

Trust - this is really pioneering work what you are doing. What could be interesting for Laminas users is the extent of difference in signal when you us the new LNB holder . I am the owner of the older version of 120 and I have also replaced the 2 tubes with 6 mm Inox treaded rods (see the pictures)..it would be interesting using your home made LNB holder to see the possible improvement of the signal.

Humaxboy

Here it is .

 

[RimaNTSS]

Repeated CM120 tests today. 2 measurements: with original CM LNB holder and with self-made one.
How I did it: installed original CM LNB holder and tuned antenna and LNB as perfectly as I could to 7,3*W , then scanned all 44 available transponders. Then, within 15-25 minutes (weather conditions did not change) installed self-made LNB holder, tuned antenna and LNB again and scanned same 44 transponders. Data analysis shows that I got increase of performance at about 5%, which is not bad IMHO.
Question: Can anybody of you receive 11661 V 27500 2/3, if yes, what signal level is?

 

[Tururu]

I'm not a good reference, but hey, these are the levels from Madrid to 94cm, IBU of 0.2dB and 40 meters low loss cable (28dB/100m).
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No soy una buena referencia, pero bueno, estos son los niveles desde Madrid con 94cm, IBU de 0.2dB y 40 metros de cable de bajas perdidas (28dB/100m).

 

[RimaNTSS]

I'm not a good reference, but hey, these are the levels from Madrid to 94cm, IBU of 0.2dB and 40 meters low loss cable (28dB/100m).

Why not good? Great- we see that SatBeams shows more or less reliable data. But it does not show that 7,3*W also receivable more North, even in UK and Scandinavia.
Tururu, could you show pictures of your 94cm antenna, please?