My dishes collection

[a33]

What is "clearance distance" ?

'Clearance distance' in the design of an offset dish is the distance between the lowest ray to (the bottom of) the dish, and the focal point, so to say.

I use(d) the distance y-null in the spreadsheet, or distance B to line VF in the picture, of this post:

A

Advice Needed Post in thread 'Famaval dish tweaks'

Feb 7, 2020

That would be John Legon's equation for a parabolic dish.
It uses the depth at the deepest point of the parabola, and gives focal length of the mother prime focus antenna, that is the distance from focus to vertex (center of the PF dish).
When you don't know where the vertex lies, just this formula doesn't bring you much further; you need other calculations as well....



A very good program is Parabola6 by Strannik, using inputs width, height, and depth at the center of the dish.
Downloadable in the first post of this thread: Юстировка офсетных антенн...

• a33

With most offset dish designs, it is about zero, or a small positive number. So that the signal blockage of the LNB is not there, or just minimal.

On a prime focus dish, the distance is of course negative: half the dish width.

Does this make things clear?

Greetz,
A33

 

[AtOM13]

Ok that's clear thanks !
I'm not professional in antenna and I wasn't good in mathematics at school but I like to learn news things.
For dish pointing I'm very patient and persistent, and thanks to Rimants with the modified feedarms I can tune millimeters by millimeters and check SNR in real time if I gain or not. It takes a looooot of time, and unfortunately I haven't so much time

 

[AtOM13]

The blue scalar ring is optimized for the C band on offset dish. The Ku LNB already has its own ring for the Ku band under the red cover.

This feed will be perfect with a good c120 lnb or modified Megasat Diavolo :

Boutique

www.2galli.fr

 

[Beli1910]

Ta vir bo popoln z dobrim LNB-jem C120 ali modificiranim Megasat Diavolo:

Boutique

www.2galli.fr

The Diavlo will be much better than this c120. Personally, I was disappointed with the original c120 transmission.

 

[AtOM13]

43w and 45w locked despite house blocking signal and settings optimized for 25.8e Es'hail 2 !

 

[AtOM13]

Just received the Laminas offset feed ... a real piece of art !

 

[Channel Hopper]

The Laminas catalogue suggests the PO-40 feed is matched to a number of their antennas, with varying offset angles. Are the illumination patterns identical with all of them ?

https://www.laminas.com.pl/cards/po40_cc_eng.pdf

 

[AtOM13]

I made so test with Laminas feedhorn and c120 IBU ... generally 1 dB loss on the whole arc compared to Diavolo and scalar ring.
But fine tuning with this feedhorn is less sensitive.

 

[scopus]

I made so test with Laminas feedhorn and c120 IBU ... generally 1 dB loss on the whole arc compared to Diavolo and scalar ring.
But fine tuning with this feedhorn is less sensitive.

View attachment 163853

I have always found the Channel Master feedhorn with a C120 LNB gave a worse performance on my 1.8 than a standard 40mm LNB.

 

[lovelyperson]

I have always found the Channel Master feedhorn with a C120 LNB gave a worse performance on my 1.8 than a standard 40mm LNB.

Yes, I found that the 'standard' LNB - Megasat Diavolo Twin (at only €14,90) equalled my normally used Inverto C120 Quad flange reception wise.....on 1.8m Marrafa PF............pleasantly surprised! ----consistent nature of our hobby

Details in thread:- Any lnb test reviews lately? post #338.

 

[AtOM13]

I made some tests to gain few degrees to east, just by moving 2 cm on actuator's bracket :




For the moment, I can lock 68.5e and 70.5e more (66e was east limit before ). West limit is now at 37.5w, not really a problem as building block signal over till 40w.

 

[AtOM13]

Signal from Apstar 7 @ 76.5e !
Moving the actuator's bracket 2cm more ( 76.5e to 30w )
Probably the limit of my setup, also limited by trees 50 meters away ,partially blocking the signal with the low elevation required for this sat (4.5°).
Will try this winter when leaves finished to fall ...

 

[AtOM13]

Next step is changing my 18" actuator by a superjack harl3624 . Just put a order on this one :

Worldwide Satellite - Online Store - Super Jack HARL 3624 24 inch Satellite Actuator Motor

I Don't know exactly how many degrees I can gain but 80e to 45w will be perfect for my setup.

 

[AtOM13]

Some tests with Triax 100cm to find west limit.
Telstar 14 @ 63w is the limit here, others western sats doesn't provide lockable beam on Ku band.
Dishpointer.eu, clinometer and some woods are necessary to get 7° inclination for 63w !
So next step now is to find east limit @ 80e with the 150 Laminas but need a 24" actuator before.

 

[AtOM13]

Superjack 24" Installed and settled 80e to 45w.
For the moment limited at 76.5e, because I need to lowered inclination for sat over 70e

 

[AtOM13]

Yesterday, I've made some tests at a neighbor's house which have absolutely nothing to limit signal at kilometers away. Approximately, 80e signal pass just 500m up to a mountain at 1100m and 40km away (2° elevation !). The last eastern satellite reachable from my city. 63w is the west limit here, to much hill blocking signal at west... 143° arc is not so bad after all !

 

[AtOM13]

First winter pass with success, nothing has moved despite 110 kmh wind !
Just a little more green, and spider living in the scalar ring...
Leaves from neighborhood's trees are now too important to lock something after 70.5e




Dish at 80e, east theoretical limit here:




Sorry for the branche, but necessary to pass 72e to 80e

 

[AtOM13]

I bought some weeks ago a brand new Diseqc motor 80e to 80w for 20€.
I will equip my 80cm dish on the roof with it ... unless if I decide to put the Triax 100cm instead

 

[hatters1976]

from where ? did you buy this geant diseck moteck @AtOM13

 

[AtOM13]

I've got two main suppliers: Leboncoin.fr and Rimants
The motor came from Leboncoin.fr