• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

feedhorn confusion

Messages
8
Likes
0
My Satellite Setup
dm800hd se
My Location
S.E. England
#1
I'm using a C120 LNB with an Invacom ADF-120 adjustable feedhorn.

The datasheet. for the feedhorn states it has an adjustable beam width
F/D of 0.32 to 0.43. Now, the calculator here tells me that my 2.4m dish
has a F/D of 0.38, OK so far. There are 2 graphs on the datasheet.
From the first one, I can see that for a F/D of 0.38, I need to screw the
feedhorn in for a 4mm protrusion. (I guess this means the thread is
protruding 4mm proud of the corrugations).

The problem I have is with the second graph. The "Y" axis has no units.
The 4mm protrusion from graph 1 seems to correspond to "120" on the
second graph - but I don't know what it's 120 of. Can anyone shed any
light on what this graph signifies?

Thanks,
Pete
 

Low Profile

Regular Member
Messages
364
Likes
0
My Satellite Setup
DM800HD, DM7000 80GB HD with Asus WL330 wifi + 2GB usb drive, Skystar2.3, 2.2m Kinhuge Dish with Inverto LNB and Invacom ADF-120 feedhorn. Pace 1.3.25 and 80cm for Sky.
My Location
Lot, Dordogne, Correze border.
#2
Looks like beam width (in degrees).
 
Messages
8
Likes
0
My Satellite Setup
dm800hd se
My Location
S.E. England
#3
Ah ha! yes, that sounds right - thanks

It does mean that my dish os too big, as the feedhorn beamwidth
is calculated to be 133 degrees - so the feedhorn is only "seeing"
2.1 metres of the dish. :-(
 
Messages
8
Likes
0
My Satellite Setup
TM 5200 USB
My Location
Spain
#4
pete_l said:
I'm using a C120 LNB with an Invacom ADF-120 adjustable feedhorn.

The _http://www.invacom.com/documents/AdjustableFeedHorn.pdf datasheet . for the feedhorn states it has an adjustable beam width
F/D of 0.32 to 0.43. Now, the calculator _http://www.satellite-calculations.com/Satellite/reflector.htm tells me that my 2.4m dish
has a F/D of 0.38, OK so far. There are 2 graphs on the datasheet.
From the first one, I can see that for a F/D of 0.38, I need to screw the
feedhorn in for a 4mm protrusion. (I guess this means the thread is
protruding 4mm proud of the corrugations).

The problem I have is with the second graph. The "Y" axis has no units.
The 4mm protrusion from graph 1 seems to correspond to "120" on the
second graph - but I don't know what it's 120 of. Can anyone shed any
light on what this graph signifies?

Thanks,
Pete
Sorry if this looks like a stupid question.
How do you adjust the feedhorn to get the required protrusion? Which bit do you screw in/out?
I've looked but cannot figure it out! Dumb ass.