bignick
Specialist Contributor
- Joined
- Feb 13, 2005
- Messages
- 336
- Reaction score
- 0
- Points
- 16
- Age
- 56
- My Satellite Setup
- Back in the UK and missing Cyprus!!!
- My Location
- Aylesbury
Orthoclipse said:Roughly what difference is there in performance with the bare dish vs dish + petals?
Do you need to change the F/D setting on the feedhorn when you add the petals?
deepbluesky said:Nice setup you've got there bignick.
Isn't a 1.5m offset too small to have all frequencies of Astra 1G/H/KR without any breakups ?
Orthoclipse said:If focal point is the same, and diameter goes up, does not F/D decrease? Or am I missing something?
deepbluesky said:I see. I was asking since even in Rodos or Eastern Kriti 1.80m are recommended.
Thanks for your interest.
patmos said:Bignick Please can you give the height of the post(pedestal) for this antenna. i will get a 3.6m dish to point to PAS10 /63deg elevation. it will be fix. I am trying to use a short a pedestal(on roof top) as possible and at the same time being able to access the lnb when in it's lowest position. thanks
No sir I am in Mauritius . this is a fringe area for PAS 10 KU. Situation is almost similar to Cyprus case for Astra. I now use a 1.2 m offset but with occasional break. i cannot get a 1.8m offset here. my friend got a 3.4m( i think) in an auction and would give it to me. I will go to fetch the dish this week. This dish has a 7dB gain over my 1.2m. I am now refurbishing a 12 foot mesh for PAS 10 C and other hunting.deepbluesky said:Sorry but why are you going to use such a big dish for 68.5E ? As far as i know 1.80m is sufficient for IS10 (PAS10) C-Band in Cyprus.
By the way, the elevation is roughly 35°.
Orthoclipse said:@bignick - I have looked through some old books I have on satellite reception and I can only see f/D ratio being focal length divided by diameter.
If you add the panels to the dish, and the focal length stays the same, the f/D ratio must decrease.
Famaval list the focal length as 93cm. So for 230cm, f/D is 93/230 = .404 and for 310, f/D = 93/310 = 0.3.
This is the same figure quoted on the famaval website:
h**p://www.famaval.pt/en/tiki-index.php?page=antenas_310
The other way to think about it - if the focal length stays the same but the diameter increases, you need a wider illumination angle to cover all the surface of this dish. The illumination angle increases as f/D decreases.