Pictures of Members' Systems

dave branson said:
Likvid
I checked with IRTE here in Italy,they say it is not possible to extend the 1.8
dish to 2.4.
Regards
Click to expand...

Sorry, i mixed the companies toghether, i know Alcoa which made similar dishes to IRTE did have extension panels, anyone know if Alcoa still manufactures the old aluminium dishes?

They were very similar to IRTE.

IRTE did have that for the 1.5m dish only to make it 2.0m.
 
dave branson said:
Thanks Likvid
I just checked on the IRTE site for the spec,it states that the F/D Ratio is
0.41 can you tell me what that means.
Click to expand...

That's the Focal length To Diameter Of the Dish Ratio.

The value tells you have deep or shallow your dish is and how the feed will illuminate the dish.

There are pros and cons to shallow dishes, they achieve theoretically higher gain than a deep dish, however they have a tendency to pick up more noise than a deep dish do.

Deep dishes have typically approx F/D Ratio of 0.25 to 0.30, they pick up less noise, however it is extremely difficult to make efficient feeds at this ratio, Seavey Engineering have feeds at this ratio and they work very good to my experience.

I used to install the american Winegard KU-band mesh dishes in the late 80's which came in 1.8, 2,4, 3.1 meter with F/D of 0.287 which are pretty deep.

My experience with those dishes was that they performed much better than equivalent dishes with higher F/D ratios like 0.40 or similar, they were the best dishes i ever had my hands on for consumer use if properly installed with Seavey feed.

The feed means everything so it can illuminate the dish properly.
 
Likvid said:
Sorry, i mixed the companies toghether, i know Alcoa which made similar dishes to IRTE did have extension panels, anyone know if Alcoa still manufactures the old aluminium dishes?

They were very similar to IRTE.

IRTE did have that for the 1.5m dish only to make it 2.0m.
Click to expand...

Thanks Likvid
Would appreciate if you could explain what the F/D Ratio 0.41 means.
 
Likvid said:
That's the Focal length To Diameter Of the Dish Ratio.

The value tells you have deep or shallow your dish is and how the feed will illuminate the dish.

There are pros and cons to shallow dishes, they achieve theoretically higher gain than a deep dish, however they have a tendency to pick up more noise than a deep dish do.

Deep dishes have typically approx F/D Ratio of 0.25 to 0.30, they pick up less noise, however it is extremely difficult to make efficient feeds at this ratio, Seavey Engineering have feeds at this ratio and they work very good to my experience.

I used to install the american Winegard KU-band mesh dishes in the late 80's which came in 1.8, 2,4, 3.1 meter with F/D of 0.287 which are pretty deep.

My experience with those dishes was that they performed much better than equivalent dishes with higher F/D ratios like 0.40 or similar, they were the best dishes i ever had my hands on for consumer use if properly installed with Seavey feed.

The feed means everything so it can illuminate the dish properly.
Click to expand...

So if i calculate the focal length to the feed,it would be
Radius squared=8100 depth 41x 4 = 164 so,8100/164=49cm would this be correct? previously i assumed that the dish was 30 cm deep,which gave a focal length of 67.5 cm,
 
dave branson said:
So if i calculate the focal length to the feed,it would be
Radius squared=8100 depth 41x 4 = 164 so,8100/164=49cm would this be correct? previously i assumed that the dish was 30 cm deep,which gave a focal length of 67.5 cm,
Click to expand...

Ok here we go, read and enjoy.

Formulas for calculating focal distance and f/D ratios

To calculate the focal distance, you have to measure the diameter (D) and the depth (d) of the dish. Measurements should be in like units (you can't use feet for the diameter and inches for depth). For the example, we will say we have a dish that is 120 inches in diameter (D) and 18 inches deep (d).

focal distance (f) equals the diameter squared (D x D) divided by 16 times the depth (16 x d) or :

D x D = 120 x 120 = 14400
16 x d = 16 x 18 = 288
D x D/16 x d = 14400/288 = 50

focal distance f = 50 inches

After you have calculated the focal distance (f), you can use that figure to calculate the f/D ratio of your dish. In this case, using the same diameter (D) = 120; and the calculated focal distance (f) = 50

f / D = 50 / 120 = .416
f /D = .416 which you would round up to give you a setting of .42

The list below shows how far the throat is out from the scalar rings for different f/D settings.
EXAMPLE: A dish with a .42 f/D will have the throat about flush with the rings.

Inches -- f/D
.12 ------ .42
.32 ------ .40
.52 ------ .38
.72 ------ .36
.92 ------ .34
1.12 ---- .32
 
Likvid said:
Ok here we go, read and enjoy.

Formulas for calculating focal distance and f/D ratios

To calculate the focal distance, you have to measure the diameter (D) and the depth (d) of the dish. Measurements should be in like units (you can't use feet for the diameter and inches for depth). For the example, we will say we have a dish that is 120 inches in diameter (D) and 18 inches deep (d).

focal distance (f) equals the diameter squared (D x D) divided by 16 times the depth (16 x d) or :

D x D = 120 x 120 = 14400
16 x d = 16 x 18 = 288
D x D/16 x d = 14400/288 = 50

focal distance f = 50 inches

After you have calculated the focal distance (f), you can use that figure to calculate the f/D ratio of your dish. In this case, using the same diameter (D) = 120; and the calculated focal distance (f) = 50

f / D = 50 / 120 = .416
f /D = .416 which you would round up to give you a setting of .42

The list below shows how far the throat is out from the scalar rings for different f/D settings.
EXAMPLE: A dish with a .42 f/D will have the throat about flush with the rings.

Inches -- f/D
.12 ------ .42
.32 ------ .40
.52 ------ .38
.72 ------ .36
.92 ------ .34
1.12 ---- .32
Click to expand...


Likvid,your something else,thanks very much,its a pleasure to communicate
with such an informative and helpful person.
Wonder whats happening in Sicily these days.
 
There is a dish we use over here,Famaval which is 2.4m and also comes with 8 extension panels which bring it to 3.1m.They improve the signal a lot but would be better if it were a one piece dish because if the panels are not completely flush all the way round it affects the gain.
Likvid,if you calculate the focal length all in inches then isn't the resulting f/d ratio also in inches? Eg an f/d ratio of .42 should mean(as a decimal) just under half an inch(where .5 would be half inch)does that make sense?
 
zorba said:
There is a dish we use over here,Famaval which is 2.4m and also comes with 8 extension panels which bring it to 3.1m.They improve the signal a lot but would be better if it were a one piece dish because if the panels are not completely flush all the way round it affects the gain.
Likvid,if you calculate the focal length all in inches then isn't the resulting f/d ratio also in inches? Eg an f/d ratio of .42 should mean(as a decimal) just under half an inch(where .5 would be half inch)does that make sense?
Click to expand...
F/D is just a constant explaining the Focal length To Diameter Of the Dish Ratio, does not have anything to do with length in inches or mm.
 
Some women say size don't matter................(hope there's a picture here)
 
zorba said:
Some women say size don't matter................(hope there's a picture here)
Click to expand...
WOW a 3.8 Mtre Dish and living in Cyprus......
What else does a man want, other than a nice woman by his side...??!!!
Very nice..... I lived for several years in George Fatilotis street in Limissol in the early 1960's.

Regards John
 
Don't know that street,this dish is just out of Limasol in Korfi village.No problems with BBC or ITV though.
 
Likvid said:
F/D is just a constant explaining the Focal length To Diameter Of the Dish Ratio, does not have anything to do with length in inches or mm.
Click to expand...

Likvid
Could you recommend a feedhorn, to be used with my IRTE dish.
and where i can purchase it from.
 
dave branson said:
Likvid
Could you recommend a feedhorn, to be used with my IRTE dish.
and where i can purchase it from.
Click to expand...
IRTE make their own feeds for their dishes so i would recommend their own feed, contact them for quote.
 
dave branson said:
Likvid
Could you recommend a feedhorn, to be used with my IRTE dish.
and where i can purchase it from.
Click to expand...
What kind of feed do you have now?
 
Here's my new 80cm digiquest dish with Disesq motor mounted onto an ali pole in the front garden, thankfully I have high conifers to the front and back of the dish (good wind shelter and nieghbour friendly) but completely clear skies to the front with just open fields East to West.
Cracking sunrises & sunsets !! :D
 
A cosmetic update on my System:


it was a complicated mathematical exercise

30 West + TG = :)
30 West + Tree = 0
Stihl + TG = :-righton
Tree = Birch = Dirt
Wife - Tree = :P - As: House - (Tree*Birch) = less dirt
Therefore, under very strange & freak circumstances

Wife + 30 West = :)

so

Tree/Stihl+TG = TG +30 West

Also, disturbingly, as a by product of this came the theoretical conclusion

Wife + Sihl = (TG + :( ) * 1000

But that's another story :D

So now 30 West to 42 East all going!
 
Rod Hulls Aerial said:
Here's my new 80cm digiquest dish with Disesq motor mounted onto an ali pole in the front garden, thankfully I have high conifers to the front and back of the dish (good wind shelter and nieghbour friendly) but completely clear skies to the front with just open fields East to West.
Cracking sunrises & sunsets !! :D
Click to expand...
How you gonna mow that bit of grass now then? :confused:
 
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