Pictures of Members' Systems

Nice setup Dave.

This is my set up in Florence,I also have a 1meter wth DiSqe Motor fixed on the roof.
Dont seem to be able to attach the pictures

Is that a 1.8m IRTE dish or ALCOA dish?

Hi Likvid
Just measured it, it actually its 1.910,does this make a difference to the performance?

The dish got lower gain than a solid 1.8m dish due to the fact the the IRTE is made of petals, the lower gain is not much taking notice to.

IRTE makes good dishes, petalized dishes have their positive sides as well, easier to transport and repairing if something happens.

It's a good dish no doubt, been with us a while now since 15 years back or so, got good track record for quality.

You can extend the dish you have by buying exension panels from IRTE to make it 2.4m if you are in need of more signal.

Likvid
I checked with IRTE here in Italy,they say it is not possible to extend the 1.8
dish to 2.4.
Regards

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.

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.

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.

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,

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

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?

Some women say size don't matter................(hope there's a picture here)

Here is another nice picture....

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.