Dish extension panels

scooter123 · 22-02-2008

I have what I believe to be An IRTE 1.5 prime focus dish that I have been using for many years.
I seem to remember reading somewhere that extension pannels where available for this dish to increse it to a 1.8 or 2.4
The question is am I remembering corectly or is it just wishfull thinking.
If these do exist does anyone know where I might find them?

**Topper** · 22-02-2008

Well it begs the question why?

What can you not currently receive that you think you should be able to? you see I come from the "if it ain't broke dont fix it" camp

renibacterium · 22-02-2008

I have an IRTE 1.5m dish and an IRTE 2.0m dish. The later is like the 1.5m but has a set of 6 extension petals which bring it up to 2.0m. The stand alone 1.5m dish does not have the same outer edge to it as the inner 1.5m dish integral to the 2.0m ( which has pre-drill holes to add on the petals). Have a look at the IRTE web site under consumer satellite dishes and you will see the two dishes mentioned ( along with others). It may be possible to add a set of these petals if IRTE are willing to make them available. But beware these are expensive dishes. I dealt directly with IRTE UK. I would contact them. They are very helpful. Good luck.

As regards what it can get you. It gets me 7W Hor channels, but I am in SW Eng. Unlikely to make a difference in the Midlands, going from 1.5m to 2.0m with respect to 7W hor channels..

scooter123 · 22-02-2008

Im looking to fit a combined C/Ku LNB setup & was thinking that the increse in dish size would componsate for the loss caused by the feed casting a bigger shadow on the dish.
Besides doesnt bigger usualy mean better in regard to dish size

**Topper** · 22-02-2008

So what C-band transmisssions will you go for as I think there is not much to be had in our arc! and your location appears to be Derbyshire

As for the shadow, the difference will be minimal but yes for C band the bigger the better, you may however find you are swamping your stb with signal when viewing ku band transmissions. It depends on the type of stb

renibacterium · 22-02-2008

I have just bought a BSC 621-2 C-band & Ku band combined LNB to try in my 2.0m dish. Have contacted IRTE UK about how to attach this as the supplied scalar ring with the said LNB presents a tricky attachment. Will let you know how I get on. By the way, this LNB only requires one coaxial cable as there is a diseqC switch to turn between the C & Ku bands.

scooter123 · 22-02-2008

Originally Posted by renibacterium

I have an IRTE 1.5m dish and an IRTE 2.0m dish. The later is like the 1.5m but has a set of 6 extension petals which bring it up to 2.0m. The stand alone 1.5m dish does not have the same outer edge to it as the inner 1.5m dish integral to the 2.0m ( which has pre-drill holes to add on the petals). Have a look at the IRTE web site under consumer satellite dishes and you will see the two dishes mentioned ( along with others). It may be possible to add a set of these petals if IRTE are willing to make them available. But beware these are expensive dishes. I dealt directly with IRTE UK. I would contact them. They are very helpful. Good luck.

As regards what it can get you. It gets me 7W Hor channels, but I am in SW Eng. Unlikely to make a difference in the Midlands, going from 1.5m to 2.0m with respect to 7W hor channels..

Just been out to look at the dish and there are four evenly spaced holes on the rim.
The rim is quite flat and is 31mm deep

scooter123 · 22-02-2008

Originally Posted by Topper

So what C-band transmisssions will you go for as I think there is not much to be had in our arc! and your location appears to be Derbyshire

As for the shadow, the difference will be minimal but yes for C band the bigger the better, you may however find you are swamping your stb with signal when viewing ku band transmissions. It depends on the type of stb

There is no particular signal i'm looking to recieve. I just enjoy the challenge. Once I can recieve a satellite or signal I usualy find myself looking for the next one.
I used to recieve C band in the analouge days but I never had a combined C/Ku feed and swapping the feeds was a pain.
Recievers I use are Echostar 3600, Vantage & Clarke Tech HD5000C

renibacterium · 22-02-2008

scooter123

You would also need longer poles for the tripod feed holder

**Topper** · 22-02-2008

Originally Posted by scooter123

There is no particular signal i'm looking to recieve. I just enjoy the challenge. Once I can recieve a satellite or signal I usualy find myself looking for the next one.
I used to recieve C band in the analouge days but I never had a combined C/Ku feed and swapping the feeds was a pain.
Recievers I use are Echostar 3600, Vantage & Clarke Tech HD5000C

Very nice too! good luck with the hunting

**Channel Hopper** · 22-02-2008

Originally Posted by Topper

So what C-band transmisssions will you go for as I think there is not much to be had in our arc! and your location appears to be Derbyshire

There is plenty up there, as long as you can receive the majority of the arc.

**Topper** · 23-02-2008

Originally Posted by Channel Hopper

There is plenty up there, as long as you can receive the majority of the arc.

Very true CH but it is another set of equipment (for me anyhow) and for IMHO limited results

**tesla** · 24-02-2008

Originally Posted by renibacterium

scooter123

You would also need longer poles for the tripod feed holder

Exactly. If you increase the diameter of the antenna the focal length will become bigger. If you keep the old poles then the reception will get ruined. The antenna will focus in a point behind the feedhorn and you will receive no signal at all.

You need to calculate the new focal length.

**rolfw** · 24-02-2008

Perhaps being a bit dense here, but if an existing dish focuses at a certain point, surely the addition of panels to it, will not change the focus of the original part of the dish. I would have thought that extension panels would be designed to focus on the original point.

**tesla** · 24-02-2008

Originally Posted by rolfw

Perhaps being a bit dense here, but if an existing dish focuses at a certain point, surely the addition of panels to it, will not change the focus of the original part of the dish.

No my friend. Take a look at dishes with different diameter? Do their poles have the same length? Absolutely NO!!!!

1m dish: small poles
2m dish: longer poles
7m dish: much longer poles.

The focal point gets far away as diameter increases.

**rolfw** · 24-02-2008

I agree with you when relating that logic to standard dishes, but you are not comparing like with like.

If the original 1.5m dish has a certain focal length and focal point, how can adding extra panels on to it, change the focal point of the original part of the dish?

**Topper** · 24-02-2008

I have to agree with your logic there Rolf, the original geometry of the dish remains the same and the extra petals are also focussed to the existing focal point. I think that tesla is perhaps getting confused with illumination areas and waveguides. When a dish is engineered to the specific sizes that he mentions yes the focal point does increase as the diameter of the dish increases because the curvature of the dish decreases the bigger the dish diameter becomes

renibacterium · 24-02-2008

I have both the 1.5 & 2.0 m IRTE (1.5m + petals) and believe me the poles holding the feed are longer on the 2.0m dish

**Topper** · 24-02-2008

Originally Posted by renibacterium

I have both the 1.5 & 2.0 m IRTE (1.5m + petals) and believe me the poles holding the feed are longer on the 2.0m dish

that may be but the curvature of the dishes cannot be the same then.
If somebody designs a dish to be either one size with an option to have petals with a greater diameter, they are going to use the less curved option thus longer focal length whether the extensions are used or not IMHO

scooter123 · 24-02-2008

Just been reading this on www.primefocus.com/cband_instal.html
A Word About Focal Depth

The f/D ratio is the focal distance of the dish (f), divided by the diameter (D). When dealing with most prime focus antennas, the number should come out between .28 and .42. If you notice, most of those numbers are also on scale on the side of the feedhorn. You simply set the top edge of the scalar ring even with the line that corresponds to your correct f/D setting. What this adjustment actually does is determines how wide of an angle the feedhorn can "see".

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'tuse feet for the diameter and inches for depth). For the example, let's 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
Therefore 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 of (D) = 120; and the calculated focal distance (f) = 50

f / D = 50 / 120 = .416
f /D = .416

You would round up to give a setting of .42.

I had wondered about this but as I will probably never find these pannels at a reasonable price I wont get to experiment.
Ive made some alterations to the polar mount today & fitted a 36" motor arm.
I can now recieve 58w to 42e. The dish can see further east but I havent found anything yet.
Have also ordered a C/Ku lnb from Germany so the improved arc should give me plenty to try for.

renibacterium · 24-02-2008

Yes the 1.5m has an F/D of 0.41 and therefore has a focal length of 61.5cm. The 2.0m dish has an F/D of 0.40 and a focal length of 80cm. The feed tripod poles are at an angle out from the dish and are therefore longer than these values in each case.

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