2.4 DH Antenna installation

[moonbase]

Look at my F/D
View attachment 103420
Its all down to how they make the dish, various ways to get the wave length required this has a impact on F/D

I was just wondering why they are only manufacturing two antenna sizes (2.8m and 3.0m) with a choice of F/D. None of the other sizes in the range come with a choice of F/D. The F/D for the 2.8m with focal length of 1207mm works out at 0.43, that is quite high compared to the rest of their range that only come in one F/D size, all of which are around 0.35 +/- one or two hundredths

I am not up to speed on the technical aspects of the suitability of different parabolic shapes and F/D versus wave length optimisation. Would the higher F/D ratio be more appropriate for Ka Band reception?

Rgds

 

[blademedia]

Its all very complicated I only understand the basics, in a nut shell every frequency has a wave length, with a C/KU band dish they model it in a way to cover not just one frequency/band the shape can vary depending on where they want the centre frequency start and end frequency, various ways they can do this can have a impact on F/D

The dish will be a good all rounder on both C/KU, depending how its modelled will determine the F/D,

Now put KA band LNB on it it will work but not at its best, the dish is not modelled for the wavelength

Make the same size dish modelled around KA band and it would blind the C/KA dish as its modelled for the frequency, hope this makes some sense.

 

[Channel Hopper]

Rigidity is an under-rated virtue.

Oooer Missus !

 

[Channel Hopper]

I was just wondering why they are only manufacturing two antenna sizes (2.8m and 3.0m) with a choice of F/D. None of the other sizes in the range come with a choice of F/D. The F/D for the 2.8m with focal length of 1207mm works out at 0.43, that is quite high compared to the rest of their range that only come in one F/D size, all of which are around 0.35 +/- one or two hundredths

I am not up to speed on the technical aspects of the suitability of different parabolic shapes and F/D versus wave length optimisation. Would the higher F/D ratio be more appropriate for Ka Band reception?

Rgds

A parabolic equation determines the overall point at which all the reflected waves arrive at the focal point, ie the feed horn.
For any frequency there is no point in creating a dish that has waves that cancel others out, nor ending up with a shape that makes the scalar feed expensive to produce to the point where it is uneconomical to 'patch'.

Stringing a dish is all about checking for transit damage, and how well something in the field has lasted. Once you are there you need to verify the design really is what you need for the specific frequencies you are after and how much money you need to throw at the system without replacing the key components.

 

[blademedia]

This site is a good read
The Antenna Theory Website

focal length F = D (diameter) squared divided by 16 times the depth of the dish (H )

Video added

 

[moonbase]

blademedia, Channel Hopper,

Thank you for the replies and links, very useful and informative.


Rgds

 

[archive10]

Rigidity is an under-rated virtue.

...which is why SMC dishes are still good when bought second or fifth-hand.
No cowboy-handling to slightly mis-shape the reflector!
But we can still dream of the all-metal reflector performance...

 

[blademedia]

@John very nice dish why did you sell it ?

 

[John]

@John very nice dish why did you sell it ?
View attachment 103436

I didn't matey, it got severely knackered along with a Jumbo motor in some really bad gale force winds we had around here about two years ago where i unfortunately was not around to be able to crank it all down to safety. That pic was when i took it down to make a new polor mount etc..... all before the gales. She was a cracking dish.

 

[moonbase]

I didn't matey, it got severely knackered along with a Jumbo motor in some really bad gale force winds we had around here about two years ago where i unfortunately was not around to be able to crank it all down to safety. That pic was when i took it down to make a new polor mount etc..... all before the gales. She was a cracking dish.

John,

What was the part in the very centre of your old 2.2m Precision dish inside the 600mm mounting ring, was it something you fitted yourself? It looks like some type of part that accepts a spindle or similar?


Rgds

 

[John]

John,

What was the part in the very centre of your old 2.2m Precision dish inside the 600mm mounting ring, was it something you fitted yourself? It looks like some type of part that accepts a spindle or similar?


Rgds

Got it in one MB, it was the fixing for an experimental "hook" feed support

 

[blademedia]

I didn't matey, it got severely knackered along with a Jumbo motor in some really bad gale force winds we had around here about two years ago where i unfortunately was not around to be able to crank it all down to safety. That pic was when i took it down to make a new polor mount etc..... all before the gales. She was a cracking dish.

Oh dear , presume what the motor broke damage was caused to dish

 

[John]

Oh dear , presume what the motor broke damage was caused to dish

Yep, severe unrepairable damage to both items, the strength of the gales that day were frightening and it actually put me off thinking about rebuilding a Cband installation for about 7 months .
The urges finally came back to me and i decided to re-inforce the crank-down king pin arrangement and totally design / fabricate & re-build a beefed up AZ-EL mount using a Venture 36" actuator for use on a new CM1.8.

 

[blademedia]

Did the dish actually leave the mount John, the other day when strong winds was forecast I went and strapped my base to the runway even though I am 100% sure I have enough weight I wanted to make sure

 

[John]

Did the dish actually leave the mount John, the other day when strong winds was forecast I went and strapped my base to the runway even though I am 100% sure I have enough weight I wanted to make sure

No, not completely Blade ..... by the time i managed to get back to it it had shattered the Jumbo motor casing causing the dish to blow about on what was just one remaining bolt and the dish itself took a few heavy collisions with the surrounding metalwork. Sad day mate.

 

[Captain Jack]

Do you still have the dish, John? Maybe it's salvageable with some careful beating and stringing?

 

[blademedia]

No, not completely Blade ..... by the time i managed to get back to it it had shattered the Jumbo motor casing causing the dish to blow about on what was just one remaining bolt and the dish itself took a few heavy collisions with the surrounding metalwork. Sad day mate.

Yes very sad John, but a lesson learnt I guess and sounds like no one was injured, I cringe when I see some installs people don't realise the force of the wind on a dish,

This is not going anywhere, I hope

 

[John]

Do you still have the dish, John? Maybe it's salvageable with some careful beating and stringing?

No mate, scrapped & weighed in.

 

[John]

Yes very sad John, but a lesson learnt I guess and sounds like no one was injured, I cringe when I see some installs people don't realise the force of the wind on a dish,

This is not going anywhere, I hope
View attachment 103440 View attachment 103441 View attachment 103440 View attachment 103441

Yes , i think that should be ok ... crack on lol.

 

[Captain Jack]

This is not going anywhere, I hope [/ATTACH]

How much does this thing weigh?!