Dish Mesh information


Mike GD6ICR
 

I am considering building a dish from scratch. What is there a relationship between dish mesh size and frequency and aluminium or stainless (i know its heavier but more durable) or foil covered fibreglass or even lightweight aluminium sheet. I realize also that the solid type dishes have a much higher wind loading. But the aluminium sheet is free and I can form it into 6 or more sections. I have had a look at the W1GHZ microwave pages but would like to see how UK based amateurs have constructed them as we dont have the kind of suppliers US has. Any help would be appreciated.

--
Mike GD6ICR IO74PF73TW


John Fell
 

Hi Mike ,
The traditional view is to limit mesh perforation to under 1/10 of the wavelength in use .

I would not go for SS on weight and cost grounds - Aluminium alloy is used widely and is able to withstand the demands of WX in UK .It is also far easier to form and drill .

To make the call on self construction we need to know what you plan to do with the dish .

Profile accuracy requirements scale with rising frequency .

73

John
G0API

On Tue, 18 May 2021 at 10:44, Mike GD6ICR <gd6icr@...> wrote:
I am considering building a dish from scratch. What is there a relationship between dish mesh size and frequency and aluminium or stainless (i know its heavier but more durable) or foil covered fibreglass or even lightweight aluminium sheet. I realize also that the solid type dishes have a much higher wind loading. But the aluminium sheet is free and I can form it into 6 or more sections. I have had a look at the W1GHZ microwave pages but would like to see how UK based amateurs have constructed them as we dont have the kind of suppliers US has. Any help would be appreciated.

--
Mike GD6ICR IO74PF73TW


John Lemay
 

Mike

 

If you download EME Planner by VK3UM, you will be able to experiment endlessly with the effect of different mesh sizes (along with different f/d, different dish sizes, different feeds etc.). A good starting point is to keep the gap in the mesh smaller than one tenth of a wavelength.

 

I made a 2m dish using aluminium mesh and it worked well, but I eventually concluded that the wires needed to be thicker than steel to get the same strength, and consequently the wind load went up. My current dish uses galvanised steel mesh – my mesh came from F H Brundle.

 

Your biggest challenge will be to make the ribs to an accurate profile. Mine were bent by hand in a heavy vice, bit by bit, with frequent checks against a drawn profile. The first one took hours, the last one just a few minutes. It might seem obvious to bend the material against a pre-formed rigid profile, but that requires you to understand and compensate for the inevitable springback.

 

Regarding aluminium sheet, remember that it has to be formed in three dimensions to obtain a parabola – in other words it is not a straight line between each rib. That’s not easy to explain !

 

John G4ZTR

 

 

From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of Mike GD6ICR
Sent: 18 May 2021 10:44
To: UKMicrowaves@groups.io
Subject: [UKMicrowaves] Dish Mesh information

 

I am considering building a dish from scratch. What is there a relationship between dish mesh size and frequency and aluminium or stainless (i know its heavier but more durable) or foil covered fibreglass or even lightweight aluminium sheet. I realize also that the solid type dishes have a much higher wind loading. But the aluminium sheet is free and I can form it into 6 or more sections. I have had a look at the W1GHZ microwave pages but would like to see how UK based amateurs have constructed them as we dont have the kind of suppliers US has. Any help would be appreciated.

--
Mike GD6ICR IO74PF73TW


Mike GD6ICR
 

Thanks to John API  and ZTR for your advice - It seems I do have a sectional dish available to me which I hope despite the age will give one or two of us on the Island access to EME on the likes of 23/13/3cm in the future. I realize the problems with the weight of the dish if stainless mesh is used, but you must realize that aluminium mesh/perforated metal here on the Island where no-where is more than 7 miles from the sea, that the corrosive capability of salt air here is phenominal. I still need to find the right paint to coat all the dishes we have available - any advice on the right material coating whether its brushed or sprayed I do have the capability and If i dont there are a lot of skill within the community to help. Just hope they dont mind a 12 ft dish on my garage roof or moved onto the back of my trailer to tow to the best places for competitions and eme. Thanks for all your suggestions both on here and direct
We all need to find our way.
--
Mike GD6ICR IO74PF73TW