Date   

Re: Dishes and wind

Chris Bartram G4DGU
 

John and Andy:

On mesh dishes, isn't it all about turbulence around the (thin) mesh conductive elements causing a much greater effective thickness?

I understand that something like that is the case. I have a feeling that turbulence effectively applies an exponential term to the area term of the equation relating wind speed to wind pressure. Hence streamlining!


But I don't even try to understand mechanical things, and just quoting summat I read yonks ago mixed with a gut feeling.

I'd normally run a mile from such mech. things! Bad memories of a wrong turn I once took in my 'education' ...


Richard:

I'd not seen any maths or comments on vibration fatigue of dishes, but a quick search does bring-up a couple of papers. I'll see if I can make sense of them later. The Sky dishes here do seem to suffer a bit more from corrosion, but given my location is only a few km the coast, that's unsurprising. My initial response to your comment would be to de-Q the dish. That could possibly be accomplished by the choice of a composite reflector eg. GRP or by use of some form of damping material on the rear of a thin metal dish. The design of the dish bracketry would probably have a significant effect on vibration modes. I'll do some digging ...


73 All.

Chris G4DGU


Re: Dishes and wind

Richard GD8EXI
 

One of the problems with dishes in windy locations is flutter (vibration in the wind). Standard sky dishes only last about two years here because of flutter induced metal fatigue. As G8DOH has already pointed out a solid dish has a high mechanical Q so is prone to flutter. I suspect mesh dishes have lower mechanical Qs so should do better. This is born out by GD4GNH’s experience with a 1.9m mesh dish at a very windy location.
 
To get back to the original question I suggest you park it in the direction, which leads to the least flutter as found experimentally.

We had a mean wind speed of 55Knots and gusting over 70Knots here yesterday so my largest Yagis were locked into wind.

Richard
GD8EXI



On 14/01/2020, 10:50, "Chris Bartram G4DGU" <chris@...> wrote:

> I've recently been working on the design of a new mast system and I want
> it to support a reasonable dish for terrestrial operation. A lattice
> tower wouldn't be appropriate here, and I need something a bit better
> than a beefed-up domestic installation. I also need easy access to the
> antennas. As I've never been particularly interested in 2.3, 3.4, and
> 5.6GHz, I plan to use a domestic 1 or 1.2m offset dish with an efficient
> dual-band 1.3/10GHz feed. A snake yagi would be unlikely to survive for
> very long here.
>
> Living in Cornwall where it's intrinsically windy, at a location which
> is also subject to katabatic winds falling off the range of hills on
> which the GB3MCB beacons sit, I've been looking at the problems from
> first principles. This seems to be an everyday problem on a par with
> circuit analysis for structural engineers ... My initial reading of a
> number of sources does seem to suggest that a worst case calculation of
> the force developed by the wind on a dish antenna is something which
> isn't that difficult to perform: the principles behind the building
> regulations take into account the aerodynamics of the dish in arriving
> at their figures.
>
> One very relevant point - which I have seen made in amateur radio
> publications, but which doesn't seem to be generally appreciated here -
> is that mesh dishes aren't that much better in terms of wind loading
> than than solid dishes of the same diameter at higher windspeeds. The
> difference seems to equate to a small penalty in dish diameter and the
> increased efficiency of the solid dish probably counteracts that.
>
> I hope these comments are useful: I'll probably understand this a lot
> better with further reading, so please treat them as provisional!
>
> 73
>
> Chris
>
> G4DGU
>
>
>
>


Re: Dishes and wind

Andy G4JNT
 

On mesh dishes, isn't it all about turbulence around the (thin) mesh conductive elements causing a much greater effective thickness?

But I don't even try to understand mechanical things, and just quoting summat I read yonks ago mixed with a gut feeling.



On Tue, 14 Jan 2020 at 11:20, John Lemay <john@...> wrote:
Firstly, many thanks for the helpful comments yesterday. I went with my gut feeling, and pointed the dishes downwind, and all was well. There's more to come later today, probably worse than yesterday here if the forecast is correct.

My larger dish (2m diameter) is home designed and home built, so I have plenty of interest in its survival !

Chris -

I've read the same web pages as you have by the sound of it, regarding wind loading of mesh dishes v solid dishes. And I'm not convinced. But it occurs to me that we should be considering not two types of construction, but three types. These are solid, perforated material, and mesh. If we compare solid and perforated material I can understand that the difference in wind load is not great; I'm looking at a sample sheet of perforated aluminium and the holes probably represent 30% of the area. But with mesh (like RF HamDesign dishes) the gaps represent 70 to 90% of the area, depending on the mesh option chosen.

Nothing is simple, is it ?

Regards

John G4ZTR


-----Original Message-----
From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of Chris Bartram G4DGU
Sent: 14 January 2020 10:50
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Dishes and wind

I've recently been working on the design of a new mast system and I want
it to support a reasonable dish for terrestrial operation. A lattice
tower wouldn't be appropriate here, and I need something a bit better
than a beefed-up domestic installation. I also need easy access to the
antennas. As I've never been particularly interested in 2.3, 3.4, and
5.6GHz, I plan to use a domestic 1 or 1.2m offset dish with an efficient
dual-band 1.3/10GHz feed. A snake yagi would be unlikely to survive for
very long here.

Living in Cornwall where it's intrinsically windy, at a location which
is also subject to katabatic winds falling off the range of hills on
which the GB3MCB beacons sit, I've been looking at the problems from
first principles. This seems to be an everyday problem on a par with
circuit analysis for structural engineers ... My initial reading of a
number of sources does seem to suggest that a worst case calculation of
the force developed by the wind on a dish antenna is something which
isn't that difficult to perform: the principles behind the building
regulations take into account the aerodynamics of the dish in arriving
at their figures.

One very relevant point - which I have seen made in amateur radio
publications, but which doesn't seem to be generally appreciated here -
is that mesh dishes aren't that much better in terms of wind loading
than than solid dishes of the same diameter at higher windspeeds. The
difference seems to equate to a small penalty in dish diameter and the
increased efficiency of the solid dish probably counteracts that.

I hope these comments are useful: I'll probably understand this a lot
better with further reading, so please treat them as provisional!

73

Chris

G4DGU








Re: Dishes and wind

John Lemay
 

Firstly, many thanks for the helpful comments yesterday. I went with my gut feeling, and pointed the dishes downwind, and all was well. There's more to come later today, probably worse than yesterday here if the forecast is correct.

My larger dish (2m diameter) is home designed and home built, so I have plenty of interest in its survival !

Chris -

I've read the same web pages as you have by the sound of it, regarding wind loading of mesh dishes v solid dishes. And I'm not convinced. But it occurs to me that we should be considering not two types of construction, but three types. These are solid, perforated material, and mesh. If we compare solid and perforated material I can understand that the difference in wind load is not great; I'm looking at a sample sheet of perforated aluminium and the holes probably represent 30% of the area. But with mesh (like RF HamDesign dishes) the gaps represent 70 to 90% of the area, depending on the mesh option chosen.

Nothing is simple, is it ?

Regards

John G4ZTR

-----Original Message-----
From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of Chris Bartram G4DGU
Sent: 14 January 2020 10:50
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Dishes and wind

I've recently been working on the design of a new mast system and I want
it to support a reasonable dish for terrestrial operation. A lattice
tower wouldn't be appropriate here, and I need something a bit better
than a beefed-up domestic installation. I also need easy access to the
antennas. As I've never been particularly interested in 2.3, 3.4, and
5.6GHz, I plan to use a domestic 1 or 1.2m offset dish with an efficient
dual-band 1.3/10GHz feed. A snake yagi would be unlikely to survive for
very long here.

Living in Cornwall where it's intrinsically windy, at a location which
is also subject to katabatic winds falling off the range of hills on
which the GB3MCB beacons sit, I've been looking at the problems from
first principles. This seems to be an everyday problem on a par with
circuit analysis for structural engineers ... My initial reading of a
number of sources does seem to suggest that a worst case calculation of
the force developed by the wind on a dish antenna is something which
isn't that difficult to perform: the principles behind the building
regulations take into account the aerodynamics of the dish in arriving
at their figures.

One very relevant point - which I have seen made in amateur radio
publications, but which doesn't seem to be generally appreciated here -
is that mesh dishes aren't that much better in terms of wind loading
than than solid dishes of the same diameter at higher windspeeds. The
difference seems to equate to a small penalty in dish diameter and the
increased efficiency of the solid dish probably counteracts that.

I hope these comments are useful: I'll probably understand this a lot
better with further reading, so please treat them as provisional!

73

Chris

G4DGU


Re: Dishes and wind

Chris Bartram G4DGU
 

I've recently been working on the design of a new mast system and I want it to support a reasonable dish for terrestrial operation. A lattice tower wouldn't be appropriate here, and I need something a bit better than a beefed-up domestic installation. I also need easy access to the antennas. As I've never been particularly interested in 2.3, 3.4, and 5.6GHz, I plan to use a domestic 1 or 1.2m offset dish with an efficient dual-band 1.3/10GHz feed. A snake yagi would be unlikely to survive for very long here.

Living in Cornwall where it's intrinsically windy, at a location which is also subject to katabatic winds falling off the range of hills on which the GB3MCB beacons sit, I've been looking at the problems from first principles. This seems to be an everyday problem on a par with circuit analysis for structural engineers ... My initial reading of a number of sources does seem to suggest that a worst case calculation of the force developed by the wind on a dish antenna is something which isn't that difficult to perform: the principles behind the building regulations take into account the aerodynamics of the dish in arriving at their figures.

One very relevant point - which I have seen made in amateur radio publications, but which doesn't seem to be generally appreciated here - is that mesh dishes aren't that much better in terms of wind loading than than solid dishes of the same diameter at higher windspeeds. The difference seems to equate to a small penalty in dish diameter and the increased efficiency of the solid dish probably counteracts that.

I hope these comments are useful: I'll probably understand this a lot better with further reading, so please treat them as provisional!

73

Chris

G4DGU


New group set up for antenna research

 

I have set up a group on groups.io for antenna research.

https://groups.io/g/antenna-research/topics

The aim is for this to be a high S/N ratio list, with no idle chit-chat, but just material related to antenna research. To keep things in order, the first 4 posts from anyone are moderated.

The group is not aimed at amateur radio - in fact, I set it up as a place to discuss antenna research, without it going into amateur radio groups, which tend to have too much basic antenna stuff in. The two lists I am sending this to now are quite specialised, so I guess you know what I mean.

Feel free to join if you wish. Just keep in mind the groups' objectives.


Dr David Kirkby Ph.D C.Eng MIET
Email: drkirkby@... Web: https://www.kirkbymicrowave.co.uk/
Kirkby Microwave Ltd (Tel 01621-680100 / +44 1621-680100)
Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3 6DT.




Re: Dishes and wind

Ralph
 

Hello John,

 

I  point my dish so it looks down wind .

As we get many strorms and strong gales

In the SW It has proved fine for me, but

Some people may suggest differently hi.

 

73

 

Ralph

 

Sent from Mail for Windows 10

 

From: John Lemay
Sent: 13 January 2020 19:47
To: UKMicrowaves@groups.io
Subject: [UKMicrowaves] Dishes and wind

 

I have two mesh dishes on my mast. It's not obvious (to me) whether to point

them facing the prevailing wind, away from it, or somewhere else.

 

What's the usual practice ?

 

I'm not keen on luffing the mast because not everything is totally

weatherproof when it isn't upright.

 

Thanks

 

John G4ZTR

 

 

 

 


Re: Dishes and wind

Paul G8KFW
 

Hi john
As the wind is not constantly in the same direction and you are not there to
monitor it I personally would have the wind hitting the back of the dish

With the back to the wind the wind can skim over the outside causing less
force to the mounting metalwork
The problem hear is the method of mounting as the mounting bolts can putt
through the dish skin

as your dish is a mesh type I would think this is your safest option

If you had automatic control you could go for nearly side on but the
tenderncy is the dish can act as a wing of an aircraft and push back on the
mountings

-----Original Message-----
From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of
John Lemay
Sent: 13 January 2020 19:46
To: UKMicrowaves@groups.io
Subject: [UKMicrowaves] Dishes and wind

I have two mesh dishes on my mast. It's not obvious (to me) whether to point
them facing the prevailing wind, away from it, or somewhere else.

What's the usual practice ?

I'm not keen on luffing the mast because not everything is totally
weatherproof when it isn't upright.

Thanks

John G4ZTR







-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2016.0.8048 / Virus Database: 4793/15886 - Release Date: 08/14/18
Internal Virus Database is out of date.



--
Paul Bicknell G8KFW   South Coast UK


Re: Dishes and wind

John Quarmby
 

A good question! Pointing the dishes into the wind balances the torque on the rotator, but results in maximum wind load on the stub mast. Setting the dishes so the wind blows across the face of the dish reduces wind loading overall but increases the stress on the rotator. So either might be correct depending on the relative strength of the mast and braking torque of the rotator. Like you I haven't luffed over as that compromises the weather proofing.

I rather suspect I won't be coming on for tomorrow night's 70cm UKAC, with winds up to 60mph forecast here.

73

John G3XDY

On 13/01/2020 19:46, John Lemay wrote:
I have two mesh dishes on my mast. It's not obvious (to me) whether to point
them facing the prevailing wind, away from it, or somewhere else.

What's the usual practice ?

I'm not keen on luffing the mast because not everything is totally
weatherproof when it isn't upright.

Thanks

John G4ZTR



Dishes and wind

John Lemay
 

I have two mesh dishes on my mast. It's not obvious (to me) whether to point
them facing the prevailing wind, away from it, or somewhere else.

What's the usual practice ?

I'm not keen on luffing the mast because not everything is totally
weatherproof when it isn't upright.

Thanks

John G4ZTR


Re: GB3FNM on 5.7G ?

Ed G3VPF
 

Signal on 6cms at IO80RQ44 is readable, just. Not as strong as it usually is, but I suspect that is down to conditions.

I agree it is about 250Hz high.

Ed G3VPF


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Andy G4JNT <andy.g4jnt@...>
Sent: Sunday, January 12, 2020 2:50:06 PM
To: UK Microwaves groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] GB3FNM on 5.7G ?
 
Oops.  forget that post.
The UK Beacons post was about the 2.3GHz one with the same callsign




On Sun, 12 Jan 2020 at 14:45, Andy Talbot <andy.g4jnt@...> wrote:
This post appeared on the  UK Beacons Group yesterday 

"GB3FNM tweaked ahead of a proper upgade probably in March. Measurements yesterday by two stations indicated it to be about 250Hz high after adjustment. It may have "bedded in" further since then but it's a lot better than 4kHz high!
Best 73
Barry G4SJH"




On Sun, 12 Jan 2020 at 11:40, Martyn G3UKV <ukv@...> wrote:
Thanks Ed - that would be great!
Strong R/S this morning, but still no 'FNM audible.
Here in Shropshire, only 'ZME and 'OHM audible at all times on 6cm.
'KEU OK occasionally. (R/S)
73 Martyn G3UKV


On 12/01/2020 11:34, Ed G3VPF wrote:
Martin

It was OK early January, the last time I was on my /p site. If no one else responds I will nip up to the site and take a listen.

Ed G3VPF


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Martyn G3UKV <ukv@...>
Sent: Sunday, January 12, 2020 10:19:32 AM
To: ukmicrowaves@groups.io <ukmicrowaves@groups.io>
Subject: [UKMicrowaves] GB3FNM on 5.7G ?
 
GM
Can anyone confirm if GB3FNM is operational on 5760.920 MHz ?
No spots on Beaconspot since late November.
73 Martyn G3UKV


Re: GB3FNM on 5.7G ?

Andy G4JNT
 

Oops.  forget that post.
The UK Beacons post was about the 2.3GHz one with the same callsign




On Sun, 12 Jan 2020 at 14:45, Andy Talbot <andy.g4jnt@...> wrote:
This post appeared on the  UK Beacons Group yesterday 

"GB3FNM tweaked ahead of a proper upgade probably in March. Measurements yesterday by two stations indicated it to be about 250Hz high after adjustment. It may have "bedded in" further since then but it's a lot better than 4kHz high!
Best 73
Barry G4SJH"




On Sun, 12 Jan 2020 at 11:40, Martyn G3UKV <ukv@...> wrote:
Thanks Ed - that would be great!
Strong R/S this morning, but still no 'FNM audible.
Here in Shropshire, only 'ZME and 'OHM audible at all times on 6cm.
'KEU OK occasionally. (R/S)
73 Martyn G3UKV


On 12/01/2020 11:34, Ed G3VPF wrote:
Martin

It was OK early January, the last time I was on my /p site. If no one else responds I will nip up to the site and take a listen.

Ed G3VPF


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Martyn G3UKV <ukv@...>
Sent: Sunday, January 12, 2020 10:19:32 AM
To: ukmicrowaves@groups.io <ukmicrowaves@groups.io>
Subject: [UKMicrowaves] GB3FNM on 5.7G ?
 
GM
Can anyone confirm if GB3FNM is operational on 5760.920 MHz ?
No spots on Beaconspot since late November.
73 Martyn G3UKV


Re: GB3FNM on 5.7G ?

Andy G4JNT
 

This post appeared on the  UK Beacons Group yesterday 

"GB3FNM tweaked ahead of a proper upgade probably in March. Measurements yesterday by two stations indicated it to be about 250Hz high after adjustment. It may have "bedded in" further since then but it's a lot better than 4kHz high!
Best 73
Barry G4SJH"




On Sun, 12 Jan 2020 at 11:40, Martyn G3UKV <ukv@...> wrote:
Thanks Ed - that would be great!
Strong R/S this morning, but still no 'FNM audible.
Here in Shropshire, only 'ZME and 'OHM audible at all times on 6cm.
'KEU OK occasionally. (R/S)
73 Martyn G3UKV


On 12/01/2020 11:34, Ed G3VPF wrote:
Martin

It was OK early January, the last time I was on my /p site. If no one else responds I will nip up to the site and take a listen.

Ed G3VPF


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Martyn G3UKV <ukv@...>
Sent: Sunday, January 12, 2020 10:19:32 AM
To: ukmicrowaves@groups.io <ukmicrowaves@groups.io>
Subject: [UKMicrowaves] GB3FNM on 5.7G ?
 
GM
Can anyone confirm if GB3FNM is operational on 5760.920 MHz ?
No spots on Beaconspot since late November.
73 Martyn G3UKV


Re: GB3FNM on 5.7G ?

Martyn G3UKV
 

Thanks Ed - that would be great!
Strong R/S this morning, but still no 'FNM audible.
Here in Shropshire, only 'ZME and 'OHM audible at all times on 6cm.
'KEU OK occasionally. (R/S)
73 Martyn G3UKV


On 12/01/2020 11:34, Ed G3VPF wrote:
Martin

It was OK early January, the last time I was on my /p site. If no one else responds I will nip up to the site and take a listen.

Ed G3VPF


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Martyn G3UKV <ukv@...>
Sent: Sunday, January 12, 2020 10:19:32 AM
To: ukmicrowaves@groups.io <ukmicrowaves@groups.io>
Subject: [UKMicrowaves] GB3FNM on 5.7G ?
 
GM
Can anyone confirm if GB3FNM is operational on 5760.920 MHz ?
No spots on Beaconspot since late November.
73 Martyn G3UKV


Re: GB3FNM on 5.7G ?

Ed G3VPF
 

Martin

It was OK early January, the last time I was on my /p site. If no one else responds I will nip up to the site and take a listen.

Ed G3VPF


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Martyn G3UKV <ukv@...>
Sent: Sunday, January 12, 2020 10:19:32 AM
To: ukmicrowaves@groups.io <ukmicrowaves@groups.io>
Subject: [UKMicrowaves] GB3FNM on 5.7G ?
 
GM
Can anyone confirm if GB3FNM is operational on 5760.920 MHz ?
No spots on Beaconspot since late November.
73 Martyn G3UKV


GB3FNM on 5.7G ?

Martyn G3UKV
 

GM
Can anyone confirm if GB3FNM is operational on 5760.920 MHz ?
No spots on Beaconspot since late November.
73 Martyn G3UKV


seeking info on Western Microwave mixer

Wilko
 

hi,

I am seeking information on a Western Microwave MSS-5079A mixer.

This is ancient stuff, guestimate is 1970s. I tore down a Loral Radar Warning Receiver and there is quite some WM stuff in there. Plus Watkins-Johnson YIG GaAs oscillators and preselectors. Unfortunately all this is from before the Dawn of the Internet so search engines prove essentially useless.

Who can help me here please?

73 Wilko
PA1WBU


Re: Stepdown converter 50V -> 28V -- Nokia/EFORE Ratings

David GM6BIG
 

Hi Maarten

Looked one out, ratings are a little short of your needs, attached pic of ratings plate.

For the record...
IN
-48V to -60V DC in (typically a battery supply)

OUT
24/26V 19A
+12.4V 8A/11A
-12.4V 2.5V/0A
5.1/5.4V 15A


Also found some Eltek 1800W SMPS battery chargers.
My notes for these say 240V in, approx Adj to 38.5V to 58V at around 36A (1800W limit)

Cheers, David GM6BIG

On 08/01/2020 19:36, Maarten PA0MHE wrote:
Has anyone a redundant stepdown converter (22-24A @ 28V) from a ex telecom amplifier laying around ?
My other SSPA's are all 50V but 13cm requires a lower VDD, and I want to reuse these 50V SMPS's.
In most surplus UTMS PA's also a downconverter is present.


Re: Stepdown converter 50V -> 28V

Stanislaw Ziemczonek
 

Has anyone a redundant stepdown converter (22-24A @ 28V) from a ex telecom amplifier laying around ?
My other SSPA's are all 50V but 13cm requires a lower VDD, and I want to reuse these 50V SMPS's.
In most surplus UTMS PA's also a downconverter is present.


Re: Stepdown converter 50V -> 28V

David GM6BIG
 

Hi Maarten
Yes - I may have something, made by Nokia.
Will look some out today, and get the ratings off of it.
A little old, but a quality build.

Cheers David GM6BIG

On 08/01/2020 19:36, Maarten PA0MHE wrote:
Has anyone a redundant stepdown converter (22-24A @ 28V) from a ex telecom amplifier laying around ?
My other SSPA's are all 50V but 13cm requires a lower VDD, and I want to reuse these 50V SMPS's.
In most surplus UTMS PA's also a downconverter is present.