Windmills and microwave towers?

[The Natural Philosopher]

This is a curious question, which I don't believe has been asked before, and to which I couldn't actually find and answer. And only being half asleep and thinking about one thing whilst reading the paper idly, caused three things to slip into my mind together.

Namely 'rural broadband' the influence of the environment on transmission speed and quality, and the fact that here, high up in west suffolk, and hence potentially a target for windmills, we already have half a dozen radio towers dotted with aerials and dishes.

So, how do presumably metal or carbon fibre blades thwacking past or around a microwave tower affect its transmission and reception?

Nearly all mobile phone masts are fed via microwave. A HUGE amount of data backbones are built out of them - a lot cheaper than fibre. And although the towers occupy in general the highest ground around, windmills reach even higher. They would inevitably be in many line of sight beams' paths..

It seems to me as well as being ugly, noisy, and dangerous to low flying aircraft, as well as effectively screening low flying aircraft from radar, these things are likely to also totally disrupt any RF frequencies in the VHF bands and up, that rely on line of sight transmission to teh horizon.

Already the inlaws digital TV is totally disrupted by wet leaves on trees blowing in the wind..the DSP algorithms can cope if the things are static, but not if the multipath is constantly changing.

I know there are RF experts here. The question is, would a landscape with a windmill every kilometre, actually be one in which any frequency beyond short wave was usable?

[Tim Ward]

They are not dangerous to low flying aircraft, because if flying visually you can see them and avoid them, and if flying on instruments you're a thousand feet above them or on a properly surveyed instrument approach, and "properly surveyed" includes taking account of obstacles, obviously. (Of course if you're flying an unapproved GPS based DIY "instrument approach" into a farm strip using an out of date GPS database which doesn't have last week's wind farm in it then that's tantamount to suicide and not really something for the rest of us to worry about.)

They do sometimes upset radars, and it's not unknown for a wind farm developer to have to pay to upgrade radars.

You'd have to be doing some really bizarre low flying for them to get in the way of line of sight VHF radio. Not something I've ever heard of being a problem.

[The Natural Philosopher]

You must come and sit in our back garden sometime, when the military jets come over at < 250' altitude. 100' is luxury for them.

And the microlights struggle to GET to 1000 ft sometimes ;)

(Of

Er what? I am not sure my TC and FM reception requires me to get in an aircraft..

Not something I've ever heard of being a

[Dave Liquorice]

Military. Was out with the RAF just before Gulf War I, they were flying sorties out over the Saudi desert, they get seriously low when in combat rather than excercise conditions. They were down to a few tens of feet, camels were a hazard...

A wind turbine has a blade tip height of 350 to 400' the fast jets round here are below that level. We look down on some of the slower stuff, hercy birds and helos etc that are really hugging the ground.

Windmills do disrupt RF propagation it's not unknown for TV reception to be disrupted if there is a windmill close to the path.

[Andy Dingley]

Point-to-point microwave isn't arranged to run through windmills.

Broadcast microwave (i.e. cellphone) doesn't care. Diverse paths (the relevant scale at these wavelengths is far smaller than the blades) cope fine.

[Peter Crosland]

I assume you are asking about the modern wind turbines rather than old fashioned windmills. The former can, and do, cause disruption to RF links and terrestrial TV. I live near to RNAS Yeovilton and they are a statutory consultee for all large wind turbine planning applications. A contact there tells me that they are concerned about the effect on their radar installations as well as the implications for low flying. There have also been reports in the press about disruption to terrestrial TV signals has also been reported such as this link shows.

Crosland

[Andy Dingley]

Rural, small-scale cellphone systems use microwave links. Bigger ones don't. Now my knowledge here is rather outdated, but last time I looked at this (I designed the software that designed the networks) the limitation of the Abis interface (the daisy chained microwave link) was sufficient that you could only daisy-chain a handful of masts, and low-traffic masts at that, before you ran out of capacity.

A single "plastic stick up a pole" mast is an omnidirectional antenna serving a single cell. Where there's substantial traffic though, a mast (which is expensive) will be used to support two or three directional antenna, with a cell either way from the mast. You can also have multiple radios (and antennae) within a cell, increasing cell capacity, and thus data needs, from that same mast.

Abis just wasn't designed to be capable of handling too many radios worth of traffic, and the microwave links it uses are equally restricted. Really it's only useful for single-radio, single cell per mast networks, which is the rural end of things.

Also, although microwave links are cheaper than cabled links (as links), they have paltry bandwidth compared to fibre. You just can't put today's data rates over microwave. One reason why communications satellites are now a niche market for where cabling is impractical, rather than a first choice.

[Dave Liquorice]

But when the windmill pops up close to a pre existing link...

[Bill Wright]

We did a series of studies for one of the very large energy firms. The studies concerned the likely effects of proposed windfarms on local tv reception. As a result I had to read all the planning applications, and the normal procedure was for the operators of any links anywhere near were consulted and allowed to object.

In the case of the turbines near Parkway Sheffield I don't think the proper procedures were follewed, by they normally are. The Sheffield turbines have had another spectacular failure, by the way.

they are allowing a turbine to be installed on a school playing field, whilst banning cellphone towers. What a set of bloody idiots we have running out local councils.

Bill

[Woody]

Part of the application process to erect the turbines is that the applicant must accertain if they are wishing to build in the path of or very close to the path of any radio link, microwave or otherwise. If there are any that will be affected they either have to find an alternative location for the turbine(s) or pay for the link to be replaced by fibre or for the link to be rerouted - and of course they have to get the agreement of the user to these changes. If there is no alternative path then the application fails.

Simples.

[Andy Dingley]

That's supposed to be why we have planning permission for them, and most likely some compensation to the link owner to rearrange it.

Besides which, this is a rare occurence. They both favour different geographies, so there's relatively little chance of them crossing.

[Graham.]

> Meanwhile they are allowing a turbine to be installed on a school playing

I was once asked to sign a petition by some women protesting at the proposed site of a roadside cellphone mast. It was in front a gap between two pairs of semis. I refused, and suggested they should be more worried about what was currently buried under the site filling the gap; a Shell forecourt.

[R. Mark Clayton]

Ask yourself this: -

If the blade passes in front of the sun, will it blot it out?

[Dave Liquorice]

Depends on how far you are from the blade. Flicker due to the moving shadow of the blades is a serious problem. How would you like the light level to drop every few seconds or so?

[Dave Liquorice]

Curious that there are no pictures and the only news stories I can find all relate back to the telegraph one, some just quoting it.

Two things spring to mind:

The Powers That Be have applied pressure on the media to either not report it all or only give in minmal coverage.

It didn't happen.

[neverwas]

possibly

as they have an earlier dateline

Does anyone need to *apply* pressure when the media mostly know that Govnt and wind turbine companies have advertising budgets while opponents (mostly) don't?

[Cwatters]

Not just microwave coms but TV and radar as well...

[The Natural Philosopher]

Thank you for that. I think the register was the most thought provoking.

[Espen Koht]

I don't get this view of wind turbines as being having some kind of 'special' powers to affect the environment; they are just structures. Where microwaves are being used for point-to-point communication you just do what you would do in an urban environment or in mountainous regions: find a line of sight or create one by putting up a mast. These a fixed structures and are not going to come waltzing in to view unexpectedly. You figure out where they are and find a line-of-sight accordingly. If your existing line-of-sight gets disrupted you move, build higher or build another repeater to get around it. Not rocket-science.

[The Natural Philosopher]

Espen: the key here is the blades MOVE. And they are high up in otherwise clear space.

We are quite smart in dealing with multipath from fixed objects..we are far less so when the object moves.

Like wise doppler radar - the easiest way to pick low flying aircraft out of ground clutter - can't cope with stuff moving at low level.