Microwave and QO100 EMF

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G7JTT
Posts: 338
Joined: Fri Jun 10, 2016 5:05 pm

Re: CAT21 videos now on Youtube

Post by G7JTT » Thu Oct 21, 2021 6:47 am

Working my way through the videos and have a question that wasn't asked in the "EMF" talk. Reading between the lines for a QO100 setup in a small suburban garden to comply, height of the dish will help. So how are others proposing to get a 1.2m dish above ground and avoid possible planning/neighbor issues ? Or will this help with planning ?

And lastly thanks again to all involved with CAT21 ALL the talks have been most enjoyable and informative to watch.

73 John G7JTT

g8gtz
Posts: 1733
Joined: Wed Apr 07, 2010 6:26 pm

Microwave and QO100 EMF

Post by g8gtz » Thu Oct 21, 2021 7:57 am

John G7JTT said:
Reading between the lines for a QO100 setup in a small suburban garden to comply, height of the dish will help. So how are others proposing to get a 1.2m dish above ground and avoid possible planning/neighbor issues ? Or will this help with planning ?
The way I'm thinking is to imagine a round tube/cylinder coming off the face of your dish at 28 degrees, with the bottom edge at ground level I think a typical human at 1.8mts tall is safe to walk under it at about 3.3 mts away from the dish.

It's easy to do the maths particularly if you use this calculator https://www.calculator.net/triangle-calculator.html

As long as you take reasonable precautions to make sure no-one can enter that area (the exclusion zone) you are probably compliant.

Discuss!

73
Noel

radiogareth
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Re: Microwave and QO100 EMF

Post by radiogareth » Thu Oct 21, 2021 8:34 am

I've put my dish on a handy bit of flat roof that's part of my garage. I have also mounted it upside down which greatly reduces the visual impact and the wind loading.
Previous CQTV had my article about it. Nobody can get anywhere the dish, even less so the cylinder of RF coming off it when I TX.
Gareth

g0mjw
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Joined: Sat Sep 20, 2014 9:15 am

Re: Microwave and QO100 EMF

Post by g0mjw » Thu Oct 21, 2021 8:53 am

radiogareth wrote:
Thu Oct 21, 2021 8:34 am
I've put my dish on a handy bit of flat roof that's part of my garage. I have also mounted it upside down which greatly reduces the visual impact and the wind loading.
Previous CQTV had my article about it. Nobody can get anywhere the dish, even less so the cylinder of RF coming off it when I TX.
Gareth
Doesn't the cat sit on that roof when it's hot?

g0mjw
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Joined: Sat Sep 20, 2014 9:15 am

Re: Microwave and QO100 EMF

Post by g0mjw » Thu Oct 21, 2021 8:59 am

g8gtz wrote:
Thu Oct 21, 2021 7:57 am

It's easy to do the maths particularly if you use this calculator https://www.calculator.net/triangle-calculator.html

As long as you take reasonable precautions to make sure no-one can enter that area you are probably compliant.

Discuss!

73
Noel
Yes but don't forget the area behind the dish, there will be spillover. The distance isn't very far and I think you can approximate it as if the 10 dBi gain feed is the antenna as if the dish isn't there, taking account of the feed beamwidth. Ideally the level is 10 dB down at the edge of the dish but with a long F/D it will be more like -6 dB or even -3 dB. Even if it's 0 dB the distance is only a few metres with typical 50W of RF.

Mike

AdrianH
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Re: Microwave and QO100 EMF

Post by AdrianH » Thu Oct 21, 2021 9:56 am

I was unable to view the CAT21 live on Saturday so therefore unable to pose any questions on the day. Viewing the EMF section today, the chart that was shown of the exclusion zones for dishes (35 minutes in) did not seem to show, or, had a very small side-lobes exclusion area.
So I was a bit confused over this as it was something the Mike had mentioned of using a side-lobe mask in a thread I started some time ago, were Mike pointed to an article on this https://en.wikipedia.org/wiki/Side_lobe.
It was mentioned that this only goes down to a 1.2m dish as smaller dished have less than 10 wavelengths may not perform as the chart.

Anyway using the RSGB calculator my main problem area has always been in me running Linux and using Libre office after a few minutes I get this message on the screen.
Screenshot from 2021-10-21 10-32-11.png
Screenshot from 2021-10-21 10-32-11.png (39.58 KiB) Viewed 4668 times
I can not convert to Libre office type .ods files as it will not let me get passed this box and once it occurs it is hard to cancel. So if anyone knows how to solve I would appreciate it.

I have printed off PAEC-2 in case it gives me more clues on exclusion zones, but it looks as though I will still have to await the planned spreadsheet table as mentioned in the talks.

Thanks to all that took part your knowledge goes beyond some of my comprehension and I am grateful to all.

Adrian

G7JTT
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Re: Microwave and QO100 EMF

Post by G7JTT » Thu Oct 21, 2021 10:03 am

Firstly sorry I knew I should of started a new thread the minute I hit send 🙈

Ok I've had a bit more of a thought about it and think I have a plan ! Unfortunately I'm now at work till 8pm tonight and I can't insert pictures via my phone. But basically I've gone outside before work to do some measurements and I think I may be ok. The only concern I still have is the rear of the dish ! It's located in the corner of the garden and my shed, there is a retaining wall which is 1.2m high then the usual 6ft wooden fence. The dish center is 1.3m AGL so really half the dish is below ground really in relation to my rear neighbor and they have trees growing along the fence. My neighbor to the left because of the shed can get no nearer than approximately 3m, to the right it's around 6m from the dish to the fence. So really it's only the rear neighbor who potentially could get close to the side/rear of the dish.


Ok more later hopefully I'll get back in time to join the net.

73 John

G8GKQ
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Re: Microwave and QO100 EMF

Post by G8GKQ » Thu Oct 28, 2021 9:09 pm

The RSGB EMF Team of Peter G4DSE and Ian GM3SEK are progessing well with their work on EMF Compliance guidance for QO-100 DATV TX dishes.

Early findings are unsurprising for a typical ground mounted 1.2m dish fed with 50W to a POTY. The area in front of the dish (out to about 4 metres in Southern England and 5 metres further North) will need to be protected as an "Exclusion Zone". The area immediately behind the dish (where you can see the feed around the rim of the dish) will also be an "Exclusion Zone" but this is unlikely to extend beyond the boundary of your property.

If you are unable to physicaly secure the area around the dish, It may be wise to consider the use of some sort of "Intrusion Detector" to alert you to the presence of persons in this area. Google "Driveway Alarm" to get some ideas.

For high wall-mounted dishes, there might not be any restrictions for persons at ground level (depending on the dish height).

Once the data has been formatted for typical use-cases and checked, we will be able to provide more detail. Certainly before the 18 November deadline.

Dave, G8GKQ

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PA3CRX
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Re: Microwave and QO100 EMF

Post by PA3CRX » Fri Oct 29, 2021 7:05 am

Looking at the calculator I posted in viewtopic.php?f=2&t=7660 and the data
1.2m dish fed with 50W
it shows
Result fieldstrength calculator.JPG
Result fieldstrength calculator.JPG (97.27 KiB) Viewed 4241 times
So a distance of 14.7 meter in front of the dish.

However, because the dish is pointed upwards, after a few meters the beam will pass over your head.

Suppose we calculate with a person that is 2 meters tall, the dish is pointed 27 degrees up, the distance will be 3.9 meters. (20 degrees results in 5.5 meters). Of course measured from the lowest point of the dish, not the mount position :mrgreen:
It shows the distance is defined by the angle of the dish and how tall the person is :)

This totally complies the conclusions by Dave.

Powers under about 5 Watt (with this size dish) will reduce the considered safe distance.
So in fact, for ATV consider you need to have the space free in front of your dish (while transmitting).

Chris PA3CRX

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