Date   

Re: Ofcom RF Exposure limits proposal

David Redman
 

Quite a few in many well respected amateurs have put forth their view

I can only assume that a competent person(s) is able to give OFCOM guidance re the RSGB ( and UK amateurs position on this issue ) and to write a decent artical in Radcom consistent with RSGB policy and offering sample calculations covering 160m to say 3cms to comply ( or not ) with OFCOM's proposed policy.

At least we are then aware

Logical attack is the best means of amateur defence.

Dave
G4IDR

Ps I am not a competent person on this matter  but a lot of this group are............. I only use Doug,s VK3MA's program to guide me what is ' safe'  HF to even 23cms  eme 400w et all .



On Sat, 22 Feb 2020, 16:31 Neil Smith G4DBN, <neil@...> wrote:

Another useful tool from Doug's legacy.  My gut feeling about staying 10ft from the top band vertical at full chat is pretty much right, the ICNIRP settings with a ground mesh say 2.87m.  If I move to the USA though, I can go within 18 inches of the thing.

My manual calculation for the level in next-door's first-floor bedroom is confirmed by Doug's calculator at 50m on-axis, for full smoke on 70cm, but why would I transmit into their house anyway? All is good with the mast at >9m.  23cm and 13cm to the 3m dish are the worst case, but as I can't get within 15 degrees of the east and south horizon, and only have open fields from south through to north-west, there is nowhere humans could get within the beam unless they were REALLY good at climbing trees.

Neil G4DBN



On 22/02/2020 15:01, Richard GD8EXI wrote:

Suggest you try using the VK3UM EMR calculator, which can be downloaded from https://www.vk5dj.com/doug.html
before you start getting worried.

I have 400 watts to a 20dBd Yagi on 1296MHz and cannot get anyway near the danger levels at ground level. Even on axis you are safe at 29m assuming a 100% duty cycle. So unless you are a 8m tall person standing on my property you are safe.


Richard
GD8EXI

On 22/02/2020, 14:08, "GM6VXB via Groups.Io" <martin.andrew@...> wrote:

Do not forget that amateur transmissions usually are only for a few minutes, not a 'permantly on' transmission as in microwave and other commercial links.
So overall whatever maximum RF field is, it sholud be divided by 'Time on air/Hour'.
RF radiation unlike X-rays and Gamma type radiation is not cumulative. So when an RF source is not transmitting the effects (usually of heating various parts
of your body) stop.

I have done two RF radiation and safety courses (with Marconi) as at the time was working on some high power microwave equipment (2.3GHz around 2KW)
and management thought it might be a good idea for us to know and understand the risks involved.

It is a long time now since I have worked on high power microwave equipment and was involved in a incident involving loose waveguide and well above 10mW/M2
within 10 Metre of where we were working. Side effects, Non except for spending hours in hospital being checked over by doctors who new much less than we did.

Yes, you can cook things with microwaves, but I would be more concerned with standing next to a 70MHz beacon in bare feet on a metal floor. I know why but
until you read up on the effects of RF radiation you probably do not. A hint, I am 2M tall, Half a wavelength ?.

Martin, GM6VXB

 


 


 On Saturday, 22 February 2020, 13:27:37 GMT, Neil Smith G4DBN <neil@...> wrote:
 

 

 
 

I had to do an assessment of a point to point link across some schools playgrounds and playing fields, where there were loony parents concernmed their little darlings might get brain cancer from the link. I wasn't exactly onerous, but they didn't have the wit to insist on measurements. Somehow though, the RF from the phones their little darlings used all the time was "different". The clincher was the cost of digging up the cricket pitch and the new playground for fibre.  Faced with a £12k bill for the dig, they lost interest very rapidly in the health risks.  Could have been an intelligent response to my calculations showing that the only humans facing an exposure close to the ICNIRP guidelines would be to stilt-walkers close to the antennas.
 

However, looking at QRO on 70cm with a pump-up mast at 20ft, the level in my neighbour's bedroom was close to the guideline limit if you ignored the bricks, blocks, foil-backed plasterboard and metallized double glazing units . With the mast at 40ft, it was fine even at 400W.
 

It might be instructive to show some of the calculated field strengths for typical installations at various frequencies and relate those to the human body model.  Perhaps a Radcom article based on the existing ICNIRP levels would help demonstrate our commitment to public safety, even if the levels are just made-up numbers pandering to the nutjobs.  100 watts to a loft-mounted horizontal antenna on 6 or 2m gives some impressive EMFs in the rooms below.
 
 

Neil G4DBN
 
 
On 22/02/2020 12:43, Andy G4JNT wrote:
 
 


Yes, and if you actually bother to work out the watts / square metre at any reasonable range within the peak beam of the antenna, you'll realise it's not going to be that much of an issue in most cases. ....


 

As a quickie,  I once worked out the safe range fore a microwave cooker magnetron (700 Watts) used on its own, so effectively an isotropic antenna (don't ask why, I'd have to shoot you, it was for work) .   


 


 


 

Sounds a scary thing, though,  doesn't  it ....


 


 


 

Scroll Down for answer ...


 


 


 


 

You'll be surprised ...


 


 


 

Assume 50W /m^2  (5mW / cm^2) as exposure limit


 


 


 

Don't forget it's an Isotropic radiator


 


 


 


 

Keep going


 


 


 

And it is ....


 


 

A little under 1.1m


 

Isotropic so assume a sphere,  700 Watts at 50W/m^2 = 14 m^2

4.pi R^2 = 14

R = 1.06 metres


 

And yet, intuitively, does being just  1m away from a live uWave cooker magnetron 'feel' safe ?

It is...


 

Keep that same magnetron but leave it in the cooker with the door open (interlock disabled).  Assume the door cavity is a 50% efficient horn radiator (bit optimistic, but whateverrrr)

Aperture 0.08m^2, lambda = 0.125m    Gain (linear units) = 32    (or 15dBi if you prefer)

New safety distance, square law applies so gain of 32 increases that distance to 1.06 * SQRT(32) = 6 metres.


 

That's why uWave cookers have at least a double door interlock


 

 
 
 
 
 
 
 
 
 
 
Andy
www.g4jnt.com <http://www.g4jnt.com>

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
On Sat, 22 Feb 2020 at 12:18, Steve G4HTZ via Groups.Io <essexsteve@...> wrote:
 
 
Hopefully if we finally move qth in the next few months ...I was planning to mount the following at say 40ft above ground ..well above surrounding roof tops on the chimney ,qth about 140ft asl .
 
 10ghz 10w into say 28dbi sky dish
 23cms 300w at antenna into say a 19dbi 36 ele beam
 2m 400w at antenna into say a 12dbi yagi
 
 sounds like I might as well not bother at those power levels and take up stamp collecting  

 
-- 
Neil
<a href="http://g4dbn.uk/"><small>g4dbn.uk</small></a>


Re: Re path loss calculator

Dave
 

Thanks Steve, that’s great.
David G4GLT 


On 22 Feb 2020, at 17:31, Steve G4HTZ via Groups.Io <essexsteve@...> wrote:

This gives a reasonable idea ..it’s free ...but I’m sure there’s better ones ...just drag the map to your location...I use it on a IPAD 

http://www.heywhatsthat.com/


Re: Re path loss calculator

Steve G4HTZ
 

https://link.ui.com/#


or this one 


Re: Re path loss calculator

Steve G4HTZ
 

This gives a reasonable idea ..it’s free ...but I’m sure there’s better ones ...just drag the map to your location...I use it on a IPAD 

http://www.heywhatsthat.com/


Re path loss calculator

Dave
 

Hello,
I am keen to calculate a path loss
for a particular path. I looked online
and there were free programs.
Which program would be recommended
as easy to use?
Many thanks,
David G4GLT


Re: Ofcom RF Exposure limits proposal

John Fell
 

I tried to verify the 0.1dB noise quoted on my PLL LNB but after dunking in 100C water and then in an ice bucket , the RF output diminished ..........same result on the second one - I give up with this uwave lark.

73

John
G0API

On Sat, 22 Feb 2020 at 16:37, PAUL NICKALLS via Groups.Io <paulnick=btinternet.com@groups.io> wrote:
Maybe we should insist on relaxation of the planning laws so our masts are high enough to put them above any human exposure.

What about the Apple I phones that are outside limits?

https://www.dailymail.co.uk/sciencetech/article-7994811/iPhones-emitting-TWICE-legal-radiation-limit.html

The comments are interesting.

Maybe we should be able to self certify just like everyone else.

Maybe we could make measurements like the 0.1dB noise figure quoted for satellite LNBs.

Paul G8AQA


On 22/02/2020 15:01, Richard GD8EXI wrote:

Suggest you try using the VK3UM EMR calculator, which can be downloaded from https://www.vk5dj.com/doug.html
before you start getting worried.

I have 400 watts to a 20dBd Yagi on 1296MHz and cannot get anyway near the danger levels at ground level. Even on axis you are safe at 29m assuming a 100% duty cycle. So unless you are a 8m tall person standing on my property you are safe.


Richard
GD8EXI

On 22/02/2020, 14:08, "GM6VXB via Groups.Io" <martin.andrew@...> wrote:

Do not forget that amateur transmissions usually are only for a few minutes, not a 'permantly on' transmission as in microwave and other commercial links.
So overall whatever maximum RF field is, it sholud be divided by 'Time on air/Hour'.
RF radiation unlike X-rays and Gamma type radiation is not cumulative. So when an RF source is not transmitting the effects (usually of heating various parts
of your body) stop.

I have done two RF radiation and safety courses (with Marconi) as at the time was working on some high power microwave equipment (2.3GHz around 2KW)
and management thought it might be a good idea for us to know and understand the risks involved.

It is a long time now since I have worked on high power microwave equipment and was involved in a incident involving loose waveguide and well above 10mW/M2
within 10 Metre of where we were working. Side effects, Non except for spending hours in hospital being checked over by doctors who new much less than we did.

Yes, you can cook things with microwaves, but I would be more concerned with standing next to a 70MHz beacon in bare feet on a metal floor. I know why but
until you read up on the effects of RF radiation you probably do not. A hint, I am 2M tall, Half a wavelength ?.

Martin, GM6VXB

 


 


 On Saturday, 22 February 2020, 13:27:37 GMT, Neil Smith G4DBN <neil@...> wrote:
 

 

 
 

I had to do an assessment of a point to point link across some schools playgrounds and playing fields, where there were loony parents concernmed their little darlings might get brain cancer from the link. I wasn't exactly onerous, but they didn't have the wit to insist on measurements. Somehow though, the RF from the phones their little darlings used all the time was "different". The clincher was the cost of digging up the cricket pitch and the new playground for fibre.  Faced with a £12k bill for the dig, they lost interest very rapidly in the health risks.  Could have been an intelligent response to my calculations showing that the only humans facing an exposure close to the ICNIRP guidelines would be to stilt-walkers close to the antennas.
 

However, looking at QRO on 70cm with a pump-up mast at 20ft, the level in my neighbour's bedroom was close to the guideline limit if you ignored the bricks, blocks, foil-backed plasterboard and metallized double glazing units . With the mast at 40ft, it was fine even at 400W.
 

It might be instructive to show some of the calculated field strengths for typical installations at various frequencies and relate those to the human body model.  Perhaps a Radcom article based on the existing ICNIRP levels would help demonstrate our commitment to public safety, even if the levels are just made-up numbers pandering to the nutjobs.  100 watts to a loft-mounted horizontal antenna on 6 or 2m gives some impressive EMFs in the rooms below.
 
 

Neil G4DBN
 
 
On 22/02/2020 12:43, Andy G4JNT wrote:
 
 


Yes, and if you actually bother to work out the watts / square metre at any reasonable range within the peak beam of the antenna, you'll realise it's not going to be that much of an issue in most cases. ...


 

As a quickie,  I once worked out the safe range fore a microwave cooker magnetron (700 Watts) used on its own, so effectively an isotropic antenna (don't ask why, I'd have to shoot you, it was for work) .   


 


 


 

Sounds a scary thing, though,  doesn't  it ....


 


 


 

Scroll Down for answer ...


 


 


 


 

You'll be surprised ...


 


 


 

Assume 50W /m^2  (5mW / cm^2) as exposure limit


 


 


 

Don't forget it's an Isotropic radiator


 


 


 


 

Keep going


 


 


 

And it is ....


 


 

A little under 1.1m


 

Isotropic so assume a sphere,  700 Watts at 50W/m^2 = 14 m^2

4.pi R^2 = 14

R = 1.06 metres


 

And yet, intuitively, does being just  1m away from a live uWave cooker magnetron 'feel' safe ?

It is...


 

Keep that same magnetron but leave it in the cooker with the door open (interlock disabled).  Assume the door cavity is a 50% efficient horn radiator (bit optimistic, but whateverrrr)

Aperture 0.08m^2, lambda = 0.125m    Gain (linear units) = 32    (or 15dBi if you prefer)

New safety distance, square law applies so gain of 32 increases that distance to 1.06 * SQRT(32) = 6 metres.


 

That's why uWave cookers have at least a double door interlock


 

 
 
 
 
 
 
 
 
 
 
Andy
www.g4jnt.com <http://www.g4jnt.com>

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
On Sat, 22 Feb 2020 at 12:18, Steve G4HTZ via Groups.Io <essexsteve@...> wrote:
 
 
Hopefully if we finally move qth in the next few months ...I was planning to mount the following at say 40ft above ground ..well above surrounding roof tops on the chimney ,qth about 140ft asl .
 
 10ghz 10w into say 28dbi sky dish
 23cms 300w at antenna into say a 19dbi 36 ele beam
 2m 400w at antenna into say a 12dbi yagi
 
 sounds like I might as well not bother at those power levels and take up stamp collecting  

 


Info on SMPSU

Jim, GI1CET
 

Just on the off chance as my usual searches and sources have not helped this time:

 

Would anyone have any info on the following SMPSU

 

Harmer & Simmons SMF2800 , in particular any info on voltage adjust to bring it down just a few volts

 

Regards

 

Jim, GI1CET

 


Re: Ofcom RF Exposure limits proposal

PAUL NICKALLS
 

Maybe we should insist on relaxation of the planning laws so our masts are high enough to put them above any human exposure.

What about the Apple I phones that are outside limits?

https://www.dailymail.co.uk/sciencetech/article-7994811/iPhones-emitting-TWICE-legal-radiation-limit.html

The comments are interesting.

Maybe we should be able to self certify just like everyone else.

Maybe we could make measurements like the 0.1dB noise figure quoted for satellite LNBs.

Paul G8AQA


On 22/02/2020 15:01, Richard GD8EXI wrote:

Suggest you try using the VK3UM EMR calculator, which can be downloaded from https://www.vk5dj.com/doug.html
before you start getting worried.

I have 400 watts to a 20dBd Yagi on 1296MHz and cannot get anyway near the danger levels at ground level. Even on axis you are safe at 29m assuming a 100% duty cycle. So unless you are a 8m tall person standing on my property you are safe.


Richard
GD8EXI

On 22/02/2020, 14:08, "GM6VXB via Groups.Io" <martin.andrew@...> wrote:

Do not forget that amateur transmissions usually are only for a few minutes, not a 'permantly on' transmission as in microwave and other commercial links.
So overall whatever maximum RF field is, it sholud be divided by 'Time on air/Hour'.
RF radiation unlike X-rays and Gamma type radiation is not cumulative. So when an RF source is not transmitting the effects (usually of heating various parts
of your body) stop.

I have done two RF radiation and safety courses (with Marconi) as at the time was working on some high power microwave equipment (2.3GHz around 2KW)
and management thought it might be a good idea for us to know and understand the risks involved.

It is a long time now since I have worked on high power microwave equipment and was involved in a incident involving loose waveguide and well above 10mW/M2
within 10 Metre of where we were working. Side effects, Non except for spending hours in hospital being checked over by doctors who new much less than we did.

Yes, you can cook things with microwaves, but I would be more concerned with standing next to a 70MHz beacon in bare feet on a metal floor. I know why but
until you read up on the effects of RF radiation you probably do not. A hint, I am 2M tall, Half a wavelength ?.

Martin, GM6VXB

 


 


 On Saturday, 22 February 2020, 13:27:37 GMT, Neil Smith G4DBN <neil@...> wrote:
 

 

 
 

I had to do an assessment of a point to point link across some schools playgrounds and playing fields, where there were loony parents concernmed their little darlings might get brain cancer from the link. I wasn't exactly onerous, but they didn't have the wit to insist on measurements. Somehow though, the RF from the phones their little darlings used all the time was "different". The clincher was the cost of digging up the cricket pitch and the new playground for fibre.  Faced with a £12k bill for the dig, they lost interest very rapidly in the health risks.  Could have been an intelligent response to my calculations showing that the only humans facing an exposure close to the ICNIRP guidelines would be to stilt-walkers close to the antennas.
 

However, looking at QRO on 70cm with a pump-up mast at 20ft, the level in my neighbour's bedroom was close to the guideline limit if you ignored the bricks, blocks, foil-backed plasterboard and metallized double glazing units . With the mast at 40ft, it was fine even at 400W.
 

It might be instructive to show some of the calculated field strengths for typical installations at various frequencies and relate those to the human body model.  Perhaps a Radcom article based on the existing ICNIRP levels would help demonstrate our commitment to public safety, even if the levels are just made-up numbers pandering to the nutjobs.  100 watts to a loft-mounted horizontal antenna on 6 or 2m gives some impressive EMFs in the rooms below.
 
 

Neil G4DBN
 
 
On 22/02/2020 12:43, Andy G4JNT wrote:
 
 


Yes, and if you actually bother to work out the watts / square metre at any reasonable range within the peak beam of the antenna, you'll realise it's not going to be that much of an issue in most cases. ...


 

As a quickie,  I once worked out the safe range fore a microwave cooker magnetron (700 Watts) used on its own, so effectively an isotropic antenna (don't ask why, I'd have to shoot you, it was for work) .   


 


 


 

Sounds a scary thing, though,  doesn't  it ....


 


 


 

Scroll Down for answer ...


 


 


 


 

You'll be surprised ...


 


 


 

Assume 50W /m^2  (5mW / cm^2) as exposure limit


 


 


 

Don't forget it's an Isotropic radiator


 


 


 


 

Keep going


 


 


 

And it is ....


 


 

A little under 1.1m


 

Isotropic so assume a sphere,  700 Watts at 50W/m^2 = 14 m^2

4.pi R^2 = 14

R = 1.06 metres


 

And yet, intuitively, does being just  1m away from a live uWave cooker magnetron 'feel' safe ?

It is...


 

Keep that same magnetron but leave it in the cooker with the door open (interlock disabled).  Assume the door cavity is a 50% efficient horn radiator (bit optimistic, but whateverrrr)

Aperture 0.08m^2, lambda = 0.125m    Gain (linear units) = 32    (or 15dBi if you prefer)

New safety distance, square law applies so gain of 32 increases that distance to 1.06 * SQRT(32) = 6 metres.


 

That's why uWave cookers have at least a double door interlock


 

 
 
 
 
 
 
 
 
 
 
Andy
www.g4jnt.com <http://www.g4jnt.com>

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
On Sat, 22 Feb 2020 at 12:18, Steve G4HTZ via Groups.Io <essexsteve@...> wrote:
 
 
Hopefully if we finally move qth in the next few months ...I was planning to mount the following at say 40ft above ground ..well above surrounding roof tops on the chimney ,qth about 140ft asl .
 
 10ghz 10w into say 28dbi sky dish
 23cms 300w at antenna into say a 19dbi 36 ele beam
 2m 400w at antenna into say a 12dbi yagi
 
 sounds like I might as well not bother at those power levels and take up stamp collecting  

 


Re: Ofcom RF Exposure limits proposal

Neil Smith G4DBN
 

Another useful tool from Doug's legacy.  My gut feeling about staying 10ft from the top band vertical at full chat is pretty much right, the ICNIRP settings with a ground mesh say 2.87m.  If I move to the USA though, I can go within 18 inches of the thing.

My manual calculation for the level in next-door's first-floor bedroom is confirmed by Doug's calculator at 50m on-axis, for full smoke on 70cm, but why would I transmit into their house anyway? All is good with the mast at >9m.  23cm and 13cm to the 3m dish are the worst case, but as I can't get within 15 degrees of the east and south horizon, and only have open fields from south through to north-west, there is nowhere humans could get within the beam unless they were REALLY good at climbing trees.

Neil G4DBN



On 22/02/2020 15:01, Richard GD8EXI wrote:

Suggest you try using the VK3UM EMR calculator, which can be downloaded from https://www.vk5dj.com/doug.html
before you start getting worried.

I have 400 watts to a 20dBd Yagi on 1296MHz and cannot get anyway near the danger levels at ground level. Even on axis you are safe at 29m assuming a 100% duty cycle. So unless you are a 8m tall person standing on my property you are safe.


Richard
GD8EXI

On 22/02/2020, 14:08, "GM6VXB via Groups.Io" <martin.andrew@...> wrote:

Do not forget that amateur transmissions usually are only for a few minutes, not a 'permantly on' transmission as in microwave and other commercial links.
So overall whatever maximum RF field is, it sholud be divided by 'Time on air/Hour'.
RF radiation unlike X-rays and Gamma type radiation is not cumulative. So when an RF source is not transmitting the effects (usually of heating various parts
of your body) stop.

I have done two RF radiation and safety courses (with Marconi) as at the time was working on some high power microwave equipment (2.3GHz around 2KW)
and management thought it might be a good idea for us to know and understand the risks involved.

It is a long time now since I have worked on high power microwave equipment and was involved in a incident involving loose waveguide and well above 10mW/M2
within 10 Metre of where we were working. Side effects, Non except for spending hours in hospital being checked over by doctors who new much less than we did.

Yes, you can cook things with microwaves, but I would be more concerned with standing next to a 70MHz beacon in bare feet on a metal floor. I know why but
until you read up on the effects of RF radiation you probably do not. A hint, I am 2M tall, Half a wavelength ?.

Martin, GM6VXB

 


 


 On Saturday, 22 February 2020, 13:27:37 GMT, Neil Smith G4DBN <neil@...> wrote:
 

 

 
 

I had to do an assessment of a point to point link across some schools playgrounds and playing fields, where there were loony parents concernmed their little darlings might get brain cancer from the link. I wasn't exactly onerous, but they didn't have the wit to insist on measurements. Somehow though, the RF from the phones their little darlings used all the time was "different". The clincher was the cost of digging up the cricket pitch and the new playground for fibre.  Faced with a £12k bill for the dig, they lost interest very rapidly in the health risks.  Could have been an intelligent response to my calculations showing that the only humans facing an exposure close to the ICNIRP guidelines would be to stilt-walkers close to the antennas.
 

However, looking at QRO on 70cm with a pump-up mast at 20ft, the level in my neighbour's bedroom was close to the guideline limit if you ignored the bricks, blocks, foil-backed plasterboard and metallized double glazing units . With the mast at 40ft, it was fine even at 400W.
 

It might be instructive to show some of the calculated field strengths for typical installations at various frequencies and relate those to the human body model.  Perhaps a Radcom article based on the existing ICNIRP levels would help demonstrate our commitment to public safety, even if the levels are just made-up numbers pandering to the nutjobs.  100 watts to a loft-mounted horizontal antenna on 6 or 2m gives some impressive EMFs in the rooms below.
 
 

Neil G4DBN
 
 
On 22/02/2020 12:43, Andy G4JNT wrote:
 
 


Yes, and if you actually bother to work out the watts / square metre at any reasonable range within the peak beam of the antenna, you'll realise it's not going to be that much of an issue in most cases. ....


 

As a quickie,  I once worked out the safe range fore a microwave cooker magnetron (700 Watts) used on its own, so effectively an isotropic antenna (don't ask why, I'd have to shoot you, it was for work) .   


 


 


 

Sounds a scary thing, though,  doesn't  it ....


 


 


 

Scroll Down for answer ...


 


 


 


 

You'll be surprised ...


 


 


 

Assume 50W /m^2  (5mW / cm^2) as exposure limit


 


 


 

Don't forget it's an Isotropic radiator


 


 


 


 

Keep going


 


 


 

And it is ....


 


 

A little under 1.1m


 

Isotropic so assume a sphere,  700 Watts at 50W/m^2 = 14 m^2

4.pi R^2 = 14

R = 1.06 metres


 

And yet, intuitively, does being just  1m away from a live uWave cooker magnetron 'feel' safe ?

It is...


 

Keep that same magnetron but leave it in the cooker with the door open (interlock disabled).  Assume the door cavity is a 50% efficient horn radiator (bit optimistic, but whateverrrr)

Aperture 0.08m^2, lambda = 0.125m    Gain (linear units) = 32    (or 15dBi if you prefer)

New safety distance, square law applies so gain of 32 increases that distance to 1.06 * SQRT(32) = 6 metres.


 

That's why uWave cookers have at least a double door interlock


 

 
 
 
 
 
 
 
 
 
 
Andy
www.g4jnt.com <http://www.g4jnt.com>

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
On Sat, 22 Feb 2020 at 12:18, Steve G4HTZ via Groups.Io <essexsteve@...> wrote:
 
 
Hopefully if we finally move qth in the next few months ...I was planning to mount the following at say 40ft above ground ..well above surrounding roof tops on the chimney ,qth about 140ft asl .
 
 10ghz 10w into say 28dbi sky dish
 23cms 300w at antenna into say a 19dbi 36 ele beam
 2m 400w at antenna into say a 12dbi yagi
 
 sounds like I might as well not bother at those power levels and take up stamp collecting  

 
-- 
Neil
<a href="http://g4dbn.uk/"><small>g4dbn.uk</small></a>


Re: Ofcom RF Exposure limits proposal

Richard GD8EXI
 


Suggest you try using the VK3UM EMR calculator, which can be downloaded from https://www.vk5dj.com/doug.html
before you start getting worried.

I have 400 watts to a 20dBd Yagi on 1296MHz and cannot get anyway near the danger levels at ground level. Even on axis you are safe at 29m assuming a 100% duty cycle. So unless you are a 8m tall person standing on my property you are safe.


Richard
GD8EXI

On 22/02/2020, 14:08, "GM6VXB via Groups.Io" <martin.andrew@...> wrote:

Do not forget that amateur transmissions usually are only for a few minutes, not a 'permantly on' transmission as in microwave and other commercial links.
So overall whatever maximum RF field is, it sholud be divided by 'Time on air/Hour'.
RF radiation unlike X-rays and Gamma type radiation is not cumulative. So when an RF source is not transmitting the effects (usually of heating various parts
of your body) stop.

I have done two RF radiation and safety courses (with Marconi) as at the time was working on some high power microwave equipment (2.3GHz around 2KW)
and management thought it might be a good idea for us to know and understand the risks involved.

It is a long time now since I have worked on high power microwave equipment and was involved in a incident involving loose waveguide and well above 10mW/M2
within 10 Metre of where we were working. Side effects, Non except for spending hours in hospital being checked over by doctors who new much less than we did.

Yes, you can cook things with microwaves, but I would be more concerned with standing next to a 70MHz beacon in bare feet on a metal floor. I know why but
until you read up on the effects of RF radiation you probably do not. A hint, I am 2M tall, Half a wavelength ?.

Martin, GM6VXB

 


 


 On Saturday, 22 February 2020, 13:27:37 GMT, Neil Smith G4DBN <neil@...> wrote:
 

 

 
 

I had to do an assessment of a point to point link across some schools playgrounds and playing fields, where there were loony parents concernmed their little darlings might get brain cancer from the link. I wasn't exactly onerous, but they didn't have the wit to insist on measurements. Somehow though, the RF from the phones their little darlings used all the time was "different". The clincher was the cost of digging up the cricket pitch and the new playground for fibre.  Faced with a £12k bill for the dig, they lost interest very rapidly in the health risks.  Could have been an intelligent response to my calculations showing that the only humans facing an exposure close to the ICNIRP guidelines would be to stilt-walkers close to the antennas.
 

However, looking at QRO on 70cm with a pump-up mast at 20ft, the level in my neighbour's bedroom was close to the guideline limit if you ignored the bricks, blocks, foil-backed plasterboard and metallized double glazing units . With the mast at 40ft, it was fine even at 400W.
 

It might be instructive to show some of the calculated field strengths for typical installations at various frequencies and relate those to the human body model.  Perhaps a Radcom article based on the existing ICNIRP levels would help demonstrate our commitment to public safety, even if the levels are just made-up numbers pandering to the nutjobs.  100 watts to a loft-mounted horizontal antenna on 6 or 2m gives some impressive EMFs in the rooms below.
 
 

Neil G4DBN
 
 
On 22/02/2020 12:43, Andy G4JNT wrote:
 
 


Yes, and if you actually bother to work out the watts / square metre at any reasonable range within the peak beam of the antenna, you'll realise it's not going to be that much of an issue in most cases. ....


 

As a quickie,  I once worked out the safe range fore a microwave cooker magnetron (700 Watts) used on its own, so effectively an isotropic antenna (don't ask why, I'd have to shoot you, it was for work) .   


 


 


 

Sounds a scary thing, though,  doesn't  it ....


 


 


 

Scroll Down for answer ...


 


 


 


 

You'll be surprised ...


 


 


 

Assume 50W /m^2  (5mW / cm^2) as exposure limit


 


 


 

Don't forget it's an Isotropic radiator


 


 


 


 

Keep going


 


 


 

And it is ....


 


 

A little under 1.1m


 

Isotropic so assume a sphere,  700 Watts at 50W/m^2 = 14 m^2

4.pi R^2 = 14

R = 1.06 metres


 

And yet, intuitively, does being just  1m away from a live uWave cooker magnetron 'feel' safe ?

It is...


 

Keep that same magnetron but leave it in the cooker with the door open (interlock disabled).  Assume the door cavity is a 50% efficient horn radiator (bit optimistic, but whateverrrr)

Aperture 0.08m^2, lambda = 0.125m    Gain (linear units) = 32    (or 15dBi if you prefer)

New safety distance, square law applies so gain of 32 increases that distance to 1.06 * SQRT(32) = 6 metres.


 

That's why uWave cookers have at least a double door interlock


 

 
 
 
 
 
 
 
 
 
 
Andy
www.g4jnt.com <http://www.g4jnt.com>

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
On Sat, 22 Feb 2020 at 12:18, Steve G4HTZ via Groups.Io <essexsteve@...> wrote:
 
 
Hopefully if we finally move qth in the next few months ...I was planning to mount the following at say 40ft above ground ..well above surrounding roof tops on the chimney ,qth about 140ft asl .
 
 10ghz 10w into say 28dbi sky dish
 23cms 300w at antenna into say a 19dbi 36 ele beam
 2m 400w at antenna into say a 12dbi yagi
 
 sounds like I might as well not bother at those power levels and take up stamp collecting  

 


Re: Ofcom RF Exposure limits proposal

Steve G4HTZ
 

Thanks to those who have provided more technical answers ....after seeing the initial posting this morning I was a bit concerned .

andy ...your equation totally lost me ...not hard ....I am one of those non professionals who still think it’s amazing that I managed to cobble some parts together and work stations on 10ghz over non line of site paths !! 

cheers
steve G4HTZ 


Re: Ofcom RF Exposure limits proposal

GM6VXB
 

Do not forget that amateur transmissions usually are only for a few minutes, not a 'permantly on' transmission as in microwave and other commercial links.
So overall whatever maximum RF field is, it sholud be divided by 'Time on air/Hour'.
RF radiation unlike X-rays and Gamma type radiation is not cumulative. So when an RF source is not transmitting the effects (usually of heating various parts
of your body) stop.

I have done two RF radiation and safety courses (with Marconi) as at the time was working on some high power microwave equipment (2.3GHz around 2KW)
and management thought it might be a good idea for us to know and understand the risks involved.

It is a long time now since I have worked on high power microwave equipment and was involved in a incident involving loose waveguide and well above 10mW/M2
within 10 Metre of where we were working. Side effects, Non except for spending hours in hospital being checked over by doctors who new much less than we did.

Yes, you can cook things with microwaves, but I would be more concerned with standing next to a 70MHz beacon in bare feet on a metal floor. I know why but
until you read up on the effects of RF radiation you probably do not. A hint, I am 2M tall, Half a wavelength ?.

Martin, GM6VXB



On Saturday, 22 February 2020, 13:27:37 GMT, Neil Smith G4DBN <neil@...> wrote:


I had to do an assessment of a point to point link across some schools playgrounds and playing fields, where there were loony parents concernmed their little darlings might get brain cancer from the link. I wasn't exactly onerous, but they didn't have the wit to insist on measurements. Somehow though, the RF from the phones their little darlings used all the time was "different". The clincher was the cost of digging up the cricket pitch and the new playground for fibre.  Faced with a £12k bill for the dig, they lost interest very rapidly in the health risks.  Could have been an intelligent response to my calculations showing that the only humans facing an exposure close to the ICNIRP guidelines would be to stilt-walkers close to the antennas.

However, looking at QRO on 70cm with a pump-up mast at 20ft, the level in my neighbour's bedroom was close to the guideline limit if you ignored the bricks, blocks, foil-backed plasterboard and metallized double glazing units . With the mast at 40ft, it was fine even at 400W.

It might be instructive to show some of the calculated field strengths for typical installations at various frequencies and relate those to the human body model.  Perhaps a Radcom article based on the existing ICNIRP levels would help demonstrate our commitment to public safety, even if the levels are just made-up numbers pandering to the nutjobs.  100 watts to a loft-mounted horizontal antenna on 6 or 2m gives some impressive EMFs in the rooms below.

Neil G4DBN

On 22/02/2020 12:43, Andy G4JNT wrote:
Yes, and if you actually bother to work out the watts / square metre at any reasonable range within the peak beam of the antenna, you'll realise it's not going to be that much of an issue in most cases. ....

As a quickie,  I once worked out the safe range fore a microwave cooker magnetron (700 Watts) used on its own, so effectively an isotropic antenna (don't ask why, I'd have to shoot you, it was for work) .   



Sounds a scary thing, though,  doesn't  it ....



Scroll Down for answer ...




You'll be surprised ...



Assume 50W /m^2  (5mW / cm^2) as exposure limit



Don't forget it's an Isotropic radiator 




Keep going



And it is ....


A little under 1.1m

Isotropic so assume a sphere,  700 Watts at 50W/m^2 = 14 m^2
4.pi R^2 = 14
R = 1.06 metres

And yet, intuitively, does being just  1m away from a live uWave cooker magnetron 'feel' safe ?
It is...

Keep that same magnetron but leave it in the cooker with the door open (interlock disabled).  Assume the door cavity is a 50% efficient horn radiator (bit optimistic, but whateverrrr) 
Aperture 0.08m^2, lambda = 0.125m    Gain (linear units) = 32    (or 15dBi if you prefer)
New safety distance, square law applies so gain of 32 increases that distance to 1.06 * SQRT(32) = 6 metres.

That's why uWave cookers have at least a double door interlock



On Sat, 22 Feb 2020 at 12:18, Steve G4HTZ via Groups.Io <essexsteve=icloud.com@groups.io> wrote:
Hopefully if we finally move qth in the next few months ...I was planning to mount the following at say 40ft above ground ..well above surrounding roof tops on the chimney ,qth about 140ft asl .

10ghz 10w into say 28dbi sky dish 
23cms 300w at antenna into say a 19dbi 36 ele beam 
2m 400w at antenna into say a 12dbi yagi 

sounds like I might as well not bother at those power levels and take up stamp collecting 
-- 
Neil
<a href="http://g4dbn.uk/"><small>g4dbn.uk</small></a>


Re: Ofcom RF Exposure limits proposal

Neil Smith G4DBN
 

I had to do an assessment of a point to point link across some schools playgrounds and playing fields, where there were loony parents concernmed their little darlings might get brain cancer from the link. I wasn't exactly onerous, but they didn't have the wit to insist on measurements. Somehow though, the RF from the phones their little darlings used all the time was "different". The clincher was the cost of digging up the cricket pitch and the new playground for fibre.  Faced with a £12k bill for the dig, they lost interest very rapidly in the health risks.  Could have been an intelligent response to my calculations showing that the only humans facing an exposure close to the ICNIRP guidelines would be to stilt-walkers close to the antennas.

However, looking at QRO on 70cm with a pump-up mast at 20ft, the level in my neighbour's bedroom was close to the guideline limit if you ignored the bricks, blocks, foil-backed plasterboard and metallized double glazing units . With the mast at 40ft, it was fine even at 400W.

It might be instructive to show some of the calculated field strengths for typical installations at various frequencies and relate those to the human body model.  Perhaps a Radcom article based on the existing ICNIRP levels would help demonstrate our commitment to public safety, even if the levels are just made-up numbers pandering to the nutjobs.  100 watts to a loft-mounted horizontal antenna on 6 or 2m gives some impressive EMFs in the rooms below.

Neil G4DBN

On 22/02/2020 12:43, Andy G4JNT wrote:
Yes, and if you actually bother to work out the watts / square metre at any reasonable range within the peak beam of the antenna, you'll realise it's not going to be that much of an issue in most cases. ....

As a quickie,  I once worked out the safe range fore a microwave cooker magnetron (700 Watts) used on its own, so effectively an isotropic antenna (don't ask why, I'd have to shoot you, it was for work) .   



Sounds a scary thing, though,  doesn't  it ....



Scroll Down for answer ...




You'll be surprised ...



Assume 50W /m^2  (5mW / cm^2) as exposure limit



Don't forget it's an Isotropic radiator 




Keep going



And it is ....


A little under 1.1m

Isotropic so assume a sphere,  700 Watts at 50W/m^2 = 14 m^2
4.pi R^2 = 14
R = 1.06 metres

And yet, intuitively, does being just  1m away from a live uWave cooker magnetron 'feel' safe ?
It is...

Keep that same magnetron but leave it in the cooker with the door open (interlock disabled).  Assume the door cavity is a 50% efficient horn radiator (bit optimistic, but whateverrrr) 
Aperture 0.08m^2, lambda = 0.125m    Gain (linear units) = 32    (or 15dBi if you prefer)
New safety distance, square law applies so gain of 32 increases that distance to 1.06 * SQRT(32) = 6 metres.

That's why uWave cookers have at least a double door interlock



On Sat, 22 Feb 2020 at 12:18, Steve G4HTZ via Groups.Io <essexsteve=icloud.com@groups.io> wrote:
Hopefully if we finally move qth in the next few months ...I was planning to mount the following at say 40ft above ground ..well above surrounding roof tops on the chimney ,qth about 140ft asl .

10ghz 10w into say 28dbi sky dish 
23cms 300w at antenna into say a 19dbi 36 ele beam 
2m 400w at antenna into say a 12dbi yagi 

sounds like I might as well not bother at those power levels and take up stamp collecting 
-- 
Neil
<a href="http://g4dbn.uk/"><small>g4dbn.uk</small></a>


Re: Ofcom RF Exposure limits proposal

John Quarmby
 

I would expect that enforcement will be as rigorous as it is for radiated EMC from switched mode supplies and similar?

Perhaps we should start a rumour that wallwart power supplies and solar panel optimisers cause all manner of illnesses?

73

John G3XDY

On 22/02/2020 00:26, Murray Niman wrote:

[Edited Message Follows]


A better attempt with links etc - 

GB2RS
refers to the new Ofcom consultation on RF Exposure/Safety at
https://rsgb.org/main/blog/news/gb2rs/headlines/2020/02/21/ofcom-consults-on-emf-exposure/ 
and
 
The small print of the proposed new licence condition/guidance as broadly drafted at the rear is all encompassing (and potentially quite impractical) for any thing and any licensee with >10W eirp. 

Watch out....

AND
This stuff even cropped up in WRC process last year via some other countries, so its not just tin hats and nimbys 

   Murray G6JYB




Re: Ofcom RF Exposure limits proposal

Andy G4JNT
 

Yes, and if you actually bother to work out the watts / square metre at any reasonable range within the peak beam of the antenna, you'll realise it's not going to be that much of an issue in most cases. ....

As a quickie,  I once worked out the safe range fore a microwave cooker magnetron (700 Watts) used on its own, so effectively an isotropic antenna (don't ask why, I'd have to shoot you, it was for work) .   



Sounds a scary thing, though,  doesn't  it ....



Scroll Down for answer ...




You'll be surprised ...



Assume 50W /m^2  (5mW / cm^2) as exposure limit



Don't forget it's an Isotropic radiator 




Keep going



And it is ....


A little under 1.1m

Isotropic so assume a sphere,  700 Watts at 50W/m^2 = 14 m^2
4.pi R^2 = 14
R = 1.06 metres

And yet, intuitively, does being just  1m away from a live uWave cooker magnetron 'feel' safe ?
It is...

Keep that same magnetron but leave it in the cooker with the door open (interlock disabled).  Assume the door cavity is a 50% efficient horn radiator (bit optimistic, but whateverrrr) 
Aperture 0.08m^2, lambda = 0.125m    Gain (linear units) = 32    (or 15dBi if you prefer)
New safety distance, square law applies so gain of 32 increases that distance to 1.06 * SQRT(32) = 6 metres.

That's why uWave cookers have at least a double door interlock



On Sat, 22 Feb 2020 at 12:18, Steve G4HTZ via Groups.Io <essexsteve=icloud.com@groups.io> wrote:
Hopefully if we finally move qth in the next few months ...I was planning to mount the following at say 40ft above ground ..well above surrounding roof tops on the chimney ,qth about 140ft asl .

10ghz 10w into say 28dbi sky dish 
23cms 300w at antenna into say a 19dbi 36 ele beam 
2m 400w at antenna into say a 12dbi yagi 

sounds like I might as well not bother at those power levels and take up stamp collecting 


Re: Ofcom RF Exposure limits proposal

Steve G4HTZ
 

Hopefully if we finally move qth in the next few months ...I was planning to mount the following at say 40ft above ground ..well above surrounding roof tops on the chimney ,qth about 140ft asl .

10ghz 10w into say 28dbi sky dish 
23cms 300w at antenna into say a 19dbi 36 ele beam 
2m 400w at antenna into say a 12dbi yagi 

sounds like I might as well not bother at those power levels and take up stamp collecting 


Re: Ofcom RF Exposure limits proposal

Andy G4JNT
 

Indeed
It's hardly a difficult thing to work out




On Sat, 22 Feb 2020 at 11:50, Mike Willis <willis.mj@...> wrote:
Is there some reason we should not comply with public health exposure limits?
--
Mike G0MJW


Re: Ofcom RF Exposure limits proposal

Mike Willis
 

Is there some reason we should not comply with public health exposure limits?
--
Mike G0MJW


Re: Ofcom RF Exposure limits proposal

Ian White
 

On the positive side, this is not new in the world of amateur radio - US amateurs in particular have been doing this for years - but there are also some ghastly lessons from countries that have implemented it badly.

The main threat is always going to be the British tendency to take any international regulations and gold-plate them until nobody dares to do anything. This is actually bad Radiation Protection because the true objective is to work out how to say "yes" in a safe but practical way. THis is done by identifying and managing the risks - which is rarely the same as eliminating them completely.

With that issue in mind, the HSE may be a much better ally than PHE, because HSE does have an interest in what is reasonably practical. PHE... not really their business.

For amateurs in particular, there is also a legal aspect that might be turned in our favour. Arguably, this whole issue is already covered by the same body of law as householder responsibilities for potential hazards such as garden ponds within the domestic property boundaries. OFCOM might be persuaded to accept a less formal assessment of compliance with ICNIRP guidelines by amateurs as a way of having demonstrated sufficient diligence.

73 from Ian GM3SEK



On 22/02/2020 00:26, Murray Niman wrote:

[Edited Message Follows]


A better attempt with links etc - 

GB2RS
refers to the new Ofcom consultation on RF Exposure/Safety at
https://rsgb.org/main/blog/news/gb2rs/headlines/2020/02/21/ofcom-consults-on-emf-exposure/ 
and
 
The small print of the proposed new licence condition/guidance as broadly drafted at the rear is all encompassing (and potentially quite impractical) for any thing and any licensee with >10W eirp. 

Watch out....

AND
This stuff even cropped up in WRC process last year via some other countries, so its not just tin hats and nimbys 

   Murray G6JYB




Re: Ofcom RF Exposure limits proposal

Murray Niman
 


Hi Mark

I note your useful reply!  

Also, for info
RSGB EMC Committee folk have in the past worked with IARU on calcs and test methods (mainly at HF). If you ever do a VHF/UHF Ofcom SRP submission, then ICNIRP turns up and other volunteers with expertise have been really helpful too. However Ofcom's current proposal has all sorts of practical issues 

For info in other countries something like this has been around for a while and this led to the free ICNIRP tool on herel:-
https://www.iaru-r1.org/about-us/committees-and-working-groups/emc-committee-c7/links-to-emc-resources/ 


No doubt more in due course

73

  Murray


  Murray