Safety concerning ERP of transmitter

[VivaLaFisica]

I'm curious to figure out if I'm operating a transmitter with safety compliance regarding its HERP (Hazards of Electromagnetic Radiation to Personnel).

Put simply, the transmitter has a low and high output capability of 2w and 10w. The antenna it operates on has an 11db gain. Radiating around 2000 MHz is usual here.

Things to consider, if the transmitter is on low power, but I need to physically go near it to flip the switch to the high option, am I (as the operator) in danger? What is the minimum distance I can safely be away?

Any advice on the subject is appreciated. Please let me know if other info may be required.

 

[berkeman]

11db gain.

That is pretty directional. Just stay off to the side?

 

[VivaLaFisica]

That is pretty directional. Just stay off to the side?

It's an Omni-directional antenna. I know receivers are picking up the signal at many spots around the point of transmission.

 

[berkeman]

It's an Omni-directional antenna. I know receivers are picking up the signal at many spots around the point of transmission.

How do you get 11dBi out of an omni?

 

[sophiecentaur]

How do you get 11dBi out of an omni?

Same way that big TV stations do when placed at the centre of their service area. A high vertical aperture and stacked dipoles round a mast. 11dB is not excessive.
I screen shot this info from a presentation from Alan Dick Broadcast Ltd: It has 8 tiers. Big Boys' stuff at 120kW

@OP: If the switch is below the bottom of the array the exposure would be pretty small but it is a health and safety matter so you should perhaps get hold of an RF Hazard Meter. If this is a commercial setup then you will be aware of your liability and the risks to staff and public.

 

[davenn]

the antenna it operates on has an 11db gain. Radiating around 2000 MHz is usual here.

How do you get 11dBi out of an omni?

Same way that big TV stations do when placed at the centre of their service area. A high vertical aperture and stacked dipoles round a mast. 11dB is not excessive.

yeah but we would like to specifically know how the OP is doing it
I doubt that he is using the type of antennas used for a commercial TV transmitter station

 

[sophiecentaur]

I doubt that he is using the type of antennas used for a commercial TV transmitter station

Right enough but he would only need eight stacks. For 2GHz they would be perhaps 1/4 the height of a UHF transmission antenna. and if he just used single vertical dipoles against a narrow mast, his HRP would be cardioid shape. That's practically 'omni' if you put the null where it doesn't matter. His consumer-led reception survey could well miss the null.
It would be interesting to know where he gets the 11dB figure from, though.
Whilst we're being picky, I wonder what this means:

Radiating around 2000 MHz is usual here.

 

[berkeman]

we would like to specifically know how the OP is doing it

@VivaLaFisica -- Can you post a picture of your antenna and mast setup? Which one does it look like?

http://www.arcantenna.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/p/c/pc9010n.jpg

Or https://upload.wikimedia.org/wikipe...ater.JPG/220px-NHK-JOHG-FM_Akune_Repeater.JPG

 

[davenn]

Put simply, the transmitter has a low and high output capability of 2w and 10w. The antenna it operates on has an 11db gain. Radiating around 2000 MHz is usual here.

well to help you
lets get a bit more technical about what you are actually using
some photos would be of great help of the transmitter, any feedlines and antenna

a mate and I are regularly doing amateur TV on 2.4GHz (2400MHz) with ERP TX powers of over 200W

Jack standing by his 2.4GHz antenna. We were firing the signal over 100km to another hilltop.
20W into a 20dBi gain gridpack antenna

Jack is using a 144MHz handheld for liaison to the other end of the linkDave

 

[sophiecentaur]

I doubt that he is using the type of antennas used for a commercial TV transmitter station

You are right but, as I said earlier, a stack of 8 dipoles would give you something like that gain. (Like Mobile Phone base stations.)
We must await his response to Berkeman's pictures.
Antenna manufacturers are full of smoke and mirrors because it's very hard to disprove their claims.

 

[VivaLaFisica]

Thanks for all the input.

The antenna is something like this: https://southwestantennas.com/omni-...-array-22-25-ghz-11-dbi-flange-mount-1085-084

In the meanwhile, I've been looking at some power density equations and actually walking a spectrum analyzer closer/further away to check readings at certain distances... I'm hoping to crunch some numbers and be able to say for certain if things are safe.

 

[berkeman]

The antenna is something like this: https://southwestantennas.com/omni-...-array-22-25-ghz-11-dbi-flange-mount-1085-084

I don't see a picture or diagram of the antenna setup in your link, but it does say this: "Collinear Dipole Array"

So how high is your mast? Can you walk under the main radiation beam as asked about in an earlier post? Can you please post enough information in your next post so that we can stop wasting time guessing about your situation? Thanks.

 

[berkeman]

Jack standing by his 2.4GHz antenna. We were firing the signal over 100km to another hilltop.
20W into a 20dBi gain gridpack antenna

Jack is using a 144MHz handheld for liaison to the other end of the link

100km with a 5W handheld with its stock "rubber ducky" antenna -- impressive!

Must be pretty flat -- no hills in the way, right?

 

[davenn]

Must be pretty flat -- no hills in the way, right?

yup, line of sight, else the 2.4GHz wouldn't make it

here's some of the paths ... very hilly terrain, us guys spent lots of hours looking over maps, doing path plots etc for 2.4 through 5.8, 10 and up to 24GHz trying to find long paths
174km was my best achieved with FM ATV on 2.4 GHz
Can't remember if Jack VK2TRF and Dan VK2GG my "other partners in crime" have done further

You can also see the red sea path that the 3 of us did on 24GHz ATV, 76km
since my major heart illness 5 yrs ago, I have done very little amateur radio and no hill-topping
I just don't have the umph to lift dishes and other gear in and out of the car on hilltopsDave

 

[davenn]

Thanks for all the input.

The antenna is something like this: https://southwestantennas.com/omni-...-array-22-25-ghz-11-dbi-flange-mount-1085-084

In the meanwhile, I've been looking at some power density equations and actually walking a spectrum analyzer closer/further away to check readings at certain distances... I'm hoping to crunch some numbers and be able to say for certain if things are safe.

awesome :)

You will find levels drop off really fast

if you get a chance, show a pic of your TX setup as well
what are you using this stuff for ? extending wifi?

It would be preferable that you didn't stand within ~ 3 metres (10ft)
get the antenna mounted well above head height if possible and use decent low loss coax RG213, RG214, CFD400 or similar

Dave

 

[Baluncore]

Put simply, the transmitter has a low and high output capability of 2w and 10w. The antenna it operates on has an 11db gain. Radiating around 2000 MHz is usual here.

There are two concerns. Both are heating problems. Firstly; there is the possibility of a contact RF surface burn if high voltages are present. Secondly; the microwave heating of a small closed volume such as an eyeball is possible. 10W microwaves are usually not dangerous so long as you do not spend a long time in the beam.

 

[davenn]

Firstly; there is the possibility of a contact RF surface burn if high voltages are present.

which RF surface ?

 

[Baluncore]

which RF surface ?

The surface of your skin.

The problem with any highly tuned element is that at a high impedance point, where corona might be expected at higher powers, there can be high voltages present. I was once burnt by less than 10 watts of UHF. Expect it when you least expect it.

 

[VivaLaFisica]

awesome :)

You will find levels drop off really fast

if you get a chance, show a pic of your TX setup as well
what are you using this stuff for ? extending wifi?

It would be preferable that you didn't stand within ~ 3 metres (10ft)
get the antenna mounted well above head height if possible and use decent low loss coax RG213, RG214, CFD400 or similar

Dave

At this point, there isn't a standard setup of mounting the antenna. At its worst, another individual would be holding the antenna (yes, with their hand). Otherwise it'd be mounted at a height that puts the lower end of the antenna at head height.

The cables used are RG59. Maybe I'm being overly concerned, but I admit that I definitely operate within ten 10ft of transmission.

 

[sophiecentaur]

At its worst, another individual would be holding the antenna (yes, with their hand)

The vertical pattern of the array you have shown us is pretty narrow and I would worry about someone standing there, holding it. The main (omni) beam could end up pointing way above the horizon and also down on the crowd of users. If you have such a high end piece of kit then you really shouldn't be standing and holding it at ground level. At the very least, it should be elevated above nearby landscape features and held strictly vertical.
I can't see the point of using such an antenna if you are not making sure that it's used properly. If you are just running a transmitter test then use a simple directional antenna (yagi) that will be pointing in a known direction so that someone can do a useful remote signal strength measurement.

This is yet another example of a question that's been posted with meagre information to support it. It's frustrating for PF and it is unlikely to yield useful answers for the OP.

 

[VivaLaFisica]

I'm using the power density equation, PD = (R*4pi)/(G*W^2)
Where R is the received power, G is the antenna gain and W is the wavelength.

I should be focusing on the received antenna gain and not the antenna gain through transmission, right? That 11db I gave earlier is irrelevant in this calculation when I really should be using the antenna gain on the spectrum analyzer to check things.

Working under the assumption that anything greater than 10w/m^2 is unsafe, am I really ok to stand one foot away from the transmitting antenna then?

 

[VivaLaFisica]

The vertical pattern of the array you have shown us is pretty narrow and I would worry about someone standing there, holding it. The main (omni) beam could end up pointing way above the horizon and also down on the crowd of users. If you have such a high end piece of kit then you really shouldn't be standing and holding it at ground level. At the very least, it should be elevated above nearby landscape features and held strictly vertical.
I can't see the point of using such an antenna if you are not making sure that it's used properly. If you are just running a transmitter test then use a simple directional antenna (yagi) that will be pointing in a known direction so that someone can do a useful remote signal strength measurement.

This is yet another example of a question that's been posted with meagre information to support it. It's frustrating for PF and it is unlikely to yield useful answers for the OP.

That's actually a helpful suggestion. It certainly removes the most risk of radiating in any enclosed space where testing is done. My concern stems from "how do we safely test this in-house before we apply it operationally?"

 

[davenn]

At this point, there isn't a standard setup of mounting the antenna. At its worst, another individual would be holding the antenna (yes, with their hand). Otherwise it'd be mounted at a height that puts the lower end of the antenna at head height.

OK for temporary experimenting, mount it on a long (3-4 metre) wooden pole so that it stood up well above head height
anything else would not be safe

The cables used are RG59. Maybe I'm being overly concerned, but I admit that I definitely operate within ten 10ft of transmission.

dreadfully lossy at 2.4 GHz ... you seriously need to rethink you plan using my suggestions

you didn't answer my questions on your use of the transmitter ... PLEASE DO SO
There are power limitations on this band ( ~ 1W) unless, like me, you are a licenced user

The surface of your skin.

Huh ? ... that didn't answer the Q, doesn't even make sense in the context of your original comment and my Q

This is yet another example of a question that's been posted with meagre information to support it. It's frustrating for PF and it is unlikely to yield useful answers for the OP.

Totally agree ... drives you nutz when good info isn't given, even when asked forDave

 

[VivaLaFisica]

dreadfully lossy at 2.4 GHz ... you seriously need to rethink you plan using my suggestions

you didn't answer my questions on your use of the transmitter ... PLEASE DO SO
There are power limitations on this band ( ~ 1W) unless, like me, you are a licenced user

Dave

This is to transmit a live video feed that can be viewed at a remote location. How does the cable affect my seen image? What can I expect with one of your suggestions?

I ended up taking horizontal and vertical measurements with a 10db gain horn antenna on my spectrum analyzer. Plugging in some numbers near the transmitting antenna, I'm getting a power density of around 0.08 watts/m^2. Would this sort of exposure over time induce headaches, burns, etc...?

 

[davenn]

This is to transmit a live video feed that can be viewed at a remote location.

OK

so a $500 Omni-directional antenna is a waste of money and not going to give you the directionality you need
you need yagi antennas, one at each end ... some one posted an image of one earlier in the thread ... mite have been @berkeman

You do understand that 2.4 GHz is primarily line of sight ? ... .that is, if there isn't a clear path between the 2 antennas
then you are unlikely to get a signal between them

Hope you have got a license to use this ... else you are likely to upset other users of the band

How does the cable affect my seen image?

I already commented on how RG58 or RG59 is very lossy, that means you loose power, that means less radiated signal
because less power is getting to the antenna.
How much is lost depends on the type and length of coax. Even the cables I mentioned earlier have losses at 2.4GHz
but is cable lengths are kept under 10m, the losses are manageable

The CFD400 ( LMR400) coax that I mentioned earlier is the best of the 3 choices I gave.
it's going to have approx 2 dB loss at 2.2 Ghz for a 10 metre length. That's getting close to loosing 1/2 the input power
10W in one end = ~ 6 or 7W out the other end
And don't forget this happens on the receive end as well where you are dealing with tiny received signal levels 10's of uVDave

 

[Baluncore]

Huh ? ... that didn't answer the Q, doesn't even make sense in the context of your original comment and my Q

If you do not specify whose and which Q you are referring to, it confirms there is a misunderstanding. Without information I cannot identify where that misunderstanding lies. An empty response is unconstructive and just serves to widen the gap.

 

[davenn]

If you do not specify whose and which Q you are referring to, it confirms there is a misunderstanding.

come on now don't tell fibs ... I specifically quoted you in post #17

 

[sophiecentaur]

I think the OP just wanted someone to say "It's nothing to worry about - just carry on."
I think he must have very little idea about what he is doing because he has not picked up on the questions we have asked. He wants to stand and hold the antenna !? for an experimental setup. This is not something I would want to be involved with.

 

[berkeman]

He wants to stand and hold the antenna !?

Yeah, I think that is worriesome to all of us.

come on now don't tell fibs ... I specifically quoted you in post #17

If you do not specify whose and which Q you are referring to, it confirms there is a misunderstanding.

Good technical responses so far in the thread, folks. Let's stay on topic. Thanks.

 

[davenn]

I think he must have very little idea about what he is doing because he has not picked up on the questions we have asked.

agreed

He wants to stand and hold the antenna !? for an experimental setup

yup, which is why I specifically suggested ...

OK for temporary experimenting, mount it on a long (3-4 metre) wooden pole so that it stood up well above head height
anything else would not be safe

he definitely needs some direct on-hand/on-site guidance

Dave

 

[sophiecentaur]

he definitely needs some direct on-hand/on-site guidance

Are you after some plane tickets?

 

[tech99]

I'm curious to figure out if I'm operating a transmitter with safety compliance regarding its HERP (Hazards of Electromagnetic Radiation to Personnel).

Put simply, the transmitter has a low and high output capability of 2w and 10w. The antenna it operates on has an 11db gain. Radiating around 2000 MHz is usual here.

Things to consider, if the transmitter is on low power, but I need to physically go near it to flip the switch to the high option, am I (as the operator) in danger? What is the minimum distance I can safely be away?

Any advice on the subject is appreciated. Please let me know if other info may be required.

The maximum intensity near the antenna is easily found approximately by dividing the power by the area of the antenna aperture.
For an antenna with a gain of 11dBi we expect an aperture of A = lambda^2 x G / 4 x pi = 15^2 x 12.5 / 4 x pi = 225 cm^2
So the intensity is 10 / 225 W/cm^2 = 0.04 W/cm^2 = 40mW/cm^2
The international recommendations for exposure to non ionising radiation are published by the ICNIRP (http://www.icnirp.org/cms/upload/publications/ICNIRPemfgdl.pdf).
At 2 GHz the Reference Exposure Level is 5mW/cm^2. This is the calculated level above which actual measurements are recommended.
In the UK , and I expect in the USA something similar, there is a legal requirement to make a Risk Assessment and to have a Safe System of Work.
It is apparent that the initial; rough calculation shows your exposure level is 40/5 = 8 times above the NCIRP Reference Level, so further work is required before exposing anyone to this radiation.

 

[sophiecentaur]

The maximum intensity near the antenna is easily found approximately by dividing the power by the area of the antenna aperture.

That could be a very good start but there would be a variation in local E field on the way up the column with maxima at the dipole feed points.

8 times above the NCIRP Reference Level

I think that implies PF should not be involved any further as the safety aspect is now significant.

 

[berkeman]

think that implies PF should not be involved any further as the safety aspect is now significant.

I think it's okay for now, with good safety information being the theme here. It may depend on how the OP responds next. "Can I wear a tinfoil hat for protection?" would probably not be a good response by him...

EDIT/ADD -- I do think that the OP should change to Yagi antennas, for the directional reasons mentioned for this application, and to make it easier to approach the antenna when it is transmitting (from the side). The legal issues of unlicensed high power Tx may be more of a problem for the OP in the end...

 

[sophiecentaur]

I do think that the OP should change to Yagi antennas, for the directional reasons mentioned for this application,

If an omni is not actually required, an omni is not good value. The same gain for a Yagi would mean that the VRP could be much wider and would mean that pointing would be less critical. And, of course, it is not neighbourly to spread signals in directions where they are not needed.

The legal issues of unlicensed high power Tx

If this project is not totally kosher then there is more chance of getting caught if an omni is being used. But we have to assume the OP is legit or we shouldn't be having this conversation.