Safety concerning ERP of transmitter

[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.

 

[davenn]

But we have to assume the OP is legit or we shouldn't be having this conversation.

probably a really bad assumption
don't think I have ever seen one of these styles of posts where the OP was operating in a legit way

 

[GrahamN-UK]

The cables used are RG59.

As well as the high losses mentioned by davenn, RG-59 cable has a characteristic impedance of 75 ohms whilst the antenna you proposed is 50 ohm (from its data sheet). You need to use a low-loss cable with the same impedance as your chosen antenna to reduce matching losses and ghosting on analogue video (at least on long feeder runs).

Antennas used for broadcast reception tend to be 75 ohm whilst antennas used for transmit/receive systems are usually 50 ohm. You should check the specification for the antennas you choose then get matching cable and connectors.