[Namaste-dev] RF Safety Considerations: Namaste ground Station

Stan, W1LE stanw1le at verizon.net
Wed May 21 19:48:39 PDT 2008


Hello The Net:

Attached please find my comments to the latest Tuesday challenge.


Summary:
RF MPE limits of other satellite bands are no worse or better than at 
5668 MHz.
It is an overall operator responsibility to live within the MPE limits.


If you disagree. let me know. If you have better numbers, let me know.

Is the frequency of the uplink centered at 5660 MHz or 5668 MHz ?

It is important to get this detail straight for designers, vendors,  as 
well as operators.

It is also important to have compatibility with other satellites.
P3E is using 5668 MHz as a uplink.
If Namaste offers compatible modes with other satellites, that is great 
goal.
If not, maybe some parts of the system can be used for other satellites.
Or even terrestrial microwave communications.

For a well designed 0.5 meter diameter, round, parabolic dish:
Gain is 26.5 dBi at a feed efficiency of 50%
or 27.4 dBi at 60% and 28.0 dBi at 70%

The 3dB beamwidth is 7.3 degrees, first sidelobe max at 12.5 degrees 
from main beam,
10 dB beamwidth 14 degrees, first null at (+/-)10 degrees from the main beam

I believe this to be true of the classic round parabola dish, fed at the 
focal point or
 a section of a parabolic dish with an offset feed.
F/D ratios will change requiring different feed patterns.

Feed design usually minimizes sidelobe impact.

For RF safety MPE levels, I use the calculator at:

http://n5xu.ece.utexas.edu/cgi-bin/rfsafety.cgi

All of the other satellite uplink bands have similar MPE limits
Namaste does have MPE considerations, but no different than any other 
satellite uplink band.
The exact limits of MPE would be determined for the actual Namaste RF system

*Average Power at the Antenna* 	10.000 watts
*Antenna Gain in dBi* 	25.70 dBi
*Distance to the Area of Interest* 	100.00 feet
*Frequency of Operation* 	5668.000 MHz
*Are Ground Reflections Calculated?* 	Yes
*Estimated RF Power Density* 	0.0815 mw/cm^2

  	Controlled
Environment 	Uncontrolled
Environment
*Maximum Permissible Exposure (MPE)*

	
5.00 mw/cm^2

	
1.00 mw/cm^2

*Distance to Compliance From Center of Antenna*

	
12.81 feet

	
28.59 feet

*Does the Area of Interest Appear to be in Compliance?*

	
yes

	
yes


12.81' = 3.9 M        28.59' = 8.7 M

 I assume a 100% duty cycle because of the full duplex operation,
as well as 10W high duty cycle RF power, (like FM, not like SSB/CW)

Yes, RF exposure is very important, but once the distance thresholds are 
identified,
it is easy to live within these limits. If you can not, do not operate. 
It is federal law.

Most applications of a ground station will be on a tower on one's property.
On occasion a portable station will be used and it is the operators 
responsibility
to control access to the unsafe areas, with either roping off and/or 
signage.

At this time a accessory system to identify penetration of the 
established safe
perimeter and to notify or automatically reduce RF output power is a 
dillution of project effort.

Yes it is possible, like a passive IR intrusion detector, but in my 
opinion not needed.
It is the operators responsibility to observe the federal MPE laws.
It is easy to do at a home station.

Possibly this safety mechanism is better applied in a commercial 
(non-ham) application.

Right now I would estimate the population of microwave satellite operators
to be less than 10% of the entire population of satellite operators.
That includes 1.2 GHz uplinks, 2.4 GHz downlinks as well as the higher 
microwave bands.

But that 10% is a dedicated core of technically savvy Hams.

My numbers may be off, it would be interesting to actually determine the 
mix.

If the Namste end product is as simple as a plug and play radio 
accessory (system),
then many, many more, folks from within and outside the satellite community
 can be recruited. And will come on board.

If Namaste is only a radio box that has to be integrated with DC power, 
RF feedlines,
digital data connections like RS-232 or ethernet, as well as a antenna 
system with
mechanical azimuth and elevation positioner, then it will not reach its 
true potential.
It is not horribly complex to integrate everything together and to make 
it work,
but it is complex to the average satellite operator.


An example for a 1.2 GHz uplink has reduced safe operating distances
primarliy due to the lower antenna gain

*Calculation Results*
*Average Power at the Antenna* 	10.000 watts
*Antenna Gain in dBi* 	18.00 dBi
*Distance to the Area of Interest* 	100.00 feet
*Frequency of Operation* 	1269.000 MHz
*Are Ground Reflections Calculated?* 	Yes
*Estimated RF Power Density* 	0.0139 mw/cm^2

  	Controlled
Environment 	Uncontrolled
Environment
*Maximum Permissible Exposure (MPE)*

	
4.24 mw/cm^2

	
0.85 mw/cm^2

*Distance to Compliance From Center of Antenna*

	
5.77 feet

	
12.84 feet

*Does the Area of Interest Appear to be in Compliance?*

	
yes

	
yes

































Another example at 2M:

*Calculation Results*
*Average Power at the Antenna* 	100.000 watts
*Antenna Gain in dBi* 	12.00 dBi
*Distance to the Area of Interest* 	100.00 feet
*Frequency of Operation* 	145.600 MHz
*Are Ground Reflections Calculated?* 	Yes
*Estimated RF Power Density* 	0.0348 mw/cm^2

  	Controlled
Environment 	Uncontrolled
Environment
*Maximum Permissible Exposure (MPE)*

	
1.00 mw/cm^2

	
0.21 mw/cm^2

*Distance to Compliance From Center of Antenna*

	
18.69 feet

	
41.74 feet

*Does the Area of Interest Appear to be in Compliance?*

	
yes

	
yes
































An example for 436 uplink:

*Calculation Results*
*Average Power at the Antenna* 	50.000 watts
*Antenna Gain in dBi* 	12.00 dBi
*Distance to the Area of Interest* 	100.00 feet
*Frequency of Operation* 	436.000 MHz
*Are Ground Reflections Calculated?* 	Yes
*Estimated RF Power Density* 	0.0174 mw/cm^2

  	Controlled
Environment 	Uncontrolled
Environment
*Maximum Permissible Exposure (MPE)*

	
1.46 mw/cm^2

	
0.30 mw/cm^2

*Distance to Compliance From Center of Antenna*

	
10.98 feet

	
24.50 feet

*Does the Area of Interest Appear to be in Compliance?*

	
yes

	
yes



Another example for the 2439 MHz uplink for AMSAT-DL's P3E:


*Calculation Results*
*Average Power at the Antenna* 	100.000 watts
*Antenna Gain in dBi* 	21.00 dBi
*Distance to the Area of Interest* 	100.00 feet
*Frequency of Operation* 	2439.000 MHz
*Are Ground Reflections Calculated?* 	Yes
*Estimated RF Power Density* 	0.2761 mw/cm^2

  	Controlled
Environment 	Uncontrolled
Environment
*Maximum Permissible Exposure (MPE)*

	
5.00 mw/cm^2

	
1.00 mw/cm^2

*Distance to Compliance From Center of Antenna*

	
23.55 feet

	
52.59 feet

*Does the Area of Interest Appear to be in Compliance?*

	
yes

	
yes


































Stan, W1LE   Cape Cod  FN41sr 




ZZZZz


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