smarts II RF monitor is installed near the visitors viewing
platform at the visitors center. It is used to check the RF levels
when the transmitter is on. The output from the monitor is
read at a 5 hz rate, averaged to 1 second, and then written to disc.
The device will also generate an alarm in the control room when the
radiation rises beyond a preset level. The current alarm
threshold is set to 50% of the maximum allowable exposure.
28feb13: new rfmonitor installed.
29jun12: rfmonitor daily data for feb09
29jun12: rfmonitor data for the 1st day of
each month: feb09 to jun12
23Aug06:test rfmonitor with the 430
- 04mar13: sign of output flipped to give positive output.
- 28feb13 new rf monitor installed
28Feb13:new rf monitor installed.
A new rf monitor was purchased and
installed at the visitors center on 04feb13.
The plots shows the output from the
monitor for 17feb13 (.ps) (.pdf)
possible that the large increase in the meter output is caused by rf
radiation from the sun? Below i've tried to estimate (worse case)
whether our radiation monitor should see the sun or not.
- The vertical scale is fraction of allowable exposure for
humans in a non controlled environment
- I think we chose the jumpers so that 1 on the plot =
50% of maximum allowable exposure.
- I looked at data from 05feb13-28feb13. 17feb13 was a typical
day (except that it included the sband transmitter 21:22 hours
- Top: this is the raw data recorded in the file.
- The value is always negative, and decreases toward noon.
- I think the value should always be positive so my guess is
that the sign is inverted
- Bottom: I've multiplied the plot by -1.
- The signal starts to increase around 8 am and peaks around
- The dashed red lines show when the sband transmitter was on
(not sure what the power level was). It looks like the
transmitter is registering on the meter.
- A solar flux unit is sfu
- 1e-22 W/m^2/Hz. The radiation standard used
- 1e-23 mW/cm^2/Hz ..
- Looking at
radio flux measurements of the sun give values like:
- 432Mhz =38 sfu
- 1296 Mhz 84
- 2300 Mhz 92 sfu
- 3300 Mhz 101 sfu
- 5650 Mhz 157 sfu
- 10368 Mhz 337 sfu
- 15400 Mhz 576 sfu
- As a worse case assume we integrate 0 to 100Ghz with an
- 1000sfu*100e9Hz= 1e-9 mW/cm^2 integrated.
- I'm assuming that sun output 15400 -> 100,000 Mhz doesn't
increase so much that the 0-100Ghz avg does not go above
- The monitor output is in fractions of allowable human
- We've asked for the uncontrolled access limits on our
- .3-1.34 Mhz : 100 mW/cm^2
- 1.34-30 Mhz: (180/Frq^2) mW/cm^2
- 30-300 Mhz : .2 mW/cm^2
- 300-1500 Mhz: frq/1500 mW/cm^2
- 1500-100,000 Mhz: 1.0 mW/cm^2
- So the max allowable maxes out at .2 mW/cm^2 so our
integral above could be multiplied by 5 or 10 to get the
fractional allowable radiation from the sun.
- The monitor antenna looks to be a few cm^2..
- So the sun worse case would be 1e-8 times the allowable
maximum. So we shouldn't see it.
- The change in output may be a thermal issue (with either the
meter, or the sbc computer with a/d that is being used to record
- The monitor is inside a plastic box mounted about 10 feet up
on the south facing wall of the visitors center.
- I stood below it for a few minutes at the beginning of
feb13 and i felt pretty hot.
29jun12: daily RF monitor day for feb09:
The RF monitor data for each day of feb09 was
plotted. The data processing was:
The plots show the daily results for feb09
- Median filter each days 1 seconds to 1 minute
An image was made using each day of feb09
- I've scaled the Y axis to be the maximum allowed exposure
(most plots in the other sections are .5*(maxexposure))
- Top frame:
- All 28 days are over plotted.
- It gets up to about .24 of max allowable around 10am (i
don't know whether this is the sun or not?)
- Each day has been plotted with an offset to separate out the
processing: x101/120629 radmon.pro
- You can see the peak strength 11feb09 around 10am
- The vertical strips are dropouts. For the line plots above, i
excluded these points (since they covered up the other data).
The data from the first day of each month 2009
-> jun2012 was examined.
- Plots were made ( pwr vs time) for the first day of each
- The y scale is .5*(the maximum allowable exposure). When the
scale reads 1., you are at 50% of the maximum allowable value
(i think the device is set for controlled access areas).
- The data was median filter by 13 samples to remove the
glitches that occur every 47 seconds (see 23Aug06 discussion
- The table gives a brief summary of the 1st day of each month.
The codes used are:
- DP - data
- ND - no data
- 0's -
data all zeros
- NC - cable not
Notes on the various years:
- These notes only refer to the 1st day of each month.. I didn't
look at every day of every month..
- data present for most months.
- Dropouts occur 11:am to 3:pm on some days
- no data apr09
- Most of the 2010 data is garbage.
- not data for jan,feb then unplugged mar-jun12..
- Jun12 the monitor was taken down to the lab. It was full of
water. Someone opened the waterproof box to unplug the cable
(so it would stop beeping, and they didn't close the
waterproof box correctly..).
- We need a new monitor.
- We currently have a narda smarts II model A8830. It has a
safety profile for controlled access areas. For the visitor
center we should probably buy the D8830 which i think has a
profile for uncontrolled access areas.
- A new monitor costs about $3500.
23Aug06: Test monitor which 430 Mhz
The RF monitor was tested on 23Aug06 using the
430 Mhz transmitter. The manual RF monitor was also used during the
test. The visitors center is at an azimuth of +7 degrees
azimuth. The test sequence was:
- lf: line feed transmitter
- gr: gregorian dome transmitter
- az (xx): the azimuth is the physical location
of the transmitter. 180 (xx) is always on the far side, 0(xx) is
always on the near side.
||Bring up xmiter (lf)
||Test1. az swing two times (lf)
||lf on far side
||Test2: az swing 3 times (lf)
||-10 to +15 (lf)
||lf on near side
||Test3: az swing 2 times (lf)
||-10 to +15 (lf)
||lf on near side
||Switch to tx gregorian.
||1.9 MW to
||Put full power thru gregorian.
Check for arcing.
||Test4: az swing 2 times (gr)
||-10 to +15 (gr)
||gr on near side
The RF monitor output goes from 0 to 1 and is linear in
power. The value 1. corresponds to a power level that was 50% of
the maximum allowable value (weighted by frequency range).
So a value of .1 would be .05 time times the maximum allowable
NOTE: later it was found that the meter is using the wrong
radiation profile (see below). It uses a maximum values that is 5
times too high. Given a value on the plots, you should multiply it
by 2.5 (5/2) to get the fraction of the maximum allowed value. A
value of .1 would be .25 of the maximum allowed value.
The first set of plots shows the RF
power versus time (.ps) (.pdf):
The 2nd set of plots shows therf
monitor power versus azimuth (.ps) (.pdf):
- Top: The rfmonitor power versus time 4:00 to 14:00.
- Black was taken on 23Aug06 (the day of the test).
- Green was taken on 22Aug06 (the previous day when the
transmitter was not on).
- The red vertical lines show the time when the xmter was on
- On both days the reading is quiet until around 6 am. It
rises and begins to oscillate (with a period of about 45
- The level rises to about twice the morning value at 12:00.
It comes back down to the nighttime value around 14:00.
- Middle: rfmonitor power vs time 10:00 to 14:00 xmiter on.
- This is a blowup of the 23Aug06 data during the xmiter
- The black data is the RF monitor.
- The green data was taken during the first test (lf,
za=19.5, far side)
- The blue data was taken during the 2nd test (lf, za=19.5,
- The purple data was taken during the 3rd test (lf, za=15,
- The light blue data was taken during the 4th test (gr,
za=19.5 near side).
- The red solid line shows the transmitter power. It
came on about 11 am. It went off about 13.25. The dashed red
line is a tx power of 2 MW.
- The RF monitor level did start to rise when the xmter came
on. It went back down before the xmter went off (it did start
to move in azimuth). This bump may or may not be caused by the
- Bottom: azimuth vs hour of day.
- The azimuth position (dome side) during the tests. The
colored areas show when the tests occurred.
- Top: test 1. Linefeed far side, 19.5 za. You can see an
increase in the power level when the azimuth is at 187. This
is when the line feed is aligned 180 degrees from the
radiation monitor. The increase is about .02/.10=20%. The
absolute value of the increase is .02*50%= .01 of the maximum
- 2nd test 2: linefeed near side, za = 19.5. There is no
noticeable azimuth dependence of the power.
- 3rd test 3: Linefeed at near side, za=15. No azimuth
dependence of the power.
- 4th test 4: dome at near side, za=19.5. No azimuth
dependence of the power.
Glitches in the RF monitor:
The RF monitor is seeing a glitch that goes to
full scale every 46.2 seconds (the period is not constant over a
day). It is high for 1 or two seconds and then under shoots for
about 3 to 4 seconds. These glitches were not present when the
device was tested in the lab. They also went away when a mesh was
put around the monitor. The RF alarm in the control room is not
being triggered by these values so the alarm must not be enabled.
- The measured power value of the RF monitor changes by a
factor of two day to night. The levels peak around noon. The
device output may be changing with temperature.
- We saw a small change in the power level versus azimuth when
the dome was on the far side and at 19.5 degrees. We did not see
any azimuth dependence of the power when the transmitters were
on the near side.
- There was an increase in the power level when the transmitter
started to come on. The change was a slow rise (10 to 15
minutes). There were no sudden jumps when we increased the
transmitter power (usually this took a minute or two).
- The RF monitor is seeing glitches that go full scale every 46
to 48 seconds. They stay high for 1 or 2 seconds and then
undershoot for 3 or 4 seconds. They were not there in the lab or
when the device was covered with a mesh. We need to determine
whether this is real or a glitch in the device. The alarm in the
control room is not being triggered by these glitches so the
alarm must be disabled.
- The power levels measured by the RF monitor do not agree with
the hand held RF monitor. The hand held monitor read a maximum
value of .12 mW/cm^2. This is 41 % of the maximum allowed value
at 430 Mhz (using .29 mW/cm^2). The maximum value read by
the RF Monitor was .13 *(50% of max allowable Value) =
6.5% . So the two devices differ by a factor of
..41/.065= 6.3. This discrepancy is probably
coming from the standard being used by the fixed RF monitor :
fcc 1997 occupation/controlled.
- For uncontrolled access areas the 430 Mhz limit is
- For controlled access areas the 430 Mhz limit is 430/300 =
- The ratio of these values is 5 which agrees with the
measured difference above.
- Taking the above into consideration, the power levels on the
plot should be multiplied by 2.5 to get the fraction of
- We need to switch the RF Monitor to use the
uncontrolled/general population access RF limits for the
visitors center overlook.
- Current model:
- A8830: FCC 1997 occupational/Controlled access
- What we should have is uncontrolled access. Probably:
- D8830: ICNIRP 1998 or ENV 50166-2 Occupational.