Simplex Hospital
Communications Study
by
Andy Elliott – K8LE
Nov. 19, 2014
Simplex Communications Study
A study was conducted by Central Ohio Amateur Radio
Emergency Service (COARES) to determine the capability to
communicate between Franklin County Emergency
Management & Homeland Security (FCEM&HS) and each of the
Franklin County, Ohio area hospitals, using simplex
communications on 2 meters and 70 cm.
Why do the Study?
• A general repeater failure is a possibility
• A secondary objective is to obtain a more thorough
understanding of the circumstances affecting simplex
communications, including hospital antenna siting
and features of the terrain between each of the
hospitals and FCEM&HS.
Simplex Communications Study
The study was conducted between October 2013 and
October 2014. Although both 2 meters and 70 cm
simplex transmissions were evaluated, the emphasis in
this report is on 2 meters as it is more suitable for
simplex communications over a wide area.
Methodology
•
COARES members who are experienced participants in the Hospital Antenna &
Radio Testing Program, volunteered to conduct the tests from FCEM&HS.
•
One simplex test was conducted per month, and it was integrated into the regular
monthly test of the dual band TM-D700 Kenwood radio (and the Motorola
console radio which was not used in the simplex tests).
- volunteers agreed to be trained in the use of both radios
- this resulted in eight additional hams trained on these radios
•
The ham volunteer made arrangements with another ham who was scheduled to
conduct a regular monthly antenna and radio check at one of the hospitals.
•
At the scheduled time, simplex communication was attempted between FCEM&HS
and the hospital, at three output power levels (high, medium and low) on 2 meters
and 70 cm. The results were recorded on report forms, in terms of signal strength,
clarity and noise.
Acknowledgements
• A number of COARES volunteers took part in this study.
• Some operated from FCEM&HS, some operated from various hospital
locations, and several operated from both locations. For each test,
scheduling had to be done and volunteers freely gave their time and travel
expense for the good of the study. Their contribution is greatly appreciated.
Here are the volunteers:
• Operating from FCEM&HS: Richard Wynkoop-KD8PHG, Jim Birk-KD8HVX (2
tests), John Buck-KD8RTP, Wayne Walls-KA8CEJ (2 tests), Paul FlauttKB8CMW, Patrick Gibson-KD8ION, Bill Biggs-KC8PDR, and Andy Elliott-K8LE.
(4 tests).
• Operating from hospitals: Jim Birk-KD8HVX (3 tests), Hugh Czerwonky-K8UB,
Wayne Walls-KA8CEJ (2 tests), John Buck-KD8RTP (2 tests), Bob RectorW8RWR, Phil Moore-KB8YVI, Lynn Moore-KD8SYT, Richard WynkoopKD8PHG, Bill Biggs-KC8PDR, and Bob Cupples-KD8SYP.
Results
•
The results are summarized in the next slide
•
The result of the actual communications test is shown in the first column, as good
communications at low power in green (5 watts), good communications at
medium power in tan (15 watts), barely readable at high power in yellow, and no
communications at high power in red.
•
For each location, the total path loss and receive signal level (calculated values) are
shown.
•
The total path loss is the calculated signal loss due to distance and path terrain and
obstructions.
Location
Summary of Simplex Tests
Actual vs. calculated results
Simplex
Distance
communiElevation Total Path
from
cation
above sea
Loss*,
FCEM&HS,
actual
level, ft.
dBm
miles
result
Franklin County
Emergency Mgmt
& Homeland
Security
Mt. Carmel St.
OK at low
3
Anns
power
Receive
Signal
Level**
dBm
842’
Notes
base station for the study
832'
106.8
-51.9
propagation mode LOS
OSU Wexner
Medical Center
TBD
8.1
812'
121.8
-66.8
propagation mode LOS
antenna atop 293' bldg
Nationwide
Children’s
OK at low
9.4
power
787'
125.7
-70.7
propagation mode LOS
Mt. Carmel New
Albany
OK at low
6.5
power
1065’
128.5
-73.5
propagation mode diffraction
obstruction at 4.8km (3.0mi)
8.1
847
123.5
-74.4
propagation mode LOS, but
add'l cable loss due to long run
9.2
763’
129.6
-74.6
propagation mode diffraction
obstruction at 10.8 km (6.7mi)
10.1
795'
134.3
-79.3
prop. mode diffraction, DH
obstruction at 9.38km (5.8mi)
8
807'
122
-67
propagation mode LOS, but
antenna blocked to FCEM&HS
7.2
762'
129
-76.6
prop. mode diffraction, DH
obstruction at 6.34km (3.9mi)
OK at
medium
power
OK at
Grant
medium
power
OK at
Mt. Carmel West medium
power
vy weak &
OSU Hospital
noisy at
East
high pwr
Riverside
NIL at high
Methodist
power
Hospital
Mt. Carmel East
Doctors
NIL at high
14.6
power
923'
134.5
-82.5
propagation mode diffraction
obstruction at 6.0 km (3.7mi)
Diley Ridge
NIL at high
17.3
power
792'
136.9
-66.3
propagation mode scatter, DH
obstruct. at 14.46 km (9.0mi)
Coroners
NIL at high
8.4
power
752'
137
-82
prop. mode diffraction, DH
obstruction at 10.7km (6.6mi)
Dublin Methodist
NIL at high
13.4
power
936'
137.6
-84.1
propagation mode diffraction
obstruction at 6.0 km (3.7mi)
COTS
NIL at high
10.3
power
740'
145.8
-92.3
prop mode diffraction, DH
obstruction at 16.2km (10.1mi)
Radio Mobile
•
The total path loss and receive signal level was calculated by using Radio Mobile,
written by Roger Coudé, VE2DBE.
•
Radio Mobile is a free radio propagation simulation program which operates over
the frequency range of 20MHz to 20GHz.
•
It is based on the ITS irregular terrain (Longley-Rice) propagation model.
•
The program enables elevation maps to be drawn of specified areas using
downloaded SRTM (Shuttle Radar Topography Mission) data from the Space
Shuttle Radar Terrain Mapping Mission.
•
The program uses individual radio “stations” specified for performance and placed
where required (our hospital locations)
Uses data from Shuttle Endeavour
The Shuttle Radar Topography Mission (SRTM) obtained elevation data on a
near-global scale to generate the most complete high-resolution digital
topographic database of Earth. SRTM consisted of a specially modified radar
system that flew onboard the Space Shuttle Endeavour during an 11-day
mission in February of 2000
What Radio Mobile Does
•
The Radio Mobile program computes the radio transmission path between
transmitting antenna and receiving antenna, the first, second and third Fresnel
zones, and displays a graphical representation of these items along with any hills,
obstructions, etc. that may occur along the path of the link.
•
In order to compute the result, the program imports the SRTM terrain data
between the two selected points. It also determines the propagation mode for the
path, which can be line-of-sight (LOS), diffraction, or scatter propagation mode.
•
Since the exact antenna heights are not available, a standard height of 30 feet was
used for most hospital locations, and 40 feet for FCEM&HS.
Mt. Carmel St. Anns to FCEM&HS
• The radio link for simplex communication between Mt. Carmel St. Anns Hospital
and FCEM&HS shows clear line of sight propagation along the green radio LOS path
line, and a few obstructions that affect the path.
• These calculated results are consistent with the observed excellent simplex
communications at low power, and the relatively low total path loss, 106.8 dBm.
• The tan area shows the terrain features along the radio path, and the green just
above the tan area is averaged ground cover (built-up areas, trees, etc.).
• The white lines are the first three Fresnel Zones
Fresnel Zones
•
Radio Mobile calculates the first three Fresnel Zones and displays them as
concentric ellipsoids in white.
•
All the point-to-point radio path plots in this presentation include the Fresnel
Zones.
•
If the signal path exceeds 60% clearance of F1 (First Fresnel zone), the radio signal
is considered “clear line-of-sight” and will incur minimal diffraction loss.
•
As terrain obstructions reduce Fresnel clearance below the 60% value, diffraction
loss increases.
•
The Radio Mobile program calculates the diffraction loss, which is then added to
free space loss to determine the total path loss.
Fresnel Zone Clearance
•
The Fresnel zone clearance is the distance, or clearance, between the ground
and the LOS signal path.
•
If there is an obstruction protruding into the first Fresnel zone, the ratio of the
Fresnel zone clearance to the Fresnel zone radius will be less than one.
•
As long as this ratio is greater than .6, or 60%, the radio path is considered
“clear, line of sight”, and there will be minimal diffraction loss. The loss present
in this case is mainly Free Space Loss.
OSU Wexner Medical Center to FCEM&HS
• This radio link, OSU Wexner Medical Center to FCEM&HS, also displays LOS
propagation
•
Note the tall antenna at Wexner, on top of the 293’ building.
• The calculated path loss (121.8 dBm) is higher that the MC St. Anns path loss
(106.8 dBm) since the path is 5 miles longer plus additional diffraction loss (.2
F1 clearance).
• No actual results are available for OSU Wexner, as the site was not yet available
at the time of this study.
Nationwide Children’s Hospital to FCEM&HS
• This path indicates slightly higher path loss (125.7dBm) due to the slightly
longer path (1.3 miles longer that the OSU Wexner link) and nearly zero
Fresnel clearance
• Simplex communication was good at low power
• Here again, propagation is LOS. Notice that the green LOS line comes very
close to the terrain near the hospital, indicating diffraction loss is present.
Location
Simplex
Distance
communiElevation Total Path
from
cation
above sea
Loss*,
FCEM&HS,
actual
level, ft.
dBm
miles
result
Franklin County
Emergency Mgmt
& Homeland
Security
Mt. Carmel St.
OK at low
3
Anns
power
Receive
Signal
Level**
dBm
842’
Notes
base station for the study
832'
106.8
-51.9
propagation mode LOS
OSU Wexner
Medical Center
TBD
8.1
812'
121.8
-66.8
propagation mode LOS
antenna atop 293' bldg
Nationwide
Children’s
OK at low
9.4
power
787'
125.7
-70.7
propagation mode LOS
Mt. Carmel New
Albany
OK at low
6.5
power
1065’
128.5
-73.5
propagation mode diffraction
obstruction at 4.8km (3.0mi)
8.1
847
123.5
-74.4
propagation mode LOS, but
add'l cable loss due to long run
9.2
763’
129.6
-74.6
propagation mode diffraction
obstruction at 10.8 km (6.7mi)
10.1
795'
134.3
-79.3
prop. mode diffraction, DH
obstruction at 9.38km (5.8mi)
8
807'
122
-67
propagation mode LOS, but
antenna blocked to FCEM&HS
7.2
762'
129
-76.6
prop. mode diffraction, DH
obstruction at 6.34km (3.9mi)
OK at
medium
power
OK at
Grant
medium
power
OK at
Mt. Carmel West medium
power
vy weak &
OSU Hospital
noisy at
East
high pwr
Riverside
NIL at high
Methodist
power
Hospital
Mt. Carmel East
Doctors
NIL at high
14.6
power
923'
134.5
-82.5
propagation mode diffraction
obstruction at 6.0 km (3.7mi)
Diley Ridge
NIL at high
17.3
power
792'
136.9
-66.3
propagation mode scatter, DH
obstruct. at 14.46 km (9.0mi)
Coroners
NIL at high
8.4
power
752'
137
-82
prop. mode diffraction, DH
obstruction at 10.7km (6.6mi)
Dublin Methodist
NIL at high
13.4
power
936'
137.6
-84.1
propagation mode diffraction
obstruction at 6.0 km (3.7mi)
COTS
NIL at high
10.3
power
740'
145.8
-92.3
prop mode diffraction, DH
obstruction at 16.2km (10.1mi)
Summary of Simplex Tests
Actual vs. calculated results
Mt. Carmel New Albany Surgical Hospital to
FCEM&HS
• In this radio path, we see something very different, as there is an obstruction
along the radio path, located 4.8 km (3.0 mi) from FCEM&HS.
• We were still able to communicate at low power, likely aided by the short path
length (6.5 miles) and by the diffraction.
• But the propagation mode is no longer LOS, but instead it is diffraction mode
propagation. The LOS path line is shown for reference only.
Obstructions and Diffraction Loss
•
A path may be obstructed by trees, hills, buildings or other objects.
•
Diffraction loss is calculated based on the location of the obstruction along the
path and its height.
•
Diffraction loss is added to Free Space Loss to determine overall propagation
loss between transmit and receive antennas.
•
The Radio Mobile program uses the Longley-Rice model to calculate diffraction
loss.
•
If one or more obstructions take up more than 60% of the first Fresnel Zone, the
signal will be somewhat attenuated depending on the location and height of the
obstructions.
Mt. Carmel New Albany Surgical Hospital to
FCEM&HS
•
Notice also that there are two signal paths shown in green when diffraction
is the propagation mode.
•
One is the LOS path that would exist were it not for the obstruction.
•
The other path shown is the actual signal path caused by diffraction.
•
Let’s take a look at the actual obstruction. To do this, we go to Google
Earth and draw a straight line path between the two radio sites.
•
Then we can actually “fly” the path, monitoring the distance as we go.
Mt. Carmel New Albany Surgical Hospital to FCEM&HS
- Google Earth View
As we travel along the path, we find the obstruction right where it is
calculated to be, at 3.0 miles from FCEM&HS. The elevation of the
obstruction is 990 ft.
Mt. Carmel New Albany Surgical Hospital to FCEM&HS Google Earth View
An close-up look at the obstruction, which is a hill along Rt. 161.
Mt. Carmel East Hospital to FCEM&HS
• Here again the propagation mode is LOS, and the path loss is low (123.5 dBm)
• We were able to communicate along this path using medium power.
• With the low path loss and LOS propagation, we would have expected to
communicate at low power.
• The nearness of an obstruction to the hospital (.5 mi) may be the factor
Grant Medical Center to FCEM&HS
• This is another obstructed path, as indicated by the higher loss (129.6 dBm)
• The propagation mode is diffraction, with no Fresnel zone clearance.
• We were able to communicate along this path using medium power.
• The obstruction is 10.8 km (6.7mi) from FCEM&HS, at a high point of 849’.
Grant Medical Center to FCEM&HS – Google Earth View
In this Google Earth view we can see the path crossing a building, north of
the railroad tracks and just west of Joyce Avenue. The building and the land
close-by to the north is the obstruction area.
Mt. Carmel West Hospital to FCEM&HS
• Here the propagation mode is diffraction - double horizon, with an obstruction
zone beginning at 4.3 miles and extending to 6.7 miles from FCEM&HS.
• There is no Fresnel zone clearance. We were still able to communicate on this
path using medium power because of the diffraction.
•
In this case, actual results are much better than expected (high path loss of 134.3
dBm, low receive signal level of -79.3 dBm)
•
Looking at the Google Earth view in the next slide, we can see a wide obstruction
zone.
Mt. Carmel West Hospital to FCEM&HS – Google Earth View
In this Google Earth view, we can see a wide obstruction zone. The high ground is
about 2.5 miles wide along this path.
Location
Simplex
Distance
communiElevation Total Path
from
cation
above sea
Loss*,
FCEM&HS,
actual
level, ft.
dBm
miles
result
Franklin County
Emergency Mgmt
& Homeland
Security
Mt. Carmel St.
OK at low
3
Anns
power
Summary of Simplex Tests
842’
Notes
base station for the study
832'
106.8
-51.9
propagation mode LOS
OSU Wexner
Medical Center
TBD
8.1
812'
121.8
-66.8
propagation mode LOS
antenna atop 293' bldg
Nationwide
Children’s
OK at low
9.4
power
787'
125.7
-70.7
propagation mode LOS
Mt. Carmel New
Albany
OK at low
6.5
power
1065’
128.5
-73.5
propagation mode diffraction
obstruction at 4.8km (3.0mi)
8.1
847
123.5
-74.4
propagation mode LOS, but
add'l cable loss due to long run
9.2
763’
129.6
-74.6
propagation mode diffraction
obstruction at 10.8 km (6.7mi)
10.1
795'
134.3
-79.3
prop. mode diffraction, DH
obstruction at 9.38km (5.8mi)
8
807'
122
-67
propagation mode LOS, but
antenna blocked to FCEM&HS
7.2
762'
129
-76.6
prop. mode diffraction, DH
obstruction at 6.34km (3.9mi)
OK at
medium
power
OK at
Grant
medium
power
OK at
Mt. Carmel West medium
power
vy weak &
OSU Hospital
noisy at
East
high pwr
Riverside
NIL at high
Methodist
power
Hospital
Mt. Carmel East
Actual vs. calculated results
Receive
Signal
Level**
dBm
Doctors
NIL at high
14.6
power
923'
134.5
-82.5
propagation mode diffraction
obstruction at 6.0 km (3.7mi)
Diley Ridge
NIL at high
17.3
power
792'
136.9
-66.3
propagation mode scatter, DH
obstruct. at 14.46 km (9.0mi)
Coroners
NIL at high
8.4
power
752'
137
-82
prop. mode diffraction, DH
obstruction at 10.7km (6.6mi)
Dublin Methodist
NIL at high
13.4
power
936'
137.6
-84.1
propagation mode diffraction
obstruction at 6.0 km (3.7mi)
COTS
NIL at high
10.3
power
740'
145.8
-92.3
prop mode diffraction, DH
obstruction at 16.2km (10.1mi)
OSU Hospital East to FCEM&HS
• As we move down the table (previous slide), path loss increases and actual
communication along the paths becomes less feasible.
• But OSU Hospital East is an exception, with propagation being LOS and low
path loss (122 dBm). Note that these are calculated values, without knowledge
of the antenna location!
• We were barely able to hear the signal along this path as it was very weak and
noisy at high power.
• The radio path and low loss would predict good communications at low power,
so something else is in play here.
OSU Hospital East to FCEM&HS
antenna
Antenna is above left corner of white structure
(Thanks to KB8CMW for problem antenna location!)
OSU Hospital East to FCEM&HS
Red line is radio path to FCEM&HS, obstructed by hospital building
OSU Hospital East to FCEM&HS
• The signal was just barely readable with high noise level – not
usable for communications.
• The likely cause is the very poor antenna location for this path,
since the hospital building is between the antenna above the ER,
and FCEM&HS
Riverside Methodist Hospital to FCEM&HS
• This obstructed radio path shows a diffraction propagation mode - double
horizon.
• There is no Fresnel zone clearance at all.
• The loss is high (129 dBm) and we were not able to communicate on this path
even at high power.
Riverside Methodist Hospital to FCEM&HS – Google Earth View
In this Google Earth view, there is an obstruction area about 0 .7 miles
wide along the path where it crosses Kenney Rd. near Morse Rd.
Doctors Hospital to FCEM&HS
• Looking at this 14.6 mile radio path we see high path loss (134.5 dBm) with a
diffraction propagation mode and an obstruction at 6.0km (3.6 mi) from
FCEM&HS
• Comparing this path to others, one would expect communications might be
possible - but we were not able to communicate along this path.
• What else might be going on?
• A Google Earth view of the obstruction is on the next slide
Doctors Hospital to FCEM&HS –Google Earth View
Doctors
FCEM&HS
• The obstruction at 6.0km (3.6 mi) is near Dresden St. and E. Cooke Rd.
• Note that the obstruction is some 60’ higher than the elevation at
FCEM&HS
Doctors Hospital to FCEM&HS –Actual antenna location
W8RWR Photo
antenna
Antenna is blocked by structures to the east & north
Doctors Hospital to FCEM&HS –Google Earth View
• Radio path to FCEM&HS (longer red line to right) is blocked by hospital
structure
• Coax run to antenna drop is long, approximately 160’ (excessive cable loss)
• Multiple problems: path obstruction, very poor antenna location, long coax
run, long radio path
Diley Ridge Medical Center to FCEM&HS
• This long path has high path loss (136.9 dBm), multiple obstructions and zero
Fresnel zone clearance.
• The propagation mode is tropospheric scatter - double horizon.
• We were unable to communicate along this 17.3 mile path.
Diley Ridge Medical Center to FCEM&HS -Google Earth View
One of the obstructions is near I270 and the railroad tracks (just SW of the I70/I270
interchange), where the break in the red LOS path line can be clearly seen.
Franklin Co. Coroners Office to FCEM&HS
• The radio path has high path loss (137 dBm), diffraction propagation - double
horizon, major obstructions, and zero Fresnel zone clearance.
• Simplex communication was not feasible on this path.
Franklin Co. Coroners Office to FCEM&HS Google Earth View
Coroners
One obstruction is about 1.5 miles long along the path
Dublin Methodist Hospital to FCEM&HS
• This path shows major obstructions, high total path loss (137.6 dBm) and zero
Fresnel zone clearance.
• These calculated results are consistent with poor simplex results: no
communications with FCEM&HS even at high power.
Central Ohio Trauma System to FCEM&HS
• This heavily obstructed path has extremely high loss (145.8 dBm) and the
propagation mode is diffraction - double horizon.
• The current antenna (slated to be replaced by a rooftop antenna) is a J-pole
mounted in a second story window facing the “wrong” way from FCEM&HS
• Simplex communication was not possible (but ok by repeater.)
COARES 147.06 Repeater to Mt. Carmel New Albany Surgical Hospital
• Impediments to simplex communication are not a factor when compared to
communication using a repeater.
• To emphasize the contrast, consider this path, from our 147.06 repeater, K8DDG,
to its farthest (15.4 miles) location, Mt. Carmel New Albany Surgical Hospital.
• The path loss is only 125.6 dBm and the LOS propagation is mostly unaffected by
terrain features.
Conclusions
• Several conclusions can be drawn from the Summary of Simplex Tests - actual
vs. calculated results.
• One is the effect of distance between the two locations attempting simplex
communication. In general, the greater the distance, the less likely that
simplex communication is possible. This is due to the inverse-square law
which states that the power density is proportional to the inverse of the
square of the distance.
• However, the data indicates that additional factors often come into play.
Coroners is located only 8.4 miles from FCEM&HS and yet the actual results
places Coroners among locations that are 10 to 17 miles from FCEM&HS. The
analysis showed the cause to be multiple obstructions resulting in high path
loss (137 dBm), diffraction propagation - double horizon, and zero Fresnel
zone clearance.
Conclusions, continued
• Riverside Methodist Hospital is another surprise. With a distance of only
7.2 miles from FCEM&HS, good communications at low or medium power
would be expected, instead of no communications at high power. The path
analysis indicates a major, high obstacle at 6.3 km (3.9mi) from FCEM&HS,
and zero Fresnel zone clearance.
• OSU Hospital East, with its poor antenna location for simplex
communication to FCEM&HS, shows how important antenna siting is.
• Mt. Carmel West had much better communication than the calculated data
predicts, due to beneficial diffraction of the signal.
• With the exception of Mt. Carmel West, total path loss (calculated)
provides good correlation to simplex results
Location
Simplex
Distance
communiElevation Total Path
from
cation
above sea
Loss*,
FCEM&HS,
actual
level, ft.
dBm
miles
result
Franklin County
Emergency Mgmt
& Homeland
Security
Mt. Carmel St.
OK at low
3
Anns
power
Summary of Simplex Tests
Actual vs. Calculated Results
Receive
Signal
Level**
dBm
842’
Notes
base station for the study
832'
106.8
-51.9
propagation mode LOS
OSU Wexner
Medical Center
TBD
8.1
812'
121.8
-66.8
propagation mode LOS
antenna atop 293' bldg
Nationwide
Children’s
OK at low
9.4
power
787'
125.7
-70.7
propagation mode LOS
Mt. Carmel New
Albany
OK at low
6.5
power
1065’
128.5
-73.5
propagation mode diffraction
obstruction at 4.8km (3.0mi)
8.1
847
123.5
-74.4
propagation mode LOS, but
add'l cable loss due to long run
9.2
763’
129.6
-74.6
propagation mode diffraction
obstruction at 10.8 km (6.7mi)
10.1
795'
134.3
-79.3
prop. mode diffraction, DH
obstruction at 9.38km (5.8mi)
8
807'
122
-67
propagation mode LOS, but
antenna blocked to FCEM&HS
7.2
762'
129
-76.6
prop. mode diffraction, DH
obstruction at 6.34km (3.9mi)
OK at
medium
power
OK at
Grant
medium
power
OK at
Mt. Carmel West medium
power
vy weak &
OSU Hospital
noisy at
East
high pwr
Riverside
NIL at high
Methodist
power
Hospital
Mt. Carmel East
Doctors
NIL at high
14.6
power
923'
134.5
-82.5
propagation mode diffraction
obstruction at 6.0 km (3.7mi)
Diley Ridge
NIL at high
17.3
power
792'
136.9
-66.3
propagation mode scatter, DH
obstruct. at 14.46 km (9.0mi)
Coroners
NIL at high
8.4
power
752'
137
-82
prop. mode diffraction, DH
obstruction at 10.7km (6.6mi)
Dublin Methodist
NIL at high
13.4
power
936'
137.6
-84.1
propagation mode diffraction
obstruction at 6.0 km (3.7mi)
COTS
NIL at high
10.3
power
740'
145.8
-92.3
prop mode diffraction, DH
obstruction at 16.2km (10.1mi)
Conclusions, continued
• No particular significance can be attributed to any location’s height
above sea level. The height is only significant in terms of the terrain
between the two locations and any advantage that provides in helping
to minimize obstructions.
• In the event of repeater failure, the simplex test results can serve as a
guide to suggest where relay stations should be located to provide
simplex communications.
• For example, in the case of Diley Ridge Medical Center a relay station at
Nationwide Children’s Hospital, OSU Wexner or Mt. Carmel East could
likely pass communication back and forth to FCEM&HS.
• Due to its great antenna height atop the 293 ft. building, OSU Wexner
should have excellent simplex capability for many locations.
Conclusions, concluded
Here is a summary of recommended relay station locations:
Hospital Location
Recommended Relay Station Locations
Riverside Hospital……………………..OSU Wexner
Doctors Hospital………………………. OSU Wexner, Mt. Carmel West,
Nationwide Children’s
Diley Ridge………………………………..OSU Wexner, Mt. Carmel East,
Nationwide Children’s
Coroners…………………………………..OSU Wexner
Dublin Methodist……………………..OSU Wexner, Mt. Carmel St. Anns
COTS……………………………………….. OSU Wexner, Mt. Carmel West,
Nationwide Children’s
Clearly, OSU Wexner with its very high antenna location, would be
the “go to” location if relays are required. (OSU Wexner
performance remains to be verified at this writing)
Appendix A - Data used in the Radio Mobile analysis
Latitude and longitude was obtained from Google Earth for each site
Frequency 145 to 147 Mhz
Vertical polarization
Mode of variability: broadcast (90% of time/90% of locations/70% of
situations) - this is a reference to the communications reliability of the path.
Reliability and availability of any radio path is always given as a probability.
Signal probability/availability is related to the fade margin and other
factors. Percentages refer to time/locations/situations as in “90% of the
time, signal will at or greater than the calculated value”.
Climate: continental temperate
Transmit power: 50 watts (47 dBm)
Receiver threshold signal level: -122 dBm or .18uV for 12 db S/N ratio for
the ICOM ID-800H
Line loss 0.5 dB
Antenna type: omnidirectional
Antenna gain 4.5 dBi
Antenna height: 9.1 m for most locations, 12m for FCEM&HS
Topology: Voice Net (Command/Subordinate/Rebroadcast)
Appendix B - Fresnel Zones
Radio Mobile calculates the first three Fresnel Zones and displays them as
concentric ellipsoids in white. All the point-to-point radio path plots in this
report include the Fresnel Zones. If the signal path exceeds 60% clearance of F1
(First Fresnel zone), the radio signal is considered “clear line-of-sight” and will
incur no diffraction loss. As terrain obstructions reduce Fresnel clearance below
the 60% value, diffraction loss increases. The Radio Mobile program calculates
the diffraction loss, which is then added to free space loss to determine the
total path loss.
The following, based on a Wikipedia article, is a brief introduction to the
subject:
In radio communications a Fresnel zone (pronounced fray-NELL), named for
physicist Augustin-Jean Fresnel, is one of a number of concentric
ellipsoids which define volumes in the radiation pattern of a (usually) circular
aperture. Fresnel zones result from diffraction by the circular aperture.
The cross section of the first (innermost) Fresnel zone is circular. Subsequent
Fresnel zones are annular (doughnut-shaped) in cross section,
and concentric with the first.
Appendix B – Fresnel Zones, page 2, continued
If unobstructed, radio waves will travel in a straight line from the transmitter to
the receiver. But if there are obstacles near the path, the radio waves reflecting
off those objects may arrive out of phase with the signals that travel directly
and reduce the power of the received signal. On the other hand, the reflection
can enhance the power of the received signal if the reflection and the direct
signals arrive in phase. Sometimes this results in the counterintuitive finding
that reducing the height of an antenna increases the signal to noise ratio.
Fresnel provided a means to calculate where the zones are, where obstacles will
cause mostly in phase and mostly out of phase reflections between the
transmitter and the receiver.
Appendix B – Fresnel Zones, page 3, continued
Fresnel zone: D is the distance between the transmitter and the receiver; r is
the radius of the first Fresnel zone (n=1) at point P. P is d1 away from the
transmitter, and d2 away from the receiver.
Appendix B – Fresnel Zones, page 4, concluded
The concept of Fresnel zone clearance may be used to analyze interference by
obstacles near the radio path. The first Fresnel zone must be kept largely free
from obstructions to avoid introducing loss which will affect radio reception.
The Fresnel zone clearance is the distance, or clearance, between the ground
and the actual signal path. If there is an obstruction protruding into the first
Fresnel zone, the ratio of the Fresnel zone clearance to the Fresnel zone radius
will be less than one. As long as this ratio is greater than .6, or 60%, the radio
path is considered “clear, line of sight”, and there will be no diffraction loss. The
only loss present in this case is Free Space Loss.
If the signal path is not line of sight, and obstructions reduce the Fresnel zone
clearance to less than 60%, diffraction loss is present, and this loss can be
calculated using the Longley/Rice irregular terrain model, which is used by the
Radio Mobile program.
Appendix C: Longley-Rice (Irregular Terrain Model)
“The Longley-Rice model is applicable to point-to-point communication systems in the frequency
range from 20 MHz to 100 GHz, over different kinds of terrain. The median transmission loss is
predicted using the path geometry of the terrain profile and the refractivity of the
troposphere. Geometric optics techniques (primarily the 2-ray ground reflection model) are used
to predict signal strengths within the radio horizon. Diffraction losses over isolated obstacles are
estimated using the Fresnel-Kirchoff knife-edge models. Forward scatter theory is used to make
troposcatter predictions over long distances, and far field diffraction losses in double
horizon paths are predicted using a modified Van der Pol-Bremmer method. The Longley-Rice
propagation prediction model is also referred to as the ITS irregular terrain model.
The Longley-Rice model is also available as a computer program to calculate large-scale median
transmission loss relative to free space loss over irregular terrain for frequencies between 20
MHz and 10 GHz.
For a given transmission path, the program takes as its input the transmission frequency, path
length, polarization, antenna heights, surface refractivity, effective radius of earth, ground
conductivity, ground dielectric constant, and climate. The program also operates on path-specific
parameters such as horizon distance of the antennas, horizon elevation angle, angular transhorizon distance, terrain irregularity and other specific inputs.
Appendix C: Longley-Rice (Irregular Terrain Model), concluded
The Longley-Rice method operates in two modes. When a detailed terrain path profile is available,
the path-specific parameters can be easily determined and the prediction is called a point-to-point
mode prediction. On the other hand, if the terrain path profile is not available, the Longley-Rice
method provides techniques to estimate the path-specific parameters, and such a prediction is
called an area mode prediction.
There have been many publications and corrections to the Longley-Rice model since its original
publication. One important modification deals with radio propagation in urban areas, and this is
particularly relevant to mobile radio. This modification introduces an excess term as an allowance
for the additional attenuation due to urban clutter near the receiving antenna. This extra term,
called the urban factor (UF), has been derived by comparing the predictions by the original
Longley-Rice model with those obtained by Okumura.
One shortcoming of the Longley-Rice model is that it does not provide a way of determining
corrections due to environmental factors in the immediate vicinity of the mobile receiver, or
consider correction factors to account for the effects of buildings and foliage. Further, multipath is
not considered.”
[Rappaport, Theodore S. 1996. Wireless Communications Principles and Practice
Upper Saddle River, New Jersey:Prentice Hall, Inc. pp. 102-106, 110-111, 116-118, 167, 170-176,
188-189.
Appendix D - References
En.wikipedia.org/wiki/Fresnel_zone
www.tapr.org/ve3jf.dcc97.html
http://www.dxzone.com/catalog/Software/RF_Coverage_Mapping/
An excellent tutorial for Radio Mobile software is “Radio Mobile
Program Operating Guide” Version 4.0, by Brian J. Henderson