Copyright: Copyright (c) 1998 Teledesign Systems Inc.


Contents
 AirCalc Help Contents

Introduction

Controls on Main Form

Antennas

Cables

Range Equations

Contacting Teledesign

Copyright (c) 1998 Teledesign Systems Inc.


Link Margin
Link Margin - Link margin or fade margin is the amount of extra signal provided in a link above the minimum necessary for a usable link.  The link margin is used to account for fades and propagation problems which occur when the link is in use.  The amount of link margin should depend on the desired reliability of the link and the conditions under which the link operates.  Mobile links should allow for a higher fade margin than fixed links in order to account for fading from terrain and multi-path conditions.


Frequency
Frequency - The frequency of operation of the radio link.


Cable Loss
Cable Loss - The loss in RF power (in dBs) due to the antenna cable (see Cables).


Antenna Height
Antenna Height - The vertical height (above the average terrain height) of the base of the antenna.


Antenna Gain
Antenna Gain - Antenna gain in the selected units.


Transmit Power
Transmit Power - The transmit power in watts.


Main Form
AirCalc Form


Introduction

AirCalc provides estimates of the flat terrain range of wireless data communication systems.  Actual range of a system can vary dramatically, and therefore it is important that range is verified with in field tests in the area of operation.

AirCalc is provided free so that our customers and potential customers can evaluate their wireless links.  We hope you find this software useful and easy to use.  If you have questions or comments please contact us.


Contacting Teledesign

Teledesign Systems Inc. can be reached during our business hours of 9 AM to 5 PM (Pacific Standard Time) Monday through Friday.

Phone numbers:

(800) 663-3674 or (800) MODEMS4 (USA & Canada only)

(408) 232-0180

(408) 232-0188 Fax

Internet:

www.teledesignsystems.com

Email:

corpcomm@teledesignsystems.com

sales@teledesignsystems.com

support@teledesignsystems.com

Mail:

Teledesign Systems Inc.

2635 North First Street, Suite #205

San Jose, CA  95134


Range Equations

Effective Radiated Power

ERP = Pt + Gt - Lt

Where:

ERP 	= Effective Radiated Power (same units as Pt)

Pt 	= Transmit Power (in dBm or dBW)

Gt 	= Transmit Antenna Gain (in dBi)

Lt 	= Transmit Cable Loss (in dB)

Radio Horizon Range

Range = K x (Ht ^ 0.5 + Hr ^ 0.5)

Where:

Ht 	= Transmit Antenna Height

Hr 	= Receive Antenna Height

K 	= 4.10 - for Ht and Hr in meters

   	= 1.41 - for Ht and Hr in feet

Free Space Range

Range = 10 ^ ((MPL - 20 Log F - K) / 20)

Where:

F 	= Frequency - in MHz

K 	= 32.4 - for range in km

   	= 36.5 - for range in miles

MPL = Maximum Path Loss = ERP - RxSens - Gr - Lr - Lm

ERP = Effective Radiated Power - in dBm

RxSens = Receive Sensitivity - in dBm

Gr 	= Receive Antenna Gain - in dBi

Lr 	= Receive Cable Loss - in dB

Lm 	= Link Margin - in dB

Estimated Flat Terrain Range - Egli Model

Range = 10 ^ ((MPL - 20 Log F + 20 Log (Ht x Hr) - K) / 40)

Where:

F 	= Frequency - in MHz

Ht 	= Transmit Antenna Height

Hr 	= Receive Antenna Height

K 	= 88 - for range in km and Ht, Hr in meters

   	= 117 - for range in miles and Ht, Hr in feet

MPL = Maximum Path Loss = ERP - RxSens - Gr - Lr - Lm

ERP = Effective Radiated Power - in dBm

RxSens = Receive Sensitivity - in dBm

Gr = Receive Antenna Gain - in dBi

Lr = Receive Cable Loss - in dB

Lm = Link Margin - in dB


Antennas

Antenna Types

Omni-directional: Omni-directional antennas radiate equally in all directions in the horizontal plane.

Directional: Directional antennas focus their radiation in a specific direction.  A Yagi is the most common type of land mobile radio directional antenna.

Antenna Gain

Antennas performance is specified by antenna gain which indicates the degree to which the antenna focuses the signal into the desired direction.  Antenna gain is specified in terms of decibels which are measured with respect to a reference antenna radiator.  There are several different references used to specify antenna gain.

dBi: Antenna gain in decibels measured with respect to a theoretical isotropic radiator (radiates uniformily in all directions).  Mobile and portable antennas are typically characterized in dBis.

dBd: Antenna gain in decibels measured with respect to a half wave dipole antenna.  Dbds are typically used to characterize base station antennas.

There is a difference in gain between dBd and dBi as follows:

0 dBd = 2.15 dBi

Antenna Setup

Some antennas require a ground plane for proper operation.  It is important that antennas of this type are mounted to a well grounded metal surface.  Otherwise, the antenna could have a poor radiation pattern and/or a different characteristic impedance, both of which reduce the effective gain of the antenna.


Cables

Characteristic Impedance

Coaxial cables have a characteristic impedance which must match the characteristic impedance of the other components in the system.  Most radio systems components have a characteristic impedance of 50 ohms.

Note that most coaxial cable used for video have a characteristic impedance of 75 ohms.  Because the characteristic impedance is not 50 ohms, this cable is not suitable for use in radio systems.

Attenuation

The attenuation of a signal through a coaxial cable is dependent on the cable type and the frequency of the signal.  The following table shows the attenuation for various cable types at various frequencies.

Note that for every 3 dB of attenuation the signal power drops by half (see decibels).

Outside	Attenuation (dB/100 ft, dB/30.5 m)

Cable Type	Diameter	150 MHz	450 MHz	900 MHz
RG-58	0.193"	6.2	12.5	20.0
Teflex	0.195"	5.8	10.0	14.5
RG-8X	0.242"	3.6	6.8	10.7
RG-213	0.405"	2.3	4.5	7.6
LMR-400	0.405"	1.5	2.7	3.9

Connectors

Each connector or adapter added to a cable adds about 0.25 dB to the cable attenuation.


Effective Radiated Power
Effective Radiated Power (ERP) - The ERP is the amount of effective power out of the antenna when transmit power, antenna gain and cable losses are accounted for.


Free Space Range
Free Space Range - Free space range is the expected range if the link was operating in a perfect free space environment (see Range Calculations).  A perfect free space environment has no fading due to the earth, other objects or other interferers.


Radio Horizon Range
Radio Horizon Range - The radio horizon range is the maximum distance (between the transmitting and receiving antennas) that the signal can propagate before there is fading caused by shadowing by the earth (caused by the curvature of the earth).  Because fading due to shadowing by the earth is high, the radio horizon range is the practical upper limit of range for most systems.  The radio horizon range is dependent on the height of the transmit and receive antennas (see Range Equations).  Note that the practical radio horizon range can change due to atmospheric conditions.


Flat Terrain Range
Flat Terrain Range - This is the estimated range over flat terrain.  This is calculated using models which are estimates of the actual range.

Egli Model:  This Egli model (developed by John Egli in 1957) is commonly used due to its simplicity (see Range Equations).

Okumura/Hata Model - This model was developed by measuring actual path losses in the field and then fitting mathematical equations to this empirical data.  The Okumura/Hata model is most accurate for the following conditions.

Frequency: 150 - 999 MHz.

Transmit (Base) Antenna Height: 30 - 200 m.

Receive (Mobile) Antenna Height: 1 - 10 m.

Range: 1 - 20 km.


Decibels
Decibels (dBs)

Power change in decibels:

Power gain in dBs = 10 * Log (Pout / Pin)

dBs	Pout / Pin	dBs	Pout / Pin
+1	1.26	-1	0.79
+2	1.58	-2	0.63
+3	2.01	-3	0.50
+4	2.51	-4	0.40
+5	3.16	-5	0.32
+6	3.98	-6	0.25
+9	7.94	-9	0.13
+10	10.0	-10	0.10
+20	100.0	-20	0.01
+30	1000.0	-30	0.001

Power in dBms:

Power in dBms = 10 * Log (Power in watts / 1 mW)

Power	dBm	Power	dBm
1 mW	0	1 W	30
2 mW	3	2 W	33
5 mW	7	5 W	37
10 mW	10	10 W	40
100 mW	20	20 W	43
200 mW	23	50 W	47
500 mW	27	100 W	50


License
Software License

By using this Software, you are agreeing to be bound by the terms of this agreement. If you do not agree to the terms of this agreement do not use the software.

1) USE AND COPIES.  You may install and use an unlimited number of copies of this Software ("Software" refers to all the program files and documentation) and you may also make unlimited copies of the software and give them away as long as you meet the following requirements.

A) The Software is not modified in any way.

B) Any copies are provided with all the necessary (included) files and documentation.

2) RESTRICTIONS.  You agree not to sell, rent or lease the Software.  You also agree not to modify, reverse engineer, decompile, or disassemble the Software.

3) COPYRIGHT.  This Software is owned by Teledesign Systems Inc. and is protected by United States copyright laws and international treaty provisions.

4) NO WARRANTY.  THIS SOFTWARE IS PROVIDED TO YOU AS IS AND TELEDESIGN SYSTEMS INC. MAKES NO WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

TELEDESIGN SYSTEMS INC. SHALL IN NO EVENT HAVE OBLIGATIONS OR LIABILITIES TO THE USER OR ANY OTHER PERSON FOR LOSS OF PROFITS, LOSS OF USE OR INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES, WHETHER BASED ON CONTRACT, TORT (INCLUDING NEGLIGENCE), STRICT LIABILITY, OR ANY OTHER THEORY OR FORM OF ACTION, EVEN IS TELEDESIGN HAS BEEN ADVISED OF THE POSSIBILITY THEREOF, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS PRODUCT (INCLUDING DOCUMENTATION).


Receive Sensitivity
Receive Sensitivity - This is the minimum signal level required by the receiver to achieve the desired BER (Bit Error Rate).