1 A TECHNICAL BRIEFING FOR AMATEUR RADIO OPERATORS “HOW FAR CAN YOU TALK ON A 2 METER HANDHELD RADIO” PRESENTED TO: ARASWF Naples, FL MARCH 2015 PRESENTED BY: DR. AL TORRES KP4AQI

2 PRESENTATION OUTLINE Reviewing the Basics: –Line of Sight –Space Propagation Loss Space Loss Factors Computer Program Inside Walls Attenuation Grazing Angle Loss Polarization Loss Squelch Setting Summary Questions

3 REVIEWING THE BASICS Talking distance is a variable of two primary factors: –Line of Sight (to the horizon) –Space Loss (atmospheric propagation) Line of Sight: –Unobstructed distance to the Horizon –Normally defined as: d (miles) = Square-root of height (h) in feet d is statute miles (5,280 feet) Example: –A 6 ft tall person will see the Horizon at: –d =  6 ft = 3.24 miles

4 STILL REVIEWING THE BASICS If an object (tower, building, etc.) is at the horizon, then the line of sight is: d (miles) = (  h-object + (  h-person) Example: 100 ft tower at the horizon, 6 ft person d (miles) = (  100 ft +  6 ft) = miles Atmospheric Refraction will increase distance by 8%

5 GRAPHICAL REPRESENTATION 100 ft 6 ft miles

LINE OF SIGHT VS. HEIGHT 6

7 SPACE PROPAGATION LOSS (dB) Space Propagation Loss is a function of frequency, and distance It is defined as: SL = log (frequency) + 20 log (distance) SL is in dB Example: At MHz, at 1 km (0.62 miles) SL = km (0.62 miles) SL = km (1.24 miles) SL = km (1.86 miles) SL = km (2.49 miles)

SPACE LOSS VS DISTANCE AT MHz 0.5 to 10 miles 8

SPACE LOSS VS DISTANCE AT MHz miles 9

10 SPACE LOSS FACTORS The following are parameters which influence the space loss propagation: –Antenna Gain (Receive/Transmit) (dB) –Transmit Power (dBm) –Receiver Sensitivity (dBm) –Feed-line Losses (dB) –Frequency (MHz) –Pointing Loss (dB) –Polarization Loss (dB) –Internal Walls (dB) –Grazing Angle to Structures (buildings) (degrees) –Noise Figures (dB) –Required Signal to Noise (S/N) (dB) –Bandwidth (Hz)

11 SPACE LOSS FACTORS (Cont.) How can I keep track of all those Parameters? –Call Al Torres for a Solution (…….not really!) –Use the Simple Computer Program (Ham Proof) For the following examples, we will be using an Icom IC-V80 with the following parameters: –Receiver Sensitivity: 0.14  12 dB (SINAD) or -124 dBm –Transmitter: 2.5 Watts (mid power level) –Frequency: MHz (2 meter band) –Antenna Gain: -5 dB (Rubber Duck) –Squelch Setting: + 6 dB –Bandwidth: 5 KHz (Narrow Band FM)

12 SIMPLE COMPUTER PROGRAM

13 COMPUTER PROGRAM

14 INSIDE WALLS Typically, inside walls will attenuate your signal depending on the composition of the wall Wall could be made of wood, drywall, concrete or logs Each material will have specific attenuation as a function of freq uency Good average number to use is 7 dB per wall

15 GRAZING ANGLE When dealing with a beam that is nearly parallel to a surface, it is sometimes more useful to refer to the angle between the beam and the surface, rather than that between the beam and the surface normal. In other words, 90  minus the angle of incidence We call this angle the Glancing or Grazing Angle Determining the Grazing angle with respect to a planar surface is trivial but the computation for almost any other surface is very difficult For calculation purposes: Ga = 20 (1-sin  ) 2

GRAZING ANGLE vs. ATTENUATION FACTOR 16

POLARIZATION LOSS Most ham radio antennas are polarized Handheld antennas are also polarized; the intent is to make them vertically polarized but because of the fabrication techniques (rubber ducks are radiating coils), they are not fully vertically polarized Between linear polarization and circular polarization there is a 3 dB change When the EM wave bounces of a metallic surface there is a polarization shift; bounces can take place on structures A good number for polarization loss is 3 dB 17

SQUELCH SETTING Squelch setting can reduce the sensitivity by as much as 24 dB Normal squelch setting is at 6 dB over the noise (open squelch) Some receivers have squelch circuits which can track down the signal approximately -6 dB below the noise before shutting down Below noise squelch tracking is also a function of time (between 0.5 seconds to 1.5 seconds typically) 18

19 SUMMARY An approximate distance (range) for a 2 meter handheld transceiver and ways to approximate such distance was provided Line of Sight, Space Propagation Loss, Polarization, Inside Walls, Grazing angles, and Squelch Setting will also affect the communication range Other items which we have not addressed are: –Knife Edge Diffraction Theory –Atmospheric Diffraction impact –Foliage Attenuation –Structures within Line of Sight –Space Loss vs. Frequency (450 MHz generates 9.4 dB more loss) –Shadowing –Ground effects and attenuation

For Next Year 2016 January 2016: “Antenna Gain: Myths and Truths” February 2016: “Slot Antennas: Wire Reciprocity” March 2016: “Motor Oil: When do you Change?” 20

21 MORE INFORMATION or COPY OF PRESENTATION SEND AN TO THE FOLLOWING URL: CONTACT ME AT: AL TORRES KP4AQI P. O. BOX DAYTON, OH