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2 METER EH ANTENNA EXPERIMENT

 

This document describes a 2 meter antenna the reader may build and test to validate the performance, and to learn more about the EH Antenna. To make life really simple, a flat antenna was chosen. Tests in an anechoic chamber indicate that it has close to the same performance characteristics as a round antenna. A round one this size would have a diameter of 3/8 inch. I chose that size to make it easier to build than a smaller one and it has more bandwidth, so it will be less critical. It should be noted that a flat antenna using the same amount of material for the cylinders except spread out to make a flat antenna will have about ½ the bandwidth as a round cylinder.

At the bottom of the page I have included a sample output of the spreadsheet used to calculate the antenna parameters. The only difference is that the diameter should be multiplied by p to give the width (effective circumference) for the flat antenna. Also, because the bandwidth will be less than a round antenna the effective radiation resistance will be less.

The antenna will work if the copper is glued to a piece of paper, but it is preferable if you glue the copper to a piece of clear plastic. For the test antenna I used a plastic ruler. Run the feed line out to the side of the antenna and down to the radio. This is illustrated in the photograph below. For testing tape the ruler to the radio. If copper is not available, use a thin piece of aluminum cut from a soft drink can. Bend over a corner and clamp the connecting wire in the crimp. Note the photograph does not reveal a 10 pFd chip capacitor connected between the hot side of the feed line and the tap on the coil.

I suggest that the tuning coil and the twisted pair feed line be made of #24 or smaller enamel covered wire because that is readily available at Radio Shack, or at a local motor rewind shop. Tap the tuning coil at about 1 turn from the cold end. Spread the wires as needed for tuning and matching.

The twisted pair is simply a pair of wires twisted together. The amount of twist is not critical, but I use about 3 complete turns per inch because that is easy when using an electric drill. To prevent distortion of the radiation pattern be sure to use an ohm meter to validate that the ground end of the tuning coil is the same as the ground on the radio.

 

2-meter EH Antenna

The test results from the example antenna are documented in the attached analysis. I hope you will install the antenna on your handheld radio and compare the communication range against the standard antenna. Please share the results of your experiment on the EH Antenna Forum.

As a general comment, tuning and matching the antenna takes only a few minutes if you have the proper test equipment, i.e., a network analyzer. If you only have a field strength meter it takes longer to change frequency on the radio to verify the frequency of maximum radiation and to adjust the tap for best match.

 

Sample of design program for EH Antenna:

Parameters specified in BLUE cells:

Frequency =

146

MHz

flat

Cylinder Diameter =

0.375

Inches

1.17825

L/D ratio =

6

 

 

Total Length =

4.88

Inches

 

Total Length =

0.41

Feet

 

Capacity =

2.0

pFd

LINE A

Inductance needed

0.6

uHy

 

Coil Capacity

0.86

pFd

LINE B

Total Capacity

2.9

add lines A AND B

Modified inductance

0.4

uHy

 

Reactance

545.1

Ohms

 

Coil Diameter =

0.375

Inches

 

Wire Spacing =

0.013

Inches

#28 wire

# Turns=

6.5

turns

 

Coil Length=

0.1

Inches

 

Wire Length

0.6

Feet

 

USE THE ABOVE TO BUILD AND RESONATE THE ANTENNA AND TO MATCH IT TO 50 OHMS. INSERT THE MEASURED BANDWIDTH AFTER MATCHING.

Measured +/- 3 dB BW=

19400

KHz

 

Measured 2:1 VSWR bandwidth

6000

KHz

 

Radiation Resistance

72.4

Ohms

 

Antenna Q

7.5

 

 

CALCULATE ANTENNA EFICIENCY

Assume coil Q =

200

 

 

RF Resistance in coil=

2.7

ohms

 

Antenna Efficiency =

96.4

%

 

Antenna Efficiency =

-0.16

dB

 

ANTENNA POWER PARAMETERS

Transmitter Power

5

Watts

 

Transmission line Z

50

Ohms

 

Transmission Line Voltage

15.8

Volts RMS

 

Transmission Line Current

0.3

Amps RMS

Current between Cylinders

0.3

Amps RMS

Voltage between Cylinders

143.2

Volts RMS

 

Voltage between Cylinders

401.0

Volts P-P