Modelling Performance of Small Antennas for 3999 khz Portable Operation

by Alan Biocca WB6ZQZ 12/3/2002 (updated 1/19/03)

The following article will present and discuss results of modelling various configurations of small antennas for 3999 khz that are, or might be used for Pedestrian Mobile operation (see http://www.hfpack.com for more info on this popular and growing aspect of Ham Radio).

This article is being posted incrementally, this document will grow as sections are inserted. I have already analyzed many antennas, but it will take some time to collect the details into this document from my notes.

If you have any feedback for this please send it to me via wb6zqz at qsl.net.

In this section several antennas will be covered, plus some variations. Many of the basic configurations are very similar in that they are based on a whip vertical with the base at 5 feet above ground, and a drooping counterpoise that begins at this 5 foot height, angles down toward the ground at 45 degrees, and then hovers at 0.1 foot above the ground out horizontally to the 50 foot point. It does not lie on the ground because Eznec would connect it to ground, some spacing is required. The effect of this spacing should be small, think of it as thick insulation on the counterpoise.

Default Modelling Conditions

Unless otherwise specified: The ground conditions are High Accuracy Medium Ground. Losses are Copper. Measurements are in DBi, or decibels over an isotropic antenna. The gain given for an antenna is the gain of the peak lobe. Note that most of these antennas have less peak field strength than an isotropic antenna, so they will be expressed in negative DBi. The more negative the value, the less effective the antenna. The antenna loads (if any) were adjusted to resonance (near zero reactive component at feedpoint). Load coil default Q is 500. Tuner coil Q default is 200. Tuner capacitor Q default is 1000. The Fishpoles are www.cabelas.com 14 foot telescoping crappie poles. For the dipole, a 4' tube is assumed to slide the pole handles into, making the assembly 31 feet. For the verticals the rod handle is fixed to the packframe making the length available for the antenna a bit less - I used 12 feet.

The antennas are:

The software used to perform these calculations will be discussed at the end of the article.

Just to remind us, here is a DB scale refresher:

Modelling Results

Radiation Pattern Overview

The vertical whips have directivity favoring the direction of the counterpoise. There is a null in the opposite direction. The depth of the null varies from 10 to 25db down from the peak lobe, depending on the vertical angle. The favored signal is in the direction of the countepoise when over real ground. Over more conductive surfaces the directionality changes (see details below). All the vertical patterns are substantially similar, the most variation is with the full quarterwave. The dipole (and loop) patterns are more symmetrical, with the best gain straight up (Near Vertical Incident Skywave style).

Gain Summary Table

DBi Description
-1.63 Fullsize Quarterwave Vertical
-6.48 Whip and tuner, not including tuner loss (1-15db) or lineloss (47.32 - J 1330)(at 10w 600v is required)
using 2' rg58 tuner to antenna (swr 426) 0.023db line loss but tunerloss rises to 2+ db
using 100' rg58 tuner to antenna 18.5db line loss
-6.66 Base loaded whip. Q500 Coil at the base, tuned to resonance.
-5.88 Loaded whip, load up 4 ft (Q500, top #12,#20 cp 52' #14 at 0.1')
+1.08 Loaded whip in Free Space (Z 14.5 -j 153) peaks at 4 deg above horizon, main lobe perpendicular to wires
+2.21 Loaded whip over Perfect Ground (Z 7.9 -j89) peak gain at horizon
+0.68 Loaded whip over Saltwater (Z 10.6 - J17.4) peak gain at 10 deg
-5.10 Loaded whip raised counterpoise to 0.3'
-4.78 Loaded whip raised counterpoise to 5' above the ground over the whole length
-5.61 Loaded whip with Lighter wire counterpoise #14 to #20
-5.86 Loaded whip with Heavy top wire - #20 changed to #14
-6.29 Loaded whip with Lower Q coil 200
-6.91 Loaded whip with even lower Lower Q coil 100
-4.64 Taller vertical 18' (sd-20 lashed to packframe) Q500 loading coil up 6'
-3.22 Taller yet vertical 31' (mfj-33 lashed to packframe) Q500 loading coil up 6'
-8.75 Vertical Dipole 17' hi with inverted T counterpoise (no drag wire) (includes load loss of 3db)
-2.92 Fullsize Halfwave Dipole up 8' (peak lobe straight up)
+0.89 Halfwave dipole up 16'
+3.51 Halfwave dipole up 25'
-3.23 Fishpole loaded Dipole 31' long up 16' (lobe straight up, -7dbi at 45 degrees)
-7.4 Fishpole loaded dipole lowered to 8'
-0.36 Fishpole loaded dipole raised to 25'
-3.31 Fishpole vertical loaded dipole (135 deg) on 16' mast peak at 30 deg
-2.71 Fishpole vertical loaded dipole on 25' mast peak at 30 deg
-3.12 Fishpole dipole 45 degrees Sloper up 16' peak at 34 deg
-12.18 Smaller Loaded Dipole, 18 foot, big Q500 coils up 8'
-18 Small Loop, 1 turn #14 4'x4' base 12' high (0.5 + j 160)
-17 Small 1 turn Loop, change wire from #14 to #12
-13.5 loop, 2 turns #12 (1.1 + j 410)
-6 loop, 2 turns 1" aluminum (0.18 + j270)(2kv 7.5a 10w) (plus -5.3db loss in default tuner)

Observations and Conclusions

Software Tools and Techniques

The antenna modelling was performed using Eznec 3.0. The transmission line and tuner analyses was done with Transmission Lines for Windows, included with the ARRL Antenna book.

About the Author

Alan Biocca has been a licensed Amateur Radio operator since 1967. He currently holds the Extra class license and has been modelling antennas for several years to gain understand of the real ones he has been building and using for 35 years. In his work life he holds BSEE and MSCS degrees from UC Berkeley and leads the Control Systems Group for the Advanced Light Source at Lawrence Berkeley National Laboratory.

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