Impedances and SWR’s of Typical 43 Foot Vertical Antenna

To determine what tuners will work with a 43 footer the impedances need to be known for each band so tuners can be utilized that can handle those impedances.

For an interesting read on radials for vertical antennas see an extensive article by Al Christman, K3LC. http://ncjweb.com/bonus-content/k3lcmaxgainradials.pdf

The vertical tested here is a DX Engineering DXE-MBVE-5A 43 foot vertical. Radials are four pieces of welded wire fencing each 25 feet long laid flat and terminated on a DX Engineering DXE-RADP-3 radial plate. The fencing is 48 inches wide. A RigExpert model AA-55 was used to make the measurements. Each band was tested, 160 meters through 10 meters, except 12 meters. Here are the results including the (poor) snapshots of the AA-55 screens.

160 Meters

|Z| = 506.9 ohms (notice the R component is only 11.8 ohms)

SWR = infinity

80 Meters

|Z| = 216.6

SWR = infinity

60 Meters

|Z| = 58.6 ohms

SWR = 3.5

The 60 meter frequency of 5357 kHz is very close to the resonance of a 43 foot vertical. A dip at 5957 confirms the expectation.

A quarter wave vertical with a perfect ground system should have an impedance of 36 ohms. For curiosity the AA-55 was adjusted to the antenna’s resonance at 5957. Here is what this antenna measures:

|Z| = 45.7 ohms

SWR = 1.10

This reading of 45.7 ohms indicates a ground loss of 9.7 ohms (45.7 – 36 = 9.7) or approximately 10 ohms. This value agrees with the amateur literature for a typical ground system. One example is Phil Salas, AD5X’s presentation on The 43-Foot Vertical : “Assume 10 ohms of ground loss — Probably a much better ground than most hams have”. The efficiency calculation in the AD5X presentation should match the vertical in today’s test very closely. AD5X calculates 78%. For every 100 watts delivered to the antenna 78 watts is radiated.

An idea for improving this blog post would be to test a 43 Footer over a better radial system for comparison.

40 Meters

|Z| = 131.9 ohms

SWR = 4.8

30 Meters

|Z| = 636 ohms

SWR = 12.77

20 Meters

|Z| = 227.7 ohms

SWR = 17.03

17 Meters

|Z| = 102.7 ohms

SWR = 2.93

Notice another dip. This one at 17180 is the third harmonic of the fundamental frequency of 5957 kHz.

15 Meters

|Z| = 385.3 ohms

SWR = 7.8

10 Meters

|Z| = 61.2 ohms

SWR = 1.23

Conclusion

Matching 30 meters should be the most difficult at 636 ohms but that’s well within the range of most automatic tuners. An additional challenge should be 160 and 80 meters with their infinite swr’s. One of many good tuners to use as an example is the MFJ 998RT. It is specified to handle impedances from 12 to 1600 ohms and swr’s up to 32:1. In practice with this model of tuner installed on this 43 foot vertical it matches beautifully on 80 thru 10 but not on 160, maybe because the R component is only 11.8 ohms on 160. Optional coil and relay kits are available to add 160 meters. No matching problems have been noticed on 30 or 80.

A note of caution. Just because an antenna matches does not guarantee it is getting out possibly due to objects nearby or due to radiation patterns on each band. It may match perfectly at 10 meters but all of the energy is straight up to the clouds, with only a little radiation at low angles.

On the other hand antennas with a poor match still can make contacts with even a small amount of power being radiated, although inefficiently.

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