Engineering Report on the Avanti Astro Plane - July 1969

[FPR1981]

(*Transcribed from CB Radio Magazine, July 1969)

ENGINEERING REPORT

AVANTI “ASTRO PLANE” ANTENNA

AVANTI R&D was originally founded April 15, 1965 as a research and Development laboratory whose business consisted of project development in electronics and electro mechanics for other companies.

While doing work for the Naval ordinance bureau on some depth gaging devices, an engineer was hired who had an interest in communications antennas. He asked if he could use the laboratory in the evenings to develop a new dual-polarity loop antenna he was interested in building for his CB set. This was allowed and the PDL was created. Some of these antennas he sold to friends but eventually the supply could not meet the demand and AVANTI agreed to manufacture this antenna in order to fill the need.

Later another new lightweight omnidirectional antenna was created and its sales were growing larger than expected.

A REPORT ON THE MEASURED PERFORMANCE OF THE AVANTI “ASTRO PLANE ANTENNA, AND A REVIEW OF THE DESIGN FEATURES OF THE ANTENNA.

• At the request of Mr. Louis J. Martino, President, Avanti Research & Development Inc., 45 West Fullterton Avenue, Addison, Illinois, I measured the radiation characteristics of the Avanti “Astro Plane” antenna model that had been designed and adjusted for operation at a frequency of 144 MHz. 144 MHz was used for convenience sake – operation on 27 MHz would be similar.
• During the radiation tests, the support rod of the antenna was secured to a section of Philippine mahogany whose dimensions were 1.0 x 0.75 x 61 inches, which was clamped to a wooden support. The total assembly was positioned to place the axis of the antenna in a position normal to the earth, with the feed point of the antenna located 6.84 feet above the earth, or about one-wavelength above the earth.
• The transmission line supplied with the antenna model was extended by the addition of a fifteen-foot section of RG58/U cable, and the 100 mg signal, amplitude modulated 30% at 400Hz, from Measurements Corporation model 80 Standard Signal Generator, serial no. 26104. The tangential component of the electric field produced by the antenna was measured at a distance of 6.84 feet from the feed point of the, over a range of zero to 90 degrees from the line through the antenna axis. The pattern of radiation observed at this distance will have the same shape as the tangential field pattern measured at a great distance from the antenna. Measurements Corporation UHF Radio Noise and Field Strength Meter model 58m serial no. 589, was used for the field intensity measurements. The field intensity meter was calibrated using a 6 db balun and the model 80 signal generator before the field intensity measurements are given in Figure 1, along with the calculated performance of a half-wave antenna in free space for comparison.

DEGREES	Avanti “Astro Plane”	Half-Wave Antenna
0	0.067	0.00
10	0.191	0.138
20	0.105	0.277
30	0.162	0.418
40	0.190	0.552
45	0.248	--
50	0.543	0.693
55	0.610	-
60	0.525	0.819
65	0.620	-
70	0.780	0.916
75	0.810	-
80	0.950	0.978
90	1.00	1.00

FIGURE 1 – Normalized tangential electric field intensity of Avanti “Astro Plane” antenna

• It may be observed from the test data and the graphs of the radiation characteristics that the Avanti “Astro Plane” antenna has a radiation pattern in the vertical plane that has a maximum at 90 degrees and a 3db beam width of only22 degrees. The beam width to the 3 db point for the half-wave antenna in free space is 37.5 degrees; thus the “Astro Plane” antenna has a gain of about 4.46 decibels over the isotropic radiator
• It appears that the modified folded monopole that makes up the lower half of the Avanti “Astro Plane” antenna isolates the antenna from the support rod to the extent that there is little or no current in the support rod. It is possible that this isolation might be attributed to the symmetry of the folded monopole in relation to the support rod. If such isolation had not been achieved, it would not have been possible to have obtained the unusually low angle of maximum radiation.
• I believe that the Avanti “Astro Plane” antenna is best described as a hybrid-arrangement of a folded monopole element and a top-loaded monopole element, quasi-coaxially arranged in tandem about a support rod, with the top-loaded element occupying the upper position and the folded monopole occupying the lower position in the arrangement. In the arrangement, capacitive loading is used on both elements; a crossed rod assembly is used on the top element and a ring is used on the lower element. Thick elements have been used in the structure to give broad bandwidth and good mechanical characteristics, and the spacing between the conductors in the folded monopole section has been made to follow an exponential or other appropriate law to give the desired driving point resistance of 50 ohms over a wide bandwidth.
• In the patent application, prior art could include various ground-plane antennas as well as the coaxial antenna forms. Finally, reports from the field on the antenna performance are in agreement with the radiation pattern that I obtained for the antenna.
• Prepared by Alva C. Todd, Ph.D., P.E.
  Consulting Engineer

 

[iMONITOR]

I had one back in the late 70's on a 20 ft. mast on the peak of a two story home. Performance was excellent.