They gave me a homemade television antenna, assembled from two disks from a large computer, with the words “the antenna does not work.”

Introduction

On the roofs of country houses you can sometimes see an antenna made of a wide disk. This is a part from a mainframe computer - part of a data storage drive that was used in the 1980s before the collapse of the USSR.

Problem

Antenna diagram from two disks are given in article on the amateur radio portal QRZ.ru, but it was obviously written before the advent of instruments for measuring antenna parameters and before the writing of programs for modeling antennas.

I checked the antenna on the nanoVNA antenna analyzer. Indeed, an antenna consisting of two disks not tuned to the UHF range 470-690 MHz.

The article "TV antenna from a storage disk from large computers of the EC type" in the second part contains error. When the antenna is fed from the outer radius of the disk, the resonant frequency shifts below the UHF TV range.

Fmin=300 MHz
Fmax=360 MHz

Solution

If the antenna feed points are selected at central radius disk, it turns out tuned_ to the UHF TV range. In this case, the antenna consists of one disk as shown in the figure above.

Fmin=260 MHz
Fmax=560 MHz

An antenna from one computer disk, when fed from the central radius, is capable of receiving the entire UHF range from 260 to 470 MHz and UHF TV channels 21-31 (from 470 to 560 MHz) with excellent matching (SWR<2, R_input=36-40 Ohms). Above the frequency of 560 MHz, the coordination with the cable deteriorates, but remains acceptable for reception - channels 31-45 (SWR = 3...4).

Modeling an antenna from an ES computer disk

Outer radius = 356 mm
Inner radius = 170 mm
Air gap = 10 mm.

Instead of a solid disk, the model uses a grid of wires, because MMANA cannot calculate conductive surfaces.

The calculated SWR graph is in general similar to the practical one obtained on the nanoVNA device.

The SWR<2 band is wide: 360-750 MHz. That is, the disk antenna is very broadband.

The radiation pattern above 600 MHz goes up a little.

Model disk_uhf.maa for the MMANA program or MMANAGal Basic is in a ZIP archive.

• disk_uhf.maa.zip

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