A simple satellite antenna that took South Africa by storm

January 18th, 2019, Published in Articles: EngineerIT, Featured: EngineerIT

When South Africa was invited to host the International Amateur Radio Union’s Youngsters on The Air (YOTA 2018) summer event there were several challenges. The main one was: What could South Africa offer young people, aged between 16 and 25, coming from all over Europe and Africa that was different and something they had not experienced before? The ultimate decision for the South African host team, under the leadership of South African Radio League (SARL) president, Nico van Rensburg, turned out to be an easy one: build a number of pseudo CubeSats and launch them into near space on a high-altitude balloon. It was a great idea but in a short period of time a lot of water had to flow under the bridge, including designing a portable antenna that could be used to track the balloon.

The Secunda Amateur Radio Club offered their expertise in devising a pseudo CubeSat, now named BACARSat (Balloon Carrying Amateur Radio Satellite), and arranged the launch. The Makerspace group, BinarySpace, 3D printed components to make up space frames and a number of volunteers guided the young people, assembled in five teams, through the process of designing the payload with a number of sensors and the software required to encode and decode the output of the sensors. The next challenge was an antenna that could be used with their dual band (2 m/70 cm) handheld transceivers to track the balloon.  The antenna had to be portable and be able to be taken apart so that it could be packed in their luggage when flying home.

After much research, it was decided to develop a local version of the design of an “open sleeve” antenna by German radio amateur, Martin Steyer (DJK7ZB), incorporating design enhancements made by US amateur, Larry Brown (WB5CXC).

The open sleeve is a unique design on a Yagi antenna which places the director very close to the driven element. The driven element is sized for 2m with an impedance of 50 ohm. When operating on 70 cm the open sleeve acts as part of the driven element on 70 cm (third harmonic of 2m).

The original concept was developed in 1946 by Dr J T Bolljahn of the Stanford Research institute but was not introduced into amateur radio until the 1950s. Many radio amateurs have used this concept in the design of high frequency (HF) multiband antennas where by adding additional elements near the driven element, the antenna is resonant on several other frequency bands.

Dr Gary Immelman.

The first South African version supplied to the YOTA 2018 participants was a collaborative design by Guy Eales (ZS6GUY) and Dr Gary Immelman (ZS6YI).

The same evening after the young people had assembled their antenna, they were searching the sky for amateur satellites and it was not long before they made contact through several amateur radio satellites with other radio amateurs. During their week in South Africa, YOTA participants also received a very high frequency (VHF) dongle sponsored by MultiChoice and could be seen during their free time looking for other signals from space. The antenna was a winner!

After YOTA, the mechanical structure was redesigned by Dr Immelmann. A choke around the boom was added to isolate the antenna from the coax and reduce the effect human contact has on the antenna. A handle was added on the boom end which makes it more comfortable to hold and further isolates the antenna from the handler.

Now called the AMSAT SA dual band Yagi, it is manufactured in one of Dr Immelman’s factories in Vereeniging. It has two elements on 145 MHz and three elements on 435 MHz. He has donated 200 antennas to AMSAT SA to generate funds for their two satellite projects “KLETSKOUS and AFRIcube”. He also attached the condition that the antenna had to be made available at a very low price. “I like to contribute to the development of the AMSAT SA satellite projects but I also would like to encourage more radio amateurs and in particular the younger generation to become involved in space activities”, he said.

For its size the antenna has excellent gain:

  • 145 MHZ: 4.12 dBd or 6.3 dBi
  • 435 MHz: 6.23 dBd or 8.4 dBi

The Yagi is broadband with measured SWR almost flat over the entire bands as follows:

  • 145,800: SWR 1.1
  • 435,000: SWR 1.12

The antenna is plug-and-play. No tools are needed except for soldering on a connector to suit the application. It comes complete in a carry bag with full instructions. This antenna can be assembled and dissembled in minutes.

The Yagi has taken South Africa by storm with over 150 units already in use. AMSAT SA has received enquiries for the antenna from the USA, Europe and the Far East. Currently individual export is not feasible due to the high international courier cost but AMSAT SA is exploring bulk shipping to local distribution centres in other countries. Currently the main focus remains on South Africa.

The antenna has various applications which will be discussed in a paper to be presented at the annual AMSAT SA Space Symposium to be held in Midrand on 16 March 2019. More details can be found on www.amsatsa.org.za

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