News from Madagascar is that Tropical Cyclone Enawo-17 has blown itself out in to the Southern Indian Ocean, and been downgraded to a Tropical Depression. Its worst day was Thursday the 9th, when close to 1,6 million people were suffering winds of the order of 230kph as Enawo chiselled its way down central Madagascar. Fortunately, advance warning and precautionary planning seems to have prevented a major loss of life and limb, and the country now scrambles to count the cost.
A message received from Roy Walsh ZS3RW of HAMNET Northern Cape announces that the new HAMNET banners crafted for all the divisions have been completed and are ready for distribution. Some 40 banners were ordered by the various divisions, and there remains only to distribute them to all corners of the country. So be on the lookout at the next HAMNET-supported event in your Province for sight of our new brand-labelling. We think they’re pretty smart.
Today sees the Cape Peninsula inundated with some 35000 cyclists riding their hearts out during the Cape Town Cycle Tour, perhaps better known formerly to the populace as “The Argus”! A mild sunny day with maximum temperature of 23 has been forecast, but as always, it is going to be the wind that makes or breaks the race. Riding into or away from a South-Easter or North-Wester has the ability to knock the stuffing out of riders, and the sweep vehicles are sometimes kept very busy. We’ll let you know next week if anything interesting arises as a result of weather conditions.
HAMNET Western Cape is also gearing up for the Old Mutual Two Oceans Marathon, taking place on Easter Saturday, the 15th April. Sixteen operator volunteers are needed to man the route by HAMNET, and all the Usual Suspects are encouraged to contact the bulletin reader soon with their intention to participate. Grateful thanks to all who do volunteer every year.
And, in a small potential disaster you may have missed, researchers at the Catalina Sky Survey in Arizona spotted a small asteroid as it came very close to Earth last Thursday week. Asteroid 2017 EA, which is smaller than 3 meters across (not much bigger that your double bed) passed within 14,500 kilometres of Earth on the morning of March 2. That distance is closer than several communication and weather satellites and about one-twentieth the distance of Earth to our Moon.
Sadly, according to a statement from NASA’s Centre of Near-Earth Object Studies (CNES), 2017 EA won’t be back for at least another 100 years. So you can put up your tower and Yagi without fear that it will be knocked down any time soon.
Software Defined Radio, or SDR, technology is going to be the way of the future. The days of superheterodyne receivers with two intermediate frequencies, and mixers, will soon be over, as the technology of software processing, with Field Programmable Gate Arrays, takes over. Several radio manufacturers already provide transceivers in which ordinary received signals are digitized, and fed through a chain of software manipulations, before being converted back to analogue signals, and fed to an audio amplifier for us to listen to. In reverse order, the microphone audio is digitized, and manipulated or equalised to suit the voice of the operator, before being converted to an analogue signal and transmitted via the antenna. All the digital stuff in between then gets managed by software on an attached computer or hardware in the radio itself. There is then almost no restriction on the number of manipulations possible. All you do is update the firmware of the chip in the radio.
Presumably miniaturisation will follow, as only the power modules need to be very big to put out the customary 100 watt signal.
Well, why not have the whole radio on a single chip, you ask? Mainly because the transmitted signal will destroy the receiver on the single chip each time you transmit. Not quite true anymore. Peter Dekker, ZS1PDE, has sent me an item from ECN, discussing the Transceiver on a Single Chip. In essence it goes like this.
Two-way communication requires, of course, both send and receive capabilities. But putting them in the same device requires a filter between the send and receive circuits to provide signal isolation.
Without a significant filter, communication would be impossible.
“Your transmit signal is 1014 times stronger than your receive signal,” said Alyosha Molnar, associate professor of electrical and computer engineering (ECE). “That’s 100 trillion times stronger – that’s a really hard problem.”
But researchers in Molnar’s lab have offered up a solution.
Molnar and collaborator Alyssa Apsel, professor of ECE, have devised a method for both transmitting and receiving a radio signal on a single chip, which ultimately could help change the way wireless communication is done.
Their work is described in “A wideband fully integrated software-defined transceiver,” published online Jan. 27 in the Institute of Electrical and Electronics Engineers’ Journal of Solid-State Circuits.
Separating the send and receive bands is difficult enough, but Molnar and Apsel have come up with an ingenious way of doing so. Their idea lies in the transmitter – actually a series of six sub-transmitters all hooked into an artificial transmission line. Each sends its signal at regular intervals, and their individually weighted outputs are programmed so that they combine to produce a radio frequency signal in the forward direction, at the antenna port, while cancelling out at the receive port.
The programmability of the individual outputs allows this simultaneous summation and cancellation to be tuned across a wide range of frequencies, and to adjust to signal strength at the antenna.
“In one direction, it’s a filter and you basically get this cancellation,” Apsel said. “And in the other direction, it’s an amplifier.”
“You put the antenna at one end and the amplified signal goes out the antenna, and you put the receiver at the other end and that’s where the nulling happens,” Molnar said. “Your receiver sees the antenna through this wire, the transmission line, but it doesn’t see the transmit signal because it’s cancelling itself out at that end.”
Very clever indeed! We hope this technology will not be long in being launched, and that emergency communications will greatly benefit from its ingenuity.
This is Dave Reece ZS1DFR reporting for HAMNET in South Africa.