Doctor Gardner-Stephen using his reprogrammed cellphone to talk to his team of researchers during testing in the Outback desert and Flinders Mountain ranges of South Australia.

It is stories like this that make me proud to be an Australian. A team of Aussie scientists from Flinders University have found a way to re-program mobile phones (cell phones) so they can talk to each other over short distances without working cellphone tower or a communications satellite. This would make these cellphones ideal for emergency communications in a disaster situation, like the recent major earthquake in Port au Prince, Haiti.

These radio boffins have been testing out their modified mobile phones in remote desert areas of South Australia that are hundreds of miles or kilometers from the nearest cellphone towers. The researchers have even been in deep canyons, and the cellphones are able to talk to each other over a distance of a few hundred yards (meters) or so.

The modified cell phones are models that already have an inbuilt WiFi feature, and the boffins re-programmed the phones to make calls to each other using just the WiFi signals. Normally wifi transmissions are used over very short distances, to link computers and their peripheral devices, such as wireless-enabled printers, optical scanners, hard disk drive remore storage, or from computer to computer. But here the WiFi works from phone to phone, making phone towers (computer controlled radio repeaters) unneccesary.

It was Aussie ingenuity like this that created the original Outback pedal-operated radio transmitter-receiver that remote Outback cattle stations (ranches) could use to call for help from the Royal Flying Doctor Service.

For further details, click on the photo (above). The link will send you to the original article, which is on the Australian ABC News web site.

To get the maximum possible range for a radio transmitter, the radio’s antenna should be up as high as possible. That is why professional radio installations, business, government agencies, police fire and emergency services all have their radio antennas placed up as high as possible. And they often use radio repeaters as well.

Base station antennas are mounted on the tops of buildings or, even better, on top of radio towers or on tall public structures such as water towers or grain silos. The higher the antenna, the further your transmissions can be heard.

Government departments, emergency services, the military and business radio users also make use of radio repeaters, as do many licensed Amateur Radio operators – often called Radio “Hams”. Hams are not CBers, but many CBers eventually get their licenses and become Hams or Radio Amateurs. Hams have to study and qualify for their “Amateur” radio operator’s licenses. And if they break the rules they can lose the license, be fined and even have their equipment confiscated. They also have to use their legal callsigns on the air.

And as for two-way radio repeater stations, a radio repeater is an automated radio signal relay station for VHF, UHF and higher-frequency 2-way radios and walkie talkies. The radio repeater listens all the time on one assigned radio frequency. Then, when it receives an incoming radio signal on that channel that is strong enough, it instantly re-transmits the same information out again on a different radio frequency. The repeater’s output frequency is close, but not too close to its receive frequency. And that pair of frequencies are often referred to as a particular channel, or as the same channel.

Most simple two way radios, and cheap walkie talkies, can only send or receive on one frequency, and this is what is called operating your radio in simplex mode. Sending and receiving using two different radio frequencies or channels is operating your two-way in duplex mode.

Maximum radio range comes from having your base antenna high up on a tower

Just as an example, here in Australia, the frequency 146.500 MHz in the VHF 2-meter Amateur Radio band has been assigned as our National Voice Calling Frequency. It is a simplex channel because anyone speaking over that channel has their radio set up to receive and transmit on the same frequency. The audio information that they send and receive in that part of the band is in FM (frequency modulated) mode. We hams sometimes send and receive in other modes, such as CW (Morse code) or SSB (single-sideband) but that does not involve the use of repeaters.

However if you are working repeater station VK2RGR in North Ryde (about 15 Kms north of Sydney) then your radio must be set to listen on 146.925 MHz but transmit on 146.325 MHz. There is a spacing of 600 kHz between the input frequency and the output frequency. I just label the channel North Ryde, but some miht label it as VK2RGR. Either way, it is a duplex channel – it has a pair of radio frequencies.

Please be aware that all these people and organizations that use UHF and VHF two-way radios and radio repeaters are licensed by the Federal Communications Commission (FCC) in the United States. And in other countries, they have to be licensed too by that country’s government agency for radio communications. Here in Australia our federal government radio agency is now referred to as the ACMA – the Australian Communications and Media Authority. (Years back when I first got my license it was called the DOC – Department of Communications. Before that, I believe it was just the Post Office that controlled the monopoly on who could transmit any radio frequencies over here.)

The radio frequency spectrum is a resource that is controlled by the govermnent in every country. There is much money to be made on the sale of licenses to everybody. So if you don’t have a license, you cannot use any 2-way radios unless your government has said so. CB and FRS radios are license-free in the USA. Here in Australia, our CB radios are license free as well.

For talking over any distance you and your radio should be able to “see” the antenna of the other person and 2-way radio you want to communicate with. That will give you your maximum possible range but, in reality, your radio signals may get bounced around a bit by various obstructions. These are buildings, and other features of the landscape which can block or enhance your radio signal. So you might do a bit better than that or you could do worse.It is a matter of luck and of geography.

So if you are on one side of a big hill and the other radio set is on the other side, you are not going to be able to talk at all together – unless you have the use of a radio repeater station.

The radio repeater is a special two way radio that has been built and designed specially for repeater work. Its radio transmissions and signals are modulated in the FM mode (frequency modulation). Not all radios use this mode. The repeater is actually two separate high quality radios – one very sensitive and selective radio receiver coupled to one very powerful radio transmitter.

The repeater station ‘listens’ for incoming radio signals on one radio channel (known as the input frequency), and when it hears a strong enough signal, it relays whatever it hears on another radio channel (the output frequency).The repeater station needs to have a very selective radio receiver, because it is has to transmit at the same time that it is receiving the incoming signal, and although connection circuit uses two different frequency channels, they are still fairly close together in the VHF or UHF band. Ordinary radios cannot do this without one signal swamping the other, breaking through and causing terrible audio feedback – the loud screeching howl when a live microphone is placed in front of a loudspeaker.

So repeaters have to be more sophisticated than ordinary radio transceivers or two-way radios.

Sometimes the transmitting radio (that’s you, with your portable radio or mobile transceiver) have to program in a tone frequency to “unlock” the repeater. (For example, one CTSS frequency for a repeater near me here in Sydney Australia is 123 Hz.) Without that tone, you can transmit all you like on the repeater’s input frequency, but it will not open the squelch to relay your signal.

But because two way radios which use repeaters can get out a whole lot further than simple walkie talkie radios that transmit and receive on the same frequency, you cannot operate such a transceiver in the US (and most other countries) without having a valid radio license.

But then the radio engineers and designers quickly discovered that fairly low-frequency radio signals in the MF or HF bands could often travel hundreds of miles, and sometimes thousands of miles. In the very early 1900s, it became possible for two way radio stations to communicate from one side of the Atlantic ocean to another, and for shore-based radio stations to send and receive morse code messages to and from ships at sea.

This meant better safety for the passengers on those ships, and the companies building these two-way radios would lease their equipment – complete with trained radio operators – to handle all the radio traffic from ship to shore, or from ship to ship. Every message was sent as a radio telegram, and was charged for at so many cents per word.

Ships radio operators (telegraphists) who worked the maritime radio bands were often nicknamed Sparks or Sparkie because of the buzzing sparks which sounded from their radio transmitter every time the morse key was pressed closed. Those radio telegraphists could send and receive morse code signals quickly and copy the incoming messages in their heads before writing the words to paper. And they could often hold a conversation with you at the same time!

The early spark gap morse transmitters were large and cumbersome and required vast banks of big heavy lead-acid batteries to power them, and they needed big wire antennas that were hung between antenna towers on land or between the ships masts at sea.

By the end of World War One, the military had discovered two way radio, valves had been invented and the radio sets were a bit smaller and much better quality. By now, they could fit into a horse-drawn wagon. But the early valve radios still used morse code.

Voice signals came during World War Two, but morse code was still used extensively because it could be send and received where the inefficient AM mode voice signals could not be heard. By the end of WWII, the radios were small enough to fit into suitcases and were often used that way by spies and secret agents. And yes, they still used morse code, and they had to string up their wire aerials and send their messages without being caught. By now the military everywhere had security agencies who could trace where the radio signals were coming from and would rush to try and capture the radio operator who was sending them.

These HF (shortwave) radio signals that needed to travel hundreds of miles would only be able to get through at certain times of the day or night. They rely on the radio signal going up into the sky and bouncing off the different layers of the atmosphere so the signals could come back to earth a long distance away. If you picked a bad time of day the atmospheric propagation wouldn’t reflect your signal back to earth, so it couldn’t reach the people you were trying to send it to. But it could be picked up locally where, if you were a spy, you didn’t want anyone local to hear it.

By around 1940, the Motorola corporation created the first-ever walkie talkie radio. It was a clumsy tin box with separate built-in microphone and earpiece. It had tiny valves inside (because transistors had not been invented yet) and  pretty heavy battery pack, and it had a telescopic arial or antenna. It could transmit in AM mode (amplitude modulation) and, if you were lucky, it was good for talking over a distance of about half a mile.

That half mile or so distance that simple radios are good for is what we call line-of-sight, and that’s just about the distance you can get today with most cheap walkie talkie portable radios – such as FRS/GMRS radios in the US or the little handheld UHF-CB radios we use here in Australia. Their signals go up into the sky as well, but at those high frequencies (VHF and UHF) they don’t bounce back to earth. It takes a satellite to bounce those radio signals back to the ground, and I (and probably you too) cannot afford them.

73 de David, vk2dmh

Now, I understand that there are MANY factors involved, such as urban usage – buildings, houses, cars, trees, etc., but seriously, that is more than a 75% difference. Where are “they” coming up with those astronomical figures? Are the using the ocean, or airspace as their testing grounds?

You know, Walt Disney World covers about 47 square miles which is about the size of San Francisco or two Manhattan islands – so what good are these or any other two-way radios?

If you mention skiing in the mountains, don’t bother cause I was using a 2-way radio while skiing in Colorado and took a wrong turn and ended up literally in the streets of town and I couldn’t contact any of my party for assistance which led me to walking 2 miles in my rented ski-boots just to find a bus. Now, I am from Florida and let me tell you, we aren’t used to ski boots when they are attached to skis, so don’t think us boys down here like them any better now.

A GMRS license? Yeah, right. Then why don’t they include one (or information)when you purchase any GMRS 2-way radios that are for sale to the public? The ones I am referring to are the maximum power output allowed by law.

It sounds to me like “false advertising”, in which case, a lawsuit should be filed, eh?

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