Long Range Two Way Radios
Long range two way radios are usually what are called HF radios, which use frequencies in the short wave bands, usually between 3 Mhz and 30 Mhz. This is because the more commonly-used VHF and UHF radios normally work line of sight and not over the horizon. However some VHF and UHF radios can operate right across a city area.
The HF shortwave radio signals can operate much longer distances, from a few hundred miles out or even further because the radio waves go up into the atmosphere and then bounce back to earth far away over the horizon.
VHF or UHF signals can go up into the sky as well, but they just keep going on and up into space. They don’t bounce back from the atmosphere.
HF long range two way radios are used by airplanes and ships at sea as well as by all branches of the military services. And HF 2-way radios are also used in remote locations where there are no cellphone services, such as parts of Africa, Alaska, South America, the Middle East and in the remote Outback deserts of Australia.
These HF radios normally use single side band (SSB) mode for voice signals. The days of morse code (CW signals) are long gone, except for licensed Ham Radio operators, many of whom still like to use a morse key. Some long range HF two way radios can send digital messages from computer to computer (all without any Internet or telephone lines).
The downside to HF radios for long range communications is that they need big tall antennas, sometimes hundreds of feet long and maybe 50 feet or higher up in the air to be effective. HF radios can be fitted in vehicles, but any antenna that fits on a car is always going to lose a lot of the signal in the coils and other circuits that allow it to be shrunk enough in size to fit the vehicle.
That is one reason why many large organizations and governments – those who can afford the high charges – often use Satellite Phones instead. (They don’t have to have a skilled operator.) But there are still some places where satellite phones won’t work, and that is where long range two way radios are especially useful.
hello,
i want to use a fm transmitter which could transmit for 500-700 metres.i have a long range phone antenna.can i use that antenna to trasmit the audio??will it work??help needed..please..
There is a misunderstanding here. Radios that use FM modulation normally only work line-of-sight. From one high tower to the next, that distance can be city-wide or quite a few miles. But getting the signl to work at that kind of range relies on a transmitter that puts out maybe 100 watts of power. And often the point-to-point radio circuit uses directional antennas, such as a Yagi beam or a Log Periodic antenna design (which looks like a common TV reception antenna, but much better made). You don’t state the radio frequency (in MHz) of your radio transmitter or the type of antenna your so-called ‘long range phone antenna’ actually is. Chances are the transmitter is not on the same frequency as the antenna, which would give high VSWR and result in your transmit power being lost as heat. It could also damage the transmitter. Your 700 meters does not count as a ‘long distance’. When engineers refer to long distance radio, they usually mean HF radios (not VHF or UHF), with decent power (maybe 100 Watts or higher) that punch out a signal that bounces off the layers of the atmosphere and come down again on the other side of the world! The signal is usually single side band (SSB) for voice, or it may be a digital signal such as PSK31 (for computer to computer, thru screen and keybord). And some folks still like to use CW or Morse Code. This is what radio hams (licensed operators holding Amateur Radio certificates and callsigns issued by the government) do to talk to and make friends all over the world. Your FM radio device probably works in the 88 to 108 MHz part of the radio spectrum, and is almost certainly low power… probably less than 1 Watt. It just might work for you if you can match it to a good-quality Yagi antenna of maybe 4 or 5 elements in the design. But it seems more trouble and money than its worth, especially if you are new to all this technology. Good luck, David VK2DMH (my callsign).
I am trying to figure out what would be the best amateur frequency to use for direct radio communication between central Indiana and central to northern Minnesota. A frequency that is least affected by sunspots, weather and daytime temperatures. SSB or PSK31 is ok, but can it be mobilized and could it run off a longwire or di-pole?
Thanks,
Kevin(N6FOZ)
Hi Kevin. I live in Australia and I don’t know how many miles it is between your locations. But that is just one factor of many. The season of the year, the time of day… all of these make a difference to the Ionosphere – the upper levels of the air above our heads. It gets changed by electroromagnetic radiation from the sun, and that is affected by an 11-year sunspot cycle. ALL of these things can be factored into some intense calculations, but when it all comes down to the nitty gritty, it is really a matter of “suck it and see”. I would advise you to try the 80m band at night time, when atmospheric noises are at their lowest, and also give it a go on 40m both during the daytime and the night. You could try some of the new 60m band channels as well, if the ham you are trying to reach has them. See how you go with that. SSB needs a very good connection to work, whereas PSK31 will get through with a much weaker signal…just like CW (morse code) can usually manage. And as for antennas, a dipole tuned for the frequency you are going to use will be the best by far. For longer distances, get your antenna up high – more than 1/4 wavelength if possible. At lower heights it will act as an NVIS antenna, which sends the signal straight up – like hosing water into an umbrella above your head. This is good for comms for a local to a few hundred miles away. But not for DX. 73 David vk2dmh.