Walkie Talkie Two-Way Radios » two way radio

Radio Repeaters Extend the Range of VHF and UHF Two Way Radios

Admin — Sun, 11 Jul 2010 06:35:31 +0000

Two way radios that use these short wavelengths (very high frequencies, ultra high frequencies and above) are normally only useful for line-of-sight communications over modest distances.

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.

Difference between FRS and GMRS two way radios

Admin — Wed, 07 Apr 2010 09:43:27 +0000

I don’t understand whet the difference is between FRS radios and GMRS radios, especially since some two-way radios you can buy seem to have BOTH.

Can anyone help clarify things for me? Thank you.

Related Blogs

Homebrew a Half-Wave Dipole Antenna

Admin — Fri, 03 Apr 2009 02:21:23 +0000

dipole antenna

If you own a soldering iron and a few simple tools, you can build and erect your own half-wave dipole antenna in about half a day.

All you need to have is somewhere with enough space to erect the antenna, some copper wire, three insulators and a length of 50 Ohm coaxial cable to connect your radio transceiver to the center of the dipole aerial.

You will also need two end supports to hold your half-wave wire antenna off the ground. Trees, posts, antenna masts or poles, the sides of a building can all hold up one end of an antenna. For best long-distance results you should get the antenna as high up as you can – with a half-wavelength off the ground being ideal or optimal. That way you get the strongest signal radiated out broadside to the antenna wire.

Your end insulators can be made of ceramic, glass or plastic. For low power (below 20 Watts or so) almost anything will do… wood, plastic jar tops, buttons etc. Since the insulator at the center of your wire antenna is also where you connect your coax cable to the two sides of the dipole, you can buy a ready-made coax-to-dipole center connector, make your own homebrew dipole connector, or you can use a 1:1 antenna balun (store bought or home-made).

The standard formula for calculating the length of a dipole antenna in feet is:

468/freq in MHz

So:

An 80 meter band dipole for 3.6 MHz (in feet) would be 468/3.6 MHz = 468/3.6 = 130 feet.
A 40 meter band dipole for 7.1 MHz (in feet) would be 468/7.1 = 65.9 feet.
A 20 meter band dipole for 14.15 MHz (feet) would be 468/14.15 = 33 feet.
A 15 meter band dipole for 21.100 MHz (in feet) would be 468/21.1 = 22.2 feet.
A 10 meter dipole for 28.6 MHz (in feet) would be 468/28.6 = 16.4 feet.
And just for CB users, so you don’t feel left out, an 11m dipole for 27.1 MHz is 468/27.1 = 17.27 feet (17′ 3.25″) end to end. Thus each side of the dipole would be 8.635 ft (8′ 7.6″).

Always cut the antenna wires about one foot longer than you need and only prune to resonance with a VSWR meter or an antenna analyzer after it has been hung in the air where you want it. (If you tune it in one location and move to another, the SWR reading will differ. But not by too much, we hope!)

You can cut off excess wire with wire cutters, or you can fold it back at the end insulators instead. That way, if you remove too much, you just unwind some of the unused wire… you don’t have to splice and solder more wire back on!

Various dipole connectors and wire antenna insulators available from Buxcomm. The big white cylinder at left is a 50 Ohm antenna balun.

If you are using an antenna to dipole connector at the center of your antenna, then you will usually need to have a PL-259 (sometimes called a UHF connector) at the end of your coaxial cable. The other end of the coax cable, which plugs in to your two way radio, will usually need a PL-259 connector as well. If in doubt, read the manual or ask at the shop where you bought the radio.

Just remember, the PL259 (male plug) plugs into the SO239 (female) socket.

For most HF radio frequencies you can get by with the thinner RG-58 grade coax cable. But for longer cable runs (or for VHF and UHF frequencies) you should use the thicker cable such as RG-213 or better.

You can often buy lengths of cable with the plugs already installed, but most Hams will want to have the skill to solder the plugs onto these cables themselves. Find someone to show you how.

You may also find another article useful. It shows you how to build a Homebrew Quarter-Wave Vertical Antenna.