HAM Radio 101 - Intro to Repeaters

There are so many unanswered questions for the new HAM licensee. in HAM Radio 101 – Intro To Repeaters: We’ll start to answer these questions to make HAM simple.

 

HAM Radio 101 – Intro To Repeaters

 

  Simplex Communications The simplest method to communicate on a HAM radio is simplex. This means that you have the same channel for transmitting and receiving. On the 2 meter band, you can use 146.520 MHz. This is the National Simplex Frequency. This channel should not be used to chew rag (talk) on, but only to sync up with another HAM. You should make your connection then decide on an alternate frequency to communicate on, so that you don’t tie up that high usage channel. If you can’t reach anyone, then you may have to take things to the next level and use a repeater. You can find a list of repeaters, nationwide in the ARRL Repeater Directory.

 

What is a Repeater? A repeater is just another two-way radio. It receives transmissions on one frequency, then re-transmits those same transmissions on another frequency; at the same time.

 

Why do use a Repeater? Your handheld transceiver or mobile ham radio, has a very limited range. This is due to it’s short (small) antenna and it’s fairly low height with respect to the radio horizon (unless you are on the side of a mountain). A Repeater is used to rebroadcast your transmissions and received signals to much higher levels, electronically, using large, very efficient, high gain antennas, low loss feed-lines and transmitters and receivers, that rated for heavy duty or continuous use. A repeater boosts your signal and receives the station you are talking to, over a far greater range and coverage area! You benefit from the repeater’s higher elevation, which increase your effective transmitting and receiving area!

 

What is a Repeater Offset? Repeaters need to listen and transmit at the same time, therefore they use two different frequencies. One frequency is for it’s transmitting frequency and the other is it’s receiving frequency. Think about it this way, if the repeater used the same channels for both transmit and receive, it would only hear itself. That would be a loop, and that seems really, really bad. The 2 meter band’s offsets are set 600 kHz apart (As a rule of thumb),

 

• If the output frequency (transmit) of the repeater < 147 mHz, then the input frequency (listening) is 600 kilohertz lower. This is called a “negative offset”.
• If the output frequency (transmit) of the repeater > 147 mHz, then the input frequency (listening) is 600 kilohertz above. This is called a “positive offset”.

 

The 70 cm band offsets are 5MHz apart (again, rule of thumb)

 

• If the output frequency (transmit) of the repeater < 447 MHz, then the input frequency (listening) is 5 megahertz lower. This is called a “negative offset”.
• If the output frequency (transmit) of the repeater > 447 MHz, then the input frequency (listening) is 5 megahertz above. This is called a “positive offset”.

 

On other bands, the offsets will be different. The good news is, that most of the modern ham radios take the offsets into account and will compensate automatically.

 

Example: If the repeater output is 443.700 Mhz (70cm band). The input, or the frequency the repeater receiver transmits on 443.700, but recieves on 448.700 (+5 MHz offset) If I have your radio tuned to 443.700 Mhz, and hit my transmit button, the radio transmits on 448.700, 500kHz (5MHz) up from 443.700. As soon as I release the transmit button so I can listen, the radio switches back to 443.700. Then I can hear transmissions on the repeater’s output frequency. The good news is, that most of the HAM radios sold today, will set the offset automatically, once you have chosen your desired operating frequency.

 

Note: There are always exceptions, so check your local repeater listings or the ARRL Repeater Directory (a must have!).