Repeaters do exactly what is sounds like. Repeaters take an incoming signal and retransmit it. With radio one of the most important things is line of sight. Because of the curvature of the earth. HF frequencies bounce off of the ionosphere and come back down to the earth hundreds of miles away. The MUF (Maximum Usable Frequency) is the highest frequency that will bounce back to the earth. It changes hourly due to sunspots and other dynamic conditions. This MUF is usually below 54 mhz. Anything higher than the 6 meter (54 mhz) ham band goes right through the atmosphere into space and keeps going. On VHF and higher frequencies we need a clear line of sight between locations. For the average human, radio waves above the MUF will travel at most 20 miles on even ground. Any mountains, buildings or trees will inhibit this. If however one puts a transmitter at the top of a mountain, the curvature of the earth has a line of sight hundreds of miles away. Think about what you can see on a valley floor compared to the top of a high mountain; line-of-sight is much better up high. For this reason hams find places on high mountains and place two radios; a transmitter and a receiver. The repeater takes incoming signals and automatically retransmits it.This way when you transmit up to the repeater your signal is retransmitted over hundreds of miles.

Simplex Vs. Duplex

Simplex means that both parties are transmitting and receiving on the same frequency. CBs and walkie-talkies are simplex. Duplex means that the transmit and receive frequencies are offset. A repeater must use an offset because if it tried to transmit on the same frequency that it received on, the signal would jam anyone trying to use the system. Repeaters use "half duplex" This means that only one person can transmit at a time, but the transmit and receive frequencies are different. "Full Duplex" is where both sides can transmit and receive at the same time. A telephone is full duplex; if someone else is talking, you can talk and they will hear you. You can interrupt them because they hear everything even while they are talking. 99% of ham radio is half duplex or simplex. On a ham radio if someone is transmitting and you key up while they are talking they wont hear you.

Repeater split:

Each band has a different repeater split. For 2 meters the split is 600 khz. This means that a repeater on the 2 meter band will have a receive frequency that is 600 khz away from the transmit signal. The transmit frequency can either be 600 khz above the receiver, or 600khz below. This is where the repeater's "offset" comes into play. If someone says "The repeater is on 145.150 minus" that means that the repeater has a negative offset. It says that you receive on 145.150 and transmit on 144.550 (.600 less). The radios today have what is called ARS (Automatic Repeater Shift). Manufacturers have integrated the ARRL band plan into the radios so that when you input a frequency that is supposed to be a repeater frequency it knows if it is supposed to have a + or - based on where it is. If one puts in a frequency that is supposed to be simplex, the radio knows that it is a simplex frequency and will not assign a split.

If you have a radio you can give it a try:

Put your radio on low power and type in the frequency 145.150; key up and say your callsign.(assuming its clear). As you transmit you will see your frequency in the display automatically change from 145.150 to 144.550.

Put your radio on 146.520 and if clear key up and say your callsign. As you transmit your frequency in the display will not change. The radio is smart enough to know that it is a simplex frequency and should not have an offset.

Squelch is usually a knob but it can also be defined in the menus. With squelch all the way down all one hears is static. This can be annoying to hear constant static. As a result we have Squelch. This stops all signals below a certain point from being heard. With squelch all the way up faint signals will never be heard.


PL Tone:

PL Tone is a motorola standard that is copy written but it is in common usage. The technical definition is CTCSS encoding. PL stands for "Private Line". What this does is it enables multiple people to use the same frequency without hearing each other. CTCSS is a sub-audible tone. This is a tone that is below the human ability to hear. When CTCSS is enabled it superimposes this tone under everything you say. Receivers that are set to decode CTCSS will listen for this tone and will not open the squelch unless it is heard. Repeaters use these tones to stop interference. Sometimes certain conditions make temporary propagation possible to very remote repeaters. Many times it is just barely enough to break squelch but not enough to be intelligible. This means that static is retransmitted over the repeater; very annoying. As a result repeaters enable CTCSS decoding on the receiver. This way it will only retransmit signals that have the correct tone. If you set your radios frequency and offset correctly but do not enable CTCSS encoding it will not work.


Digital Private Line is the Motorola name for DCS or "Digitally Coded Squelch". It works identically to CTCSS but instead of using sub audible tones it uses a digital code that's transmitted instead. It makes for many more combinations.


Read the Finicky Manual; Each radio is different on how to configure these options. It is important to review the manual for the proper programming procedure. If you do not take the time to familiarize yourself with your radio it will be useless.


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