You’ve just purchased your first handheld transceiver and have been chatting with both old and new friends around town on the 2 Meter band. There are many different frequencies to choose from, so how do you find an appropriate frequency to use?
The first thing we need to know are the frequencies that the FCC has authorized for our particular license class. For the HF bands, the frequency privileges depend greatly on the license class of the operator. Above 50 MHz, the frequency allocations are the same for Technician licenses and higher. In particular, the 2M band extends from 144 MHz to 148 MHz. The FCC Rules say that any mode (FM, AM, SSB, CW, etc.) can be used on the band from 144.100 to 148.000 MHz. The FCC has restricted 144.0 to 144.100 MHz to CW operation only.
Knowing the FCC frequency authorizations is a good start but we need to check a bit further. Amateur radio operators use a variety of modulation techniques to carry out communications. Often, these modulation techniques are incompatible since a signal of one type can’t be received by a radio set to another modulation type. For example, an SSB signal can’t be received on an FM receiver (and vice versa). We need to use our authorized frequencies wisely by sharing the band with other users and avoiding unnecessary interference. Thus, it makes sense to have aband plan that divides the band up into segments for each type of operation.
2 Meter Band Plan
As shown in the table, the ARRL 2 Meter amateur band plan supports a wide variety of radio operation. Large portions of the band are dedicated to FM operation, consistent with the popularity of the FM mode. There are portions of the band designated for repeater outputs(which is the frequency that we tune to receive the repeater) and repeater inputs (which is the frequency we transmit on to use the repeater). Notice that these segments are positioned 600 kHz apart consistent with the standard 2M repeater offset. There are also frequencies designated for FM simplex.
On the low end of the band, we see segments for some of the more exotic modes. At the very bottom is the CW portion, which includes Earth-Moon-Earth (EME) operation. EME operators communicate by bouncing their signals off the moon.
|2 Meter Band Plan Adapted from the ARRL web site|
|144.100-144.275||Single-sideband (SSB Calling Frequency = 144.200)|
|144.300-144.500||OSCAR (satellite) APRS Frequency = 144.390 MHz|
|144.500-144.900||FM Repeater Inputs|
|145.100-145.500||FM Repeater Outputs|
|145.500-145.800||Misc. and experimental modes|
|146.010-146.385||FM Repeater Inputs|
|146.400-146.595||FM Simplex (National Simplex Frequency =146.52 MHz)|
|146.610-147.390||FM Repeater Outputs|
|147.600-147.990||FM Repeater Inputs|
Further up the band, we see segments for SSB operation and beacon operation. SSB is the preferred voice mode for so-called “weak signal” operators. The mode is more efficient than FM when signals are weak, so it is the way to go when you are trying to push the limits of 2M DX. Beacons are transmitters that are always on, transmitting a short CW message as a propagation indicator for distant stations. We often think of 2 Meters as a local coverage band but when conditions are right, contacts can be made with stations over a thousand miles away. Of course, conditions are not always right so having a beacon on the other end of the desired communication path lets you know how propagation is in that direction.
Radio amateurs also use 2 meters for OSCAR (Orbiting Satellite Carrying Amateur Radio) operation, sending signals to a satellite (uplink) or receiving signals from the satellite (downlink). The OSCAR segments don’t specify a particular modulation type since CW, SSB and FM are all used for OSCAR operation. Because of their elevation above the earth, satellites can hear signals from all over the US simultaneously, so they are very susceptible to interference.
Most of this non-FM operation can be easily interfered with by signals from other users. EME signals, for example, are usually quite small since the signal has to make the round trip from the earth to the moon and back. If a local FM operator fires up in the EME portion of the band, an EME signal that can’t be heard by an FM receiver can be wiped out by the FM signal. Similarly, an operator chatting across town on 2M could interfere with a satellite hundreds of miles away and not know it. This is particularly a problem with FM receivers, which won’t even notice low level CW and SSB signals.
The most common VHF radios are basic FM mobile or handheld transceivers. These radios usually tune the entire 2M band from 144 MHz to 148 MHz in 5 kHz steps. The band plan indicates the proper range of frequencies for FM operation but there is more to the story. FM operation is “channelized”, meaning that specific 2M FM frequencies are identified by the band plan. The use of channels is especially important for repeaters, since they don’t easily move around in frequency and are coordinated to minimize interference. The idea is to have all stations use frequencies that are spaced just far enough apart to accommodate the signal without interfering with the adjacent channels. You might think that the spacing between channels would be 5 kHz, which is the tuning step of most FM radios. This doesn’t work because a typical FM signal occupies a bandwidth that is about 16 kHz wide.
The channel spacing needs to be at least as wide as the bandwidth of the signal, which allows room for each signal without interfering with the adjacent channel. In Colorado, the channel spacing is 15 kHz, which is a bit tight for our 16 kHz-wide signal. In other parts of the country, a 20-kHz spacing has been adopted to provide for more separation between channels. Obviously, you get more channels on the band with 15 kHz spacing than with 20 kHz, but you have to put up with more adjacent channel interference.
When using a repeater, you just need to dial in the published repeater frequency and set the transmit offset, usually either + 600 kHz or – 600 kHz. In some parts of North America, non-standard repeater offsets may be used, which will be indicated in the repeater directory. For repeaters that require a CTCSS tone for repeater access, you will have to set the proper tone frequency on transmit.
Choosing an appropriate simplex frequency can be a little tricky, since it depends on whether your region uses the 15-kHz or 20-kHz channel spacing. Across all of North America, the National Simplex Frequency (also referred to as the calling frequency) is 146.52 MHz. In areas that use 15-kHz channels, the adjacent channels are 146.535, 146.550, 146.565 MHz, etc. moving upward. Below the calling frequency are 146.505, 146.490, 146.475 MHz and on. In areas that use 20 kHz channels, the frequencies are 146.540, 146.560, 146.580 MHz moving up and 146.500, 146.480, 146.460 MHz moving down.
There is usually another group of FM simplex frequencies in the 147 MHz. The typical layout of simplex channels is the table below. However, it is important to note that your local band plan may be different than this.
|2M FM Simplex Frequencies (typical usage, check your local band plan)|
|15 kHz Channels||146.400, 146.415, 146.430, 146.445, 146.460, 146.475, 146.490, 146.505,146.520, 146.535, 146.550, 146.565, 146.580, 146.595 147.405, 147.420, 147.435, 147.450, 147.465, 147.480, 147.495,147.510, 147.525, 147.540, 147.555, 147.570, 147.585|
|20 kHz Channels||146.400, 146.420, 146.440, 146.460, 146.480, 146.500, 146.520, 146.540, 146.560, 146.580, 146.600 147.400, 147.420, 147.440, 147.460, 147.480, 147.500, 147.520, 147.540, 147.560, 147.580|
While the ARRL band plan sets the guidelines for band use across the US, VHF band plans are really defined on a statewide or regional basis. This means it is best to find the specific band plan for your region. This may be a challenge to find the right information, but try searching the web for “2 meter band plan” and your state. A good source is your local frequency coordination body, which is listed on the ARRL web site.
For the Colorado VHF/UHF band plans, see the Colorado Council of Amateur Radio Clubs web site.
The fine points of the band plan can be a bit confusing. However, a few simple guidelines can help, especially if you are operating only FM.
- FM voice simplex and repeater operation should only occur in the designated band segments for your area. Stay out of the weak signal and satellite sub-bands.
- When operating through a repeater, make sure you are tuned to the published repeater frequency with the proper transmit offset.
- When operating simplex, use a simplex frequency designated by your local band plan.
We’ve only covered the 2 Meter band in this article. If you are operating on other bands, be sure to check the appropriate band plan before transmitting. In a future article, we’ll take a look at the 70 cm band.