XC Frequency Committee Preliminary Report

Noted: to show final frequency choice of 146.46 MHz

Introduction

Pursuant to the minutes of the last SCPA meeting (2/7/2001), a committee was formed to study and propose a new frequency dedicated to cross country flight activities such as air to air in flight communication and ground chase. The objective behind establishing a separate frequency for such activities is primarily to eliminate the heavy chatter associated with flight activities in the vicinity of popular sights and landing areas.

The 2 meter Amateur Radio Band: A Primer

The 2 meter amateur radio band is allocated by the FCC for the exclusive use of licensed amateur radio operators nationwide. It starts at 144.0 Mhz and ends at 148.0 MHz. The band is divided into sub bands allocated for specific uses and specific types of transmissions. Figure 1 shows a graphical representation of the sub bands (Courtesy of Utah VHF Society). Some of these allocations are mandated by FCC rules and the rest have been agreed upon by national and regional amateur radio associations.

 

.GIF with 2m bandplan shown here

2 Meter Bandplan

144.000-144.100:  CW - No voice modes allowed per FCC section 97.305

144.000-144.050:  CW EME (e.g. "moonbounce")
144.050-144.100:  CW/Weak signal

144.100-144.300:  Phone (SSB), etc. (no FM voice)

144.100-144.200:  SSB (Weak Signal and EME)
144.200:  SSB/CW weak signal calling frequency
144.200-144.275:  General SSB operation
144.275-144.300:  Propagation Beacons

144.300-144.500:  OSCAR (Satellite and Spacecraft) subband (new) - Please avoid other types of operation.
144.390:  Nationwide APRS (Automatic Position Reporting System) Packet
144.500-144.900:  2 Meter FM repeater inputs (odd-numbered 20 KHz channels)
144.900-145.200:  Simplex/Duplex Packet operation
145.200-145.500:  2 Meter FM Repeater outputs (odd-numbered 20 KHz channels beginning with 145.210 MHz)
145.500-145.800:  Simplex, miscellaneous/experimental (no repeater operation allowed per FCC part 97.205) using various modes (odd-numbered 20 KHz channels beginning with 145.510)
145.800-146.000:  OSCAR (Satellite and Spacecraft) subband - Please avoid other types of operation.
146.000-146.400:  2 Meter FM repeater inputs (even-numbered 20 KHz channels beginning at 146.020 MHz)
146.420-146.600:  2 Meter FM simplex operation (even-numbered 20 KHz channels beginning at 146.420 MHz)
146.600-147.400:  2 Meter FM repeater outputs (even-numbered 20 KHz channels beginning at 146.620 MHz)
147.400-147.600:  2 Meter FM simplex operation (even-numbered 20 KHz channels beginning at 147.400 MHz)
147.600-148.000:  2 Meter FM repeater inputs (even-numbered 20 KHz channels from 147.620 MHz to 147.980 MHz)

 

Of particular importance to us are the sub bands allocated to FM Simplex transmissions. This is the term used to describe direct station-to-station FM transmissions that do not go through a repeater. This is what is most commonly used in our paragliding activities.

Most pilots are unaware of the other modes of transmissions that go on in this band, for example FM repeaters (more on that later), packet radio, amateur satellite uplinks and downlinks, single side band voice  (a mode used mainly for long distance communication with weak signals), automatic position reporting, and CW (Morse code). Of all these modes, the only ones you can hear on a typical 2 meter FM handheld radio are FM repeaters and packet radio. In other words, if you are transmitting over and interfering with other types of transmissions you will not even know that you are doing it.  This is why sub-bands and specific allocations exist.

A quick glance at figure 1 shows that 144.15 and 144.25 MHz are in an area dedicated for single side band voice only and specifically exclude FM simplex.

Three sub-bands are allocated for FM Simplex. The total width of those sub-bands is 0.68 MHz which is enough for 32 individual frequencies. In other words, we basically have 32 choices for what frequency we would like to use as our XC frequency.

There are a few frequencies within those FM simplex ranges that have specific uses. For example, 146.52 is the national calling frequency. This is where operators trying to make contact with other stations broadcast their call sign and location. This would obviously not be a good frequency to use if you are trying to avoid chatter. Another one is 145.55 which is used occasionally by operators to make contact with the Mir space station and space shuttle missions. I would like input from the local radio community as to other "busy" frequencies which are best avoided. However, these will be few and we will still have many choices. The ideal range is probably 147.40 - 147.60 MHz in 0.02 MHz increments (e.g.147.42, .44, .46, .48, ..etc). A number like 147.50 would be easy to remember.

Protocol

An important issue to consider for successful implementation is to agree on radio protocol as well as when to switch to the XC frequency and making sure that chase is on the same channel.

Pros and Cons

Using the FM simplex portion of the 2 meter band will be a double edged sword. On the positive side, many people monitor this portion of the band all the time. So there is always someone out there listening, especially considering how far the signal will travel when transmitting from thousands of feet above ground. In an emergency, that can be very useful. On the other hand, operators who pick up our signals may try to contact us out of curiosity or just to make the contact with someone who is tens of miles away. This is often exciting for them as long distance contacts on the 2 meter band over FM simplex are rare. Also, radio "cops" may come on and demand that you follow proper ham protocol and identify with your call sign (which you are supposed to do anyway).

All these problems can be greatly minimized by keeping our transmissions short and to the point. The reason is that most operators who are monitoring scan through the band rather than sit on one frequency. Therefore, the shorter the transmission, the less likely the signal will be detected by someone scanning through the band.

A Word About Repeaters

Most pilots who are not licensed hams are not even aware that their radios have the capability to access amateur repeaters located on mountain tops. In the "back country" were cellular phones don't work, there are often repeaters that can be accessed. This can be used to make short phone calls to get help or to relay your position. In addition, operators who monitor these repeaters take pride in their readiness and skill when it comes to relaying messages in an emergency situation. As an example, there is a repeater on Sulfur Mountain.

To use repeaters, it is absolutely required that a proper call sign be used and protocol be observed. Failing to do so is a guaranteed way to antagonize many people.

Solicitation for Input

The committee would like to solicit feedback on this preliminary report and on the proposal to use 147.50 MHz as the cross country frequency. The committe would also like input on formulating a protocol for this frequency. A thread will be started in the non-flight discussion section on this subject. You can also contact the author directly at hesham@ghobarah.net 

Many happy XC flights this season ! Hesham Ghobarah

Update

Note:   After trying several frequencies, we settled on 146.46 MHz.
Report revision update published prior to the February 04 membership meeting: