Radio Interferences and Annoyances

How and why our instrumens go haywire

by Josh Cohn

: I took a poll of around 600 San Francisco Bay Area pilots via a Telegram chat and found that 34%, or 13 of 30, who responded had experienced electromagnetic interference between the electronic devices that they carry while flying. We rely on these devices for communication, navigation, vertical speed, and emergency calls, so it’s essential to understand the sources of and mitigations for interference to keep them functional. In my experience, interference issues typically exist between some varios and nearby transmitting radios. Some varios can register a dramatic climb if a radio transmits too close to them (for example, if both are

OTHER SOURCES OF INTERFERENCE

• HAM radio

• Battery pack/charging cable

• Mobile phone

• GPS

• Satellite tracker (InReach, etc.)

• Telecom equipment

• Bluetooth transceiver

• FANET/FLARM transceiver

• Avalanche beacon

• Heated gloves

VICTIMS OF INTERFERENCE

• HAM radio

• Flight instrument/vario

• Mobile phone

• GPS

• Satellite tracker (InReach, etc.)

• FANET/FLARM transceiver

• Avalanche beacon mounted on the same flight deck). Also, some older models of Oudie have issues with producing noise that can be picked up on a nearby radio. The problem is reported to be worse with cheaper radios and longer antennas. Finally, flying close to telecom antennas can often lead to a reaction from a vario.

Theory

When electric currents flow through conductors, they produce magnetism, and when the current is switched rapidly, electromagnetic waves in the radio frequency range are produced. These waves can, in turn, induce currents in other conductors, thus allowing radio reception, wireless charging, electric motors, transformers, etc.

Some devices are designed to emit radio waves, while others do so incidentally, particularly if they are not adequately shielded. The FCC has testing requirements that attempt to limit RF interference, but your experience may vary.

Interference occurs when the radio emissions from other devices are strong enough to trip the squelch and be heard or when the radio’s signal interacts with the sensitive electronics of other devices, causing them to malfunction. Radio frequency interference (RFI) is a subset of electromagnetic interference (EMI) in the radio frequency spectrum, which occurs when the radio signal overlaps with the frequency range of other electronic devices. RFI can affect various electronics, including mobile phones, variometers, satellite trackers, and Bluetooth devices.

Examples pilots reported:

• A phone connected to an external battery leads to static on the radio.

Glossary

CW: Morse code

EME: Earth–Moon–Earth communication, also known as moon bounce

Linear Translator: an exotic kind of repeater

OSCAR: Orbital Satellite Carrying Amateur Radio

Simplex: Radio stations that are communicating with each other directly, on the same frequency. This is what pilots generally use (when not using a repeater). Probably the best bet for avoiding noise from repeaters, data transmission, etc.

SSB: Single Sideband

• A radio antenna too close to a helmet with a Bluetooth headset (a BT source) causes radio static.

• Varios and radios affected by flying in front of microwave transmission dishes on mountain tops.

• Very cheap (looking at you, Baofeng) radios have been reported to be worse.

Solutions

Fortunately, there are several ways to minimize interference between HAM radios and other devices. The easiest solution is to put the devices farther apart. Since signal strength drops inversely with the square of distance, even a little more separation can have a significant effect when the signals are in close proximity. For example, having a radio on the flight deck next to a vario can cause problems, which are often solved by putting the radio in a radio harness or harness pocket. The most common form of radio-to-vario interference is that when transmitting on the radio, the vario indicates lift. And conversely, RFI from a vario can lead to hearing static on the radio.

The squelch, which causes the radio to be quiet if the signal strength received is below a certain threshold, can be adjusted. However, what works well for a radio on the other side of launch may be too high when you’re trying to talk to your buddy some miles away.

Adding a ferrite bead may help filter out interference on a charging cable. Loop power cables through the donut a few times. Hinged versions are also available that will clamp around a cable.

Aside from the RFI issues, it’s probably good for your health to avoid flying right in the path of powerful microwave transmissions for any length of time. The antennas that look like big bass kick drums are parabolic dish antennas. They are very directional (safer at least 10 degrees off-axis) and used for point-to-point communication, so it’s not so hard to avoid hanging out in their beam for long enough to get cooked. The FCC publishes safe exposure standards, so in theory, if you knew the power output and some other details, you could figure out where it’s safe to be. But it may be easier to not hang out in their vicinity any longer than necessary.

Another DIY solution is to ensure that your non-radio device(s) are sufficiently RF shielded, using a near-field probe and installing extra shielding if needed. There are videos showing how to do this, such as: https://www.youtube.com/watch?v=YAsKROQK5LQ https://www.youtube.com/watch?v=ayf3SfyGFzA

Radio mounting

Thanks to Bill Hetzel for contributing the following (and a few other) comments. I prefer to devote as little attention to my radio as possible while flying, so I personally don’t follow these suggestions though they make sense. Then again, maybe if I paid more attention to the radio, I’d find it more useful.

There are numerous advantages to mounting your 2-way radio within reach and full view on your flight deck. For one, it will be easier to make any necessary changes while flying, such as adjusting squelch and volume or changing to a different frequency.

And with an eye on your radio display, it’s possible

BAND PLAN FROM ARRL.ORG 2 METERS (144-148 MHZ)

144.00-144.05

EME (CW)

144.05-144.10

General CW and weak signals

144.10-144.20

EME and weak-signal SSB

144.200

National calling frequency

144.200-144.275

General SSB operation

144.275-144.300

Propagation beacons

144.30-144.50

New OSCAR subband

144.50-144.60

Linear translator inputs

144.60-144.90

FM repeater inputs

144.90-145.10

Weak signal and FM simplex (145.01,03,05,07,09 are widely used for packet)

145.10-145.20

Linear translator outputs

145.20-145.50

FM repeater outputs

145.50-145.80

Misc./experimental modes

145.80-146.00

OSCAR subband

146.01-146.37

Repeater inputs

146.40-146.58

Simplex

146.52

National Simplex Calling Frequency to check your battery level, see if you are accidentally transmitting, ensure your keypad is properly locked, check your transmit power level, and see if someone else is transmitting but you aren’t hearing them (this could be due to a volume or speaker issue on your end or because they are accidentally transmitting). Having your radio handy lets you unplug the speaker mic and PTT connections to work around in-flight equipment issues, too.

Other (not strictly RFI) sources of radio annoyance

Overly chatty pilots: It’s important to consider what to transmit before putting it out to everyone within range. That generally allows brief and to-the-point transmissions instead of the dreaded stream of consciousness that causes other pilots who are trying to concentrate on flying to turn their radio down or off. An actual transmission I heard at a comp in the remote Australian countryside: “I’m in a field with a windmill and a cloud

146.61-146.97

Repeater outputs

147.00-147.39

Repeater outputs

147.42-147.57

Simplex

147.60-147.99

Repeater inputs passing over it … NOW.” Talking about what to have for lunch after you’re picked up can wait until you’re in the vehicle. Of course, sustained teasing has sometimes been effective in reforming the worst offenders, but it’s no guarantee.

The frequency 146.40 MHz is used in some areas as a repeater input.

This band plan has been proposed by the ARRL VHF-UHF Advisory Committee.

Chatty ground-based HAM operators: There is little that can be done about this one. You can station identify since you have a HAM license (you do, right?*) and politely ask the ground-based operator to switch to another frequency since your hands are occupied. However, this hardly ever works because they are likely transmitting with hundreds of watts instead of your several watts, and they won’t hear you. Solution? Don’t use that frequency next time. It can also help to consult a band plan, which is a voluntary division of the frequency band to avoid conflicts. Choosing from within the bands marked Simplex would be a good start for finding usable frequencies.

Equipment issues: The internal connections to the antennas or the antennas themselves can be flakey, particularly with cheaper radios. Problematically, a typical radio check on launch might be loud and clear, but when the radios are a few hundred meters apart, the signals will drop way off due to poor antenna connectivity. It’s good to check this before you’re in the air by testing over a longer distance with a buddy or keying a distant repeater. If you can, get to know your area repeaters—they can sometimes be useful.

Pilots keying microphones: When there are 100+ pilots on one frequency at a competition, it’s almost guaranteed that someone will be keying their mic, making everyone’s radios worse than useless until the offender’s battery dies. A solution to this is to set the Transmit Time Out on the radio to something like 30 seconds. A well-thought-out and concise sentence doesn’t take more time than that. It’s surprising that confirming this setting isn’t generally a required part of registration.

: As with all your pre-flight planning, putting a little time and thought into how you set up your electronic devices (and investing in higher-quality items) can help make your flight more enjoyable, with less interference. I hope you’ve found something useful here and that you fly to places where you need your radio, and that it works well when you do!

*Need to get your HAM technician license? There is online testing available. The pool of questions from which the test is drawn is available at the below link. If you remember some physics and/or are good at memorizing or guessing on multiple-choice tests, it might only take you an hour or two: https://www.arrl.org/getting-your-technician-license