Radio Interference

Radio Interference

Dennis Travassaros shares with us some of his thoughts on the nature of radio interference and its effect.

What are radio waves and where are they?

· You cannot see radio waves, just as you cannot see the output of your Radio Control transmitter;

· They exist on a multitude of frequencies / bands

· They exist anywhere a mobile phone, radio, or TV works

· If they were opaque, you’d be lucky to see 5 feet ahead

· The ACMA website allows you to search by postcode, and you will see emissions exist everywhere www.acma.gov.au

What exists around our club?

· Digital phone network and transmission
· PA systems
· 40 Mhz to 5.8 Ghz frequency range
· Broadband as well as focused narrowband – with the broadband noise the most likely cause of some of our recent interference issues
· Ourselves – don’t ignore the risk of getting swamped, especially around flight line

What is the effect of radio interference?

· Multiple signals on the same frequency confuses a receiver, and a confused receiver is likely to mean no control over your model
· Broadband noise is more likely to cause bumps / ‘on & off’ or intermittent problems
· The receiver ultimately responds to the strongest and clearest signal
· For IC models (unless they have on-board ignition systems) the primary causes are typically external
· Electric models interference from the drive train also needs to be considered

Equipment

· Pulse Position Modulation (PPM, commonly referred to as FM) and Pulse Code Modulation (PCM) style receivers handle interference differently
· Failsafe on PCM Receivers can help

o They can hold controls rather than allow random effects on loss of signal by receiver

o They need to be preset/programmed, and you must turn the transmitter on before receiver

o There are peculiarities, eg. throttle reverse might give full throttle rather than no throttle if failsafe isn’t programmed last

· Electronic receiver filtration differs – budget equipment is more susceptible

· Certification -- every 2 years minimum is the Doncaster Aeromodellers’ rule

o Tests the overall output of transmitter, but primarily the output module and crystal

o If you change crystals / frequency, you need to recertify

o ‘V’ marking means the transmitter is certified variable, and can accept different, certified, modules (certified in same transmitter)

Avoiding problems

· Maintenance

o Wipe aerial clean regularly; talk to a radio technician regarding sprays

o Service / certify transmitter every 2 years at a minimum

o Field tests: some debate, but always do a range check as a matter of course after any changes or problems

· Setting up

o Separate receiver aerial from other electronics (Receiver aerial must be fully extended, not coiled)

o Refer to radio manufacturer’s instructions, they’re there to help

o Handle with care, don’t pull on leads (grasp the plugs)

o Run suppression (electric models)

o Take extra care with digital servos (high current drain) and tail servos (be careful with long leads, particularly close to aerial)

o Test your nicads before, during, and after a day at the field

What to do if you experience interference in flight

· Hold transmitter high with aerial vertical (flying thumb and finger can make it easier)

· Call to see if another transmitter was just turned on, if yes, yell please turn it off immediately

· When any control works use it and pretend it’s a dead stick, kill the engine / glide down safely, away from spectators if possible

· The closer the model gets, the more control you’ll have, aim for the field, but well away from spectators.

· Don’t give up, fight to keep control, models have landed safely behind trees

· Even if you’ve no chance of saving the model / equipment, try to kill the throttle, and land or crash without further loss or injury

· Analyse the incident objectively, get equipment checked by technician, try and find a real cause, look to more experienced pilots for help

*** 10 January, 2010 10:26 PM +1000 ***

Last updated 10 January, 2010