Sunday, August 11, 2013

Reducing RFI (Radio Frequency Interference) in PPG Communications

This post is a summary of some suggestions on ways to mitigate or eliminate RFI (radio frequency interference) when using handheld radios and communication headsets.  These suggestions came from recent posts on the Yahoo group PPGBiglist.

Robin Rumbolt, a PPG pilot and engineer at Oakridge National Labs made a video on how to combat radio/electromagnetic interference from PPG motors.
http://www.youtube.com/watch?v=JeEo54Rau2Y&feature=youtu.be
He explains that if you are getting static in your headset the cause may be the proximity of your radio to your spark plug and ignition wire, which during operations also generates a radio signal that can result in static on your radio.  This RFI can also override the functionality of your sub-channels  if you use them, and even mess up your GPS.

He suggests you first try relocating the radio, or using a lower power setting on the radio if that's an option.

If that doesn't resolve the problem, Robin said that the best way is to eliminate the electromagnetic interference is by shielding the ignition wire.  He shows how in the video, and to accede to many requests for assistance, he sells a DIY kit to do this for $35.00.

He suggests that you take this in steps:
-Start by just replacing  the spark plug, and trying a resistor plug instead. (The resistor counterpart of your existing plug has a letter "R" in the label.)
-If that doesn't work, use a regular plug and replace the cap with a resistor cap. (Don't use both at the same time, however.)
-Then try shielding the cable as per the video instructions above.

If this still doesn't,t completely eliminate the interference, then try shielding the kill switch wire in your throttle cable. Robin's $35 dollar kit also includes a length of shielded cable for this as well.

Keith Pickersgill, of www.xplorer.co.za had this to say about killing  static, or perhaps even random shuffling on your iPod Shuffle while flying:
"Move the MP3 player to as from the radio antenna as possible. Use the shortest possible earbud leads. Shorten the earbud leads by passing them through a ferrite bead (snap core choke) a few times. Your earbud leads are acting like an antenna, bringing surplus RF energy into the MP3 player."

The more wraps the better. Here is what mine looks like, with six wraps around a fairly large ferrite bead of about 12 gauge or so.  This is six wraps around the bead, which also helps manage some 15" of speaker wire.
Robin Rumbolt agreed about the ferrite bead:
"Radio Shack sells a couple of different kinds of snap core chokes - 273-069 or 273-104. (See http://www.radioshack.com/product/index.jsp?productId=3012599)
Wrap the wire a couple of loops through the choke just after it comes from the iPod. That might help if the EMI is getting in through the iPod wire."
"The choke adds inductance to the wire. Inductance stops currents from changing rapidly. Hence, high frequency currents are blocked or at least greatly attenuated. Pushing the PTT button causes your radio to transmit. The high requency signals from the radio causing frequency currents to be generated in the cable. The choke "chokes" them. Simple! Lot's of other stuff going on, but that's the simple explanation."

The only down side is that if you are flying with pilots who don't have this modification,  they
may still transmit with all their noise and static.

Pilot KJ in Biglist post #105013 adds:
"I use (substitute) USB cable for the Tach and kill switch wire as well. Even the cheap Ebay
tachs that come with a single wire work well once equipped with that cable type.  Audio cable works far less well, probably too much capacitance. Unlike a TinyTach these are not potted so a new cable is quite easy to install."

Gene Davies had this to say about radios:
"We build lots of ground ops headsets and flight helmets, and one thing we have found is to stay away from the ICOM line of av-band radios. They are predisposed to (RF) feedback problems and are almost completely useless with a headset. ICOM even put a disclaimer on one of their web pages that these radios are for ground use only."
"The VERTEX-YAESU radios do not have this problem and you can find a new one for a pretty decent price at several on-line pilot shops. Despite the claims otherwise, they do not work particularly well with commonly used electret microphone elements. We prefer the use of a specially designed electret or an amplified dynamic mic element such as ones produced by Acousticom."

The pilots who contributed to the original discussion can all be contacted at the open forum PPG Biglist.  Robin can be reached at flyguy@knology.net


NB: If you are looking to dramatically improve your airborne radio range and radio signal many times overwith minimal expense and just a few hours work, look into the "Wonder-Whip" radio antenna for Paragliding and PPG flying a project post by Keith Pickersgill of Xplorer Ultraflight, Cape Town, South Africa at http://xplorer.co.za/wonder-whip/

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