BuildingRadioRig

When I first started flying PPGs over 5 years ago, I flew alone. There were no other PPG pilots that I was aware of near Chicago, let alone in Illinois. So there was nobody to talk to. Also, accessories like radios and radio helmets capable of blocking out the sound of a screaming 2-stroke inches from your head were hard to find.

Before long though, I decided I’d like to go long distances (well, long for a PPG anyway) from home and have my wife follow me in the car. I’d need a radio helmet and radios for that to work. FRS radios were just being introduced at the time, and they seemed to be a perfect candidate for the job. So I set out to build myself a practical radio headset. This article is the culmination of about 4 years of experimenting with this subject.

This article is two parts, Part 1 is making the in-helmet ear pieces and Part 2 is making the microphone.

Choices - full face or half, build or buy

Today’s off-the-shelf options for a radio headset suitable for PPG use are somewhat limited. Most consist of a small half-helmet for the top of the head, with earmuff-style speakers and a boom mic. They can be ordered with connectors that will fit any radio you choose. They do their job very well. There are two main disadvantages that I see with them: 1) you can’t have a full-face helmet if you use earmuff-style speakers, and 2) they’re pretty expensive (on the order of $250, not including the radio).

As an ex-motocrosser, I have developed the philosophy that if you are going to engage in an activity that you feel requires the use of a helmet, it may as well be a decent full-face helmet. During my motocross days, several of my friends performed a maneuver we dubbed the "lip-ripper". This maneuver consists of falling face-first from the dirt-bike while wearing an open-face helmet. One friend required three rows of 25 stitches each to sew his lip back on. I’ve been a full-face helmet wearer ever since.

So, if you’d like to use a full-face helmet, or if you already have a helmet that you like and don’t want to spend $250 on a new helmet/radio setup, this "how-to" article might be for you. In it I’ll explain how to develop the three necessary components of the under-helmet radio headset. These components are:

The Radios

The radio we’ll use will be one of today’s FRS radios. There are MANY different brands of FRS radios out there, and most are very good. All but one (the Kenwood brand) use the same connector scheme, so this article will aim at the common connector scheme. I’ll put in a plug for the Kenwoods, though. Of all the FRS radios I’ve tried, the Kenwoods seem to have the overall best sound quality and reliability. But they’ve got a non-standard connector scheme.

Tools

With that, if you know how to strip wires, do some simple soldering, and are reasonably handy, let’s begin.The tools you’ll need are:

Drill bits sizes 0.149" and 0.161” (I have a drill index with &quo;numbered" drills, so that’s what I refer to in this article. Any drills that are close will work, though.)

The complete setup
A full face helmet has the mic hanging out of it. The mic has a Velcro "dot" and that goes into the receiving Velcro stuck to the front of the chin-guard. The FRS radio goes into the "igloo" drink container during flight. The blue box is a minidisc player.

Part 1: Constructing In-Ear Mini Speakers

Many folks have tried to use simple “ear buds” that can be purchased at Radio Shack for about $10. Unfortunately, these devices don’t block out the huge amount of motor/prop noise that exists on our PPGs. What a successful mini speaker must do is 1) be small, light, and fit under a helmet, 2) be reasonably comfortable, 3) block out a large amount of the ambient noise (hopefully at least 25dB NRR), and 4) pipe the radio reception through to your ears.

Plain-old earbuds do all but #3 above. Fortunately there are two ways to make a really good mini speaker that meets all of the above criteria. An interesting note, I believe that the NRR of the mini speakers we’ll build here is at least as good, if not better, than the ear-muff style noise suppressors used on the radio helmets.

Custom Molded Earplugs

The first method is to have some custom molded earplugs made for you (as pictured right). They typically cost in the neighborhood of $50 or so, but I feel they are well worth it and they are what I use. They can be obtained at a local hearing aid store such as a Beltone store. The best way to go about this is to first buy a pair of earbuds. The best ones for this use are Radio Shack part number 33-175 (This part number comes singly, not as a pair, so you’ll need two of them, they are $2.19 each and come with a 3’cord). As can be seen below, they have a little “cone” that goes in your ear. Cut this off with a razor as depicted below. The reason these are the best for our use is because they are completely sealed and will hence keep the ambient noise out. Other earbuds have holes in the back and the ambient noise passes right through.

Cut the cones off and take these earbuds with you to Beltone; they’ll use them in the molding process. Take this article too because some Beltone places don’t understand what you’re asking for, so show them these pictures. When they figure out what you want, they’ll squirt some caulk into your ears to make a mold, and then they’ll send it out to their lab. In about a week you’ll have the nicest custom molded earplugs you’ve ever seen. And they’re very comfortable. I typically wear mine for 2 hour flights without problem, my friend wears his for 3 hour flights without problem. Keep in mind that when you first put them in they may not be comfortable and you have to get used to them. Don’t give up on them if they’re not comfortable in the first five minutes, give them a chance.

A final note. You’ll need to combine the two earbud connectors into a single 3.5mm mono audio plug. There are two ways to do this. One is to purchase an adapter such as Radio Shack part number 910-0743, which is a "Y" adapter. The other is to purchase a 3.5mm mono plug (Radio Shack part number 274-286) and solder the wires from both earbuds into it. I like that method best because you can cut the wires to the correct length and then you won’t have lots of extra wire to deal with.

Latex Earplugs - An Alternative

After considerable experimentation with foam earplugs and other methods of building a non-custom earbud, I’ve found that foam earplugs don't work well for our purposes. You can't consistently get good noise reduction, and also consistently let the radio transmissions through. You can get one or the other, but not both, consistently. The method presented here using latex plugs allows me to get both good noise reduction and good sound transmission consistently.

Here’s how to make them: Use the same earbuds from Radio Shack as above (Radio Shack part number 33-175, $2.19 each), and the latex earplugs shown above. I don’t know where to obtain this earplug other than McMaster-Carr (www.mcmaster.com), part number 54875T4 for about $.89) Unlike the "Custom Molded Earplug" approach above, leave the cone on the earbud for this approach. Instead, drill out the hole in the "cone" of the earbud to about 0.149". Be careful not to crack the cone when you’re drilling it, and it might help to wrap a bunch of electrical tape around the drill bit about ¼” from the tip to keep the drill from plunging into the cone too deeply and damaging the speaker element of the earbud. I used a wheel collar from an R/C airplane as a drill stop, as can be seen in the picture to the right.

Now, take a piece of 14AWG solid copper wire (a good source is to strip it out of a piece of Romex) about 16 inches long, heat it up with a propane torch, stove, cigarette lighter, etc. and burn a hole down the center of the latex earplug. This will allow the radio sound through. This is actually a pretty tricky step, and you might want to purchase several pairs of earplugs because it might take you that long to get the hang of it. The best thing I’ve found is to heat the wire up and then rapidly push it through the earplug in one direction. Don’t use a push/pull motion.

Also, heat the wire to soften the melted latex on it, and clean with a paper towel between earplugs. If you leave the melted latex on the wire, the next earplug will not like it very much, and the hole will not be straight and true. Sight through the hole in the earplug. Make sure it is straight and true with no obstructions. Fig. 6 illustrates the process.

Another note about the melting process, is that a #12 wire makes a nicer hole than a #14 wire, but I’ve found a #12 wire to be too difficult to deal with on the first run through. I recommend using the #14 wire to make the initial hole, and after you’ve got the hole nice and centered, then run a #12 wire through it to make it a little larger.

Slice off about 1/8” of the "stem" of the earplug, then insert the end of the latex plug into the hole in the earbud. The hole is purposely small and requires a bit of work to get the earplug into the earbud. This is to keep the earplug from falling out. Once you’ve got it in, you’re done. Almost. Now repeat for the other ear, then solder the wires from the two earbuds together into a single 1/8” mono plug and you’ll have a really dandy headset.

Careful in your ear!

Important Note: The latex earplug takes some practice to insert and remove in your ear. This latex plug goes further into your ear than you can imagine. I didn’t know my ear canals were that deep! You have to keep pushing until the whole thing just about disappears. A method I use to test if you’ve got it inserted correctly is to take my thumb and fingers and gently rub them together very close to my ear. With no earplug in you can easily hear the "scratching" noise your skin makes. If the earplugs are inserted correctly, you won’t be able to hear this noise at all. If you can still hear it, you haven’t gotten the plug in correctly.

Caution!
Removal from your ear is another story. These latex plugs seal in your ear so well that if you just yank them out they’ll create a vacuum that will likely damage your hearing. DON’T try this! Instead, VERY gently press on the earplug until you break the seal, and then slowly extract them. One try and you’ll see what I mean.

Advantages and Disadvantages

The advantages of the Custom Molded approach is that it is very comfortable, and it’s easy to insert/extract. The disadvantages are that it is more expensive, the noise reduction isn’t as good as the latex, and it doesn’t fit anybody but you (so you can’t let somebody borrow your setup).

The advantages of the Latex earplug approach are just the opposite. It’s very inexpensive, the noise reduction is very good, and it can fit anybody (that learns how to insert/extract it!) The disadvantages are it isn’t quite as comfortable, and it’s harder to insert/extract. Another note, you’ll notice some earwax deposits on the latex plugs over time. Simply remove them from the earbuds and wash them with soap and water, and they’ll be like new.

Part 2: Now You're Talking
Microphone/PTT For About $15

Here’s a quick and easy way to make a microphone/PTT that will work with most FRS radios. It can be attached in various ways to any helmet.

Both the microphone and the PTT can be made as a set because they need to be electrically connected in series with one-another. Each can be connectorized and plugged together, but my experience has been that the most unreliable parts in a setup like this are the connectors, so the method presented here will be to hard-wire them together.

Electronic parts you’ll need are all available at Radio Shack (Radio Shack part numbers and cost are in parenthesis). Other parts you’ll probably have around the house, or you can get them at any hardware store, except the elastic, which might require a trip to a fabric store.

Basic Mic Parts

Boom Mic Extras

PTT (Push To Talk) Switch Parts

Layout and Wire Length

Start by determining the overall “layout” of your system. What I mean by this is where and how will you mount your radio, which hand will you hold the PTT in, etc. This will determine wire lengths. For this article, I will mount the radio at my chest by putting it in a small camera case (available at “Target” for about $2.49) that has a strap around the neck.

First, cut the wire (42-2434) into three pieces. Cut the first piece about 8” from the 3.5mm mini-plug. This 8” piece will go from the “junction box” to the radio. Next, measure the length of the mic lead. To do this, hold one end of the remaining wire where your radio will be, and tilt your head all the way back. Hold the other end of the wire where you mouth is, and cut the wire to this length. It needs to be long enough to allow you to tilt your head all the way back, but don’t make it too long because you’ll need the remaining wire for the PTT and because you don’t want to have too much extra wire to manage. Mine was about 18” long. The remaining wire should be long enough to reach from your outstretched hand to the radio.

Prep all of the ends of the wire. To do this, use a razor knife and gently cut through the insulation about ½” from the end. Twist all of the fine copper wires into a braid, and tin the end of the braid (“tinning” just means to apply some solder to the end of the wire). Strip about 1/8” of insulation from the center wire, and tin the end. All of the cut, prepped wires can be seen above.

NOTE about the wire. Radio Shack doesn’t sell a wire with a 2.5mm mono plug on the end, which is what we really want. So we have two choices. One choice is to use the wire with the 3.5mm plug on the end and then add an adapter to get to 2.5mm. The other choice is to cut the 3.5mm plug off and solder a 2.5mm plug on. My experience has been that the 2.5mm solder-on plugs are very hard to solder, and are very unreliable. I chose the first option above.

Basic Mic Construction

Next, clip off the “legs” that come on the mic (# 27-090). Note which of the two connections is “ground”. It is the side with several little “webbings” of metal that lead to the case.

Prep the fuse holder. This will be the mic casing. It works pretty well for this. Drill a couple of holes in the “female” side of the fuse holder. Remove the metal inserts from the fuse holder and discard. Cut the “male” side of the fuse holder to make a “hat”, see above. Be careful with that razor, and don’t ask me why I know that. Wipe up any blood.

Run your 0.161” drill through the input of the fuse holder. Thread the wire into the fuse holder. Solder the uninsulated copper wires to the mic’s ground connection, and solder the center wire to the other connection on the mic element.

Insert the mic into the housing. Align the mic so that it faces the holes. nUse a little Super Glue to glue the “hat” on. Almost done (see right)!

Now put the mic muff on and secure with a cable tie or electrical tape. If you want to secure it to a full-face helmet, wrap one layer of electrical tape around the muff, add a velcro dot to the tape on the muff and one to the chin-guard of your helmet. Done!

Regarding engine noise, we've had pretty good luck with using the mic muff above. Put it over the mic element and it should block enough engine and wind noise for your system to be workable. We've had 4 pilots in the air all communicating with this system and everyone could hear everyone else just fine. Make sure to use the big muff recommended above, the little ones don't seem to work well enough.

Boom Mic Construction

Similar to above, except: Before you thread the wire into the fuse holder, slip the heat-shrink tubing onto the wire.

When you’ve completed the steps for the Basic Mic, lay the 12AWG wire alongside the mic cable. Shrink the tube around the wire, holder, and cable. Now, you can mount the “boom” portion to your helmet using whatever method you choose, and it will stay in whatever position you place it!

PTT Construction

Solder one end of the PTT cable (the 48” piece) to the leads of the switch. Remove the washer and nut from the switch, and discard.

Next, cut the ½” CPVC tube to about 3.5” in length. Tie a simple knot, for strain relief, in the wire. The distance between the flat shoulder of the switch and the far end of the knot should be about 3/8” longer than the length of the PVC pipe. Drill a hole (0.161”) in the center of the end cap.

The above picture shows the results of these steps. Now, thread the wire through the PVC pipe, and then place the endcap over the wire. Using Super Glue, Hot Glue, PVC cement, glue the switch in place. Wait for it to dry. Now, glue the end cap in place. If the knot is in the correct place, you will have to compress the wire slightly and hold the end cap on while the glue dries.

Next, use electrical tape or duct tape to tape an elastic band to the PVC pipe to hold it onto your hand as shown in the picture above.This completes the construction of the PTT switch.

Joining the PTT and Mic Together

Now, tie strain relief knots about 1” from the three remaining ends of wire. Drill 0.161” holes in the Project Box as shown below. Solder the ends of the wires together as shown. It is important to get the wiring polarity correct, so make sure your setup looks just like it does in Figure X. Specifically, the center lead from the wire going to the radio needs to go to the center lead of the wire leading to the mic. That wire needs to be soldered onto the “plus” side of the mic element, not the “ground” side of the mic element.

It is a lot easier to write about how to do this step, than it is to do it. You need to adjust knot position, wire lead length, etc. But you want to get it to look like it does in the photo (right).

Place the wires in the project box, put the lid on, snap the 3.5mm to 2.5mm adapter on the end, and you’re done! The picture at the top of Part 2 shows the completed setup.


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Under-Helmet Radio Headset Under $10