There are two jacks to plug a headset into the cockpit radios: a quarter-inch (1/4") jack--the bigger one--for the headphones and a 0.206" jack--the smaller one--for the microphone/push-to-talk. When I talk into the microphone, it goes in through the 0.206" jack, through the radio stack, and comes back out to me through the 1/4" jack along with all the other communication, so all the audio is carried out through the 1/4" jack. This makes life much easier.
Parts list:
- Y-adapter: stereo 1/4" male to twin stereo 1/4" female ($6)
- mono 1/4" TRS plug ($2)
- 3.5mm TRRS plug (mine cost $4 but the one I linked to is really nice at $7)
- 1.6 kOhm resistor ($1, or someone you know probably has one lying around)
- 10kOhm audio taper potentiometer ($2)
- at least 2 feet of two-conductor wire, 16 gauge is fine ($2, but I'd recommend sacrificing a 2-prong power cord if you have one to spare)
- small project box ($3 if desired)
(Note: you can buy something very similar to this--even though the picture shows the wrong 3.5mm connector--all put together, but it's a lot more expensive and it lacks a volume control. Based on my experience the volume control is essential, but because I'm cheap I did not buy the pre-made connector to compare.)
The first thing I did was connect the two plugs (1/4" TRS and 3.5mm TRRS) with the two-conductor wire. (Two-conductor is sufficient because the iPad can only record mono, so one conductor will carry the audio signal and the other will be a ground connection.) With one conductor of the wire, connect the signal contact of the 1/4" TRS connector with the signal contact of the 3.5mm TRRS connector. With the other conductor, join the respective ground contacts of the connectors.
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On a mono 1/4" TRS connector,
the signal contact is at the tip of the plug.
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| On a TRRS connector for use with an Apple device, the signal contact is at the base of the plug. |
After verifying that all the connections are good, snip the conductor that is carrying the signal and strip the insulation so you have two leads facing each other. This is where you will wire in the resistors and the volume control. Then, at the same location on the wire, strip a little bit of insulation away from the conductor that is connected to ground. The wire should look like this:
Now attach one side of the 1.6 kOhm resistor to one of the signal leads (it doesn't matter which). Per this website, the resistor is necessary to bring the line to an appropriate impedance so the iPad can detect the connection, and it's working for me. I actually used a 1.5 kOhm and a 100 Ohm resistor in series, because I didn't have a 1.6 kOhm readily available. Now the wire should look like this (note that I've also tinned the leads):
Then do the wiring:
- Connect the small bare section of the ground conductor to terminal 1.
- Connect the signal lead on the 3.5mm TRRS side to terminal 2.
- Connect the signal lead on the 1/4" TRS side to terminal 3. If you were like me, this means you'll attach the loose end of the resistor to terminal 3.
(Full disclosure, in my final version I added a short lead to each terminal on the potentiometer to make things easier.) The potentiometer wiring should look like this when you're done:
Now insulate everything with electrical tape and stick the potentiometer and resistor connections inside a project box, and you're done! This is what my finished product looks like:
Now, to actually use the device (!!) you need to plug the male end of the Y-adapter into the 1/4" jack in the cockpit. Then put your headset's 1/4" plug in one of the Y-adapter's female jacks and plug the 1/4" end of your new contraption into the other one. Connect your headset's 0.206" plug to the panel as usual, and insert the 3.5mm plug into your iPad. It should look like this:
On the software side, you need to have an app running on your iPad that can capture audio from the mic jack. My first attempt was with an extremely lightweight app called Instant Audio Recorder (IAR). The problem I ran into with IAR was that it doesn't have an input level indicator or a dynamic range compressor (DRC). The output volume from the airplane's audio stack was overpowering (hence the inclusion of the volume knob in the first place), and without an input level indicator it was very cumbersome to get an appropriate volume setting. Further, if the volume setting was too high, the signal would clip and the recording would sound choppy (a DRC would solve this latter issue), which you definitely noticed if you listened to the recording in the last post.
So I ditched IAR and went to the other extreme, downloading the iPad version of Apple's GarageBand. That has an input level indicator, but it's a huge app and I found it unwieldy to use for such a simple task.
It was only then that I realized the solution had been right under my nose the whole time. I use Notability in the cockpit to copy down weather information and clearances (I even converted at least one other person to this app), and Notability has a built-in audio recorder to accompany note-taking. Not only that, but it has a functional (albeit tiny) input level indicator. But there's more! When I first plugged in the cable, the input was clipping. I turned down my volume control to fix that, but when I listened to the recording later even the clipped sections sounded OK. Based on that, I suspect Notability has a DRC. After the dust settled, I realized they have better data compression as well, because the audio file size was substantially smaller than a similar file recorded with IAR.
For those who care, here is over an hour of raw audio captured by Notability during a flight with my CFI instructor on June 15. I'll start using such recordings as illustrative examples of radio phraseology in later posts.
Until then, blue skies!
Until then, blue skies!
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