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Poor Man's Cockpit Voice Recorder
Eric WoudenbergStudent pilots in particular can often benefit from a review of their radio work after a flight. Generally however, the radio conversations over the course of a flight are fairly sparse. This is where the analog synchro-start feature of Sharp and other non-Sony portable recorders becomes invaluable, because it strips out all the dead-air time in between each radio contact.
April 2000
I made a simple aircraft intercom (i.e. headphone level) to line-input adapter with a 1k trim-pot (set roughly in the middle) and a 1/4" and 1/8" phone plug (I think you can probably buy the equivalent adapter from Radio Shack however). I adjust the Sharp's recording level so that the intercom background noise (with the mic squelched off) is below the syncho-start threshold. I recommend setting the recording level with the engine running and extraneous noise sources from things like the beacon lamp present, so that you don't end up recording constantly due to added noise once you're airborne.
The recorded audio comes out great, allowing me to listen afterwards for things I missed while flying (``Gosh, the tower really said "FOLLOW THE TRAFFIC" to me after all!''). I have also titled a few of the recordings, allowing me to pinpoint interesting segments. The only problem I have with the arrangement is that the syncho-stop time for the Sharp is about 12 seconds, leaving a long tail after every audio event (even things like clearing my throat). Fortunately MD makes it easy to delete the tracks without content. Still, it would be great if the synchro-stop time were settable.
Cessna Minidisc In-flight Audio Entertainment
Bob LocherI am a private pilot and own a small Cessna, a 172. On longish VFR cross country trips I love to listen to classical music. I have a built-in intercom in the airplane, a PS Engineering PM 1000. I always fly with noise-cancelling headphones, which include active noise reduction (done by adding signals out of phase with the cabin noise to cancel it out. They help a lot). The headphone system is monaural, and since my MD deck, a Sony MDS-JE510, has a mono recording mode that puts twice as much music on each MD, mono mode recording is the perfect choice.
December 1998
The intercom I use has an entertainment audio input, and is designed so that whenever a signal comes through the communications radio, the entertainment input is silenced and the communications overrides it. When communication is finished, the entertainment audio ramps back up.
To play Minidiscs in the air I wired a cable to go from the headphone jack of my Sony MZ-E40 to the input of the intercom. But there was one problem, I found that the intercom was not getting anywhere near enough signal to drive it. After playing around with several possible solutions, I ended up buying an impedance transformer from Radio Shack for about $2.00 that goes from low impedance to high impedance. I put the low impedance side to the MZ-E40, and the high impedance output to the intercom. That has largely solved the problem, and has the additional benefit of being entirely passive, with no power source required.
I'd still like a little more output, but I guess it really wouldn't make any difference - the intercom has an input limiter so that if an input signal exceeds its threshold limit it clamps it for a second or so and this is very annoying. So instead I turn up the volume on the intercom, and rebalance the navigation and communication inputs as appropriate. The whole setup works very nicely indeed and pleases me greatly on long cross country flights.