The Airsport Altitude Alerters are designed and intended to be used
as a portable piece of equipment, perhaps held on the glare shield or elsewhere
with the supplied Velcro. However, a number of aircraft owners are electing to
have the units permanently installed and approved via a 337. Here are some
points to consider if you are planning an installation:
1... DC power requirement is 0.5 Amps, 9 volt minimum, 32 volt maximum, so it is directly compatible with 14 or 28 volt DC aircraft systems. The power connector is 5.5mm 0D, 2. lmm ID, commonly available from electronic parts suppliers. While it is possible to cut and use the supplied cigarette lighter cord, this wire is not aircraft quality. We suggest obtaining a connector and field fabricating suitable wiring. The connector is center positive. The connector should be safetied to protect from vibration, the lower screw holding the horn can be used to support a safety.
2... Power to the unit should be supplied thru an appropriate fuse or circuit breaker, with a rating of 1 amp. The power should be from the avionics bus or from an appropriate point that is off when the master switch is off.
3... The BATTERY switch on the rear of the unit has three positions. Here are some considerations when you choose the setting: In the OFF position, the internal battery is completely disconnected, it will neither charge nor supply power to the unit. The unit will operate only when you supply DC power to the connector. The pilot can leave the front panel Power switch on, just as he might do with other avionics, and the unit will go off when the aircraft master switch is turned off. However, with no battery, settings such as volume, baro pressure, and others will be lost, and will return to their factory-set defaults when the unit is next turned on.
In the CENTER position, the internal battery is connected, and will charge if needed. It will also power the unit when the aircraft is shut down. This means the pilot must remember to turn the unit off after each flight using the front panel Power switch. His preferred settings will be preserved. If he forgets to turn the unit off, it will operate until it runs the internal battery down, typically 10 to 40 hours. No immediate damage is done, but battery life is reduced if that happens repeatedly. And when the battery runs down, the preferred settings are lost.
With the battery switch to the RIGHT, operation is the same as the center position, this is why they are both labeled 'ON'. The difference is that the internal horn is also on. In a permanent installation, it is unlikely that the horn will be needed, as the audio connections will be routed to the aircraft audio panel.
4... The Audio output from the unit should be fed to the audio panel if available, or to an aux input on the audio amplifier that feeds the speaker and headphones. The unit's audio is transformer isolated from ground, and is low impedance. Depending on the installation, it may be desirable to install an attenuator between the unit and the aux input. This attenuator may be as simple as a single resistor (perhaps 47K) in series with the audio signal. Alternately, the audio jack may be used to add the units audio to the existing communications audio. See the audio connection drawings in the User's Manual. In either case, the pilot always has the option of silencing the unit with the Horn switch on the Front panel. If there is no audio output from the unit, check this switch.
5... Physical location should be verified in flight before permanent installation if possible. The AirSport unit is a receiver that picks up the 1090 MHZ output from the transponder antenna. The location is usually not critical, but on most aircraft some spots can be found where the signals cancel. For example, in one Piper the AirSport unit found a signal cancellation at dead center on the glare shield, while an inch either left or right worked fine. Most aircraft can be expected to have one or more cancellation spots. Alternately, you may mount the unit in the desired location, and change the internal PRO antenna if cancellation occurs. Consult with our engineering staff if you have a problem here. (Hint: Function #11 displays the number of successfully decoded transponder replies. This number is a function of the ATCRBS activity, and is higher when more radar sites are within range. But it is also a means for the installer to check for signal cancellation, as the number of replies will decrease greatly, going to zero for total cancellation. By watching the display as the unit is moved around the cockpit in flight, it is easy to find any dead locations.)
6...The means of mounting the unit is up to the installer, according
to the specifics of the particular aircraft. If the unit is placed in the
avionics stack surrounded by shielding, for instance, it may be necessary to
modify the unit's antenna as mentioned above. Effects of heat from nearby
equipment should also be considered. Some installers have fabricated a u-shaped
aluminum tray and mounted the unit under the instrument panel. This has worked
out well. It is possible to mount the unit in such a way that it may be removed
by the pilot for use in another aircraft when desired.
Questions? If looking at a schematic of the unit would help, there is a copy inside the unit. Or give us a Call. We support our products, and are ready to discuss any questions you may have.
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