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Mounting WAAS antenna on glare shield

I'm installing a Garmin 400w and want to mount the antenna on the glare shield. Is is OK to mount it crossways (turned 90 degrees)? My glare shield is too narrow to mount the unit in the normal orientation.

John

If the antenna is inside the aircraft, then as long as it is mounted on a (nearly) horizontal surface with a good view of the sky, it should work just fine in any rotated orientation on that horizontal surface.

Hello John,

GPS antennas are not directional, aside from aerodynamic considerations which don't apply when mounting the antenna inside the aircraft. As long as the antenna is situated where it has a good view of the sky in all directions you should be just fine. A further thing to consider when mounting a TSO WAAS GPS antenna on the glareshield is to take into account the minimum cable length requirement from the installation manual:

Quote:

Once the antenna mounting position has been prepared, route the coax cable from the antenna to the 400W Series unit. Proper selection of coax cable and assembly of connectors is critical to GPS signal performance. The cable loss from the GPS antenna shall be between 1.5 dB and 6.5 dB in order to aintain proper rejection to interference signals.

The coaxial connectors and adapters, such as TNC to BNC, add additional loss to the cable and should be considered when computing the cable loss. A typical loss of 0.2 dB can be used for each connection.

NOTE: If RG-142B or RG-400 is used, 1.5 dB equates to a length of approximately 6.5 feet of cable with a connector on each end. RG-142B or RG-400 cable can be used as long as the length is less than 35 feet.

Many times, when the antenna is mounted close to the unit, the installer will choose to simply coil up the extra coax cable required to meet the minimum length requirement, which should work fine.

- Matt

I have a couple antenna mounted on my glare sheld and don't like them there.

Reflections from them are on the window at times and is a bit distracting.

Recommend putting them behind you if able or under the engine cowling.

Good luck,

RC

Quote:

Originally Posted by Rotorheadrob (Post 824273)

I was going to use the same mounting position -- wouldn't covering the antenna with black felt reduce (remove?) the problem?

Have you considered mounting it under the cowl

Quote:

Originally Posted by az_gila (Post 824280)

I was going to use the same mounting position -- wouldn't covering the antenna with black felt reduce (remove?) the problem?

Will that just cook the antenna?
John

Thanks all. Lots to think about. My antenna cable is about 4'. Didn't realize that it could be too short. I hadn't considered the reflection of the antenna on the canopy either.

John

Quote:

Originally Posted by Rotorheadrob (Post 824273)

Paint them black. Works great and no glare. I have two different gps antennas on the glare shield.

I was thinking of covering it with electrical tape.