Originally Posted by wawrzynskivp
First time trying to attach pic, hope it works.
Keeping to the "safety margins" theme, this installation may at first blush appear to meet the manufacturer's installation recommendations. However, when checking the TSO documents we'll find the antenna has been tested for lightning only when installed in the swept stroke zones of an aircraft. Normally this means somewhere on top of the fuselage itself.
Is there a degradation of safety margins associated with this installation? One could argue that an increased probability of the antenna becoming a lightning attach point represents a degradation of safety margins.
Equally, one could argue that, by placing the antenna in a locale free from other negatively-impacting factors (temperature, obstruction, being level with the horizon, etc) this location actually provides an enhancement in overall safety margin for the majority of the time.
There is no truly black-and-white answer to this question, only varying shades of grey, with each of us applying our own personal 'quality factor' to the variables before we produce our final assessment as to whether this particular shade of grey suits our own personal safety margins. This last point is critical - what's a show stopper to one person is no big deal to another person.
Coming back to earlier comments about GPS antennae mounted in the engine bay, an earlier poster provided temperature ranges for various antennas along with the caveat that operation within these temperatures would cause no significant performance degradation. Given that GPS antennas contain active pre-amplifiers, it's the noise contributed by those pre-amplifiers that's of concern. Generally speaking, the warmer the amp, the noisier it becomes (referred to as gain over temperature or g/t). Simply put, keeping the antenna cool means the GPS receiver is getting a better, more reliable signal. As with all things, you, the builder, must decide how much of the safety margins built into the GPS equipment you are comfortable eroding by intentionally choosing a consistently hot antenna mounting location.
Oh, one other interesting data point... When a G3X-equipped Grumman AA5B Tiger was being shown off at Oshkosh at the Garmin booth I noted the glaringly-white GA35 antenna was mounted on the glareshield. Now how much safety margin was eroded in that installation by placing that glaring white blob of plastic in front of the pilot's eyes? It's all a trade-off where we get to choose the compromises with which we are comfortable.