GPS antenna location on fwd cowling - thoughts?

avee8tor13 · #1 01-31-2009, 06:21 PM

Thoughts on mounting the GPS antenna in front of windshield on upper cowling.
I saw one of the other builders do this. Looked pretty cool.

DGlaeser · #2 01-31-2009, 06:44 PM

Under the cowl forward of the firewall - can't see it at all, but works great!

Bob Martin · #3 01-31-2009, 08:18 PM

Mine is located on the forward fuselage skin between the canopy and the top cowling. It makes for a short coax run from the GPS!
Lucky for me my plane is white and the white antenna blends right in.
Good Luck

Greg Arehart · #4 01-31-2009, 08:37 PM

I did mine like Dennis - under the cowl on a small shelf I built. Works fine. I would only worry about this if you plan a metallic paint job, and even then, I'm not sure that the "metallic" part is really metal.

greg

AFulmer · #5 01-31-2009, 08:38 PM

Does the WAAS GPS antenna require any special mounting method or location different from the "regular" GPS antenna? In other words, will it still work fine mounted under the upper cowl?

Would it work fine if mounted under a fiberglass access panel in front of the windshield as Dan Checkoway did?

Thanks,

avee8tor13 · #6 01-31-2009, 08:40 PM

I did not see any minimum length of cable or criteria to mount the antenna a minimum distance from the radio on the GNC300XL.

Are you saying you can mount the antenna 1 or 2 feet from the GPS radio and it would be ok?

Thanks

pierre smith · #7 02-01-2009, 06:39 AM

....with both the 496 antenna and the XM weather antenna mounted on a firewall mounted plate and they both receive very well, even with silver paint.

Regards,

Ron Lee · #8 02-01-2009, 08:13 AM

It is like a wart.

AlexPeterson · #9 02-01-2009, 09:13 AM

Quote:

Originally Posted by AFulmer

Does the WAAS GPS antenna require any special mounting method or location different from the "regular" GPS antenna? In other words, will it still work fine mounted under the upper cowl?

Would it work fine if mounted under a fiberglass access panel in front of the windshield as Dan Checkoway did?

Thanks,

Allen, I can only speak for the 430w, but yes, there are some concerns. I don't recall the exact length, but there is a minimum coax length recommended. I don't know if one could simply coil up the coax or if physical distance from the comm antennae are also important. The test specified by Garmin for the 430w install is to power things up, and go to the satellite page of the 430w. Then, there are a series of comm frequencies to transmit on while watching the satellite page. I'm not so sure of just what is being observed, but the avionics guy who sat with me in the plane said my install was clean. I recall he told me that it is not uncommon to see indicated satellite signal strengths drop significantly during transmitting on certain freq's in certain installs.

All that being said, I suspect there are many experimentals flying with the 430w that did not have these checks performed. I wouldn't think Garmin made the requirement up for fun.

Christer · #10 02-01-2009, 09:48 AM

There is a minimum coax antenna length to maintain proper rejection to interference signals. This is about 1.5 dB - 6.5dB. If you are using RG400 coax (recommended) that is about 6.5 feet of cable minimum and 35 feet max assuming one connector at each end. You can coil it if you need to. The WAAS antenna also uses a TNC connector vs the BNC. If you get VHF interference there are also filters to help this (1575.42Mhz notch filter) but this is not a common problem.