iFly GPS Forum

Rich & all, if you could email us the log file for those flights with a bogus terrain warning, along with your best guess as to where the alert occurred, it would help us debug & correct the problem. (email to support@adventurepilot.com, and reference this post)

Thanks,
Walter

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Walter Boyd
President, Adventure Pilot

My issue was not with the WAAS and the antenna, just the antenna. I think that I just had one of those "better is the enemy of good enough" situations. I never had problems in my C172 without the antenna except a couple of times flying to the Caribbean. However, just in case the antenna was going to do better I bought it and used it for the first time this weekend on a trip from Central Florida to the Atlanta area. The IFly froze four times in the trip over and twice on the trip back! Most likely the culprit was the looped excess cable, as the cable supplied is really very long.

Shane, you said that you put the antenna in the back window in your C172. Do you route the wire under the floor or just under the seats? I may try the remote location.

The issue is the small coax cable has a very high signal loss at the GPS frequency band. That extra 10' of cable you don't need adds about 4dB of signal loss. Measured in millivolts, a 3dB signal loss represents a 50% power loss.
Also, when you store the excess cable or route it, don't bend it too tight (talking less then a 1/2" bend radius). This can cause a "mismatch" that causes some of the energy to be reflected back at the antenna.
Now, is the extra wire a real issue with the external antenna for the iFly? In my playing with it, the antenna looks to perform fine. I have some 20 hours now with it in my C-182 with the antenna up on the dash. Always have WAAS lock and all or nearly all signal bars. I still have had faults attitude alerts a few times (only last a few seconds), but the unit in my C-182 shows better signal then without the remote antenna. The pre-amp in the antenna seems to have a high output. I have not played with it as much in my Grumman Yankee since it is under a bubble canopy on the yoke.
I looked at cutting the cable. I use MCX connectors at work, but do not have any for this cable. I thought about ordering a few, but then they take different tools then the ones I use. You need the correct connector for the cable type, the correct tools, and the knowledge to do the job right. Done wrong, you could introduce a signal mismatch and have worse signal. These small coax cables are very craft sensitive.
The antenna I received had the cable in a nice about 2" bend radius coil. I just undid the amount of cable I needed, found a point to conceal the coil and a secured it. After a few flights I decided to not bother with the idea of cutting the wire, it would be too much trouble, and other then easier wire management in the cockpit, I don't think it would add any improvement to the GPS performance.