On 07/30/2010 08:26 PM, John Wighton wrote:
>
> Hell everyone, I am installing a Garmin SL30 into G-IPOD and wish to
> know the best place for the NAV antenna. It's a tri-gear and l have
> the standard fin mounted COMM antenna.
I have built the NAV antenna for my Garmin SL30 into the belly of the
airplane. There is a picture of this in my build log
www.privatepilots.nl/europa/building.htm
I decided to mount the antenna on the floor, because I have the strobe
power supply mounted against the roof. This provides better routing of
the cables (I could wire the wing tip strobes and tail strobe
symmetrically so the noise spikes null themselves out) and in case of a
fuel leak the strobe unit doesn't ignite the fuel as easily.
Another reason to mount the antenna on the floor is that there is simply
more space there for an antenna.
The NAV antenna works very well in this position. Sensitivity is
omni-directional, and I have no signs of strobe or other noises leaking
into the NAV system. The anntenna consists of two aluminium tubes in a
V-shape and I tuned them to the proper frequency. The coax is coiled up
close to the antenna to work as a balun.
Don't believe marketing stories, a simple V-shaped dipole is the best
you can get in terms of efficiency and radiation pattern. It is mainly
omni-directional, with a slight favor for the forward position, which is
probably the best for our purposes.
Don't worry about the engine "shadowing out" the antenna, the engine is
smaller than the wavelength and has little influence on the reception of
the signal. Apart from that, I believe that the NAV signals are
transmitted off the ground, so the engine is simply above the "line of
sight" of the antenna. ;-)
Frans
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