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1. 04:07 AM - Re: Antenna Question (wsimpso1)
2. 04:20 AM - Re: Antenna Question (wsimpso1)
Message 1
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| Subject: | Re: Antenna Question |
Two VHF antenna on one wingtip is generally bad practice.
RST Engineering (Jim Weir) talks about the de-tuning effects of having any piece
of metal near antennas. Specifically, Jim Weir tells us that any piece of metal
with a dimension bigger than 1/8 wavelength within 1/4 wavelength of the tips
of antenna will mess with radiation patterns. The exception is the ground
plane normal to and at the base of antenna arm or even the vertical stabilizer
between the two legs of a NAV dipole. But put that metal anywhere else... Two
VHF antenna and their cabling in the same space will probably give you dead spaces
in some directions and poor range and reception in the directions where
it works at all.
Much better to split the VHF antenna to the opposite wingtips...
Now the miniaturized antenna in the uAvionics Tailbeacon is an order of magnitude
smaller than the VHF antenna, so you might be tempted to hang it in the wingtip
with one VHF antenna, but the wiring is also a big piece of metal that will
be too close to the tips of the VHF antenna. Then there is the matter of the
VHF antenna messing up the Tailbeacon, leaving you non-compliant on ADS-B Out.
If you pair up some of these items that usually need to be apart from each other,
you could have so much fuss over trying (and likely failing) to get them all
to work nice that figuring out how to put the Tailbeacon where uAvionics intends
for them might seem a real bargain.
Billski
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=506325#506325
Message 2
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| Subject: | Re: Antenna Question |
Another temptation is to drive two VOR receivers off one VOR antenna. This might
be acceptable. What happens is splitters divide the received power in half between
the two output cables. (Again, from RST Engineering and Jim Weir) No receiver
even needs to be in the airplane for this split to occur. That makes the
range of each of the VOR receivers 70% what it would have been with a dedicated
antenna to each receiver. In an airplane as fast as an RV, this is likely
to deny you VOR reception until closer than you might like.
The counter argument is that many spam cans are running around with a single VOR
antenna on the vertical fin with a splitter. Yeah, I have one of those, and
the range on the VOR can be pretty poor. Sure would be nice to have that 100%
instead of 70%... The up side is GPS in both the panel and the iPad may make the
VOR range issue ... less important.
Billski
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=506326#506326
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