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wv4i(at)bellsouth.net
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 Posted: Mon Nov 13, 2006 4:14 am Post subject: Antenna Location |
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Seeing comments on antenna location in other threads, I thought a couple
of points have perhaps not been considered. First, I've been involved
with amateur radio for about 25 years, both mobile and fixed ops, and
including from my RV-6. My FCC callsign is WV4I, for the other hams on
this forum.
The problem with wing tip antennas, or antennas not located on the
fuselage or vertical stab leading edge or tip, would seem to be twofold.
One, re the wing tip location, such would likely cause a null in
reception (and transmission) primarily oriented in the direction of the
wing. Also, if the aircraft antenna is of one orientation, e.g.
horizontal, and the target station is vertical oriented (polarized, to
be precise), typically a 20db path loss occurs. Every 3db loss equates
to roughly a 50% drop in signal strength.
Another issue that may arise with antennas mounted parallel to metal
structures is that they become detuned. As an antenna is "cut" to
resonate at a desired frequency, with a given bandwidth, e.g. 118-136mhz
at <2:1 SWR, this resonance point can be be altered, diminished, or even
eliminated by nearby metal objects. Antenna resonance is important to
good receiver or transceiver performance, and in the case of
transmitters without high SWR protective circuitry, high SWR can damage
final output transistors.
This gets to be a very complex subject quickly, and I'm no electrical
engineer, but just some thoughts to consider on antenna placement.
Link McGarity
#40622
RV6/N42GF/flying, non-builder
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LessDragProd(at)aol.com
Guest
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| Posted: Mon Nov 13, 2006 7:44 am Post subject: Antenna Location |
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Bob Archer's Sportcraft wingtip antenna's are gamma antenna's.
If the wingtip antenna is a gamma antenna, instead of a dipole antenna, do your comments still apply?
It's my simplistic understanding that a gamma antenna receives on the ground plane, which is the airframe of the aircraft. That's why it is so important to get good electrical contact along a distributed attachment of the base of the Sportcraft wingtip antenna to the wing skin.
(With the antenna mounted inside the fiberglass wingtip, the wing skin dimples for the antenna attachment need to have the paint removed for good electrical contact through the attaching screws.)
Jim Ayers
In a message dated 11/13/2006 4:16:35 AM Pacific Standard Time, wv4i(at)bellsouth.net writes:
| Quote: | --> RV10-List message posted by: Link McGarity <wv4i(at)bellsouth.net>
Seeing comments on antenna location in other threads, I thought a couple
of points have perhaps not been considered. First, I've been involved
with amateur radio for about 25 years, both mobile and fixed ops, and
including from my RV-6. My FCC callsign is WV4I, for the other hams on
this forum.
The problem with wing tip antennas, or antennas not located on the
fuselage or vertical stab leading edge or tip, would seem to be twofold.
One, re the wing tip location, such would likely cause a null in
reception (and transmission) primarily oriented in the direction of the
wing. Also, if the aircraft antenna is of one orientation, e.g.
horizontal, and the target station is vertical oriented (polarized, to
be precise), typically a 20db path loss occurs. Every 3db loss equates
to roughly a 50% drop in signal strength.
Another issue that may arise with antennas mounted parallel to metal
structures is that they become detuned. As an antenna is "cut" to
resonate at a desired frequency, with a given bandwidth, e.g. 118-136mhz
at <2:1 SWR, this resonance point can be be altered, diminished, or even
eliminated by nearby metal objects. Antenna resonance is important to
good receiver or transceiver performance, and in the case of
transmitters without high SWR protective circuitry, high SWR can damage
final output transistors.
This gets to be a very complex subject quickly, and I'm no electrical
engineer, but just some thoughts to consider on antenna placement.
Link McGarity
#40622
RV6/N42GF/flying, non-builder
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[quote][b]
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AV8ORJWC
Joined: 13 Jul 2006
Posts: 1149
Location: Aurora, Oregon "Home of VANS"
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| Posted: Mon Nov 13, 2006 8:04 am Post subject: Antenna Location |
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It is great to have a clear, concise and valued response to this easily
misunderstood subject of RF propagation and SWR.
John Cox
#40600
N49CX and amateur W7COX
--
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apilot2(at)gmail.com
Guest
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| Posted: Mon Nov 13, 2006 8:36 am Post subject: Antenna Location |
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Your comments are certainly on target for com antennas. However, for
nav antennas you NEED horizontal polarization, as all VOR and GS
signals are horizontally polarized. Fuselage is no more blanking of a
wing tip than it is blanking for antenna on vertical fin recieving
signal below the aircraft.
On 11/13/06, Link McGarity <wv4i(at)bellsouth.net> wrote:
| Quote: |
The problem with wing tip antennas, or antennas not located on the
fuselage or vertical stab leading edge or tip, would seem to be twofold.
One, re the wing tip location, such would likely cause a null in
reception (and transmission) primarily oriented in the direction of the
wing. Also, if the aircraft antenna is of one orientation, e.g.
horizontal, and the target station is vertical oriented (polarized, to
be precise), typically a 20db path loss occurs. Every 3db loss equates
to roughly a 50% drop in signal strength.
|
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http://www.matronics.com/Navigator?RV10-List |
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wcurtis(at)core.com
Guest
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| Posted: Mon Nov 13, 2006 1:33 pm Post subject: Antenna Location |
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With respect to your rf experience, there is no problem with wingtip for VHF navigation antennas. You have explained below why only navigation antennas are primarily placed in the wingtip. Comm antennas do not work well in the wingtip. Notice that all VHF navigational antenna are mounted horizontally and are polarized as such. Communication antennas on the other hand are mounted vertically and polarized as such. Since the wingtips are set up very well for horizontal installation, they work quite well for navigational antennas. I think the question was in regard to navigational antennas only. Search the archives, I think this has been previously discussed ad nauseam. >The problem with wing tip antennas, or antennas not located on the >fuselage or vertical stab leading edge or tip, would seem to be twofold. >One, re the wing tip location, such would likely cause a null in >reception (and transmission) primarily oriented in the direction of the >wing. Also, if the aircraft antenna is of one orientation, e.g. >horizontal, and the target station is vertical oriented (polarized, to >be precise), typically a 20db path loss occurs. Every 3db loss equates >to roughly a 50% drop in signal strength. William Curtis http://wcurtis.nerv10.com/ [quote][b]
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