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BRogers(at)fdic.gov
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 Posted: Mon Jun 19, 2006 8:34 am Post subject: VOR/GS Antenna Installation |
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I know that a VOR/GS antenna is a dipole antenna and does not need a
ground plane. The RG-400 co-ax cable that connects my Nav radio to the
VOR/GS antenna in my all-aluminum kit plane has a center wire and the
outer shield. The shield is attached to the outer portion of the BNC
connector, which mates to a female connector on the radio that touches
the metal radio frame - thus the outer shield on the cable is grounded.
Also, the way my antenna is currently mounted, the outer shield portion
of the female BNC connector of the antenna also touches the airframe and
is thus, grounded.
What effect does the fact that one side of the antenna connection is
grounded have on the performance of the VOR/GS antenna? I know that the
antenna does not have to be grounded to work, but what happens if it is?
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Hopperdhh(at)aol.com
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| Posted: Tue Jun 20, 2006 3:33 am Post subject: VOR/GS Antenna Installation |
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Bob,
That depends somewhat on exactly what the configuration of your antenna is.
Please describe the antenna in some detail.
VOR antennas from the "factory" use a balun to make the antenna balanced
with respect to ground. This balun device (meaning BALanced to UNbalanced) is
often a special small 1:1 transformer. A balun makes the pattern symmetrical
with respect to ground, or more ideal. From antenna information given in
Narco VOR manuals, it is important to be sure the antenna is horizontally
polarized. Without the balun the feedline can become part of the antenna system and
the polarity may no longer be purely horizontal. This would make the
antenna more prone to respond to reflected signals which of course would come from
a direction other than where the VOR station is located.
A broadband balun which can be used for VOR (because the VOR band is between
TV channels 6 and 7) can be found in almost all older TV sets which have
both balanced (300 ohm twin lead) and unbalanced (75 ohm coax) antenna
connections on the back.
When the received signal is fairly strong, the grounded coax shield will not
make any difference. When the signal is weak is when the "ideal" antenna
becomes more necessary.
Dan K9WEK
Walton, IN
RV-7A
In a message dated 6/19/2006 12:40:01 P.M. Eastern Daylight Time,
BRogers(at)fdic.gov writes:
I know that a VOR/GS antenna is a dipole antenna and does not need a
ground plane. The RG-400 co-ax cable that connects my Nav radio to the
VOR/GS antenna in my all-aluminum kit plane has a center wire and the
outer shield. The shield is attached to the outer portion of the BNC
connector, which mates to a female connector on the radio that touches
the metal radio frame - thus the outer shield on the cable is grounded.
Also, the way my antenna is currently mounted, the outer shield portion
of the female BNC connector of the antenna also touches the airframe and
is thus, grounded.
What effect does the fact that one side of the antenna connection is
grounded have on the performance of the VOR/GS antenna? I know that the
antenna does not have to be grounded to work, but what happens if it is?
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BRogers(at)fdic.gov
Guest
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| Posted: Tue Jun 20, 2006 6:08 am Post subject: VOR/GS Antenna Installation |
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My antenna is a factory manufactured Comant V dipole VOR/GS antenna with
an integral balun (hockey puck style). My main concern is whether the
shield portion of the feed line (RG-400 cable) must be isolated from the
airframe. Right now, it is connected to ground at both the antenna end
and at the radio end. I do not know whether that makes a difference in
the performance of the antenna/nav radio.
--
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nuckollsr(at)cox.net
Guest
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| Posted: Tue Jun 20, 2006 7:30 am Post subject: VOR/GS Antenna Installation |
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At 09:02 AM 6/20/2006 -0500, you wrote:
| Quote: |
My antenna is a factory manufactured Comant V dipole VOR/GS antenna with
an integral balun (hockey puck style). My main concern is whether the
shield portion of the feed line (RG-400 cable) must be isolated from the
airframe. Right now, it is connected to ground at both the antenna end
and at the radio end. I do not know whether that makes a difference in
the performance of the antenna/nav radio.
|
Probably no problem but it's only necessary that the coax
shield have good connection at the balun and radio connectors.
If the coax shield becomes grounded to airframe at the antenna
end due to the way the antenna is designed, then so be it.
Comant knows what they're doing. But if I were building a cat-whisker
antenna to attach to the end of a coax, I'd leave the shield free
of airframe ground at the antenna end.
Bob . . .
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Hopperdhh(at)aol.com
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| Posted: Tue Jun 20, 2006 3:12 pm Post subject: VOR/GS Antenna Installation |
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Bob,
It is probably OK to ground the shield at both ends. In any case, the
recommendations of the manufacturer should be followed. If it has a balun, that
should solve the problem of making both sides of the antenna equally "hot."
Dan
In a message dated 6/20/2006 10:10:29 A.M. Eastern Daylight Time,
BRogers(at)fdic.gov writes:
My antenna is a factory manufactured Comant V dipole VOR/GS antenna with
an integral balun (hockey puck style). My main concern is whether the
shield portion of the feed line (RG-400 cable) must be isolated from the
airframe. Right now, it is connected to ground at both the antenna end
and at the radio end. I do not know whether that makes a difference in
the performance of the antenna/nav radio.
-----Original Message-----
[mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of
Hopperdhh(at)aol.com
Sent: Tuesday, June 20, 2006 6:30 AM
Bob,
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