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trigo(at)mail.telepac.pt Guest
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Posted: Mon May 01, 2006 11:26 am Post subject: Comm Antennas |
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I'm building an RV-9A and planning to install 2 comm antennas, one for the
panel radio (ICOM A-200) and the other for an handheld backup radio.
If I put both on the tail cone, one on the upper side and the other on the
bottom side of the fuselage, thus on the same vertical plan and some 3 ft
apart, are there any location associated problems?
Carlos
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gmcjetpilot(at)yahoo.com Guest
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Posted: Tue May 02, 2006 1:37 am Post subject: Comm Antennas |
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Carlos:
To answer you question, yes that would be fine, but.....
Do you plan on using them at the same time. On near same freq
you could have an issue. Most dual panel mount radio setups
have an interconnect between dual COMs. It protects the
radio when the other one is transmitting.
Do you really need two radios? The handheld can just use
the attached portable antenna for say getting ATIS. If you
need to use it as the main radio in a pinch, like the ICOM dies,
I have a suggestion below.
Instead of two external antenna put just one bent whip antenna
on the belly forward of the main spare off to the pilot side. You
will have short coax run. ALSO if you need to, you can reach
down disconnect the coax from the antenna mounted in the floor
under the pilots leg and attach the coax to the handheld in an
emergency. The coax is out of the way just forward of the spar,
but it is still accessible. You could put a coax break anywhere.
They make commercial antenna switches to attach a portable
to the same antenna.
99% or the RV's put the antenna on the belly fwd of the spar.
Also most RV's use just one external COM antenna. Each
antenna is about 1/3 to 1/2 mph lost off of top speed. Also with
the long coax runs you will add extra weight. The area under
the belly is fine. You may worry about the gear leg blocking
the signal but this has prove to be a non issue.
The tail cone is fine but ugly in my opinion.
I assume you will have the audio out from the handheld going
into one of the ICOM aux inputs.
Cheers George
--------------------------------------------------------------------------------
From: "Carlos Trigo" <trigo(at)mail.telepac.pt>
I'm building an RV-9A and planning to install 2 comm antennas,
one for the panel radio (ICOM A-200) and the other for an handheld
backup radio. If I put both on the tail cone, one on the upper side
and the other on the bottom side of the fuselage, thus on the same
vertical plan and some 3 ft apart, are there any location associated
problems?
Carlos
---------------------------------
Blab-away for as little as 1/min. Make PC-to-Phone Calls using Yahoo! Messenger with Voice.
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Speedy11(at)aol.com Guest
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Posted: Tue May 02, 2006 5:12 am Post subject: Comm Antennas |
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Regarding Carlos' question below, it seems to me that his antennae could be
mounted close together IF only one antenna were used at a time. Correct?
Stan Sutterfield
I'm building an RV-9A and planning to install 2 comm antennas, one for the
panel radio (ICOM A-200) and the other for an handheld backup radio.
If I put both on the tail cone, one on the upper side and the other on the
bottom side of the fuselage, thus on the same vertical plan and some 3 ft
apart, are there any location associated problems?
Carlos
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nuckollsr(at)cox.net Guest
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Posted: Wed May 03, 2006 5:10 am Post subject: Comm Antennas |
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At 09:09 AM 5/2/2006 -0400, you wrote:
Quote: |
Regarding Carlos' question below, it seems to me that his antennae could be
mounted close together IF only one antenna were used at a time. Correct?
Stan Sutterfield
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"Close together" isn't very quantified. Certainly while
one antenna is being used to transmit, power intercepted
by the other one is likely to overload the receiver on the
other system . . . some receivers may take seconds to recover
from overloads. I'd like to see a couple of feet separation or
top/bottom mounted as Carlos suggested. You can TRY anything
else. There's little risk to hardware.
Quote: | I'm building an RV-9A and planning to install 2 comm antennas, one for the
panel radio (ICOM A-200) and the other for an handheld backup radio.
If I put both on the tail cone, one on the upper side and the other on the
bottom side of the fuselage, thus on the same vertical plan and some 3 ft
apart, are there any location associated problems?
|
When mounted on upper and lower surfaces, they are
well isolated. It's when mounted on the same surface that
we like to see some horizontal separation.
Bob . . .
---------------------------------------------------------
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
---------------------------------------------------------
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BigD(at)DaveMorris.com Guest
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Posted: Wed May 03, 2006 6:25 am Post subject: Comm Antennas |
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Vertical separation is much better than horizontal separation. You
may still overload your receiver unless you have a switch to
disconnect it when the other one is transmitting.
Dave Morris
At 02:19 PM 5/1/2006, you wrote:
Quote: |
<trigo(at)mail.telepac.pt>
I'm building an RV-9A and planning to install 2 comm antennas, one for the
panel radio (ICOM A-200) and the other for an handheld backup radio.
If I put both on the tail cone, one on the upper side and the other on the
bottom side of the fuselage, thus on the same vertical plan and some 3 ft
apart, are there any location associated problems?
Carlos
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BobsV35B(at)aol.com Guest
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Posted: Wed May 03, 2006 6:40 am Post subject: Comm Antennas |
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Good Morning All,
This is from an electronics illiterate, but when I have been involved with
radio installations, I have always been told that any metal device that is
parallel and close to any vertical antenna will sap some of the strength from
the signal and drastically affects the reception pattern by absorbing and/or
reflecting the signal.
Two VHF comm antennas closer together than two or three feet will be very
directional. The same problem occurs when an antenna is within a couple of
feet of a fixed landing gear leg or the vertical fin containing a metal leading
edge.
Any truth to all that or is it just another Old Wives Tale?
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Air Park LL22
Downers Grove, IL 60516
630 985-8503
In a message dated 5/3/2006 9:29:22 A.M. Central Standard Time,
BigD(at)DaveMorris.com writes:
<BigD(at)DaveMorris.com>
Vertical separation is much better than horizontal separation. You
may still overload your receiver unless you have a switch to
disconnect it when the other one is transmitting.
Dave Morris
At 02:19 PM 5/1/2006, you wrote:
Quote: |
<trigo(at)mail.telepac.pt>
I'm building an RV-9A and planning to install 2 comm antennas, one for the
panel radio (ICOM A-200) and the other for an handheld backup radio.
If I put both on the tail cone, one on the upper side and the other on the
bottom side of the fuselage, thus on the same vertical plan and some 3 ft
apart, are there any location associated problems?
Carlos
|
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BigD(at)DaveMorris.com Guest
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Posted: Wed May 03, 2006 7:21 am Post subject: Comm Antennas |
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A quarter wavelength on the aircraft band is about 23 inches. Keep
the antennas farther apart than that, and they won't interfere very
much with each other. I don't think you'll notice any directivity
created from landing gear legs or vertical fins, but the larger the
metal mass and the closer it is to the antenna, the more the antenna
will be influenced by the foreign metal object and create problems
especially in transmitting.
In order to create directivity, you have to put the antennas a
particular distance apart, generally 15-25% of a wavelength, and then
either feed them both in a particular phase relationship, or make
them a particular length shorter or longer (about 10-20%) than each
other. Otherwise, you just have random interference.
Dave Morris
At 09:37 AM 5/3/2006, you wrote:
Quote: |
Good Morning All,
This is from an electronics illiterate, but when I have been involved with
radio installations, I have always been told that any metal device that is
parallel and close to any vertical antenna will sap some of the
strength from
the signal and drastically affects the reception pattern by absorbing and/or
reflecting the signal.
Two VHF comm antennas closer together than two or three feet will be very
directional. The same problem occurs when an antenna is within a couple of
feet of a fixed landing gear leg or the vertical fin containing a
metal leading
edge.
Any truth to all that or is it just another Old Wives Tale?
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Air Park LL22
Downers Grove, IL 60516
630 985-8503
In a message dated 5/3/2006 9:29:22 A.M. Central Standard Time,
BigD(at)DaveMorris.com writes:
<BigD(at)DaveMorris.com>
Vertical separation is much better than horizontal separation. You
may still overload your receiver unless you have a switch to
disconnect it when the other one is transmitting.
Dave Morris
At 02:19 PM 5/1/2006, you wrote:
>
><trigo(at)mail.telepac.pt>
>
>I'm building an RV-9A and planning to install 2 comm antennas, one for the
>panel radio (ICOM A-200) and the other for an handheld backup radio.
>If I put both on the tail cone, one on the upper side and the other on the
>bottom side of the fuselage, thus on the same vertical plan and some 3 ft
>apart, are there any location associated problems?
>
>Carlos
|
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nuckollsr(at)cox.net Guest
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Posted: Wed May 03, 2006 10:02 am Post subject: Comm Antennas |
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At 10:37 AM 5/3/2006 -0400, you wrote:
Quote: |
Good Morning All,
This is from an electronics illiterate, but when I have been involved with
radio installations, I have always been told that any metal device that is
parallel and close to any vertical antenna will sap some of the strength
from
the signal and drastically affects the reception pattern by absorbing and/or
reflecting the signal.
|
Metallic conductors in the near field (less than 1 wavelength) of
an antenna will produce measurable distortions of antennas
pattern compared to it's free space situation.
Here's an exemplar horizontal radiation pattern for a highly
distorted, otherwise omni directional antenna:
http://www.aeroelectric.com/Pictures/Misc/Antenna_Pattern.gif
Note that as one marches around the horizon talking to this
installation, there are directions of communication that
suffer 40+ dB of attenuation (1/10,000th the max power).
However, in actual practice, this seemingly terrible antenna
may never come to the attention of a pilot. Signal margins for
air to ground communications are generally large. Further,
likelihood that any given attempt to communicate will fall
into the center of one of those deep notches is small.
Quote: |
Two VHF comm antennas closer together than two or three feet will be very
directional. The same problem occurs when an antenna is within a couple of
feet of a fixed landing gear leg or the vertical fin containing a metal
leading
edge.
Any truth to all that or is it just another Old Wives Tale?
|
Lots of truth, the task is to assign significance. We installed
tens of thousands of dual comm antennas on the cabin tops of
Cessnas for decades and they were only about 24" apart as I
recall. Testing on Gordon Wood's mini-antenna range at Cessna's
Pawnee Plant (single engine group) showed measurable but
insignificant effects.
I wouldn't agonize over it. Install for most convenience but
be aware of the POTENTIAL for noticeable effects. If at some time
you find that a particular station you've been talking too
"disappeared" . . . change heading 30 degrees and see if they
come back. If so, return to original heading and see if they
disappear again. This is a good way to demonstrate a significant
condition. Another way is to get some unicom station 20+ miles
away to give you a 3-minute count while you conduct a 360 degree
flat turn. See if they drop out at any time in the turn.
I'm betting that the vast majority of "questionable" installations
are adequate performers in real life.
Bob . . .
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Jim Baker
Joined: 30 Mar 2006 Posts: 181 Location: Sayre, PA
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Posted: Wed May 03, 2006 5:30 pm Post subject: Comm Antennas |
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From: "Robert L. Nuckolls, III" <nuckollsr(at)cox.net>
writes
Quote: | I'm betting that the vast majority of "questionable" installations
are adequate performers in real life.
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Look. If I can build an antenna from a section of stainless (correct length, of
course), silver solder that to a BNC bulkhead connector, screw it to the floor
pan of my Kolb UL, and then power that with a KLX100 to over 30 miles,
you'd have to really work at making a bad antenna.......not saying it can't be
done. I'm proof of the "questionable installation".
Jim Baker
580.788.2779
Elmore City, OK
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