Today's Message Index:
----------------------
1. 06:10 AM - Re: Re: Comm Antennas (Robert L. Nuckolls, III)
2. 07:25 AM - Re: Comm Antennas (Dave Morris \)
3. 07:40 AM - Comm Antennas (BobsV35B@aol.com)
4. 08:21 AM - Re: Comm Antennas (Dave Morris \)
5. 11:02 AM - Re: Comm Antennas (Robert L. Nuckolls, III)
6. 02:03 PM - departure from Z-13/8 (Erich_Weaver@URSCorp.com)
7. 06:30 PM - Re: Comm Antennas (Jim Baker)
8. 10:35 PM - Converting IFR GPS to Terminal (DEAN PSIROPOULOS)
Message 1
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| Subject: | Re: Comm Antennas |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 09:09 AM 5/2/2006 -0400, you wrote:
>--> AeroElectric-List message posted by: Speedy11@aol.com
>
>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
"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.
>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 >
---------------------------------------------------------
Message 2
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| Subject: | Re: Comm Antennas |
--> AeroElectric-List message posted by: "Dave Morris \"BigD\"" <BigD@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:
>--> AeroElectric-List message posted by: "Carlos Trigo"
><trigo@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
>
>
Message 3
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--> AeroElectric-List message posted by: BobsV35B@aol.com
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@DaveMorris.com writes:
--> AeroElectric-List message posted by: "Dave Morris \"BigD\""
<BigD@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:
>--> AeroElectric-List message posted by: "Carlos Trigo"
><trigo@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
Message 4
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| Subject: | Re: Comm Antennas |
--> AeroElectric-List message posted by: "Dave Morris \"BigD\"" <BigD@DaveMorris.com>
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:
>--> AeroElectric-List message posted by: BobsV35B@aol.com
>
>
>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@DaveMorris.com writes:
>
>--> AeroElectric-List message posted by: "Dave Morris \"BigD\""
><BigD@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:
> >--> AeroElectric-List message posted by: "Carlos Trigo"
> ><trigo@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
>
>
Message 5
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| Subject: | Re: Comm Antennas |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 10:37 AM 5/3/2006 -0400, you wrote:
>--> AeroElectric-List message posted by: BobsV35B@aol.com
>
>
>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.
>
>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 . . .
Message 6
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| Subject: | departure from Z-13/8 |
--> AeroElectric-List message posted by: Erich_Weaver@URSCorp.com
Howdy
The Z-13/8 architecture includes a wire leading from the battery contactor
to the S704-1 relay for the back-up alternator. Im proposing to move the
starting point of this wire from the battery contactor to the main terminal
of the battery bus. This will mean one less wire through the firewall for
me, not that that would kill me. I will keep the fusible link (which
will now be at the battery bus), and the battery will still get charged
when using the backup alternator since there is already an existing
separate wire from the battery bus to the battery contactor to the
battery. Anyone see any downside to this? Always makes me nervous to
depart from a plan...
regards,
Erich Weaver
Message 7
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| Subject: | Re: Comm Antennas |
--> AeroElectric-List message posted by: "Jim Baker" <jlbaker@msbit.net>
From: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
writes
> I'm betting that the vast majority of "questionable" installations
> are adequate performers in real life.
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
Message 8
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| Subject: | Converting IFR GPS to Terminal |
--> AeroElectric-List message posted by: "DEAN PSIROPOULOS" <dean.psiropoulos@verizon.net>
I have a Tommorrow (UPS AT) GX-65 GPS/COM. This unit can be used for
En-route IFR operations and has a TSO-C129a Class A2 certification. This is
basically the same unit as the GX-60 which is also certified for IFR
terminal and approach operations. My question is this, I'm guessing that
the only difference between the GX60 and 65 is the operational software
load. It may even be as simple as a change to a software configuration
table that activates additional features to enable the terminal and approach
capabilities. So.....is there any ex-UPS Aviation Technologies employees
lurking on this list that can tell me if my hypothesis is correct? And if
it is, would they be willing to help me get this software load configured so
I can do approach and terminal ops with the GX65? Since the GX series is no
longer sold (now that Garmin has taken over UPS AT) I can't get my GX-65
upgraded to a GX-60 by sending it back to the factory. I'm not too keen on
buying a Garmin 430 at this point (every time I think I'm done spending
money on this airplane something else comes along) so I'm looking for some
compromise here that won't break the bank.
Dean Psiropoulos
RV-6A N197DM
Finishing panel and wiring, ya hoo!!!
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