Today's Message Index:
----------------------
1. 07:03 AM - ELT antenna performance (Robert L. Nuckolls, III)
2. 08:42 AM - Unfortunate Antenna Instructions (Robert L. Nuckolls, III)
3. 08:42 AM - Re: lan tracer (jonlaury)
4. 08:52 AM - Re: ELT antenna performance (Richard Tasker)
5. 10:21 AM - Re: ELT antenna performance (Robert L. Nuckolls, III)
6. 10:41 AM - Re: Re: lan tracer (Bob McCallum)
7. 11:58 AM - Re: Comm Antenna & SWR: More Information (Noel Loveys)
8. 12:22 PM - Re: coax antenna cable length (Noel Loveys)
9. 12:30 PM - Re: ELT antenna performance (kuffel@cyberport.net)
10. 12:38 PM - Re: Comm Antenna & SWR: More Information (Noel Loveys)
11. 12:57 PM - Re: Comm Antenna & SWR: More Information (Noel Loveys)
12. 03:07 PM - Re: Comm Antenna & SWR: More Information (Robert L. Nuckolls, III)
13. 04:28 PM - Re: ELT antenna performance (Noel Loveys)
14. 04:28 PM - Re: ELT antenna performance (Noel Loveys)
15. 04:56 PM - Re: ELT antenna performance (Mike Welch)
16. 06:51 PM - Re: Graphene (Bill Watson)
17. 09:58 PM - BNC connectors (John F. Herminghaus)
18. 10:20 PM - Re: BNC connectors (Robert L. Nuckolls, III)
19. 11:39 PM - OT-potting with RTV silicone (rayj)
20. 11:39 PM - Re: BNC connectors (John F. Herminghaus)
Message 1
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Subject: | ELT antenna performance |
At 11:54 PM 1/27/2011, you wrote:
>Bob and all,
>During an emergency landing too many aircraft go over on their backs.
or suffer severe deformation/disassembly
> I suspect that the back contact and sliding in too many instances
> scrapes off or otherwise damages antenna like the ELT typically use.
which is why the preferred location for ELT antenna
is just forward of the vertical fin. Studies of
wreckage remains determined that this was the lowest
risk location for the antenna . . . unfortunately,
"lowest" is not a nice number near zero.
>
> From that situation, I have wondered about a design concept that
> would allow the ELT to feed either two or one antennas with enough
> radiation to get someone's attention. The thought goes something
> like this. Have an antenna both top and bottom of the fuselage
> region. Hoping that one survives the impact and will radiate the ELT signal.
Having the system upside down is not as deleterious
as one might imagine. UHF behaves quite a bit differently
than VHF.
When I first got into electronics as a profession,
I was working for a two-way radio company in Wichita.
We serviced a few systems in the 72 mHz band but
most were in the vicinity of 150 mHz and a few
were up about 450.
This was all vacuum tube stuff. The 450 mHz
equipment was at the upper fringe of what
was practical. It was harder to develop power,
losses in feedlines was higher, keeping
receiver sensitivity to less than 1 microvolt
was more demanding. All-in-all, higher
cost of ownership.
You'd think that customers would shy away from
this equipment. On the contrary. Antennas were
more efficient. Terrestrial noise was a small
influence. Signals behaved much better in the
confines of tall buildings. The cab companies
wouldn't have anything different. The police
wanted it but the FCC decreed that public
services will conduct business in the 150 mHz
band. 150 mHz was subject to much more multi-
path nulls and noise.
121.5 mHz was picked for the first ELTs
because it was a frequency already serviced
by aviation communication services. Same
with 243 albeit military. The idea was
that folks having nothing better to do
on long trips might monitor the emergency
frequencies and report any contacts. Heaven
knew that the satellite location technology
was EXCEEDINGLY crude. Location accuracy was
poor (100 square miles or more), it took
three or more satellite passes to get that
good (meaning many hours after first contact)
and that assumed that they could sort out
the distressed aircraft from several dozen
false triggers that every satellite could
hear within it's line-of-sight cone.
Combine this with the relatively poor
performance of VHF propagation in general
and you begin to see why the system was
doomed to poor performance from the
beginning. 6% find-rates was considered
great performance by some.
Then came solid state UHF electronics
where communications at 2,000 Mhz was
no big deal. Add ship's i.d. GPS location
features to the ELT's transmitted signals and
that 6% number took a big jump.
They have a better chance of sorting
out your distress from other people's
false alarms.Haven't seen the latest
figures but I'll bet there are no
more than 25% of found wrecks where
attributed to ELT performance where
rescue outcomes were good . . .
I'd be delighted to be wrong.
Getting back to upside-down wrecks.
The UHF propagation performance is so
much better than the old 121.5/243
junk that antenna orientation and
shadowing is much less critical. I've
not been privy to detailed discussion
on ELT systems. But given what I know
of UHF propagation behavior, if the
system is not physically disabled,
the system is going to perform about
as well as expected irrespective
of wreckage configuration.
But the real bottom line is, what
is the return-on-investment for having
installed an ELT? How many wrecks
in the history of all aviation crashes
would have had a better outcome for
the occupants had the guys in white
coats with stretchers arrived say
within two hours of the crash?
In other words, what percentage of
all events resulted in occupants
surviving for hours to days but
unable to fend for themselves due
to non-lethal injury or simple lack
of transport?
The ELT makes a lot of sense for
over-water flight where there is
higher probability of non-lethal
landing and perhaps days of post
crash survival on a float. But
pile an airplane into a mountain
or even average terrain at night
and the ELT becomes more of a
whistle in the dark. If you really
want the folks in white coats to
show up fast, make sure you've
added the GPS position data option.
At least they KNOW where you are.
Now the problem is to get to
you with what ever resources are
available for the task. Those
resources are dwindling . . . but
that's another issue.
>
>Any thoughts about a design that could "reasonably" match and feed
>either two (if both survive) or the remaining antenna....
Sure. You could install rugged, flush
mounted slot antennas on top and bottom
of the tail. Use a power divider to feed
both antennas.
This would demand some analysis and perhaps
demonstrated experiments to determine
it was really that much better. I suspect
that the numbers guys would find that
going to dual, robust antennas would
double installation costs while making that
25% go up to 26.2% or some such.
I'm pretty sure it's been explored. The
ELT guys would be DELIGHTED to have dual
robust antennas added to the mandate for
installing such systems. If it made any
sense at all, they'd be doing it.
Bob . . .
Message 2
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Subject: | Unfortunate Antenna Instructions |
I've been given a copy of S-H antenna installation
instructions for review. I have the following observations
to share with members of the List. The article has
been posted at:
http://tinyurl.com/4cwq4yy
ADJUSTING the ANTENNA CABLE LENGTH
The process described under this title is a salute
to an old hangar myth that antenna system performance
can be improved by cutting coax feed lines to (1) multiples
of half-wavelengths or (2) maximize measured field strength
on some particular frequency.
As we discussed last week, the ONLY time that observable
effects are affected by length of the transmission line
is when the SWR on that line is high. The most profound
effects for fiddling with length will be noted when SWR
is a lot higher than what is traditionally accepted as
optimum performance. 3:1 or better.
This myth has roots that go back a long way in aviation
history. I recall similar discussions back in the 60's.
I would challenge the publisher of any such document to
search any engineering text and/or any ARRL publication
on amateur built antennas. They will not find any similar
suggestion anywhere. The adequately designed antenna
presents a load to the feedline that has no observable,
deleterious effects on system performance.
An interesting feature of the S-H suggestion is that
even if there WERE a valid reason for crafting an even-
multiples-half-wave transmission line, the coax cuts
would NOT be multiples of the free-space wavelength used
to design the antenna.
Propagation velocity of energy down a transmission line
is SLOWER than in free space. Depending on how the coax is
made, the VELOCITY FACTOR will be some number near .66
This means that for a 1/4-wave, 24" antenna element length
a 1/2 wave in coax would NOT be 48" but 48 x .66 or
31.5 inches.
Unfortunately, the idea published in this document is not
only non-sense, it is poorly implemented based on bad science.
INSTALLING BNC CONNECTORS
Finally, the tri-axial cable called out was designed for
use in systems were special connectors maintain SEPARATED
shield integrity throughout the system. VERY expensive
and rare connectors. On the other hand, RG-58 has been
handily replaced throughout the TC aircraft world with
RG-400 or RG142 which are DOUBLE LAYER bi-axial feedlines
that accept the standard RG-58 connectors with no
fabrication acrobatics.
It's unfortunate that this publication has been circulated
to S-H customers for 14 years. It has no doubt generated a lot
of unnecessary no-value added taxation of their customer's
time, talents and resources.
Bob . . .
Message 3
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|
Try www.allelectroincs.com , cat#28, $12
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=328832#328832
Message 4
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Subject: | Re: ELT antenna performance |
Hey Bob, not to pick nits , but you are the example here after all... ;-)
mHz - millihertz
MHz - megahertz
Dick Tasker
Robert L. Nuckolls, III wrote:
<snip>
> When I first got into electronics as a profession,
> I was working for a two-way radio company in Wichita.
> We serviced a few systems in the 72 mHz band but
> most were in the vicinity of 150 mHz and a few
> were up about 450.
>
> This was all vacuum tube stuff. The 450 mHz
> equipment was at the upper fringe of what
> was practical. It was harder to develop power,
> losses in feedlines was higher, keeping
> receiver sensitivity to less than 1 microvolt
> was more demanding. All-in-all, higher
> cost of ownership.
>
> You'd think that customers would shy away from
> this equipment. On the contrary. Antennas were
> more efficient. Terrestrial noise was a small
> influence. Signals behaved much better in the
> confines of tall buildings. The cab companies
> wouldn't have anything different. The police
> wanted it but the FCC decreed that public
> services will conduct business in the 150 mHz
> band. 150 mHz was subject to much more multi-
> path nulls and noise.
>
> 121.5 mHz was picked for the first ELTs
> because it was a frequency already serviced
> by aviation communication services. Same
> with 243 albeit military.
Message 5
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Subject: | Re: ELT antenna performance |
At 11:15 AM 1/28/2011, you wrote:
>Hey Bob, not to pick nits , but you are the example here after all... ;-)
>
>mHz - millihertz
>
>MHz - megahertz
>
>Dick Tasker
You're quite correct. Unfortunately, when trying
to bang out a timely but extensive reply, I don't
have the luxury of coming back to edit it tomorrow
to attempt a 99% clean posting.
When I go back and read my past postings, it's
not unusual to get whacked by spelling/semantics
issues. I'll just have to beg the Lists indulgence.
That doesn't mean I don't want to hear from
folks when I've stubbed my toe. Just be forewarned
that in spite of your most honorable efforts, my
head will probably continue to run out in front of
fingers on the keyboard.
Thanks for the heads-up!
Bob . . .
Message 6
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John;
Check the link you posted. It leads to a website phishing for cell phone
numbers.
I suspect that when you wrote "allelectroincs" you might have meant
"allelectronics", but catalogue #28 does not appear to exist on their
website and all of their part numbers appear to consist of an alpha prefix
followed by a dash and then a number. There do not appear to be any numbers
fitting your posting.
Please clarify.
Bob McC
> -----Original Message-----
> From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-
> server@matronics.com] On Behalf Of jonlaury
> Sent: Friday, January 28, 2011 11:39 AM
> To: aeroelectric-list@matronics.com
> Subject: AeroElectric-List: Re: lan tracer
>
>
> Try www.allelectroincs.com , cat#28, $12
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=328832#328832
>
>
>
>
>
>
>
> _-
> ====================================================
> ======
> _-
> ====================================================
> ======
> _-
> ====================================================
> ======
> _-
> ====================================================
> ======
>
>
Message 7
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Subject: | Comm Antenna & SWR: More Information |
The stick in the tail reminds me of when I was a kid my dad had shares
in a company which carried out the seal hunt using a spotter plane and a
helicopter. Daily reports from the front (the harvesting area) were
sent form the spotter plane via HF. The plane had a trailing
=9CWet Noodle=9D antenna which could not be heard when he
was flying toward our town.. If the plane flew a direction 90 deg to
that we copied him perfectly.
With a com radio it is important that everyone be able to hear you and
the reverse too... You must be able to hear everyone else in your
vicinity... That is hard to do with a horizontally p[olarized antenna
at those frequencies.
As for telling people they can=99t do that... That=99s not
my job but I sure don=99t mind telling them of some of the
problems they probably will have with a specific set up.
Noel
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
BobsV35B@aol.com
Sent: January 27, 2011 9:53 PM
Subject: Re: AeroElectric-List: Comm Antenna & SWR: More Information
Good Evening Noel,
I don't think anyone will disagree with what you say, but the point is
that a lot of good competent and concientuous folks have found that the
crummy location does work acceptably. You and I can agree it is not
good, but if it works for others, are we supposed to tell them it is not
allowed?
As 'Lectric Bob has said, chances are a wet noodle will work most of the
time.
While I know folks who are still using the stick in the tail cone, I
know more who have given up on it and gone to a more conventional
antenna.
As Always.It All Depends! <G>
Do Not Archive
Happy Skies,
Old Bob
In a message dated 1/27/2011 6:27:12 P.M. Central Standard Time,
noelloveys@yahoo.ca writes:
The important thing with com antennas is good omnidirectional ( all
directions ) coverage. A horizontally polarized antenna in a tailcone,
outside of having too small a ground plane, will have a dead area in
front of the plane and another one behind it. I can=99t see how
this can be considered good for airplanes heading into or away from a
control zone.
Many large aircraft actually have antennae above and below the fuselage
to allow communication with other aircraft as well as ground.
Noel
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
BobsV35B@aol.com
Sent: January 27, 2011 12:14 AM
Subject: Re: AeroElectric-List: Comm Antenna & SWR: More Information
Good Evening All,
This discussion about ground planes has forced me to send another one of
my way off subject messages! <G>
Some of you may be aware of the speed modifications that Mike Smith was
selling for Bonanzas a few years ago. While Bonanzas are certainly NOT
homebuilt aircraft, Mike's work was very much in the realm of what
homebuilders do. He guaranteed a speed increase of at least ten knots on
any Bonanza that used his full set of speed kits.
In his quest for speed, he took EVERYTHING off the top of the fuselage
and as much off the belly as humanly possible. He even installed a VHF
communication antenna in a fiberglass tail cone. It was horizontally
oriented rather than vertical and the ground plane was no more than six
inches by eight inches.
Did it work? Some folks found that it was a perfectly usable solution
and are still using it regularly. Others have either eliminated it or
added another stock antenna on the belly.
Personally, I have never flown a Bonanza that was equipped with the tail
cone antenna, but I have personally spoken to a pilot who has flown his
that way in heavy IFR operations for over twenty years. Just how good do
antennas really NEED to be?
Mike also was a big exponent of using a set of VHF Navigation blades
mounted as far back on the Bonanza fuselage as possible. The
manufacturer of the antennas said they were way too close to the tail
feathers to work properly. I have personally mounted several blade
antennas in that position and they have all worked very well.
Just some data for further thought.
Happy Skies,
Old Bob
Downers Grove, IL
LL22
Stearman 3977A
Do Not Archive
In a message dated 1/26/2011 9:19:32 P.M. Central Standard Time,
nuckolls.bob@aeroelectric.com writes:
Additional detail about my ground plane installation.
My ground plane isn't symmetrical (and, contrary to my earlier post, it
is actually 24" x 34", not 24" x 36" -- I had cut 2" off the length so
that it would fit in the space I had available). I also didn't mention
that I cut two slots in the ground plane so that it would fit over a
couple of supports for the floors in my baggage compartment. These
slots are ~3" x 1/2" and are about 10" aft of the antenna base and about
4" either side of the fuselage centerline. Will these slots in the
ground plane degrade the ground plane's performance?
http://www.matronics.com/Navigator?AeroElectric-List
http://forums.matronics.com
http://www.matronics.com/contribution
List
href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.
matronics.com/Navigator?AeroElectric-List
ms.matronics.com/">http://forums.matronics.com
tp://www.matronics.com/contribution">http://www.matronics.com/contributio
n
Message 8
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Subject: | coax antenna cable length |
What I was getting at was not to reroute the wire or coil it up to take care
of excess. Cut it off. I think you agree as I agree the longer coax
appears to have a better swr but in fact it has greater line losses.
Certainly I agree that no one should ever add length to the feed wire to
achieve a mach.
Noel
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: January 27, 2011 10:00 PM
Subject: RE: AeroElectric-List: coax antenna cable length
<nuckolls.bob@aeroelectric.com>
At 06:27 PM 1/27/2011, you wrote:
>That's the first I've heard of anything like this. As Bob has said,
>the longer the feed cable (coax) the closer the match to the radio
>will be to 50 Ohms but you will then also have to contend with line losses.
>
>The question than has to be what to do with the access cable? If
>you coil it up you can be opening a whole new can or
>worms. Re-routing it can also cause problems. Best to decide on
>the best possible routing and install leaving just enough cable for drip
loops.
I did not intended proffer the idea that one
would purposely ADD coax to a feedline for
the purpose of reducing SWR. It is because
longer feedlines ADD losses that the SWR
appears to improve while in fact, the
effects of real SWR are being masked by
those losses. It was an observation of
fact, not a recommendation.
Bob . . .
Message 9
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Subject: | Re: ELT antenna performance |
After my first couple hundred aircraft searches up in
Alaska, and only two crashes myself, I've come to the strong
opinion a terrible ELT antenna inside the structure works
infinitely better than any exterior one removed in the
crash. Suggest builders consider a tailcone location for
fiberglass aircraft or somewhere, anywhere, in the cockpit
for metal ones.
It appears the 406 MHz ELTs will require one to use the
manufacturer's antenna to be legal so we probably can no
longer roll our own ELT dipoles or whips. But using a
simple ground plane in a glass tail or any handy metal
surface in the cockpit will do the job. Don't worry too
much about "seeing the sky". Orientation doesn't matter.
If you really need ELT operation you are unlikely to be
upright anyway.
Tom Kuffel
Message 10
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Subject: | Comm Antenna & SWR: More Information |
???? The VOR antenna whiskers are horizontally polarized
dipole with major lobes fore and aft with nulls off to the
sides. Further, dipole antennas require no ground plane.
VOR is not a transmitting antenna. The VOR transmitters are on the ground
and are also horizontally polarized. The receive lobes of the antennae are
part insignificant as aircraft do not approach the VOR sideways.
No such "null" exists fore and aft.
Experience as well as radio theory tells me is sure does exist on the tip of
horizontally polarized signals.
>Many large aircraft actually have antennae above and below the
>fuselage to allow communication with other aircraft as well as ground.
???? Antenna placement is largely a matter of separation
between the antennas for similar systems . . . and judicious
use of real estate. Once an airplane is airborne, relative
differences between top and bottom mounted antennas is
insignificant.
Then why do large Aircraft often have two com antennae? One on top,
Sometimes in the vert stab and one below. The reason for the two antennae
is because of shading of the signal to stations directly below the plane
(upper antenna) or shading of a other aircraft more or less directly above
the plane (Belly position antenna)
For some reason Bob I think we are off the same page again.
Noel
Message 11
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Subject: | Comm Antenna & SWR: More Information |
True the ELT antenna should be seen first and foremost by satellites. But
they must also be able to be seen by search aircraft. The new 406 ELTs do a
much better job of being seen by the satellites (Assuming an open area) and
are also more linear than the old 121.5 units thus making them superior for
the task they perform.
>From here I'm going to go on a bit of a tangent.
The new units are programmed to a specific aircraft. The first problem I
see with this is as soon as a signal is received it can be identified as a
single seat something or the other and not all the resources that could be
put in the field will be used. This is selective response and I for one am
against it.
The next item is because each unit is coded to a particular aircraft it
becomes impossible to lend a unit out while one is in for mundane battery
changing. The AMO I worked for often loaned out ELTs because we really
didn't want to see our customers going off into the wilds nude of the
security an ELT can offer. Commercial aircraft are allowed to operate
without an ELT on board forup to 90 days if the unit is in for maintenance.
Several years ago a party of executives crashed about two miles off the end
of one runway at Goose Bay, Labrador in a snow storm. Their ELT had legally
been removed for scheduled maintenance. The passengers did survive the
crash but froze to death. The wreckage was found several months later when
the snow started to melt.
Finally pilots will often monitor 121.5 enroute. This is a nice security
feature in that a down plane can be found even before a search starts.
My preference is a unit which has both frequencies activated and then using
something like the SPOT system as a backup.
Noel
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: January 27, 2011 11:44 PM
Subject: RE: AeroElectric-List: Comm Antenna & SWR: More Information
ELT's are designed to be seen by satellites. Until
the present 405 Mhz with superior locating capability
came along the
I recall hearing a report about 20 years ago that
for EVERY downed airplane located, ELT was a factor
in a very small percentage of those finds . . . about
6% if I recall correctly. Don't know how much better
the stats are now.
In any case installation of ELT antennas is a
"gee I hope this works when and if they
need it" kind of design task. There is no
place on an airplane that is immune from
crash-induced damage. Equipment placement
is based on the study of crash history.
So when on short final to the rocks, one
should endeavor to crash like most other
folks crashed such that their ELT survived.
Shadowing to the extent that some ground
based facility two miles away doesn't hear
it is the very least of concerns.
One more antenna that is not done right and still works fine. The ELT on
many RV's is horizontal and inside the tail cone fairing. Or in the baggage
area with only the top few inches not close to metal. Neither of these
install techniques have good ground planes nor the correct orientation but
they work with both the 121.5 and the 406 versions of ELT
On what basis were these installations said
to "work fine". Have these installations
been reviewed by the ELT manufacturer? I
can't imagine anyone signing off on an
installation that didn't provide the customary
ground plane combined with a good view of the
sky assuming the wreckage was still upright.
Emacs!
Here's the ELT antennas on a Beechjet. Both
are installed under a fiberglas fairing just
forward of the vertical fin.
Emacs!
The 121.5 antenna had to be folded over under the
fiberglas to clear some ductwork. This distortion
caused the ELT to go into "hi SWR shutdown".
Emacs!
I made the suggestion that we build a top-hat
loaded vertical that could be tuned for that
location and wouldn't have to be bent over under
the fairing.
Certification time-line issues shot that idea down.
They just widened the window on the SWR monitor
to prevent the shutdown. But even with this band-aid
approach, close attention was paid to adequate
radiation performance and patterns.
If one hopes to achieve better than 6% probability
of the ELT being useful, one should be wary
of pronouncements of "works fine" when deviating
from TSO approved manufacturer's recommendations.
Horizontal polarization isn't a big thing but not
having a ground plane and clearest possible view
of the sky is problematic.
Bob . . .
From: owner-aeroelectric-list-server@matronics.com [
mailto:owner-aeroelectric-list-server@matronics.com
<mailto:owner-aeroelectric-list-server@matronics.com> ] On Behalf Of
BobsV35B@aol.com
Sent: Wednesday, January 26, 2011 7:44 PM
Subject: Re: AeroElectric-List: Comm Antenna & SWR: More Information
Good Evening All,
This discussion about ground planes has forced me to send another one of my
way off subject messages! <G>
Some of you may be aware of the speed modifications that Mike Smith was
selling for Bonanzas a few years ago. While Bonanzas are certainly NOT
homebuilt aircraft, Mike's work was very much in the realm of what
homebuilders do. He guaranteed a speed increase of at least ten knots on any
Bonanza that used his full set of speed kits.
In his quest for speed, he took EVERYTHING off the top of the fuselage and
as much off the belly as humanly possible. He even installed a VHF
communication antenna in a fiberglass tail cone. It was horizontally
oriented rather than vertical and the ground plane was no more than six
inches by eight inches.
Did it work? Some folks found that it was a perfectly usable solution and
are still using it regularly. Others have either eliminated it or added
another stock antenna on the belly.
Personally, I have never flown a Bonanza that was equipped with the tail
cone antenna, but I have personally spoken to a pilot who has flown his that
way in heavy IFR operations for over twenty years. Just how good do antennas
really NEED to be?
Mike also was a big exponent of using a set of VHF Navigation blades mounted
as far back on the Bonanza fuselage as possible. The manufacturer of the
antennas said they were way too close to the tail feathers to work properly.
I have personally mounted several blade antennas in that position and they
have all worked very well.
Just some data for further thought.
Happy Skies,
Old Bob
Downers Grove, IL
LL22
Stearman 3977A
Do Not Archive
In a message dated 1/26/2011 9:19:32 P.M. Central Standard Time,
nuckolls.bob@aeroelectric.com writes:
Additional detail about my ground plane installation.
My ground plane isn't symmetrical (and, contrary to my earlier post, it is
actually 24" x 34", not 24" x 36" -- I had cut 2" off the length so that it
would fit in the space I had available). I also didn't mention that I cut
two slots in the ground plane so that it would fit over a couple of supports
for the floors in my baggage compartment. These slots are ~3" x 1/2" and
are about 10" aft of the antenna base and about 4" either side of the
fuselage centerline. Will these slots in the ground plane degrade the
ground plane's performance?
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Bob . . .
Message 12
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Subject: | Comm Antenna & SWR: More Information |
At 03:36 PM 1/28/2011, you wrote:
>
>
> b:???? The VOR antenna whiskers are horizontally polarized
> dipole with major lobes fore and aft with nulls off to the
> sides. Further, dipole antennas require no ground plane.
>
>VOR is not a transmitting antenna. The VOR transmitters are on the ground
>and are also horizontally polarized. The receive lobes of the antennae are
>part insignificant as aircraft do not approach the VOR sideways.
When you said:
"The important thing with com antennas is good omnidirectional ( all
directions ) coverage. A horizontally polarized antenna in a
tailcone, outside of having too small a ground plane, will have a
dead area in front of the plane and another one behind it. I can't
see how this can be considered good for airplanes heading into or
away from a control zone."
I didn't realize you were talking and an HF Comm trailing
wire. As soon as you mentioned horizontally polarized
antenna on the tailcone I thought you WERE talking about
a VOR antenna which IS commonly mounted on the tail and
IS horizontally polarized.
A further confusion point was your mention of a control
zone (always short range communications). I'm unaware of
any control zone services offered on any frequency where
an HF trailing wire would be the antenna of choice. The
most popular HF antenna for small airplanes produced at
Cessna was a wire that ran from the top of cabin to the
tip of the vertical fin and then out to one wing-tip.
Radiation pattern looked like a dying flower with badly
chewed petals. Here's a drawing from a kit I wrote for
a U17 HF installation way back when . . .
http://tinyurl.com/4eokmk8
> b:No such "null" exists fore and aft.
>
>Experience as well as radio theory tells me is sure does exist on the tip of
>horizontally polarized signals.
Agreed, we weren't talking about the same antenna . . .
>Then why do large Aircraft often have two com antennae? One on top,
>Sometimes in the vert stab and one below. The reason for the two antennae
>is because of shading of the signal to stations directly below the plane
>(upper antenna) or shading of a other aircraft more or less directly above
>the plane (Belly position antenna)
Because they have two radios and it's industry
practice to have one antenna for each radio and
to locate them as far as practical from each
other. "Shading" of a potential station right
over or below any given antenna is an exceedingly
rare event that lasts only seconds at the speeds
these airplanes fly.
Just got off the phone with a high-school buddy who's
been an ATP since about 1965. With 18K hours in
everything from DC-3's with dual ADF to Boeings
with cockpits full of glass, he tells me he's
never seen any difference in performance between
top and belly mounted antennas. He's a ham too
and speaks/understands radioeze . . .
>For some reason Bob I think we are off the same page again.
Correct. HF antennas on light aircraft are
EXCEEDINGLY inefficient, e-field antennas
and unless 'bent', they'll have strong nulls
off the ends irrespective of polarization. I thought
we were talking about aviation antennas likely to
be installed on airplanes flown by members of this List.
Bob . . .
Message 13
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Subject: | ELT antenna performance |
Thanks Dick... I was unaware there even was a millihertz. In English class
many snows ago we were told when it came to abbreviations, the rule was only
capitalize measurements which were peoples' names. Under that rule mHz
would be correct for either millihertz or megahertz or even gHz...gigahertz.
Noel
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Richard
Tasker
Sent: January 28, 2011 12:45 PM
Subject: Re: AeroElectric-List: ELT antenna performance
Hey Bob, not to pick nits , but you are the example here after all... ;-)
mHz - millihertz
MHz - megahertz
Dick Tasker
Robert L. Nuckolls, III wrote:
<snip>
When I first got into electronics as a profession,
I was working for a two-way radio company in Wichita.
We serviced a few systems in the 72 mHz band but
most were in the vicinity of 150 mHz and a few
were up about 450.
This was all vacuum tube stuff. The 450 mHz
equipment was at the upper fringe of what
was practical. It was harder to develop power,
losses in feedlines was higher, keeping
receiver sensitivity to less than 1 microvolt
was more demanding. All-in-all, higher
cost of ownership.
You'd think that customers would shy away from
this equipment. On the contrary. Antennas were
more efficient. Terrestrial noise was a small
influence. Signals behaved much better in the
confines of tall buildings. The cab companies
wouldn't have anything different. The police
wanted it but the FCC decreed that public
services will conduct business in the 150 mHz
band. 150 mHz was subject to much more multi-
path nulls and noise.
121.5 mHz was picked for the first ELTs
because it was a frequency already serviced
by aviation communication services. Same
with 243 albeit military.
Message 14
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Subject: | ELT antenna performance |
Don't feel in the slightest bad Bob... I'm guilty too.
Noel
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: January 28, 2011 1:47 PM
Subject: Re: AeroElectric-List: ELT antenna performance
<nuckolls.bob@aeroelectric.com>
At 11:15 AM 1/28/2011, you wrote:
>Hey Bob, not to pick nits , but you are the example here after all... ;-)
>
>mHz - millihertz
>
>MHz - megahertz
>
>Dick Tasker
You're quite correct. Unfortunately, when trying
to bang out a timely but extensive reply, I don't
have the luxury of coming back to edit it tomorrow
to attempt a 99% clean posting.
When I go back and read my past postings, it's
not unusual to get whacked by spelling/semantics
issues. I'll just have to beg the Lists indulgence.
That doesn't mean I don't want to hear from
folks when I've stubbed my toe. Just be forewarned
that in spite of your most honorable efforts, my
head will probably continue to run out in front of
fingers on the keyboard.
Thanks for the heads-up!
Bob . . .
Message 15
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Subject: | ELT antenna performance |
> Don't feel in the slightest bad Bob... I'm guilty too.
>
> Noel
> >mHz - millihertz
> >
> >MHz - megahertz
> >
> >Dick Tasker
Fortunately=2C I can honstly sya=2C I nver make any tpos. : )
Mik e
Message 16
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|
OK, that's the second time I've heard about this stuff in 24 hours...
so, if you want an entertaining survey of modern materials (including a
demonstration of graphene production) check this out:
http://www.pbs.org/wgbh/nova/tech/making-stuff.html
I expected less from this NOVA series but was entertained and informed
throughout the first 2 shows.
Bill Watson
RV10
On 1/26/2011 11:29 PM, Speedy11@aol.com wrote:
> Bob,
> I'm sure you're familiar with this, but this blog is the first I've
> heard of it.
> More info is on the CAFE Blog at http://blog.cafefoundation.org/?p=2439.
> Stan Sutterfield
>
>
> Thin, Light, Strong, and Energy Dense
>
> by Dean Sigler on 01/07/2011
>
> 2010s Nobel Prize in Physics
> <http://nobelprize.org/nobel_prizes/physics/laureates/2010/press.html>went
> to Andre Geim and Konstantin Novoselov, who extracted graphene from a
> piece of graphite when they stuck a piece of adhesive tape to it and
> peeled away a single atom-thick layer of the thinnest, strongest
> material in the world.
>
> The Nobel Prize web site explains other remarkable properties of this
> new material. As a conductor of electricity it performs as well as
> copper. As a conductor of heat it outperforms all other known
> materials. It is almost completely transparent, yet so dense that not
> even helium, the smallest gas atom, can pass through it. Carbon, the
> basis of all known life on earth, has surprised us once again.
>
> When mixed into plastics, graphene can turn them into conductors of
> electricity while making them more heat resistant and mechanically robust.
>
> /Over 28,000 square feet per gram for a single layer of the material
> or about the size of a football field/
>
> *
>
> *
Message 17
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Bob,
I have become aware that BNC connectors have at least two flavors: 50
and 75 ohms. Not being sure which impedance my connectors have I
measured the SWR for my com and vor antennas. The com was 1.2 to 3.1
with the 3.1 at 118.0 mhz. Above 119 mhz it was below 2. The vor was
between 1.1 and 1.9 over the full frequency range. According to your
book, they should be OK. But what about GPS, DME and transponder
antennas. Is the impedance of the connector important? In other words
should I go to the trouble of making sure all connectors are 50 ohms?
John Herminghaus
Message 18
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Subject: | Re: BNC connectors |
At 12:52 AM 1/29/2011, you wrote:
>Bob,
>
>I have become aware that BNC connectors have at least two flavors:
>50 and 75 ohms. Not being sure which impedance my connectors have I
>measured the SWR for my com and vor antennas. The com was 1.2 to
>3.1 with the 3.1 at 118.0 mhz. Above 119 mhz it was below 2. The
>vor was between 1.1 and 1.9 over the full frequency
>range. According to your book, they should be OK. But what about
>GPS, DME and transponder antennas. Is the impedance of the
>connector important? In other words should I go to the trouble of
>making sure all connectors are 50 ohms?
The connectors are "50 ohm" because they
have dimensions conducive to installation
on a piece of 50 ohm coax. If your connector
fits on the coax, then it's the right
connector.
Bob . . .
Message 19
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Subject: | OT-potting with RTV silicone |
do not archive
Is RTV silicone acceptable for potting electronics? I know Bob
recommends E6000 or equivalent but I have several 1/2 tubes of RTV I'd
like to use up. The item I'm potting is the "ballast for some cheap
fluorescent fixtures that buzz. I'm hoping I can quiet them down.
Thanks for all replies.
--
Raymond Julian
Kettle River, MN
Message 20
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Subject: | Re: BNC connectors |
Thanks a lot. That's what I suspected and hoped to hear. You saved me
a lot ot trouble
John
On 29.01.2011 06:15, Robert L. Nuckolls, III wrote:
> At 12:52 AM 1/29/2011, you wrote:
>> Bob,
>>
>> I have become aware that BNC connectors have at least two flavors: 50
>> and 75 ohms. Not being sure which impedance my connectors have I
>> measured the SWR for my com and vor antennas. The com was 1.2 to 3.1
>> with the 3.1 at 118.0 mhz. Above 119 mhz it was below 2. The vor
>> was between 1.1 and 1.9 over the full frequency range. According to
>> your book, they should be OK. But what about GPS, DME and
>> transponder antennas. Is the impedance of the connector important?
>> In other words should I go to the trouble of making sure all
>> connectors are 50 ohms?
>
> The connectors are "50 ohm" because they
> have dimensions conducive to installation
> on a piece of 50 ohm coax. If your connector
> fits on the coax, then it's the right
> connector.
>
> Bob . . .
>
> *
>
>
> *
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