Today's Message Index:
----------------------
1. 06:56 AM - Re: Re: copper foil groundplane ()
2. 07:36 AM - noise suppression (Jean Lowenhardt)
3. 08:43 AM - The Miracle Whip series antennas (Robert L. Nuckolls, III)
4. 08:49 AM - Re: noise suppression (Robert L. Nuckolls, III)
5. 09:03 AM - Noise suppression (Jean Lowenhardt)
6. 09:03 AM - 1/2 Wave Ring Antenna (user9253)
7. 09:45 AM - Re: The Miracle Whip series antennas (Robert L. Nuckolls, III)
8. 10:05 AM - Re: 1/2 Wave Ring Antenna (Robert L. Nuckolls, III)
9. 10:24 AM - Battery maintenance philosophies to meet design goals (Robert L. Nuckolls, III)
10. 10:56 AM - Re: 1/2 Wave Ring Antenna (Fisher Paul A.)
11. 03:09 PM - Accurate Altitude and Airspeed ()
12. 07:51 PM - Re: 1/2 Wave Ring Antenna (Tim Shankland)
Message 1
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Subject: | Re: copper foil groundplane |
Thanks,
Actually I'd pay $90 just for the packaging. I've now seen some of the
homemade jobs and while I've not clue on how to build antennas, I have
less of clue how any of these folks got their inventions in the
airplane. Copper strips, pipe, soldering, 3 ft tall, etc. etc. I have a
Lancair not a Suburban.
$90.00 is a no brainer. Thanks for the reference.
Do Not Archive.
Glenn
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
checkn6
Sent: Wednesday, April 14, 2010 5:32 PM
Subject: AeroElectric-List: Re: copper foil groundplane
Inside the magic box
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=294242#294242
Attachments:
http://forums.matronics.com//files/themiracleinside_131.jpg
Message 2
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Subject: | noise suppression |
Installation instructions for a 12volt, 8amp wind driven generator
specify shielding on the output lead with no other noise suppression
requirements. Electrical system schematics for later models of the
aircraft, having engine driven generators, specify 0.01 microfarad
capacitors on the armature and stator leads. On the wind driven
generator, the regulator is housed within the generator unit and the
only external wires are the output and ground leads.
Should a capacitor be installed on the wind driven generator output lead
at the generator terminal for noise suppression in addition to the
original shielding requirement? If a capacitor is recommended, it must
be weather resistant. Therefore, please advise on part number and source
information if a capacitor is recommened.
Thanks for any input to my question and request.
Message 3
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Subject: | The Miracle Whip series antennas |
Robert Victor, President (VA2ERY)
Miracle Antenna
Montreal, Canada
Good morning sir,
By way of introduction, I'm an electronics engineer
retired from Hawker-Beechcraft after 46 years in the
electronics trades with an emphasis on aircraft. I
have a hobby business that supports the owner built
and maintained aircraft industry. My website is at
http://aeroelectric.com
I've been moderating electrical/electronics discussion
forums for amateur builders on Matronics for over 10
years. Our current membership is about 1800.
I also publish a document intended to assist my readers
in the crafting of failure-tolerant electrical systems;
https://matronics.com/aeroelectric/Catalog/pub/pub.html#P-Book
I was asked about VHF Com and VOR antennas suitable for
installation inside a composite aircraft. One reader
pointed out your offerings for a end-fed, half-wave
antenna specific to that task. I've reviewed this
and ancillary products on your website and in various
postings to the Internet.
Without a doubt, the end-fed, half-wave configuration
offers an opportunity but it also has some special
needs for impedance matching. Have you performed
antenna range testing on the VHF aircraft antennas?
Have you published any performance data for this
device over the frequency range of interest? Have
there been any studies of radiation patterns
associated with recommended installation methods?
I would like to be capable of advising my readers
from a position of knowledge and understanding about
your products. Anything you can offer to assuage my
ignorance would be appreciated. I'd like to add
this technology to the discussion on antennas when
the book is updated.
Finally, would you be willing to consign an exemplar
antenna to me for testing in local facilities? I'd
be pleased to return it to you along with any data
that is developed from the testing efforts.
Kindest regards,
Bob Nuckolls (K0DYH)
AeroElectric Connection
P.O. Box 130
Medicine Lodge, KS 67104-0130
Land line: (620) 886-3403
Mobile: (316) 209-7528
Message 4
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Subject: | Re: noise suppression |
At 09:31 AM 4/15/2010, you wrote:
>Installation instructions for a 12volt, 8amp wind driven generator
>specify shielding on the output lead with no other noise suppression
>requirements.
Shielding of such leads is a pointless effort. Any
noise produced by the generator will be CONDUCTED along
its power feed wire, not electro-statically coupled to
other potential victims.
>Electrical system schematics for later models of the aircraft,
>having engine driven generators, specify 0.01 microfarad capacitors
>on the armature and stator leads. On the wind driven generator, the
>regulator is housed within the generator unit and the only external
>wires are the output and ground leads.
>Should a capacitor be installed on the wind driven generator output
>lead at the generator terminal for noise suppression in addition to
>the original shielding requirement? If a capacitor is recommended,
>it must be weather resistant. Therefore, please advise on part
>number and source information if a capacitor is recommened.
>Thanks for any input to my question and request.
Try it and see. The responsible supplier will
conduct noise tests in a lab and supply
necessary noise suppression technology as
part of the product. If the as-delivered
generator didn't come with filters (and they're
not called out on installation instructions) then
an assumption follows that no filtering is
needed.
Some rudimentary flight-testing after installation
will go to proving/disproving that assumption.
Come back to this discussion with your findings
if indeed the critter turns out to be noisy.
Bob . . .
Message 5
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Subject: | Noise suppression |
Installation instructions for a 12volt, 8amp wind driven generator
specify shielding on the output lead with no other noise suppression
requirements. Electrical system schematics for later models of the
aircraft, having engine driven generators, specify 0.01microfarad
capacitors on the armature and stator leads. On the wind driven
generator, the regulator is housed within the generator unit and the
only external wires are the output and ground leads.
Should a capacitor be installed on the wind driven generator output lead
at the generator terminal for noise suppression in addition to the
original shielding requirement?
If a capacitor is recommened, it must be weather resistant. Therfore,
please advise on part number and source information if a capacitor is
recommened.
Thanks for any input to my question and request.
Hugh Loewenhardt
aeronca2@99main.com
restoring Fairchild 24C8C, N15076
Stonington, Ct
Message 6
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Subject: | 1/2 Wave Ring Antenna |
Has anyone ever experimented with a 1/2 Wave Ring Antenna? It is described here: http://www.slvrc.org/902band/902antennas.htm
It could be mounted on a metal turtle deck and covered with non-conductive fabric
or fiberglass for streamlining. Its low profile would have less drag than
a quarter wave antenna at high speeds.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=294317#294317
Message 7
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Subject: | Re: The Miracle Whip series antennas |
At 10:41 AM 4/15/2010, you wrote:
><nuckolls.bob@aeroelectric.com>
>
>Robert Victor, President (VA2ERY)
>Miracle Antenna
>Montreal, Canada
>
<snip>
>I would like to be capable of advising my readers
>from a position of knowledge and understanding about
>your products. Anything you can offer to assuage my
>ignorance would be appreciated. I'd like to add
>this technology to the discussion on antennas when
>the book is updated.
I received a pleasant phone call from Mr. Victor.
He was unwilling to share any test data . . . backed
by the notion that such sharing left his venture
open to competition by folks who might exploit
his IR&D efforts.
This is a real risk for simple, easily fabricated
products. He did offer the idea that the Miracle
Whip was not an end-fed but center-fed half-wave
dipole. He explained that the dipole is formed by
exposing 1/4-wave of center conductor of the far end of
the feed line. One then moves 1/4-wave toward the
transmitter and inserts a high efficiency, common-
mode choke. That's what the 7-turns of coax through
the torroid core is all about.
This inserts a discontinuity in the shield. The
effect is that the INSIDE of the coax is a feed-line
out to the center and the outside of the coax shield
beyond the choke becomes one-half of the dipole.
This means that the "wire" we see wrapped through
the core in . . .
>http://forums.matronics.com//files/themiracleinside_131.jpg
is actually an unbroken length of coaxial cable. The
magic comes from core selection for high permeability
while offering the lowest possible losses at VHF
frequencies. No doubt a high quality ferrite material.
When I get the RF bench running fully and have the
time, I'll fiddle with the concept a bit and see what
I can confirm with the test equipment.
Bob . . .
Message 8
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Subject: | Re: 1/2 Wave Ring Antenna |
At 11:02 AM 4/15/2010, you wrote:
>
>Has anyone ever experimented with a 1/2 Wave Ring Antenna? It is
>described here:
>http://www.slvrc.org/902band/902antennas.htm
>It could be mounted on a metal turtle deck and covered with
>non-conductive fabric or fiberglass for streamlining. Its low
>profile would have less drag than a quarter wave antenna at high speeds.
I'm planning on building a cousin to this antenna for
my 2M storm watch transceiver. See:
http://www.antennex.com/preview/2mddrr.htm
This is the 1/4 wave version. Given that both the
1/4 and 1/2 wave antennas are vertically polarized
says that all the magic happens in that short vertical
mast that goes to ground. This becomes the same thing
as a short vertical with a strong top-hat loading
scheme. So whether the "top hat" is 1/4 or 1/2 wave
in circumference probably offers little difference in
performance.
Given the lengthening effect of so severe a
"rake angle" on this antenna, the physical length
of a 1/4-wave will be shorter than the classic
22" whip. 22" bent around in a circle would give
us less than 6" diameter and about 2" tall for VHF
Comm frequencies. This cross section, even if well
faired, could offer much more drag than the simple
whip stuck out in the breeze.
However, this form of antenna might perform well
inside a composite fuselage.
The biggest problem with heavily loaded antennas
is loss of band-width. They tend to be sharply
tuned at the design frequency with efficiency
falling off rapidly either side. The extreme example
of this phenomenon is demonstrated by small diameter
loop antennas for lower ham frequencies. They
have to be fitted with motor driven capacitors to
allow remote tuning to the frequency of interest.
Circulating currents tend to be very high, voltage
across the tuning capacitor is quite high. To keep
the losses low at such high currents, the antenna
is made from 3" DWV copper!
The DDRR antenna needs a high conductivity ground
plane that's at least 2x the antenna diameter. So
a 6" DDRR might be built on a 12" square piece of
copper clad that could become a "shelf" of sorts
in the tailcone. Further, that same sheet might
also be a good mounting location for the transponder
antenna. Food for thought.
Bob . . .
Message 9
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Subject: | Battery maintenance philosophies to meet design goals |
>If I'm going to ask an opinion of someone on the list, then I
>certainly must provide accurate information - or expect no answer.
>I'm using Odessey and happy with it so far. I have no intention of
>changing at this time. But, I was interested in the answer to the
>proposed question. I am always interested in a less expensive, but
>adequate replacements for equipment.
>Perhaps changing a battery each year is a waste of money. And I've
>been called an old FUDdy before, but it is certainly not out of
>fear, uncertainty, or doubt.
>I change a battery a year because:
>
>1. It is recommended by an expert in the field - Electric Bob
I did NOT recommend it. I suggested it as
an option to be considered and adopted pending
YOUR assessment of design goals, ways in which
you choose to spend your $time$ and tools you
plan to acquire to execute a considered preventative
battery maintenance program.
>2. My ignorance dictates that I listen to the experts
I'd rather you use my offerings more as teacher
than as expert. If you don't understand the
fundamentals upon which best decisions are made,
then you are at risk for falling victim to anyone
who wraps themselves in the mantle of "expert"
>3. It establishes a reasonable means to avoid failure
Let us assume you're going to buy a Hawker-Enersys
super battery of some kind and you plan to run
it until no longer suitable for flight? What
criteria and tools to YOU plan to use to monitor
that condition? Whether you swap every year
or run it until no longer suited for flight,
the means by which you avoid 'failure' lies
entirely in your lap, not the suggestions
of anyone else on the list.
>4. It is not overly expensive
If it's not the LEAST expensive, then
don't do it.
>5. The batteries are used in other equipment and not wasted.
Can you quantify "wasted"? Let's say you install
a shiny new 18 a.h. battery and your endurance
analysis shows that you need 12 a.h. at a 3 hour
rate to meet your battery only endurance goals.
When it's time to replace that battery, it will
still be cranking the engine just fine. When you
swap out an el-chesso battery at one year, it
too will still be cranking the engine just fine.
Both scenarios will remove a battery from your
AIRPLANE that may still have some degree of
usefulness NOT in an airplane. Which scenario
offers the most/least "waste"?
>6. The oldest battery at any moment in my RV is 2 years.
So is the main battery (which I presume was new
last year) going to replace the 2-year old
aux battery soon?
>7. I don't have to bother with capacity checks
I prefer to express it differently. You battery
preventative maintenance program is optimized
to expend the minimum $time$ to insure compliance
with your design goals.
>I also change my tires before they fail. Anyone who wants the old
>ones just let me know.
Boy . . . do I remember those days! There was a
Texaco station owner who took pity on me and
gave me a call when he had extra-ordinarily
meaty take-off tires I could buy.
>I change my hoses before they fail. Anybody want the old ones?
Naw . . . ran too many of those until they blew . . .
>I don't like being stranded in remote locations because I tried to
>stretch the life of consumables such as batteries.
In this case, the "stretching" thing doesn't have
much tension in it. Unless you're installing big lead
pigs with the idea that your battery-only endurance
requirements can be met with only 25% of as-new capacity,
then maybe you would stretch it.
Now, Z13/8 does offer an opportunity to take battery
capacity completely out of the FMEA study for
endurance. Cranking the engine is a pretty good test
of a battery to be MINIMALLY functional where a second,
engine driven power source replaces the battery as
the stand-by power source.
>Just call me an old fuddy.
Old fuddies are those among us who allow our airplanes
to get WAAaaayyyy ahead of us. For many of our brethren
in the TC aircraft world, the airplane is probably too
far "out in front" . . . and they don't have to be grey-
haired to suffer this condition! This assertion is supported
by the many dark-n-stormy-night stories we've read and analyzed
on the List over the years.
I'll respectfully suggest that if folks are participating
here just to ask for and run with an answer that appears
delivered with some expertise, you may be better off
sticking with a C-172 style electrical system. The value
to be gathered here is not the advise of experts or
a mass of anecdotal experience. It's my fondest wish that
folks flying systems crafted from ideas offered here
UNDERSTAND what's going on and are in command and control
of their electro-whizzy destiny.
>Ira, thanks for researching the correct info on the battery and
>providing your opinion. I appreciate it.
>It appears from your comment that you prefer Panasonic
>batteries. Which model do you use? Why do you believe that battery
>is better than an Odessey?
Panasonic makes no product on a par with Hawker-
Enersys. My studies of aircraft battery products
have convinced me and my colleagues that H-E
products are the cream of the battery crop. In no
way should that statement be interpreted to mean
that Panasonic products do not offer good value.
Only the builder/operator of an OBAM aircraft
can make the determination of value based on their
own cost-of-ownership studies.
> Does it have more AH capacity? Does it have faston tabs or screw
> on terminals?
There's a collection of battery manufacturer's
data including Panasonic and H-E on my website
at:
http://aeroelectric.com/Mfgr_Data.html
>Your suggestion of replacing a battery every two years seems like a
>reasonable thing to do - especially if one charges the batteries to
>capacity periodically.
How do we quantify "reasonable" . . . how many
watt seconds of energy are expected to be contained
in an 18 ah battery after 2 years of "reasonable"
use and maintenance?
Please don't think I'm picking on you my friend.
I think it's important that words be crafted to
illustrate well considered recipes for success.
It's important that meaning/understanding is not
sacrificed to misinterpretation.
Bob . . .
Message 10
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Subject: | 1/2 Wave Ring Antenna |
There has been some discussion about a ring antenna here: http://www.vansairforce.com/community/showthread.php?t=52676
The discussion was specifically about APRS which uses 144.39MHz in the ham bands,
but it's close enough to aviation frequencies that it might give you some ideas.
The biggest issue on this thread is where do you mount such an antenna
in an all metal airframe. Obviously, the problem becomes much simpler if you
eliminate that!
Paul A. Fisher
Q-200, N17PF - copper foil dipole embedded in the vertical tail
RV-7A, N18PF - 1/4 wave sticking out in the wind!
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of user9253
Sent: Thursday, April 15, 2010 11:02
Subject: AeroElectric-List: 1/2 Wave Ring Antenna
Has anyone ever experimented with a 1/2 Wave Ring Antenna? It is described here: http://www.slvrc.org/902band/902antennas.htm
It could be mounted on a metal turtle deck and covered with non-conductive fabric
or fiberglass for streamlining. Its low profile would have less drag than
a quarter wave antenna at high speeds.
Joe
--------
Joe Gores
Message 11
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Subject: | Accurate Altitude and Airspeed |
4/15/2010
Hello Mike, You wrote: "Not sure why this (altitude variation with airspeed)
would be, or more importantly, how to fix it."
Hello Bernie, You wrote: "There didn't seem to be any theory behind it."
This is not a very rare or mysterious phenomena. Inaccurate airspeed
indications can be caused by inaccurate dynamic and static air pressure
forces. Inaccurate altitude indications can be caused by inaccurate static
pressure forces.
AIRSPEED. Let's talk about inaccurate airspeed measurements first. An
airspeed indicator is a balancing mechanism. It balances the difference
between a force created by dynamic air pressure and a force created by
static air pressure. The force from the dynamic air pressure is the result
of the forward movement of the airplane. The faster the airplane moves the
greater the force exerted.
In order to get an accurate measure of that dynamic force one needs to
accurately sense the free stream dynamic air pressure and send it to the
airspeed indicator via leak and kink free tubing. That means sensing the air
movement in the actual direction that the airplane is moving and having that
air movement not affected by some local air flow direction change caused by
the airframe itself. This is why you sometimes see flight test airplanes
with a long boom sticking out forward with a small vane mechanism on the
front of it. This boom and vane mechanism, along with connecting tubing, is
a pitot tube system intended to accurately measure the force from the free
stream dynamic air pressure without any inaccuracies introduced by local
airframe air flow. See Note One below.
So much for the dynamic force side of the airspeed indicator balancing act,
what about the static force side? An accurate static force is provided by a
static port ideally located somewhere on the airframe such that it is
measuring the true static air pressure. But finding that ideal location and
making the perfect static port that does not introduce static air pressure
errors is not always so quick and easy. And what do we do if we discover
that the static port that we have installed is not producing accurate static
air pressure? See Note Two below.
ALTITUDE. An altimeter is also a balancing mechanism. It measures the
difference between the initial altitude setting of the altimeter mechanism
as compared to the static air pressure encountered by that same mechanism
while in flight and displays that difference in some lineal measurement
(usually in feet in our part of the world). If the static pressure provided
to the altimeter via the static port and the connecting tubing is in error
or changes with the airplane's airspeed, when the actual altitude is
constant, then the altimeter's altitude indication will be in error. And
what do we do if we discover that the static port that we have installed is
not producing accurate static air pressure? See Note Two below.
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
Note One: Why don't we use these long boom and vane type pitot tubes on our
experimental amateur built aircraft? Because the boom and vane would take a
terrific beating from people walking into them on the ground and because the
dynamic force errors introduced by the type of pitot tubes that we commonly
use are just not great enough to cause us concern. There is not very much we
can do about adjusting the force coming from dynamic air pressure other than
using a pitot tube located a sufficient distance from a disturbing piece of
airframe (usually the bottom surface of a wing) and avoiding a leak or kink
in the tubing going from the pitot tube to the airspeed indicator.
Note Two: So we have built our airplane, installed our static port(s), and
discovered that we are getting inaccurate airspeed and / or altitude
indications and decide to do something about it. We could just go on
installing new static ports in different locations, but that is a lot of
work and we are not assured of better results. So we should do just what the
big boy aerodynamic types do, we fudge or bandaid as needed to get the air
to give us the results that we want.
Let's say that the airspeed indicator is reading too high -- it says the
airplane is going faster than it really is. (See Note Three). The dynamic
air pressure side of the airspeed indicator is providing too much force in
the desired balancing act. How can we counteract that excess dynamic force?
We increase the static force being fed to the airspeed instrument by the
static port by installing a small wedge just aft of the opening on the
static port (thin edge of the wedge facing forward towards the hole). This
small wedge causes air to pile up and increase the static air pressure going
to the airspeed indicator (and also to the altimeter unless you have
provided separate static ports for the two instruments) and give us the
accurate force balance measurement that we want.
Let's say that the altimeter reading goes down 200 feet when you speed up 60
miles per hour (Mike, you did not say which direction your altitude was
changing with the changes in airspeed). This means that the static port is
feeding greater than static pressure as your airplane flies faster. How can
we reduce that undesired increase in static air pressure? We install a small
wedge in front of the hole in the static port (thin edge of the wedge facing
aft towards the hole) to shield it a bit from dynamic air pressure coming
from the front in order to get a more stable and accurate altitude reading.
How do we get the right size wedge facing the correct direction to get the
airspeed and altitude results that we want? The same way the big boys do:
TRIAL AND ERROR and MORE TRIAL AND ERROR. Because our airplanes are
experimental, amateur built we are permitted to do just that -- experiment.
Note Three: So now we know how to tweak our static port(s) to give us
accurate airspeed and altitude information, but how do we know that the
airspeed and altitude information is inaccurate in the first place and
during our trial and error efforts how do we know when we have achieved the
accuracy that we are seeking? The answer to those two questions is not as
simple as one might first expect. I won't attempt to answer them here
because the answers are too big and complex to answer in this forum. What I
will suggest is that the reader google "accurate airspeed" and "accurate
altitude" and delve into those subjects to the level desired. Here is just
one source you will find:
http://gpsinformation.net/main/altitude.htm
Note Four: This is a personal view point. There are several methods
available for determining accurate true airspeed. Some rather elaborate --
some use GPS. Just google "accurate airspeed using GPS".
One thing that I've never quite understood regarding these methods is the
focus on precisely determining airspeed accuracy indication in the cruising
airspeed range. If I determine that my airspeed indicator shows 150 knots
indicated airspeed and I determine through some elaborate scheme that I am
actually only going 145 knots through the air what do I do with that
information? Being 5 nautical miles short of my destination after a one hour
flight is a trivial naviagation error contribution compared to all the other
error sources (such as heading, wind, and climb airspeed) that I have to
contend with and should overcome anyway by some means of real time enroute
navigation.
I think that if I were going to invest a lot of time and effort in
determining my exact airspeed error I would be inclined to do that
determination in the approach airspeed arena, not the cruising airspeed
arena. And even then I would not be obsessed with absolute airspeed
accuracy, I'd just want to know what number on the indicator gives me the
right kind of safe approach and landing time after time.
================================================
----- Original Message -----
From: <bwilder@tqci.net>
Cc: "mike mccann" <mvmccann@gmail.com>; "Pulsar builders"
<pulsar-builders@caseyk.org>
Sent: Thursday, April 15, 2010 9:18 AM
Subject: Re: Here's an odd question
>I noticed that the back half of the round washer where the static exits on
> the SR22 had the back half of it filed down so there was in effect a
> little shield protecting the static exit hole. ((Sorry about this
> description.)
>
> I asked the people at their booth why they did that. I think I attended
> four air shows before I found someone who was involved with the
> engineering of the system. The answer - - - - "That is what we had to do
> to make the system work right". There didn't seem to be any theory behind
> it. They indicated that they had to fiddle around to get it to behave the
> way they wanted. Maybe they were just trying to get rid of me.
>
> In any event, I did the same with mine and it works fine.
>
> Bernie Wilder
=============================================
>>
>> ----- Original Message -----
>> From: mike mccann
>> To: Pulsar builders
>> Sent: Thursday, April 15, 2010 5:06 AM
>> Subject: Here's an odd question
>>
>>
>> All,
>>
>> Utilizing a GPS, I've found that my altimeter in my Pulsar varies with
>> changes in airspeed (altitude will change 100-200 feet with speed
>> changes of 60 mph).
>>
>> Has anyone ever heard of this. Not sure why this would be, or more
>> importantly, how to fix it.
>>
>> Many thanks,
>>
>> Mike
>>
>> Pulsar 1
>> N116Km
Message 12
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Subject: | Re: 1/2 Wave Ring Antenna |
Boy that brings back memories I had a two meter halo antenna on the back
of my car in the the 1960's, the principle advantage was that it was
horizontally polarized like most of the other hams base station's. By
the way a much younger version of myself is the middle one of the group.
Tim Shankland 601HD flying ( no halo antenna)
Robert L. Nuckolls, III wrote:
> <nuckolls.bob@aeroelectric.com>
>
> At 11:02 AM 4/15/2010, you wrote:
>
>> <fran4sew@banyanol.com>
>>
>> Has anyone ever experimented with a 1/2 Wave Ring Antenna? It is
>> described here:
>
>
>> http://www.slvrc.org/902band/902antennas.htm
>
>
>> It could be mounted on a metal turtle deck and covered with
>> non-conductive fabric or fiberglass for streamlining. Its low
>> profile would have less drag than a quarter wave antenna at high speeds.
>
>
> I'm planning on building a cousin to this antenna for
> my 2M storm watch transceiver. See:
>
> http://www.antennex.com/preview/2mddrr.htm
>
> This is the 1/4 wave version. Given that both the
> 1/4 and 1/2 wave antennas are vertically polarized
> says that all the magic happens in that short vertical
> mast that goes to ground. This becomes the same thing
> as a short vertical with a strong top-hat loading
> scheme. So whether the "top hat" is 1/4 or 1/2 wave
> in circumference probably offers little difference in
> performance.
>
> Given the lengthening effect of so severe a
> "rake angle" on this antenna, the physical length
> of a 1/4-wave will be shorter than the classic
> 22" whip. 22" bent around in a circle would give
> us less than 6" diameter and about 2" tall for VHF
> Comm frequencies. This cross section, even if well
> faired, could offer much more drag than the simple
> whip stuck out in the breeze.
>
> However, this form of antenna might perform well
> inside a composite fuselage.
>
> The biggest problem with heavily loaded antennas
> is loss of band-width. They tend to be sharply
> tuned at the design frequency with efficiency
> falling off rapidly either side. The extreme example
> of this phenomenon is demonstrated by small diameter
> loop antennas for lower ham frequencies. They
> have to be fitted with motor driven capacitors to
> allow remote tuning to the frequency of interest.
> Circulating currents tend to be very high, voltage
> across the tuning capacitor is quite high. To keep
> the losses low at such high currents, the antenna
> is made from 3" DWV copper!
>
> The DDRR antenna needs a high conductivity ground
> plane that's at least 2x the antenna diameter. So
> a 6" DDRR might be built on a 12" square piece of
> copper clad that could become a "shelf" of sorts
> in the tailcone. Further, that same sheet might
> also be a good mounting location for the transponder
> antenna. Food for thought.
>
> Bob . . .
>
>
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