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Some experiments fail

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echristley(at)nc.rr.com
Guest

Posted: Fri Dec 22, 2006 3:32 pm Post subject: Some experiments fail

Some ideas look good, until you try to implement them.  Like using the 

pitot tube for an antennae.  It's worth a shot, right?  There's even 

some documentation of the technique at 

http://contrails.free.fr/instruments_ant_sonex.php



Pictures of my attempt are at

http://ernest.isa-geek.org/Delta/Pictures/PitotAntennae1.jpg

and

http://ernest.isa-geek.org/Delta/Pictures/PitotAntennae2.jpg



I was able to borrow a "MFJ HF/VHF SWR Analyzer, Model MFJ-259B", do a 

sweep from 110 to 140 MHz.  A few readings are:



MHz   SWR   R   X

110   15.4   20   81

115   20.2   2   21

120   14.9   3   1

125   10.8   14   47

130   8.6   403   0 (lowest SWR)

135   14.4   9   72

140   18.6   3   25

I didn't think I could get much below an SWR of 2.5 or so, and was 

willing to accept the resulting poor performance;  but, 8.6 is really 

high.  But then I put the rubber ducky antennae from my handheld scanner 

on the instrument.  Everything in the aviation band was ">25", ie out of 

the instruments range.  It dropped into range at 130MHz and to 1.6 at 149.5.



Considering that the handheld scanner seems to work, how viable would an 

SWR of 10 to 20 work over here on the crowded eastern seaboard for 

mostly day VFR operations?

Ed Anderson

Joined: 10 Jan 2006
Posts: 475

Posted: Fri Dec 22, 2006 5:24 pm Post subject: Some experiments fail

Gee Ernest, being an old Ham radio operator, I would be horrified to see 

anything higher than 2 SWR on my antennas {:>)  But, don't have any idea how 

it would affect aircraft air ground comms.



Ed

---

_________________
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com

sportav8r(at)gmail.com
Guest

Posted: Fri Dec 22, 2006 7:18 pm Post subject: Some experiments fail

what kind of impedance matching schemes did you try?



The angle between the antenna and ground pigtails in the picture looks

really narrow for best results.  What sort of ground are you working

against?



Maybe a better approach would be to engineer a suitable antenna, then

hollow it out to act as a pitot, versus designing a pitot and then

trying to match it electrically to a transmitter.



-Bill B.



On 12/22/06, Ernest Christley <echristley(at)nc.rr.com> wrote:

 	  Quote: 	
		   



 Some ideas look good, until you try to implement them.  Like using the

 pitot tube for an antennae.  It's worth a shot, right?  There's even

 some documentation of the technique at

 http://contrails.free.fr/instruments_ant_sonex.php



 Pictures of my attempt are at

 http://ernest.isa-geek.org/Delta/Pictures/PitotAntennae1.jpg

 and

 http://ernest.isa-geek.org/Delta/Pictures/PitotAntennae2.jpg



 I was able to borrow a "MFJ HF/VHF SWR Analyzer, Model MFJ-259B", do a

 sweep from 110 to 140 MHz.  A few readings are:



 MHz   SWR   R   X

 110   15.4   20   81

 115   20.2   2   21

 120   14.9   3   1

 125   10.8   14   47

 130   8.6   403   0 (lowest SWR)

 135   14.4   9   72

 140   18.6   3   25

 I didn't think I could get much below an SWR of 2.5 or so, and was

 willing to accept the resulting poor performance;  but, 8.6 is really

 high.  But then I put the rubber ducky antennae from my handheld scanner

 on the instrument.  Everything in the aviation band was ">25", ie out of

 the instruments range.  It dropped into range at 130MHz and to 1.6 at 149.5.



 Considering that the handheld scanner seems to work, how viable would an

 SWR of 10 to 20 work over here on the crowded eastern seaboard for

 mostly day VFR operations?

Gilles.Thesee(at)ac-greno
Guest

Posted: Fri Dec 22, 2006 7:32 pm Post subject: Some experiments fail

 	  Quote: 	
		  

 Maybe a better approach would be to engineer a suitable antenna, then

 hollow it out to act as a pitot, 

Hi all,
	




In my buddy's article at

http://contrails.free.fr/instruments_ant_sonex.php, he says he designed 

the antenna out of an aluminum tube, and matched it to the particular 

form of the vertical fin, acting as a ground plane.

He as not flown yet, and advises to wait for real world tests.



Season's greetings to all,

Best regards,

Gilles

http://contrails.free.fr

echristley(at)nc.rr.com
Guest

Posted: Sat Dec 23, 2006 7:54 am Post subject: Some experiments fail

Gilles Thesee wrote:

 	  Quote: 	

 <Gilles.Thesee(at)ac-grenoble.fr>

>

> Maybe a better approach would be to engineer a suitable antenna, then

> hollow it out to act as a pitot, 

 Hi all,

 In my buddy's article at

 http://contrails.free.fr/instruments_ant_sonex.php, he says he 

 designed the antenna out of an aluminum tube, and matched it to the 

 particular form of the vertical fin, acting as a ground plane.

 He as not flown yet, and advises to wait for real world tests.

That would be the intelligent way to do it, but like Bob has said 

several times, the normal procedure is for structural guys to have their 

say, then the aerodynamics guys, yada, yada, yada, and somewhere down 

the list the antennae guys get to say something.  In my case, I'm using 

Dynon's AOA indicator.  It doesn't include a static port (which you 

think it would for $200US), and there isn't a nice place for one on the 

sides of a Delta, so I had to engineer one in.  The antennae experiment 

proceeded from that point.

I tried adding some coils of 22AWG.  Wrapped around a drill bit, and 

held with tape, I put them in series with the element.  It made things 

so much worse that I didn't even bother recording numbers.  I've got 

some ferrite beads, but don't know if it's worth disassembling the coax 

connector to install them.  I guess it couldn't hurt at this point.  The 

ground is basically the entire welded tube airframe.  The black wire 

coming from the coax connetor is grounded next to the antennae's base.  

The connector is also mounted on a strip of stainless that is riveted to 

another piece of stainless that is in turn welded to the airframe.

Is it possible that some combination of fiddling can bring the SWR down 

from the astronomical 8.6 to something below a 3?  I think something 

below 3 would be marginal but acceptable.  I think.

VE3LVO(at)rac.ca
Guest

Posted: Sat Dec 23, 2006 7:59 am Post subject: Some experiments fail

Ernest,

Tying a VHF antenna to a pitot design is very ingenious..... and deserves 

some serious thought!  Kudos to you for the idea.

What needs doing is to revise the length of the pitot to match the needs of 

a 1/4wave monopole OR devising matching circuit to adjust the pitot to 50 

ohms impedance at 127 Megs. I don't think devising apitot system from an 

antenna is the way to go.

    I am hesitant to believe the matching scheme shown would measure the 

true impedance/results, but can't offer any advice in that area.

    The latter would be the easiest if not the best (one always seems to 

prefer a natural resonance) but it cries out for a suggestion......... It 

strikes me that the vertical length might be the problem since the greater 

depth would reduce losses due to some horizontal content - the pitot need.

Is this a metal skin or fibreglass?

Good luck!

Ferg Kyle

Europa A064 914 Classic

echristley(at)nc.rr.com
Guest

Posted: Sat Dec 23, 2006 10:23 am Post subject: Some experiments fail

Fergus Kyle wrote:

 	  Quote: 	
		   



 Ernest,

 Tying a VHF antenna to a pitot design is very ingenious..... and deserves 

 some serious thought!  Kudos to you for the idea.

 What needs doing is to revise the length of the pitot to match the needs of 

 a 1/4wave monopole OR devising matching circuit to adjust the pitot to 50 

 ohms impedance at 127 Megs. I don't think devising apitot system from an 

 antenna is the way to go.

     I am hesitant to believe the matching scheme shown would measure the 

 true impedance/results, but can't offer any advice in that area.

     The latter would be the easiest if not the best (one always seems to 

 prefer a natural resonance) but it cries out for a suggestion......... It 

 strikes me that the vertical length might be the problem since the greater 

 depth would reduce losses due to some horizontal content - the pitot need.

 Is this a metal skin or fibreglass?

 Good luck!



   

Fiberglass and fabric skins over a 4130 frame with stainless steel rib 
	


structure.



I've been playing with the position of the jumper from the pitot to 

connector, and the best I've been able to come up with is a low SWR of 

6.5 or so.

khorton01(at)rogers.com
Guest

Posted: Sat Dec 23, 2006 2:05 pm Post subject: Some experiments fail

On 23-Dec-06, at 11:52 AM, Ernest Christley wrote:



 	  Quote: 	
		   I'm using Dynon's AOA indicator.  It doesn't include a static port  

 (which you think it would for $200US), and there isn't a nice place  

 for one on the sides of a Delta, so I had to engineer one in.  The  

 antennae experiment proceeded from that point.




	


Static ports need to be in a location where the pressure is very,  

very close to the ambient pressure if they are to provide an accurate  

static source.  Pitot tubes in single-engine aircraft are almost  

always mounted below the wing.  The pressure below the wing is higher  

than the ambient pressure - otherwise no lift would be generated.   

This makes a pitot tube a very poor place to locate a static source,  

unless you are prepared to test a large number of different  

locations, with several test flights at each location.



I've watched one small aircraft manufacturer do this exercise with a  

Piper pitot tube.  They invested many hours of flight testing on  

several different configurations before finding a location that  

worked acceptably well with a custom angle on the bottom of a Piper  

pitot tube - the angle changes the pressure sensed at the static source.



Kevin Horton

RV-8 (Finishing Kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

kayce33(at)earthlink.net
Guest

Posted: Sat Dec 23, 2006 4:50 pm Post subject: Some experiments fail

Hi Kevin,

I'm building an RV9A and have installed the Dynon pitot.

Besides the ram air,there's a small hole on the bottom for static air, that 

way I suspect the engineering's already been done.

Food for thought at any rate.

Harold

---

echristley(at)nc.rr.com
Guest

Posted: Sat Dec 23, 2006 5:08 pm Post subject: Some experiments fail

Kevin Horton wrote:

 	  Quote: 	

 <khorton01(at)rogers.com>

 On 23-Dec-06, at 11:52 AM, Ernest Christley wrote:

> I'm using Dynon's AOA indicator.  It doesn't include a static port 

> (which you think it would for $200US), and there isn't a nice place 

> for one on the sides of a Delta, so I had to engineer one in.  The 

> antennae experiment proceeded from that point.

>

 Static ports need to be in a location where the pressure is very, very 

 close to the ambient pressure if they are to provide an accurate 

 static source.  Pitot tubes in single-engine aircraft are almost 

 always mounted below the wing.  The pressure below the wing is higher 

 than the ambient pressure - otherwise no lift would be generated.  

 This makes a pitot tube a very poor place to locate a static source, 

 unless you are prepared to test a large number of different locations, 

 with several test flights at each location.

That's why I copped out and just used the location the plans called 

for.  Heh, I can't run but so many experiments at once!! 8*)

After 4 hours of fiddling, I was able to drop the SWR to 7.3 by moving 

the point where it attaches to the tube.  I actually was able to get it 

to drop to 1 at one point.  I installed a T connector...the antennae on 

the leg, the line coming off one side of the top and a 50 ohm 

termination on the other side.  I don't think that counts though.

echristley(at)nc.rr.com
Guest

Posted: Sat Dec 23, 2006 5:10 pm Post subject: Some experiments fail

Harold Kovac wrote:

 	  Quote: 	
		   

 <kayce33(at)earthlink.net>



 Hi Kevin,

 I'm building an RV9A and have installed the Dynon pitot.

 Besides the ram air,there's a small hole on the bottom for static air, 

 that way I suspect the engineering's already been done.

 Food for thought at any rate.

 Harold 


	


The hole in the bottom rear is a drain hole.  The hole at the front on 

the slant is for the AoA indicator.  There's no static.

kayce33(at)earthlink.net
Guest

Posted: Sat Dec 23, 2006 5:24 pm Post subject: Some experiments fail

Thanks, I don't have the instrument yet, and assumed....it's plumbed to the 

wing root...probably another year to get a look at the real thing.

Harold

---

khorton01(at)rogers.com
Guest

Posted: Sat Dec 23, 2006 5:33 pm Post subject: Some experiments fail

Harold,



1. I think that is actually a water drain hole.



2. If someone did the engineering and flight testing required to use  

a static source on a pitot tube, it would be specific to one exact  

mounting location and mounting angle on only one type of aircraft.   

It wouldn't be practical for Dynon to do the flight testing required  

to define a mounting location for each type of aircraft that people  

would want to mount this pitot on.  Each aircraft type would probably  

require at least a dozen hours of flight testing, with mod work  

required to move the pitot tube around every two or three flights.   

Huge job.



Kevin



On 23-Dec-06, at 8:48 PM, Harold Kovac wrote:



[quote] 

 <kayce33(at)earthlink.net>



 Hi Kevin,

 I'm building an RV9A and have installed the Dynon pitot.

 Besides the ram air,there's a small hole on the bottom for static  

 air, that way I suspect the engineering's already been done.

 Food for thought at any rate.

 Harold

 ---

nuckollsr(at)cox.net
Guest

Posted: Sun Dec 24, 2006 10:49 am Post subject: Some experiments fail

At 09:28 PM 12/23/2006 -0400, you wrote:



 	  Quote: 	
		  



Harold,



1. I think that is actually a water drain hole.



2. If someone did the engineering and flight testing required to use

a static source on a pitot tube, it would be specific to one exact

mounting location and mounting angle on only one type of aircraft.

It wouldn't be practical for Dynon to do the flight testing required

to define a mounting location for each type of aircraft that people

would want to mount this pitot on.  Each aircraft type would probably

require at least a dozen hours of flight testing, with mod work

required to move the pitot tube around every two or three flights.

Huge job.


	


   There are a number of probes that offer both static and pitot

   pressure sensing. Obviously, the dynamic portion has an opening

   on the end and the static portion is generally ported to the

   external environment through a ring of holes just behind the

   nose opening. Pitot-Static probes, as you already know, have two

   fluid fittings instead of one. They are much more difficult to

   build under the current ice-survival rules. See complex

   maze of passages JUST to handle ice crystals and ingested

   moisture for a pitot-only tube at:



http://www.aeroelectric.com/Pictures/Pitot_Tube/Pitot_Tube_Heater.jpg



   It may now be impossible if not simply impractical to combine

   both functions into a single device. But for non-aviation, precision

   airflow measurements, combined pitot-static probes are quite

   common.  See:



http://www.unitedsensorcorp.com/pitot_frame.html



http://www.flowkinetics.com/measurement.htm



   If I can put my hands on one of the older pitot-static probes

   I've had laying around here, I'll post some photos.



   But Kevin is right-on with his observations of the difficulty

   for achieving acceptable pitot-static measurements in a

   consumer environment (read repeatable from airplane to airplane

   and known, stable boundaries on accuracy). You wouldn't believe

   the hoops we've jumped through to meet the new RVSM (reduced

   vertical separation minimums) that have effectively doubled the

   number of over-water airways by stacking airplanes in at twice

   the old vertical density.



   Now, one of the really hot items on the pilot's pre-flight

   inspection is to spit-polish the areas around the pitot static

   system ports to make sure that no contamination has altered the

   aircraft's ability to detect and hold an assigned altitude.



   Even after all the fussing is over and the type-certificate is

   awarded, few if any systems are perfect. This give rise to the

   Calibrated Airspeed and Calibrated Altitude differential charts

   found in many pilot's operating handbooks.



   Good pitot static measurements become exponentially difficult

   as your need for accuracy drops below 2 or 3 percent. The pitot

   static systems installed on our flight test aircraft are big, heavy,

   and would look really ugly installed on your RV.



   The J-3 stuck a piece of copper tube out in the breeze ahead of

   and below the wing. The performance was adequate for that class

   of airplane and the way it was used. I used to show my renters how

   to comfortably operate that airplane with the panel completely

   covered. But as we move up in performance and our demands on

   knowing the real numbers go up, it can be difficult and expensive

   to get them all right under all conditions.



   Bob . . .

nuckollsr(at)cox.net
Guest

Posted: Sun Dec 24, 2006 12:00 pm Post subject: Some experiments fail

At 08:07 PM 12/23/2006 -0500, you wrote:

 	  Quote: 	
		  After 4 hours of fiddling, I was able to drop the SWR to 7.3 by moving the 

point where it attaches to the tube.  I actually was able to get it to 

drop to 1 at one point.  I installed a T connector...the antennae on the 

leg, the line coming off one side of the top and a 50 ohm termination on 

the other side.  I don't think that counts though.


	


   Sounds like you're attempting to "gamma-match" the mast of

   your pitot tube as a useful radiator.



http://www.vk1od.net/GammaMatch/gamma.htm



   For this technique to begin to be successful, the overall

   length of the mast must be close to 1/4 wavelength at the

   frequency of interest. In the case of comm antennas, let us

   assume a center frequency of 126 Mhz. So 300/126 yields

   2.4 meters for full-wave or .6 meteres for 1/4-wave.

   In the clumsy system currently favored by the intellectually

   unwashed, this comes to 23.4 inches. This is the length

   of pitot tube you need to start with.



   Now, a Google search of "gamma match" on the 'net

   will yield a wealth of data on the physics and techniques

   of gamma matching. In a nutshell, your goal is to attach

   a 50 ohm feedline to some point along the antenna's length

   so as to achieve the best match . . . obviously, the antenna's

   impedance at the base is damned-small-ohms and up in the

   gazillion-ohms range at the top. SOMEWHERE between the base

   and the top, we should find the utopian 50 ohm point. Problem

   is that any conductor you use to run between end of the coax

   and the physical attach point on the antenna has significant

   INDUCTANCE at our frequency of interest. This is why all

   the articles you'll find on gamma-matching will incorporate

   two variables. Physical attach-point on the radiator and

   an adjustable capacitance for "series-resonating" the

   offending inductance and making it disappear.



   You don't describe the details of your experiment but if

   you have a better description and perhaps photos to share,

   we can help you move this exercise forward. Just know that

   the first essential elements are overall length (at least

   1/4 wave), feed point location and inductive reactance

   elimination by use of variable capacitor.



   These features go ONLY to achievement of an acceptable

   standing wave ratio. Once the antenna appears to be efficiently

   accepting (or delivering) energy, then one can turn to issues

   of radiation efficiency. Is the polarization optimized? Is

   the radiation pattern acceptably devoid of performance killing

   nulls? Is the radiation resistance a significant if not major

   portion of the antenna total impedance. I've seen antennas with

   1:1 swr having impedances of 50 ohms and radiation resistances

   on the order of 1 ohm . . . the thing gets about 2% of applied

   energy launched into the ether while the rest is a feeble and

   inefficient attempt to de-ice the antenna.



   For those of us who are interested in the simple-ideas that

   support antenna performance, may I suggest a peek at:



http://www2.arrl.org/tis/info/whyantradiates.html



   Antennas are really interesting pieces of technology and it

   doesn't take a lot of equipment and even less "black art" to

   fabricate useful designs. I would only caution that if the goal

   is to achieve a 1/4 to 1/2-knot more speed by reducing antenna

   drag on your OBAM aircraft, be aware that the return on investment

   for the $time$ expended might be disappointingly small. If the

   goal is to understand more about how these critters work, then

   your return on investment can be considerably better.



   Bob . . .

ulflyer(at)verizon.net
Guest

Posted: Mon Dec 25, 2006 8:02 pm Post subject: Some experiments fail

By far I am not an antenna expert but what I've seen from the 

pictures there are several major issues.

The length of the antenna element appears to be far shorter than it 

should be for a 118-136 MHz spectrum.

The next thing I noticed is you go from coax to long simple single 

connector wires to connect to the element and the ground plane.

You don't have much of a ground plane that I can see.

Last, looks like you have the antenna element and the pitot in very 

close proximity to each other, if not at the proper spacing that has 

to impact your SWR, added together even more so.

I use nothing more than a simple SS whip from Radio Shack bent into L 

shape and sized to produce a good SWR across normal frequency 

spectrum used in our area.   I get out well and receive well.

Bob didn't comment on these items that I noticed so either he's 

biting his fingers or what I noticed isn't a factor.

jerb

At 05:28 PM 12/22/2006, you wrote:

 	  Quote: 	
		  

<echristley(at)nc.rr.com>



Some ideas look good, until you try to implement them.  Like using 

the pitot tube for an antennae.  It's worth a shot, right?  There's 

even some documentation of the technique at 

http://contrails.free.fr/instruments_ant_sonex.php



Pictures of my attempt are at

http://ernest.isa-geek.org/Delta/Pictures/PitotAntennae1.jpg

and

http://ernest.isa-geek.org/Delta/Pictures/PitotAntennae2.jpg



I was able to borrow a "MFJ HF/VHF SWR Analyzer, Model MFJ-259B", do 

a sweep from 110 to 140 MHz.  A few readings are:



MHz   SWR   R   X

110   15.4   20   81

115   20.2   2   21

120   14.9   3   1

125   10.8   14   47

130   8.6   403   0 (lowest SWR)

135   14.4   9   72

140   18.6   3   25

I didn't think I could get much below an SWR of 2.5 or so, and was 

willing to accept the resulting poor performance;  but, 8.6 is 

really high.  But then I put the rubber ducky antennae from my 

handheld scanner on the instrument.  Everything in the aviation band 

was ">25", ie out of the instruments range.  It dropped into range 

at 130MHz and to 1.6 at 149.5.



Considering that the handheld scanner seems to work, how viable 

would an SWR of 10 to 20 work over here on the crowded eastern 

seaboard for mostly day VFR operations?

nuckollsr(at)cox.net
Guest

Posted: Tue Dec 26, 2006 8:50 am Post subject: Some experiments fail

At 09:58 PM 12/25/2006 -0600, you wrote:

 	  Quote: 	

By far I am not an antenna expert but what I've seen from the pictures 

there are several major issues.

The length of the antenna element appears to be far shorter than it should 

be for a 118-136 MHz spectrum.

The next thing I noticed is you go from coax to long simple single 

connector wires to connect to the element and the ground plane.

You don't have much of a ground plane that I can see.

Last, looks like you have the antenna element and the pitot in very close 

proximity to each other, if not at the proper spacing that has to impact 

your SWR, added together even more so.

I use nothing more than a simple SS whip from Radio Shack bent into L 

shape and sized to produce a good SWR across normal frequency spectrum 

used in our area.   I get out well and receive well.

Bob didn't comment on these items that I noticed so either he's biting his 

fingers or what I noticed isn't a factor.

   Didn't see the pictures until now Jerb but you're observations are spot

   on.

   Ernest. Your interest and willingness to explore antenna options

   are commendable. The experiments are worthwhile learning tools.

   But whether you're wanting to explore a new antenna configuration

   or learn to make biscuits, the shortest path to success is to

   study what has preceded your efforts.

   Do some Google searches on antennas. There are thousands of

   articles. Get copies of ANY editions of amateur radio antenna

   handbooks. Those published by ARRL are noteworthy. Used book stores

   on the 'net can provide a wealth of low cost, detailed data on how on

   might approach the task of launching intelligence into the ether borne

   on a stream of electromagnetic radiation.  Your pictures

   and words suggest that you've acquired some useful facts about

   antennas but have yet to grasp the simple-ideas that support those

   facts.

   Get some books and study up on the relationship between operating

   frequency and physical sizes of antennas. You'll need to have a rudimentary

   grasp of transmission line theory and impedance at radio frequencies.

   There's a chapter on antennas in the 'Connection that would provide

   a beginning but what you're attempting to accomplish requires a study

   into much more detail.

   If you find something published for which you'd like more explanation

   post a question about it here on the List. There are plenty of folks

   here who would be willing to participate in some shared learning and

   teaching experiences.

   Now, if it's the 'short' answer you're looking for, I can tell you

   that the current crop of pitot tubes offer little prospect for becoming

   a useful antenna on an aircraft. But that doesn't mean we shouldn't

   study and discuss why - both for your benefit and that of perhaps

   1300 other folks who watch this list.

   A quick note on other comments you offered:

 	  Quote: 	
		  >I didn't think I could get much below an SWR of 2.5 or so, and was 

>willing to accept the resulting poor performance;  but, 8.6 is really 

>high.  But then I put the rubber ducky antennae from my handheld scanner 

>on the instrument.  Everything in the aviation band was ">25", ie out of 

>the instruments range.  It dropped into range at 130MHz and to 1.6 at 149.5.

>

>Considering that the handheld scanner seems to work, how viable would an 

>SWR of 10 to 20 work over here on the crowded eastern seaboard for mostly 

>day VFR operations?

   Please understand that SWR has only a very loose connection

   with antenna performance. SWR is a measure of the antenna system's

   ability to accept power from the transmitter (or convey it to

   a receiver). It says nothing about the antenna's ability to

   efficiently radiate or intercept a signal.

   A 50 ohm resistor has an SWR of 1:1 over the entire range of

   interest but zero ability to function as an antenna. The MFJ-259

   is of great value for improving power transfer by helping you

   optimize a "match". But 1.5:1 SWR measured on a wet-string

   does not insure that the wet-string will produce satisfactory

   performance as an antenna.

   Bob . . .

echristley(at)nc.rr.com
Guest

Posted: Tue Dec 26, 2006 6:36 pm Post subject: Some experiments fail

Robert L. Nuckolls, III wrote:

 	  Quote: 	
		     Ernest. Your interest and willingness to explore antenna options

   are commendable. The experiments are worthwhile learning tools.

   But whether you're wanting to explore a new antenna configuration

   or learn to make biscuits, the shortest path to success is to

   study what has preceded your efforts.



   Do some Google searches on antennas. There are thousands of

   articles. Get copies of ANY editions of amateur radio antenna

   handbooks. Those published by ARRL are noteworthy. Used book stores

   on the 'net can provide a wealth of low cost, detailed data on how on

   might approach the task of launching intelligence into the ether borne

   on a stream of electromagnetic radiation.  Your pictures

   and words suggest that you've acquired some useful facts about

   antennas but have yet to grasp the simple-ideas that support those

   facts.

Thank you, Bob, but I've believe I've bitten off way more than I can 
	


chew.  The problem with antennaes is what I've heard from both you and 

Jim Weir.  To paraphrase:  A wet noodle in a cast iron swimming pool 

will radiate, and it gets better from there.  The implication is that 

just about anything will work, for some qualified definition of 'work'.  

This experiment was an exercise in placing a chunk of existing metal at 

it's appropriate spot somewhere is the spectra of wet noodle to 

'dedicated ham special'.



I don't have the resources, time or energy to remanufacture the tube, 

and once I get past the basics of antennae theory I started to get 

swimmy headed.  The pitot tube has to remain unmodified so that it may 

serve its intended purpose for one very profound reason.  I've done paid 

for it and it was EXPENSIVE 8*)  I also think I know more about antennae 

than I originally set out learn...which is a good thing, but for the 

swimmy headiness.  At this point, I know the radio will transmit well 

enough to be recieved in the kitchen from the garage (put that unit in 

your metric pipe and smoke it 8*), and I can only presume that it was 

received clearly since it brought the family out to ask what I wanted 

(another great measurment unit for the international community 8*).



The next step will be to see how well it does at the airport during the 

taxi test.  It shouldn't be very hard to pre-arrange for a few strategic 

radio checks.   If it is sufficient, it will get qualified in the 

pattern.  If it proves worthwhile, I'll extend the range until I know 

how effective it is.  If it is really bad, I'll try something a little 

more conventional, though not as universally applicable.  I could fish a 

welding rod down into the foam core of my air intake, for instance.



All in all, I think this has been a worthwhile experiment for me, and 

I'm especially pleased that my little splash has stirred the neurons of 

a few that have many more to stir than I.  Marc Beranger inspired me.  I 

inspire someone else.  They develop something that exceeds, even by the 

slightest of measures, what what done before.  I LOVE this internets thing.

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