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Hand-made Glide Slope Antenna

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n585ss(at)bellsouth.net
Guest

Posted: Sat Mar 07, 2015 5:30 am Post subject: Hand-made Glide Slope Antenna

Bob -

     I am considering using/making a hand-made glideslope antenna like 

the one you show in chapter 13, figure 13-13 (it's a good thing I'm not 

superstitious!). My only issue is the ferrite beads. They are available 

in a bewildering variety. What should I use for a dedicated GS antenna?



Sam Staton

Jackonsville, FL

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Mar 07, 2015 6:20 am Post subject: Hand-made Glide Slope Antenna

At 07:28 2015-03-07, you wrote:

 	  Quote: 	
		  



Bob -

     I am considering using/making a hand-made glideslope antenna 

 like the one you show in chapter 13, figure 13-13 (it's a good 

 thing I'm not superstitious!). My only issue is the ferrite beads. 

 They are available in a bewildering variety. What should I use for 

 a dedicated GS antenna?


	


   Leave them off. Those are coming out in the

   next revision to the 'Connection. Cessna

   built thousands of similar antennas in the '60s

   with no beads. Laboratory tests have show them

   to offer no observable or even measurable

   benefit.



   Bob . . .

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henry(at)pericynthion.org
Guest

Posted: Sat Mar 07, 2015 11:05 pm Post subject: Hand-made Glide Slope Antenna

Bob,



Are you still a believer in ferrite beads for transmit antennas, if

not for receivers? I was under the impression they helped form a sort

of crude balun, preventing RF current from flowing back through the

coax sleeve rather than into the arm of the dipole.



Cheers, Henry



On Sat, Mar 7, 2015 at 6:18 AM, Robert L. Nuckolls, III

<nuckolls.bob(at)aeroelectric.com> wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)aeroelectric.com>



 At 07:28 2015-03-07, you wrote:

>

> 

>

> Bob -

>     I am considering using/making a hand-made glideslope antenna like the

> one you show in chapter 13, figure 13-13 (it's a good thing I'm not

> superstitious!). My only issue is the ferrite beads. They are available in a

> bewildering variety. What should I use for a dedicated GS antenna?

   Leave them off. Those are coming out in the

   next revision to the 'Connection. Cessna

   built thousands of similar antennas in the '60s

   with no beads. Laboratory tests have show them

   to offer no observable or even measurable

   benefit.



   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Mar 08, 2015 3:31 am Post subject: Hand-made Glide Slope Antenna

At 01:57 2015-03-08, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Henry Hallam <henry(at)pericynthion.org>



 Bob,



 Are you still a believer in ferrite beads for transmit antennas, if

 not for receivers? I was under the impression they helped form a sort

 of crude balun, preventing RF current from flowing back through the

 coax sleeve rather than into the arm of the dipole.



 Cheers, Henry 	




    Sorta . . .  but there's a lot more to the

    story than being a 'believer' in the virtues

    of any particular 'technology'. Many common

    beliefs ARE based on a modicum of physics

    but blown all out of proportion for demonstrating

    a return on investment for the practice.



    It's like an admonition handed down from 

    somewhere that keeping your tires properly

    inflated is going to save a boat load of

    oil. Yes, if you fitted a vehicle with 

    instrumentation of sufficient sensitivity

    and accuracy, you can detect and quantify

    variability in rolling coefficient of friction

    of a tire  . . . but in the grand scheme of

    things, getting the planet's population to

    march in lock step with the Tire Pressure

    Gods is probably not going to put a measurable

    dent in the demand for liquid energy.



    The BALUN does indeed serve good and useful

    purposes for improving the efficiency of

    conducting energy captured in the wild by

    your antenna into a feed line and ultimately

    to the receiver. The benefits are perfectly

    reversible. What 'good' for receiving is equally

    'good' for transmitting.



    The question then is how big is the goodness,

    does it cost and what is the observable benefit?

    In the case of a g.s. antenna, signals

    in the wild are measured in microwatts

    captured by an antenna looking right down

    the radio frequency gun barrel of an antenna

    from a distance of not more than 10 miles.



    A wet noodle with 'terrible SWR' would

    probably work just fine. Many G.S. installaitons

    use a coupler in the vor antenna feed line

    to split out a g.s. component of rf from

    the vor antenna . . . even tho it's not

    very efficient. So, fussing around with

    anything expected to lower SWR on the g.s.

    antenna is not going to produce any benefit

    you can observe in the cockpit . . . and

    requires some pretty good equipment to 

    detect in the lab.



    Then let's consider the physics of slipping

    those beads over the coax. Some months ago

    I cited a product offered by Miracle Antenna

    Company out of Canada called the "Air Whip".



    Aircraft Spruce offered this product for a time

    and it's still listed in their European catalog



     http://tinyurl.com/mgm26yh



    . . . but I understand the gentleman who built

    and ran the company died in 2012. I'm not sure

    the company is still in business. But the Air

    Whip was an EXCELLENT example for effectiveness

    and value of a 'balun'. That red heat shrink

    covered lump in the coax feeder was identified

    for us by a writer who disassembled an earlier

    version of the Air Whip



 [img]cid:.0[/img]



   Yup, there it is. A ferrite torroid. Not a string

   of torroids but a single device with 7 passes of

   coax through the center. The inductance offered by

   such a technique varies with the SQUARE of the

   turns on the core. By passing the coax through the

   core 7 times, the net effect is 49 times as effective

   as a single pass thorough one core.



   Further, this antenna's design DEMANDS the inclusion of

   this de-coupling technique . . . which is not a BALUN in

   the purest sense although it has the appearance of one.



   Coax feed lines, antennas, radiation efficiencies,

   radiation patterns, SWR and interaction between

   radios and other systems on board the airplane form

   a complex stew that yields to an analysis of the

   physics. Analysis of single beads on the g.s. antenna,

   reveals usefulness on the same order as carrying a

   couple more pounds of pressure in your tires.



   Then, as you've discovered, not all torroids are equal.

   They are fabricated from another book of recipes to

   meed design goals for the transfer of energy from one

   place to anoth4er in the system (BALUN or decoupling)

   or the conversion of energy from RF to heat (noise

   suppression). And to make the stew more interesting,

   high efficiency energy transfer ferrites are often

   used in noise suppression roles. So running down to

   the local electro-whizzy store to buy beads assumes

   that the sell of such beads can answer questions

   their suitability to any given task.



   I bought a network analyzer last fall and I've expanded

   my box of RF measurement tools, There are a couple

   of antenna projects I'd like to explore and then

   describe to the community along with numbers to support

   those descriptions. One goal will be to quantify the

   value of adding any sort of BALUN to the installation

   of DIY VOR and GS antennas.



 

   Bob . . .

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