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DIY LOC/VOR_G.S. Antenna

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nuckolls.bob(at)aeroelect
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Posted: Sat Jul 18, 2020 5:51 pm Post subject: DIY LOC/VOR_G.S. Antenna

At 12:04 PM 7/18/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "merlewagner2" <wagnermerle(at)gmail.com>



 Bob,



 Just took a couple photos of my antenna. I did two calibrations, one for Glide slope and one for Localizer.



 Not sure how the photos will come out.  These are attached.



 I don't remember the length I initially used for antenna. I bench tested and it looked OK. After install the freqs changed, most likely due to frame proximity. There are some wire and and ferrites between the connector and the foil. This will take up some length. I had to cut the foil to get in the freq range. 	


   Interesting. I'm wondering if the 'short' elements

   are not really functioning as resonant radiators, rather

   reactive elements that influence the uhf characteristics

   of the overall assembly.



   We know that the basic 1/2-wave dipole offers

   significantly effective performance at odd

   harmonics of the fundamental.  If memory serves,

   LOC/VOR transmitters operate in the 108 to 118 Mhz

   range. 3x these numbers are 324 to 354 . . . more

   than the 328 to 336 bandwidth occupied by the

   contemporary GS transmitters.



   This means that your barefoot LOC/VOR antenna

   is quite capable of providing GS signals to

   your ILS receiver. For many years, GS

   receivers have been installed using band-pass

   couplers on the LOC/VOR thus allowing one

   STOCK, LOC/VOR antenna to service both VORNAV

   and ILS systems.



   The attached photo is one of what must be

   dozens of examples for this kind of device.

   I'm thinking that if you removed the little

   'stubs' from the array, your swr plots over

   the two band widths of interest would not

   be significantly different . . . indeed

   both acceptable for the task at hand.



   Given the VHF antenna's propensity for acceptable

   performance at third harmonic, it is almost a

   certainty that the observably 'too small' size

   of these stubs is of no benefit to the antenna's

   performance.



 

 

   Bob . . .

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DM_H22-1_VOR-LOC-GS_Coupler.jpg

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merlewagner2

Joined: 01 Jun 2016
Posts: 18
Location: Spring Hill, FL

Posted: Wed Jul 22, 2020 4:11 am Post subject: Re: DIY LOC/VOR_G.S. Antenna

I agree the VHF antenna (without the GS antenna ears) will work very well for receiving the GS freqs. 



I wanted to see how the performance could be enhanced with the antenna tuned to the different bands. The only verifiable method to prove this would be testing the antenna with and without the GS elements. I just don't have the time to do this at the moment. A future test.



 I am going crazy getting the Tailwind ready for it's first flight this weekend. Everytime I try something another problem arises. Guess that is why this is experimental aviation.  



I do know that trimming the GS elements adjusted the antenna VSWR to the freq range I wanted. I did this in real time by watching my NANOVNA output while trimming. So the ears do have a major impact on the freq band.



I also ran the antenna to an antenna multi-coupler versus the splitter you show. This also guarantees improved reception as the signal level is reduced with the splitters.

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_________________
KC1DNJ
General Radiotelephone
Commercial SEL
A & P
Building scale P51, rebuilding Tailwind W10

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jul 22, 2020 10:34 am Post subject: DIY LOC/VOR_G.S. Antenna

At 07:11 AM 7/22/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "merlewagner2" <wagnermerle(at)gmail.com>



 I agree the VHF antenna (without the GS antenna ears) will work very well for receiving the GS freqs. 



 I wanted to see how the performance could be enhanced with the antenna tuned to the different bands. The only verifiable method to prove this would be testing the antenna with and without the GS elements. I just don't have the time to do this at the moment. A future test. 	


   I'm planning an experiment centered on

   Jim Wier's suggestion for a dual band

   121.5/406 Mhz ELT antenna.  These two

   frequencies are not harmonically related.

   I've got the elements built. Planning

   to explore balun options too. I'll document

   the exercise and post here.



  	  Quote: 	
		   I am going crazy getting the Tailwind ready for it's first flight this weekend. Everytime I try something another problem arises. Guess that is why this is experimental aviation.  

 	


   Sounds like the engineering flight test hangar

   at Beech!



  	  Quote: 	
		  I do know that trimming the GS elements adjusted the antenna VSWR to the freq range I wanted. I did this in real time by watching my NANOVNA output while trimming. So the ears do have a major impact on the freq band. 	


   When I get the ELT experiment done, I'll

   repeat repeat your VOR-LOC/GS experiment

   and see what I get.  We'll compare

   notes.



 

  	  Quote: 	
		  I also ran the antenna to an antenna multi-coupler versus the splitter you show. This also guarantees improved reception as the signal level is reduced with the splitters.

 	


   Be wary of distribution amplifier type couplers.

   The 'ideal' gain is zero. I.e. same output for a given

   input at the frequencies of interest. Keep in mind that

   our navigation equipment is sorta tailored to be compatible

   with legacy practices for transmitted signals, typical

   (passive) antennas, reasonably low loss coax, etc.



   Adding active devices into the feedline has some

   risk for (1) overloading the receiver(s) on

   the ILS system and/or (2) increasing risks for

   inter-modulation interference of desired signals

   by unrelated/undesired signals.



   Study the specs for your chosen device for assurance

   that the thing adds value and does not add risk.



 

   Bob . . .

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steve(at)tomasara.com
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Posted: Sat Jul 25, 2020 9:50 pm Post subject: DIY LOC/VOR_G.S. Antenna

Bob said:"I'm planning an experiment centered on Jim Wier's suggestion for a dual band 121.5/406 Mhz ELT antenna."

I needed a compact 121.5/406 antenna for my Longeze.  I tried a few configurations and the attached photo shows what worked the best.  It's a shortened dipole for 121.5 in parallel with a full size 406 dipole.  It's mounted to the pilot seat back.  The feed line needs to leave the intersection roughly along the virtual ground plane (actually, splitting the difference between the two).  I have better VSWR with this configuration than I got with a couple of different (one portable, one for permanent mount) antennas supplied by the ELT manufacturer (purchased for test - so if anyone wants them, I'm happy to sell them...)

Steve Stearns

O235 Longeze

Boulder / Longmont CO

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