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VOR/LOC/GS antenna question

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fasilpereira

Joined: 17 Jul 2011
Posts: 86
Location: Brazil

Posted: Mon May 08, 2023 9:04 am Post subject: VOR/LOC/GS antenna question

I'm installing a GNS-430W on my composite aircraft. I already have 2 VOR antennas that are currently not in use because I didn't had any NAV radio installed.



I just realized that the GNS-430W requires an input for both VOR/LOC and GS. The common solution for this is to install a Diplexer on a NAV antenna to break the signal 2 outputs, one output for VOR/LOC and other for GS. I have seen that some users reports a loss in VOR range due to the diplexer and I'm worried about it because the VORs are far from each other here where I live.



I'm considering to plug one antenna to the VOR/LOC input of the GNS and the other to the GS. I'm not sure if I'll need to add a diplexer to the GS cable and if I do, can I leave the VOR connector of the diplexer open? Additionally, if a diplexer is necessary, is there any DIY that could be used, instead of the $150-$200 ones?



Thank you,



Fabricio

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_________________
Fabricio Pereira
Engineer / Pilot

nuckolls.bob(at)aeroelect
Guest

Posted: Wed May 10, 2023 7:09 am Post subject: VOR/LOC/GS antenna question

At 12:04 PM 5/8/2023, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "fasilpereira" <fasilpereira(at)yahoo.com>



 I'm installing a GNS-430W on my composite aircraft. I already have 2 VOR antennas that are currently not in use because I didn't had any NAV radio installed.



 I just realized that the GNS-430W requires an input for both VOR/LOC and GS. The common solution for this is to install a Diplexer on a NAV antenna to break the signal 2 outputs, one output for VOR/LOC and other for GS. I have seen that some users reports a loss in VOR range due to the diplexer and I'm worried about it because the VORs are far from each other here where I live. 	


   Yes, 'diplexers' are a signal splitting network

   that routes energies from a common antenna to two

   or more receivers.  A well crafted VOR-LOC/GS splitter

   should not seriously affect the performace of either

   system. Advertised losses through such devices

   are generally on the order of 1.0 dB or less.



  https://tinyurl.com/2uams5xp



   On the other hand, there are VOR-LOC power

   'dividers' that optimize the function of TWO

   VHF receivers on a single antenna. Of necessity,

   these devices route 1/2 of the power from the

   antenna to each receiver. Hence, a 3+ dB loss

   of signal to each receiver.



 

  	  Quote: 	
		  I'm considering to plug one antenna to the VOR/LOC input of the GNS and

 the other to the GS. I'm not sure if I'll need to add a diplexer to the

 GS cable and if I do, can I leave the VOR connector of the diplexer open? 	


   Don't need one. The 'barefoot' VOR/LOC

   antenna is quite efficient when operated

   at the third harmonic of it's fundamental

   design frequency 108-118 MHz. GS signals

   cover range of 329-335 MHz.



 

   Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

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fasilpereira

Joined: 17 Jul 2011
Posts: 86
Location: Brazil

Posted: Wed May 10, 2023 9:45 am Post subject: Re: VOR/LOC/GS antenna question

Bob,



So I understood that I can connect the spare VOR/LOC antenna that I have direct to the GS BNC in the back of the GNS and that will work just fine, with no need of any additional device between. Is that correct? I thought a 1 pF capactitor could be required, but I was not sure....



Thanks again,



Fabricio

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_________________
Fabricio Pereira
Engineer / Pilot

wsimpso1

Joined: 04 Nov 2018
Posts: 33
Location: Saline MI

Posted: Thu May 11, 2023 10:28 am Post subject: Re: VOR/LOC/GS antenna question

The expensive commercial splitters and decouplers are one option. The other is building them from Jim Weir's Attenna Reference Text. It is available on this page of his website.at:



http://www.rstengineering.com/rst/products/plasticplaneantenna/plasticplaneantenna.htm



The highlighted Antenna Reference Text has a whole bunch of guidance on the topic and is downloadable as a .pdf file. Page 34 shows both his NAV splitter applying one NAV antenna to two VOR recievers, it also shows the GS splitter to get a GS off that one NAV antenna. Yeah, you have to roll up a couple 16" cables into a little box and stash it someplace, but it is way cheaper than the commercial gadget.  



Have fun.

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