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VOR/LOC/GS antenna question

 
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fasilpereira



Joined: 17 Jul 2011
Posts: 86
Location: Brazil

PostPosted: Mon May 08, 2023 9:04 am    Post subject: VOR/LOC/GS antenna question Reply with quote

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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nuckolls.bob(at)aeroelect
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PostPosted: Wed May 10, 2023 7:09 am    Post subject: VOR/LOC/GS antenna question Reply with quote

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

PostPosted: Wed May 10, 2023 9:45 am    Post subject: Re: VOR/LOC/GS antenna question Reply with quote

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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wsimpso1



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

PostPosted: Thu May 11, 2023 10:28 am    Post subject: Re: VOR/LOC/GS antenna question Reply with quote

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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