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Subject: Re: [LML] Nav antennas
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In a message dated 11/23/2006 8:29:48 A.M. Central Standard Time,  
rosenzweig2@verizon.net writes:

I currently have dual Nav/Comms that share one  antenna for the Nav side.  
This includes VOR/LOC/GS functions.  The  antenna coax goes to the input of a 
diplexer and the two outputs each go to  one of the Nav receivers.  The 
nav/comms are Apollo SL30 which have built  in recievers for VOR/LOC/GS.  The problem 
I've seen since I acquired the  airplane has been poor performance with the 
LOC & G/S from either nav  indicator.  VOR from both is good however.
 
Has anyone noticed degraded performance using a  single antenna for 
VOR/LOC/GS functions?  Are there any special diplexers  that could be used to improve 
degraded performance? or possibly a need to  install a seperate antenna for 
each receiver?  I'm not sure what kind of  Nav antenna the builder used, but it 
is installed in the horizontal  stab.



Steve,
 
The glide slope operates a quite a different frequency than VOR/LOC (LOC  
109.5 MHz has the paired GS operating at 329.6 MHz) - thus, the same antenna  
(VOR/LOC) is not the best match for it.  On the other hand, one is usually  
within 15 NM of the GS transmitter and a less efficient antenna may be ok.   
Usually the nav radio would have a separate antenna connection for VOR/LOC and  GS.
 
Maybe the problem is that each receiver is looking for 2 inputs and you  
probably have three splitters (one to feed each radio and then one at each radio  
to split for the VOR/LOC and GS).  There is a signal loss for each  connector 
and each splitter (even more as the connections age without  cleaning 
occasionally).  Try this experiment (if you have the coax length  to do it), take the 
antenna lead and connect thru only one of the splitters for  one radio and see 
if the performance improves.  Also, you could have a bad  connector or bad 
splitter in the mix too.
 
I have only one nav radio (inside the Garmin 430) that is fed directly by  
the VOR/LOC antenna in the horizontal stabilizer and the GS is fed by the 12  
inch center tapped foil antenna located in the most outboard leading-edge  part 
of the right stub-wing D-section.  
 
The VOR is only a seldom used backup for the GPS.  Nothing  is better than an 
ILS (LOC-GS) approach ---- Uh, well until my 430 becomes  a 430W...........   

Scott Krueger  AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)

A man  has got to know his limitations.


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<DIV>
<DIV>In a message dated 11/23/2006 8:29:48 A.M. Central Standard Time,=20
rosenzweig2@verizon.net writes:</DIV>
<BLOCKQUOTE=20
style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><=
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  <DIV><FONT face=3DArial size=3D2>I currently have dual Nav/Comms that shar=
e one=20
  antenna for the Nav side.&nbsp; This includes VOR/LOC/GS functions.&nbsp;=20=
The=20
  antenna coax goes to the input of a diplexer and the two outputs each go t=
o=20
  one of the Nav receivers.&nbsp; The nav/comms are Apollo SL30 which have b=
uilt=20
  in recievers for VOR/LOC/GS.&nbsp; The problem I've seen since I acquired=20=
the=20
  airplane has been poor performance with the LOC &amp; G/S from either nav=20
  indicator.&nbsp; VOR from both is good however.</FONT></DIV>
  <DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
  <DIV><FONT face=3DArial size=3D2>Has anyone noticed degraded performance u=
sing a=20
  single antenna for VOR/LOC/GS functions?&nbsp; Are there any special diple=
xers=20
  that could be used to improve degraded performance? or possibly a need to=20
  install a seperate antenna for each receiver?&nbsp; I'm not sure what kind=
 of=20
  Nav antenna the builder used, but it is installed in the horizontal=20
  stab.</FONT></DIV></FONT></BLOCKQUOTE></DIV>
<DIV></DIV>
<DIV>Steve,</DIV>
<DIV>&nbsp;</DIV>
<DIV>The glide slope operates a quite a different frequency than VOR/LOC (LO=
C=20
109.5 MHz has the paired GS operating at 329.6 MHz) - thus, the same antenna=
=20
(VOR/LOC) is not the best match for it.&nbsp; On the other hand, one is usua=
lly=20
within 15 NM of the GS transmitter and a less efficient antenna may be ok.&n=
bsp;=20
Usually the nav radio would have a separate antenna connection for VOR/LOC a=
nd=20
GS.</DIV>
<DIV>&nbsp;</DIV>
<DIV>Maybe the problem is that each receiver is looking for 2 inputs and you=
=20
probably have three splitters (one to feed each radio and then one at each r=
adio=20
to split for the VOR/LOC and GS).&nbsp; There is a signal loss for each=20
connector and each splitter (even more as the connections&nbsp;age without=20
cleaning occasionally).&nbsp; Try this experiment (if you have the coax leng=
th=20
to do it), take the antenna lead and connect thru only one of the splitters=20=
for=20
one radio and see if the performance improves.&nbsp; Also, you could have a=20=
bad=20
connector or bad splitter in the mix too.</DIV>
<DIV>&nbsp;</DIV>
<DIV>I have only one nav radio (inside the Garmin 430) that is fed directly=20=
by=20
the VOR/LOC antenna in the horizontal stabilizer and the GS is fed by the 12=
=20
inch center tapped foil antenna located in the most outboard&nbsp;leading-ed=
ge=20
part of the right stub-wing D-section.&nbsp; </DIV>
<DIV>&nbsp;</DIV>
<DIV>The&nbsp;VOR is only a seldom used&nbsp;backup for the GPS.&nbsp; Nothi=
ng=20
is better than an ILS (LOC-GS) approach&nbsp;---- Uh, well until my 430 beco=
mes=20
a 430W...........&nbsp;=20
<DIV>&nbsp;</DIV>
<DIV><FONT lang=3D0 face=3DArial size=3D2 FAMILY=3D"SANSSERIF" PTSIZE=3D"10"=
>Scott Krueger=20
AKA Grayhawk<BR>Lancair N92EX IO320 SB 89/96<BR>Aurora, IL (KARR)<BR><BR>A m=
an=20
has got to know his limitations.</FONT></DIV></DIV></FONT></BODY></HTML>

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