In a message dated 11/23/2006 8:29:48 A.M. Central Standard Time,=20 rosenzweig2@verizon.net writes:

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I currently have dual Nav/Comms that shar= e one=20 antenna for the Nav side. This includes VOR/LOC/GS functions. =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. The nav/comms are Apollo SL30 which have b= uilt=20 in recievers for VOR/LOC/GS. The problem I've seen since I acquired=20= the=20 airplane has been poor performance with the LOC & G/S from either nav=20 indicator. VOR from both is good however.

Has anyone noticed degraded performance u= sing a=20 single antenna for VOR/LOC/GS functions? 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? I'm not sure what kind= of=20 Nav antenna the builder used, but it is installed in the horizontal=20 stab.

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. 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.

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). There is a signal loss for each=20 connector and each splitter (even more as the connections age without=20 cleaning occasionally). 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. Also, you could have a=20= bad=20 connector or bad splitter in the mix too.

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 leading-ed= ge=20 part of the right stub-wing D-section.

The VOR is only a seldom used backup for the GPS. Nothi= ng=20 is better than an ILS (LOC-GS) approach ---- Uh, well until my 430 beco= mes=20 a 430W........... =20

Scott Krueger=20 AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)

A m= an=20 has got to know his limitations.