REFLECTOR: Glideslope Antenna & Combiner/Splitter

[John Tvedte]

Bob,
 
The attached drawing shows how the antennas can be hooked up for a GNS480 (CNX-80).  On the left shows hookup without a GS antenna - per the manual....emphasis added.
 
GNS480(CNX-80)
 
The GNS480 incorporates an internal diplexor circuit.  This means that the input VHF signal must not strip the glideslope (330Mhz) signal from the NAV (108Mhz) signal.  Do not install an external diplexor.  It is recommended that a single VOR/Localizer/Glideslop antenna be used for the installation.  Most VOR/LOC-only antennas will still provide an adequate glideslope signal for the GNS480 to operate normally."
 
And from the SL30 install manual....
 
"It is recommended that a single VOR/Localizer/Glideslope antenna be used for the installation.  Most VOR/LOC-only antennas will still provide an adequate glideslope signal for the Apollo SL30 to operate normally.  In rare cases, it may be necessary to combine antenna signals.  When the signals are combined the systems overall performance may be slightly degraded, but the glideslope signal may increase to an acceptable level."
 
On the right - is an alternate method described in the manuals that you can use, should you find that you do not have adequate glideslope levels.  The combiner is a Mini-Circuits ZFSC-2-1B BNC  http://www.minicircuits.com/
 
I too installed a GS antenna prior to knowing this.  I plan on flight testing the signal levels, but as Dean pointed out - his installation is working with just the NAV antenna hooked up.
 
John
 

	----- Original Message ----- 

	From: Bob Jackson <mailto:bobj at computer.org>  

	To: 'Velocity Aircraft Owners and Builders list' <mailto:reflector at tvbf.org>  

	Sent: Friday, September 07, 2007 9:52 PM

	Subject: REFLECTOR: Glideslope Antenna & Combiner/Splitter

	 

	The Apollo (Garmin) SL-30 installation manual says the SL-30 receiver has
	sufficient receiver sensitivity to pick up a good glideslope signal using
	only a standard NAV antenna.  The SL-30 only has a single NAV antenna input
	(no separate Glideslope input jack) and they advise against combining
	signals from separate NAV and Glideslope antennas to create a composite
	signal at the NAV input.  
	
	One person said that most new Velocity's no longer even install a separate
	Glideslope antenna because of the ability of the newer receivers to derive a
	good Glideslope signal from the NAV antenna input.  This would also simplify
	our desire to shoot ILS approaches with either the SL-30 or CNX80, even
	though we only put one Glideslope antenna into the airplane.
	
	My question is:  has anyone had success getting strong Glideslope
	performance on an SL-30 (or CNX80) using only the standard Velocity NAV
	antenna input?  
	
	Thanks,
	Bob Jackson
	N2XF  (flying by the end of the year?)
	
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