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GPS Antenna

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GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Mon Nov 26, 2007 12:34 am Post subject: GPS Antenna

 	  Quote: 	
		  I've been trying to find an acceptable answer as to why Garmin wants to have the coax cable for the GPS antenna to be between 13 and 15 feet.  If I can mount an antenna just 15 inches away from the unit itself, why do I need to mount the antenna 15 feet away?  

One explanation I got was the 430/530 needed a 3 db loss in the cable.  Now, it seems to me that the stronger the signal at the unit is, the better.For what it's worth, I mounted my antenna (Garmin 430) on the glareshield on my Tiger.That was 4 years ago.  I've never had any problems with losing the signal.  I'm installing another 430 and was told the 430 won't work with a 15 inch cable.  GPS antenna to be between 13 and 15 feet.  If I can mount an antenna just 15 inches away from the  	
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		  GPS antenna to be between 13 and 15 feet.  If I can mount an antenna just 15 inches away from the  	
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Gary
AuCountry Aviation
Home of Team Grumman

reichec

Joined: 23 Apr 2007
Posts: 26

Posted: Mon Nov 26, 2007 3:49 am Post subject: GPS Antenna

If you need a short cable run, install a 3db  attenuator inline and make the cable as short as you want. Otherwise you can  excpect to burn up the front end of the gps reciever due to overload, a $900+  flat rate repair follows.

 [quote]   ---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Mon Nov 26, 2007 10:10 am Post subject: GPS Antenna

The received signal is digital.  This means it only receives 1s and 0s.   

 If the signal is too strong (cable shortened) everything looks like a 1.  If the signal is too low ( cable lengthened) everything looks like a 0.  Either way no data is received.  

   

I guess the folks at Garmin knew what they were doing when they wrote the installation instructions.  Loop the excess wire in as large a loop as practicably possible.  Try to avoid bundling with Xmtr. Coax.  

   

Noel  

   

         

From: owner-avionics-list-server(at)matronics.com [mailto:owner-avionics-list-server(at)matronics.com] On Behalf Of teamgrumman(at)aol.com

 Sent: Monday, November 26, 2007 5:02 AM

 To: avionics-list(at)matronics.com

 Subject: GPS Antenna  

  

  

    	  Quote: 	
		  I've been trying to find an acceptable answer as to why Garmin wants to have the coax cable for the GPS antenna to be between 13 and 15 feet.  If I can mount an antenna just 15 inches away from the unit itself, why do I need to mount the antenna 15 feet away?  

 

  One explanation I got was the 430/530 needed a 3 db loss in the cable.  Now, it seems to me that the stronger the signal at the unit is, the better. For what it's worth, I mounted my antenna (Garmin 430) on the glareshield on my Tiger.That was 4 years ago.  I've never had any problems with losing the signal.  I'm installing another 430 and was told the 430 won't work with a 15 inch cable.   Any ideas? 	


        

  

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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Mon Nov 26, 2007 9:50 pm Post subject: GPS Antenna

So, how long does it take to burn up?  4 years and going strong.

 

 

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Gary
AuCountry Aviation
Home of Team Grumman

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Mon Nov 26, 2007 9:59 pm Post subject: GPS Antenna

I have both a Garmin 430 and an Apollo SL-60 with antennas mounted about 12 to 15 inches away.  Both work fine with no signal loss.  I've flown all over the country with them.  Maybe I'm getting a 3db loss through the plexiglass windshield.

 

 

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Gary
AuCountry Aviation
Home of Team Grumman

reichec

Joined: 23 Apr 2007
Posts: 26

Posted: Tue Nov 27, 2007 3:50 am Post subject: GPS Antenna

You have not had a WAAS 430 for 4 years thank  you... That is what we are talking about here and that is where the long coax is  mentioned.

  

  

 Do not archive

 [quote]   ---

Vince Palermo

Joined: 18 Aug 2007
Posts: 13

Posted: Tue Nov 27, 2007 4:19 am Post subject: GPS Antenna

I believe that Garmin is referring to the waas upgrades for the 430/530 series. It also requires that you use double shielded wire, RG-142 or Rg-400. You are right about the short cable length for the 430 and the sl-60, it will work, and so will the gps map series work with a short antenna cable. Also Garmin specs are between -3 and -7 db loss, I wonder if they would approve some kind of impedance matching device in the line???????

 Vincent Palermo

vpalermo(at)tampabay.rr.com (vpalermo(at)tampabay.rr.com)

 



On Nov 27, 2007, at 12:55 AM, teamgrumman(at)aol.com (teamgrumman(at)aol.com) wrote:

[quote]I have both a Garmin 430 and an Apollo SL-60 with antennas mounted about 12 to 15 inches away.  Both work fine with no signal loss.  I've flown all over the country with them.  Maybe I'm getting a 3db loss through the plexiglass windshield.

 

 

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Vincent J. Palermo

schaefer(at)rts-services.
Guest

Posted: Tue Nov 27, 2007 6:09 am Post subject: GPS Antenna

The antenna and electronics for a Garmin WAAS receiver are significantly different than the PRE-WAAS versions of these products.  

In order to allow vertical guidance the receiver must process data much more quickly and the receiver/antennae combination must maintain significantly tighter design tolerances. The antenna for a WAAS receiver is different from a NON WAAS receiver. The new SYSTEM is designed assuming high quality coax of a nominal length (that provides a defined range of loss between the antennae and the receiver). This loss is designed into the system and is part of the WAAS certification that must be measured to be IFR certified for WAAS enhanced approaches. That is the reason for a nominal length of antennae wire of course with approved connectors. There are devices that can be installed into the antennae path that add the required loss for the cases where the antennae is adjacent to the receiver. It is also why many installations with antennas remotely installed must be rewired, because the loss allowed for previous non WAAS receivers is out of limits. The days of cheap coax and/or connectors, or multiple connectors are gone for a WAAS approved system! Then entire path must be verified (by measurement) to be within design guidelines as part of the installation certification process.  

   

   

         

  

From: owner-avionics-list-server(at)matronics.com [mailto:owner-avionics-list-server(at)matronics.com] On Behalf Of Charles Reiche

 Sent: Tuesday, November 27, 2007 5:48 AM

 To: avionics-list(at)matronics.com

 Subject: Re: GPS Antenna  

  

     

You have not had a WAAS 430 for 4 years thank you... That is what we are talking about here and that is where the long coax is mentioned.  

    

   

    

   

    

Do not archive  

  [quote]    

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Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Tue Nov 27, 2007 6:10 am Post subject: GPS Antenna

With the Gallium Arsenide RF preamplifiers most of these units have there is a real chance that you can overload the pre amp and burn it out…  Perhaps your GPS doesn’t have one of those amps.  If it does have one and it burns out the whole unit will just stop operating.  It is possible that your units have preamp protection.  

   

I maintain the best thing to do is to follow the installation manual to the letter.  Then if you can afford to replace the unit, play with things like shortening cables.  If it still works, great.  If it stops working, nothing ventured nothing gained.  

   

Noel  

         

From: owner-avionics-list-server(at)matronics.com [mailto:owner-avionics-list-server(at)matronics.com] On Behalf Of teamgrumman(at)aol.com

 Sent: Tuesday, November 27, 2007 2:25 AM

 To: avionics-list(at)matronics.com

 Subject: Re: GPS Antenna  

  

  

   

I have both a Garmin 430 and an Apollo SL-60 with antennas mounted about 12 to 15 inches away.  Both work fine with no signal loss.  I've flown all over the country with them.  Maybe I'm getting a 3db loss through the plexiglass windshield.

 

 

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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Wed Nov 28, 2007 10:18 pm Post subject: GPS Antenna

I talked to a tech/engineer at Garmin.  The spec has been changed to a minimum of 1 1/2 db loss (there is that much loss in a 90 degree adapter.), maximum of 6 db.

 

 

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Gary
AuCountry Aviation
Home of Team Grumman

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