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GPS and NAV Antenna's for IFR - I would do differently

N

N523RV

Well Known Member
I started working on my IFR ticket in my RV-9A. I've noticed two things...

1) My KLN-89B gives me frequent RAIM warnings while shooting GPS approaches. I _think_ this is because I have my GPS antenna mounted under the cowling and when there are big changes in headings, it looses some satellites and has to recalculate. I intend to move the antenna either up to the glareshield or on the top of the fuselage that will hopefully correct this issue.

2) My Bob Archer NAV antenna isn't performing up to my standards. I have the wingtip antenna. I've shot a number of VOR approaches where the flags are wiggling like crazy trying to keep a signal and a couple of times have flagged all the way. In my opinion, I was close enough and high enough to receive sufficient signal. I think for normal VFR type stuff, this antenna is sufficient but I intend to switch to the Cat whiskers type antenna at my next annual.

Just something to consider for anyone still building and going the IFR route. I'll post my findings when I make my changes.
 
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N523RV said:
I started working on my IFR ticket in my RV-9A. I've noticed two things...

1) My KLN-89B gives me frequent RAIM warnings while shooting GPS approaches. I _think_ this is because I have my GPS antenna mounted under the cowling and when there are big changes in headings, it looses some satellites and has to recalculate. I intend to move the antenna either up to the glareshield or on the top of the fuselage that will hopefully correct this issue.

2) My Bob Archer NAV antenna isn't performing up to my standards. I have the wingtip antenna. I've shot a number of VIR approaches where the flags are wiggling like crazy trying to keep a signal and a couple of times have flagged all the way. In my opinion, I was close enough and high enough to receive sufficient signal. I think for normal VFR type stuff, this antenna is sufficient but I intend to switch to the Cat whiskers type antenna at my next annual.

Just something to consider for anyone still building and going the IFR route. I'll post my findings when I make my changes.
Click to expand...

The antenna location is not the problem. Been done 100s time before. Its either the performance of the radio or the installation. I too use the Archer antenna and have never lost a signal in 2 years. My GPS antennas are also under fiberglass cover plates just forward of the windshield (some would say a poorer location than under the cowling). Never have I seen less than 10 satellites tracking and never a RAIM warning (Garmin 430).

For the archer antenna make sure you have it well grounded. I placed copper tape along the edge of it and scuffed the underside of the wing skin where it contact it. This is the best VOR/ILS antenna I've ever used.

What kind of indicator are you using for the VOR/ILS? How old is the KLN-89B?

Steve
7A flying IFR for 2 years
 
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Steve,

I'm using a KX-155 and KLN-89B with a KI-209A CDI and MD41 annunciator. The 89B has all of the updates (I think). Below are pictures of my NAV and GPS antenna installs. For the NAV, I just have the screws going through the nutplates... probably need to do something better with that? I think I'll still move the GPS antenna and see if that helps.. maybe the older hardware just does't work as well with changes in satellites.

P6260131-789425.jpg



Pb260254-776825.jpg


sjhurlbut said:
The antenna location is not the problem. Been done 100s time before. Its either the performance of the radio or the installation. I too use the Archer antenna and have never lost a signal in 2 years. My GPS antennas are also under fiberglass cover plates just forward of the windshield (some would say a poorer location than under the cowling). Never have I seen less than 10 satellites tracking and never a RAIM warning (Garmin 430).

For the archer antenna make sure you have it well grounded. I placed copper tape along the edge of it and scuffed the underside of the wing skin where it contact it. This is the best VOR/ILS antenna I've ever used.

What kind of indicator are you using for the VOR/ILS? How old is the KLN-89B?

Steve
7A flying IFR for 2 years
Click to expand...
 
Copper tape

Place some copper tape on the flange of the wing tip. That way it will be sandwiched between the tip and wing skin. Scuff up the wing skin with some emery cloth along the contact point. Punch holes for the screws with a nail or something sharp. That way you'll get a really good ground contact. Like I said my ILS is very accurate every time and I can pick up VORs at longer distances than I'm used to.

The KLN89 is only a 8 channel receiver. Typically are you getting all 8 channels filled?

Another suggestion is to move the GPS antenna higher. My GPS antenna for my 430 is about 1/8" below the fiberglass panel. Almost touches it. Your antenna will not see any satellites that are in the back 180 degrees of the antenna view due to firewall blocking it.

Steve
7A
 
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Thanks Steve. I'll look for some copper tape and get that ground connection better to see if that improves the range.

Next time I go fly, I'll watch the channels to see how many I get and do some turns to see if it changes as I make turns. It does always seem to happen when I'm landing to the south.



sjhurlbut said:
Place some copper tape on the flange of the wing tip. That way it will be sandwiched between the tip and wing skin. Scuff up the wing skin with some emery cloth along the contact point. Punch holes for the screws with a nail or something sharp. That way you'll get a really good ground contact. Like I said my ILS is very accurate every time and I can pick up VORs at longer distances than I'm used to.

The KLN89 is only a 8 channel receiver. Typically are you getting all 8 channels filled?

Another suggestion is to move the GPS antenna higher. My GPS antenna for my 430 is about 1/8" below the fiberglass panel. Almost touches it. Your antenna will not see any satellites that are in the back 180 degrees of the antenna view due to firewall blocking it.

Steve
7A
Click to expand...
 
N523RV said:
Next time I go fly, I'll watch the [GPS] channels to see how many I get and do some turns to see if it changes as I make turns. It does always seem to happen when I'm landing to the south.
Click to expand...

Since GPS satellites are not geostationary, the disposition of various visible SV's within the constellation changes on a constant basis. So it's probably just your imagination. :)

mcb
 
Steve,

I owe you a beer or two.... I ordered some copper foil tape and did as you suggested. It mad a big improvement! I think the nutplates would probably work OK if you remember to polish off the finish but the foil tape certainly does the trick!

I haven't moved the GPS antenna yet to see if that resolves my RAIM issues. I'll try and tackle that this weekend.

Matthew

sjhurlbut said:
Place some copper tape on the flange of the wing tip. That way it will be sandwiched between the tip and wing skin. Scuff up the wing skin with some emery cloth along the contact point. Punch holes for the screws with a nail or something sharp. That way you'll get a really good ground contact. Like I said my ILS is very accurate every time and I can pick up VORs at longer distances than I'm used to.

The KLN89 is only a 8 channel receiver. Typically are you getting all 8 channels filled?

Another suggestion is to move the GPS antenna higher. My GPS antenna for my 430 is about 1/8" below the fiberglass panel. Almost touches it. Your antenna will not see any satellites that are in the back 180 degrees of the antenna view due to firewall blocking it.

Steve
7A
Click to expand...
 
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