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Garmin SL-30 poor VOR reception

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dean.psiropoulos(at)veriz
Guest

Posted: Thu Apr 24, 2014 8:18 pm Post subject: Garmin SL-30 poor VOR reception

Hello listers:



I have an RV-6A that I've been flying for a few years. When I first started

flying the airplane I did some rough VOR range reception checks with the

SL-30 and I had to get within 20 miles of a VOR station to get the receiver

to lock on and the OBS indicator to stabilize with no flag displayed.  I

continued with the flight test regimen and getting familiar with the

airplane and enjoying it.  Since flights have been in VFR conditions around

the busy Tampa (Florida) airspace I used the panel mounted moving map

(GPS/Comm) to make sure I stayed out of the Class B, there was no need to

have good VOR reception. The Com portion was the only thing I was using on

the SL-30 and that worked very well.  Then, a couple months ago I turned on

the SL-30 and, nothing, no display or Com so I returned the unit to Garmin

for repair.    In the meantime I'd been talking to a CFII about working on

my instrument proficiency to get back up to FAA standards after a long

hiatus.  When the SL-30 was repaired and back in the instrument panel I took

off on a flight to Ocala to check it out.  I climbed up to 4500 feet and

watched the OBS and listened for the ID code as I entered the 40 mile radius

of the Ocala VOR. Nothing so I kept going on a course straight for the

station. Around 20-25 miles out I started getting activity on the indicator

but the flags were intermittent and the radio could not maintain a lock.

Finally about 15 miles out the indicators stabilized and the flags stayed

off, obviously something is amiss. 



I'm using a Comant CI-159 VOR/ILS antenna.  This unit consists of a phenolic

"puck" with a BNC connector cast into it for the coax connection.  There are

two fiberglas elements (thin rods about 18 inches long) that screw into the

puck to form a "V" shaped antenna.  I have it mounted on the bottom of the

fuselage in the back of the airplane under the horizontal stabilizer.  The

BNC sticks through a hole in the belly and appx 25 foot length of RG-58 coax

runs inside the aircraft up to the SL-30 receiver.  No gasket was supplied

with the antenna so I just bolted the puck to the aluminum using the two

bolt holes.  After the Ocala flight I removed the puck and elements for

closer inspection and checked the connector on the coax cable at the antenna

end.  Nothing wrong that I could tell just by looking at the equipment.

There was a bit of engine oil (from the exhaust) on the puck surface facing

the skin.  I cleaned it off and made a gasket to go between the puck and the

skin to minimize the oil build up again.  I have not flown the airplane

since but I doubt that lack of a gasket was causing the poor reception,

maybe someone here can tell me.  The other thing I checked was the

resistance between the center pin and outside barrel of the BNC connector on

the antenna.  Resistance was showing basically a dead short (less than 1

ohm, same reading as touching the meter probes together).  I'm not an

antenna designer so I don't know if this is what the reading should be or

not.  Aircraft Spruce has the following description for this antenna: " "V"

Dipole VOR/Glide Slope Antenna with detachable elements is similar to the CI

158C-3 with the exception of offering 2-hole mount instead of a 4-hole

mount. This V Dipole encompasses reduced static capability with the use of

P-Stat paint. Integral ferrite balun provides for higher radiation

efficiency." .  I don't know if the construction of the antenna would cause

the meter to show such a low resistance, maybe some here could shed some

light on that.  



Any ideas, experiences with poor VOR reception here on the list? Since the

radio has been repaired and tested by the factory I'd say it's not the

radio.  I checked the connector at the back of the radio tray and it appears

secure so I'm not sure what else to do.  Since VORs are being decommissioned

there is going to be less and less need for VOR reception but if I have to

use victor airways during instrument operations I need to have good

reception at the expected range or I won't be able to comply with ATC

clearances.  Thanks for the help



Dean Psiropoulos

RV-6A   N197DM

200+ hours since 2008

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Matt Dralle
Site Admin

Joined: 08 Nov 2005
Posts: 26320
Location: Livermore CA USA

Posted: Fri Apr 25, 2014 9:05 am Post subject: Garmin SL-30 poor VOR reception

I just went and measured the resistance between the center pin and the outside connector on my CI-158C and it too is basically a short, so that part seems "normal".  I would do a similar test on your cable with both ends disconnected.  That should be infinate resistance.



Are you using "RG-58A" or "RG-58C/U"?  "RG-58A" is really lossy.  ""RG-58C/U" is better, but still not that great.  I would strongly recommend RG-142 or RV-400 for that application.  I have RG-142 installed in my RV-8 connected to an SL-30 and to a CI-158C antenna mounted in the top of my vertical stab and I get outstanding reception.



Pull the RG-58 out, get some RG-142 and some high-quality BNC connectors (the crimp-on kind NOT the screw-on kind) and then see how things work.  You may still have a problem with the NAV receiver on the SL-30, but upgrading your cable will go a long way in improving your reception in any case.



Matt

At 09:17 PM 4/24/2014 Thursday, you wrote:

 	  Quote: 	
		  



Hello listers:



I have an RV-6A that I've been flying for a few years. When I first started

flying the airplane I did some rough VOR range reception checks with the

SL-30 and I had to get within 20 miles of a VOR station to get the receiver

to lock on and the OBS indicator to stabilize with no flag displayed.  I

continued with the flight test regimen and getting familiar with the

airplane and enjoying it.  Since flights have been in VFR conditions around

the busy Tampa (Florida) airspace I used the panel mounted moving map

(GPS/Comm) to make sure I stayed out of the Class B, there was no need to

have good VOR reception. The Com portion was the only thing I was using on

the SL-30 and that worked very well.  Then, a couple months ago I turned on

the SL-30 and, nothing, no display or Com so I returned the unit to Garmin

for repair.    In the meantime I'd been talking to a CFII about working on

my instrument proficiency to get back up to FAA standards after a long

hiatus.  When the SL-30 was repaired and back in the instrument panel I took

off on a flight to Ocala to check it out.  I climbed up to 4500 feet and

watched the OBS and listened for the ID code as I entered the 40 mile radius

of the Ocala VOR. Nothing so I kept going on a course straight for the

station. Around 20-25 miles out I started getting activity on the indicator

but the flags were intermittent and the radio could not maintain a lock.

Finally about 15 miles out the indicators stabilized and the flags stayed

off, obviously something is amiss. 



I'm using a Comant CI-159 VOR/ILS antenna.  This unit consists of a phenolic

"puck" with a BNC connector cast into it for the coax connection.  There are

two fiberglas elements (thin rods about 18 inches long) that screw into the

puck to form a "V" shaped antenna.  I have it mounted on the bottom of the

fuselage in the back of the airplane under the horizontal stabilizer.  The

BNC sticks through a hole in the belly and appx 25 foot length of RG-58 coax

runs inside the aircraft up to the SL-30 receiver.  No gasket was supplied

with the antenna so I just bolted the puck to the aluminum using the two

bolt holes.  After the Ocala flight I removed the puck and elements for

closer inspection and checked the connector on the coax cable at the antenna

end.  Nothing wrong that I could tell just by looking at the equipment.

There was a bit of engine oil (from the exhaust) on the puck surface facing

the skin.  I cleaned it off and made a gasket to go between the puck and the

skin to minimize the oil build up again.  I have not flown the airplane

since but I doubt that lack of a gasket was causing the poor reception,

maybe someone here can tell me.  The other thing I checked was the

resistance between the center pin and outside barrel of the BNC connector on

the antenna.  Resistance was showing basically a dead short (less than 1

ohm, same reading as touching the meter probes together).  I'm not an

antenna designer so I don't know if this is what the reading should be or

not.  Aircraft Spruce has the following description for this antenna: " "V"

Dipole VOR/Glide Slope Antenna with detachable elements is similar to the CI

158C-3 with the exception of offering 2-hole mount instead of a 4-hole

mount. This V Dipole encompasses reduced static capability with the use of

P-Stat paint. Integral ferrite balun provides for higher radiation

efficiency." .  I don't know if the construction of the antenna would cause

the meter to show such a low resistance, maybe some here could shed some

light on that.  



Any ideas, experiences with poor VOR reception here on the list? Since the

radio has been repaired and tested by the factory I'd say it's not the

radio.  I checked the connector at the back of the radio tray and it appears

secure so I'm not sure what else to do.  Since VORs are being decommissioned

there is going to be less and less need for VOR reception but if I have to

use victor airways during instrument operations I need to have good

reception at the expected range or I won't be able to comply with ATC

clearances.  Thanks for the help



Dean Psiropoulos

RV-6A   N197DM

200+ hours since 2008 


	


Matt G Dralle | Matronics | 581 Jeannie Way | Livermore | CA | 94550

925-606-1001 V | 925-606-6281 F | dralle(at)matronics.com Email

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Matt Dralle
Matronics Email List Administrator

dlj04(at)josephson.com
Guest

Posted: Sat Apr 26, 2014 5:01 am Post subject: Garmin SL-30 poor VOR reception

Matt wrote:



 	  Quote: 	
		  

 Are you using "RG-58A" or "RG-58C/U"?  "RG-58A" is really lossy.  ""RG-58C/U" is

 better, but still not that great.  I would strongly recommend RG-142 or RV-400

 for that application.  I have RG-142 installed in my RV-8 connected to an SL-30

 and to a CI-158C antenna mounted in the top of my vertical stab and I get

 outstanding

I wonder what the source of that information is. Commercial RG-58A, mil 
	


spec RG-58 (MIL-DTL-17 M17/28-RG058) such as Belden 9203, RG-142 and 

RG400/LMR400 are all rated between 3.3 and 4.9 dB per 100 ft at 100 MHz 

-- around 1 dB for a practical airplane installation.

 	  Quote: 	
		  

 Pull the RG-58 out, get some RG-142 and some high-quality BNC connectors (the crimp-on

 kind NOT the screw-on kind) and then see how things work.  You may still

 have a problem with the NAV receiver on the SL-30, but upgrading your cable

 will go a long way in improving your reception in any case.

Original RG-58 cable was just fine for decades with receivers far worse 
	


than the Garmin. In my experience, connectors are the problem nine times 

out of ten. Commercial grade crimp connectors from a manufacturer that 

also supplies military grade connectors (Amp, Amphenol, Kings) crimped 

with the manufacturer-specified tool checked for the correct crimp 

dimensions by someone experienced with this process is the key. Original 

military soldered connectors are also OK but only if the installer is 

experienced enough to get the dimensions right without melting the 

dielectric.



Quick test, after you've confirmed that the cable has continuity end to 

end and isn't shorted: grab the cable in one hand and the body of the 

connector in the other. Using moderate force, can you rotate the 

connector body with respect to the cable? If so, cut it off and try 

again, it is not terminated correctly. This isn't the cause of all 

problems but is usually diagnostic of whether it was crimped right in 

the first place.

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