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1. 10:05 AM - Re: Garmin SL-30 poor VOR reception (Matt Dralle)
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Subject: | Re: 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:
>
>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@matronics.com Email
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