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Maintenance Bay Looking for a good mechanic? Got a question about changing a landing light or installing a new radio? Any mechanical questions you've got, someone here probably has an answer for you!

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Old April 12th, 2012, 11:53 AM   #1
Jeff F JeffFranks is offline
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Nav/VOR issues

I bought a C172H 6 years ago. When we first got it, the stock radios (yes...old) worked great for Nav (the Com is split out to a stand alone now). The OBS's were responsive and picking up a radial was simple.

After about a year, both OBS's started getting 'sluggish'. They would require more altitude or closer range to the VOR before they'd go active. Then once they were active, finding the exact radial became almost impossible (you could get it within 10-15 degrees at best).

So, fast forward to yesterday. I climb up to 3500ft and can't pick up ANY VOR's in my area (one about 15 miles away, the others about 25-30). I attempted to IDENT all three, but got nothing but static over the headphones no matter which of the two NAV's I used.

My question is this. Is there a single point of failure (e.g. a single antennae or antennae connection) that would cause BOTH NAV/OBS's to gradually fail at the same level (first both worked, then both kinda worked, then both failed at the same time)? I need the VOR's for my PPL Checkride in 3 weeks (yes, I've owned a plane for 6 years and flown on 90 day signoffs the whole time!) and I don't wont to spend a fortune on new radios.

Thanks for any help!

jf
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Old April 12th, 2012, 12:52 PM
Posted in reply to JeffFranks's post "Nav/VOR issues"
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John John Collins is offline
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Re: Nav/VOR issues

The Nav receivers antenna input are most likely connected to a splitter that in turn is connected to your Nav antenna. The points of common failure start at the Nav antenna, the coax to the splitter, then the splitter.
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Old April 12th, 2012, 01:06 PM
Posted in reply to JeffFranks's post "Nav/VOR issues"
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Re: Nav/VOR issues

Quote:
Originally Posted by JeffFranks View Post
I bought a C172H 6 years ago. When we first got it, the stock radios (yes...old) worked great for Nav (the Com is split out to a stand alone now). The OBS's were responsive and picking up a radial was simple.

After about a year, both OBS's started getting 'sluggish'. They would require more altitude or closer range to the VOR before they'd go active. Then once they were active, finding the exact radial became almost impossible (you could get it within 10-15 degrees at best).

So, fast forward to yesterday. I climb up to 3500ft and can't pick up ANY VOR's in my area (one about 15 miles away, the others about 25-30). I attempted to IDENT all three, but got nothing but static over the headphones no matter which of the two NAV's I used.

My question is this. Is there a single point of failure (e.g. a single antennae or antennae connection) that would cause BOTH NAV/OBS's to gradually fail at the same level (first both worked, then both kinda worked, then both failed at the same time)? I need the VOR's for my PPL Checkride in 3 weeks (yes, I've owned a plane for 6 years and flown on 90 day signoffs the whole time!) and I don't wont to spend a fortune on new radios.

Thanks for any help!

jf
I see two possibilities. The most likely is the antenna which is quite commonly shared between all VHF and UHF nav receivers (e.g. VOR-LOC& GS) with the use of a "splitter". If you do have that setup then any problem with the antenna, antenna cable (to the splitter) or the splitter itself could affect both VOR receivers.

Another one would be RF interference from a source on the airplane. That should be fairly obvious if you listen to the nav audio.
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Old April 12th, 2012, 01:11 PM
Posted in reply to JeffFranks's post "Nav/VOR issues"
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iHenning Henning is offline
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Re: Nav/VOR issues

I'd be looking for corrosion on the ground plane to the battery while you're chasing around as well.

Did an ACR treatment on a 172 before and the owner later commented how much better his radios were working.
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Old April 12th, 2012, 04:21 PM
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Piloto Piloto is offline
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Re: Nav/VOR issues

Jeff

Most common cause of your problem is corrosion on the antenna/splitter connectors. Disconnect each related connector and spray contact cleaner into the pin.

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