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IFR NAV-750 and 401L To/From

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IFR NAV-750 and 401L To/From

Old 5th Jun 2021, 20:45
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IFR NAV-750 and 401L To/From

I recently used my NAV 401L and NAV 750 test sets to diagnose and repair a couple of KX-170B and a couple of KI 201C Nav Indicators. I had previously only used these test sets for on aircraft equipment testing.

On aircraft both test sets give correct To/From flag sense. However, when the Nav indicator is driven directly by the composite modulation output (rather than using the modulated RF output and an intermediate receiver) the To/From flag sense is reversed. I didn't realize this when I worked on the first KI 201C and spent a lot of time looking for a non existent fault.

This sense reversal is not mentioned in the manuals for the IFR 750 or the NAV 401L. Does anyone familiar with these test sets know where this To/From flag reversal is documented?
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Old 26th Jun 2021, 09:37
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Join Date: May 2021
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I can see taking care of flight and enroute on a sear nav radio/VOR pointer on the off chance that you plan effectively. That leaves the methodology as the most hard to sort out with just a solitary VOR. Are there any? At long last, when documenting IFR, you don't record a particular methodology, so is it legitimate to anticipate a visual if the climate is conjecture to be sufficient for it? This way I figure I could design a basic course requiring just a single VOR.
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Old 27th Jun 2021, 06:00
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Probably get more results here than in Tech Log ?
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Old 8th Jul 2021, 22:57
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Originally Posted by john_tullamarine View Post
Probably get more results here than in Tech Log ?
No reply or unrelated gibberish, not sure which is less helpful. The IFR NAV 750 was a standard test set on many avionics test benches so it's hard to believe that no one except me noticed this flag sense reversal.
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Old 10th Jul 2021, 12:20
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This info may be relevant or not.

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Old 11th Jul 2021, 02:15
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Originally Posted by QA1 View Post

Not, but thanks for the reply.

Both test sets allow generation of a To flag, or a FROM flag on any test bearing. When received as modulated RF the flag sense on the instrument is as sent by the test set. When received as the raw modulation signal the sense is reversed. This has nothing to do with student pilot inability to understand the meaning of TO/FROM flags. It appears to be an undocumented phase reversal in both test sets.
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Old 22nd Jul 2021, 02:36
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Don't know about your KI-201C but some VOR converters require reverse phasing.
E.g. the KX72 described here has 3 composite inputs, one that wants standard phasing and two reversed.
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