rocketbob

rocketbob

Well Known Member
Just got a nice and shiny used KLN94 for my Rocket. No glass, intentionally so, because I don't care to spend money on that stuff so I need an OBS with a resolver. After seeing what they cost I figured out I could make a solid-state one for a couple of bucks because thats the sort of thing I like to do.

So.

As far as how a resolver works, there is a sin output from the gps, and that is a 30hz AC signal. The cos input back into the gps is a phase-shifted 30hz signal and when both are in phase the OBS should read 300 degrees.

Is this correct?
 
Hi Bob,

It's not that simple. 30 Hz is used by VORs since that's the frequency they are "rotated" at.

From the KLN 94 manual I found on line:

Box supplies an OBS signal out, 6 volts peak, 40 ma max, at 450Hz.
CDI resolver sends back two signals, a "sine" and a "cosine", 90 degrees apart. I do not know on what OBS setting the sine is in phase with the input signal.

Strictly speaking* the OBS is not necessary. Get an inexpensive CDI without one. If a resolver is not hooked up the box will ask you to enter one, using the box's knobs, if you want to use the OBS mode. It it just more awkward that way. *Manual notes that local FSDO's may require the external OBS for IFR certification.

In practice the only time I use the OBS setting is for a hold which is not on the current track (e.g., I'm going east on V244, inbound to ECA and get "Hold north of BYRON on the SAC 177 radial, etc.). That is to say, very rarely. In these older boxes OBS mode can also be of use during procedure turns.

If you intend to use the box for ifr gps approaches I think you do need to install some annunciation lights and acknowledgement switches, that should be easy.
 
OK thanks Bob. I read the part in the manual about the resolver not being necessary, but I figured it would be used more often. I have an MD41 but am considering just putting my own switches and annunciators in.
 
rocketbob said:
OK thanks Bob. I read the part in the manual about the resolver not being necessary, but I figured it would be used more often. I have an MD41 but am considering just putting my own switches and annunciators in.
Click to expand...

I'm surprised you didn't smelt your own aluminum Pooner!

You da man!

Badger/ Mutha
 
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