VOR disparity

[Rich S.]

I have a Collins VOR receiver and a connected Collins VOR/LOC display
installed in the Emeraude.

The receiver has an LED digital display for frequency or bearing. If I
select, say, "from" I will get a display of the bearing from the VOR
station. If I rotate the OBS on the panel VOR/LOC instrument until the
"from" flag appears and the needle centers, the OBS will also give me a
bearing from the station.

Problem is, these bearing don't match. I haven't done comprehensive tests to
determine the difference (it might not eve be the same depending on the
range to the VOR), but it is significant for navigation. Perhaps as much as
5+ degrees if I remember correctly.

This isn't a real problem for me as the VOR is strictly backup. (Let's think
about that, Mr. Corrigan. . .) I'm probably going to take the darn thing out
anyway and sell it before it's value goes down to that of a used SuperHomer.
When I was flying to OSH this year, my navigator (Lt. Col. USAF ret.) asked
me what I'd do if my GPS quit. I replied, "Why, land at the nearest airport
and buy a new one!".

As I write this, I'm thinking that the answer to the question is to take the
plane to an airport which has a VOR test point and check it out. Do such
things still exist? In any case, I probably won't take it to the Collins
repair station and spend a few hundred *new* dollars to get it calibrated.

Anybody else had this problem? Perhaps with two sepatate NAV-COMS giving
different headings?

Rich "A man with two clocks never knows what time it is" S.

[Rip]

Rich S. wrote:
> I have a Collins VOR receiver and a connected Collins VOR/LOC display
> installed in the Emeraude.
>
> The receiver has an LED digital display for frequency or bearing. If I
> select, say, "from" I will get a display of the bearing from the VOR
> station. If I rotate the OBS on the panel VOR/LOC instrument until the
> "from" flag appears and the needle centers, the OBS will also give me a
> bearing from the station.
>
> Problem is, these bearing don't match. I haven't done comprehensive tests to
> determine the difference (it might not eve be the same depending on the
> range to the VOR), but it is significant for navigation. Perhaps as much as
> 5+ degrees if I remember correctly.
>
> This isn't a real problem for me as the VOR is strictly backup. (Let's think
> about that, Mr. Corrigan. . .) I'm probably going to take the darn thing out
> anyway and sell it before it's value goes down to that of a used SuperHomer.
> When I was flying to OSH this year, my navigator (Lt. Col. USAF ret.) asked
> me what I'd do if my GPS quit. I replied, "Why, land at the nearest airport
> and buy a new one!".
>
> As I write this, I'm thinking that the answer to the question is to take the
> plane to an airport which has a VOR test point and check it out. Do such
> things still exist? In any case, I probably won't take it to the Collins
> repair station and spend a few hundred *new* dollars to get it calibrated.
>
> Anybody else had this problem? Perhaps with two sepatate NAV-COMS giving
> different headings?
>
> Rich "A man with two clocks never knows what time it is" S.
>
>
VOR test points certainly do still exist. Check the Airport and
Facilities Directory for one near you. Keep in mind that up to a 6
degree error is permissible between units when doing an airborn check
(as it sounds like you have been doing).

Rip

[Rich S.]

"Rip" > wrote in message
t...
> VOR test points certainly do still exist. Check the Airport and Facilities
> Directory for one near you. Keep in mind that up to a 6 degree error is
> permissible between units when doing an airborn check (as it sounds like
> you have been doing).

Thanks Rip!

6 degrees, huh. Well, I'm likely right at the limit. When the weather gets
better, that'll be a good excuse to go someplace - "Sorry hon, can't go to
the company lunch - gotta verify the VOR".

I never did like VOR much anyway. A/N ranges, that's more like it!

Rich "Dit-dahhhhh" S.

[Jackal24]

Rip > wrote in
t:

> VOR test points certainly do still exist. Check the Airport and
> Facilities Directory for one near you. Keep in mind that up to a 6
> degree error is permissible between units when doing an airborn check
> (as it sounds like you have been doing).
>
> Rip

It is 6 degrees for an airborne checkpoint. It is only 4 degrees when you
are checking one VOR against the other, which is basically what is going on
in this case.

There are many ways to check which one is correct. You can use a VOT
(available at some airports), an approved ground checkpoint, or an approved
airborne checkpoint. These are all listed in the AFD. You can also make
your own airborne checkpoint, or do the dual VOR check (which doesn't
really tell you if the receiver is incorrect, only that the two receivers
agree). If you are not going to take it to a shop, I would recommend the
VOT first, the the ground checkpoint, then the approved airborne. Jim Weir
has also been working on a navigational tester in Kitplanes for the last
few months.

[RST Engineering]

Make that the last three years {;-)


Rich, there ought to be a little tweaky either on the rear of the OBS case
or by removing a knob and finding a hollow shaft for a long, tiny
screwdriver. Find your appropriate ground checkpoint using (as the fellow
suggested) the AFM and tweak it in. Save yourself a few tenths of an AMU.
However, you are merely adjusting, not CALIBRATING, which requires a
certificated repair station.

Jim


> VOT first, the the ground checkpoint, then the approved airborne. Jim Weir
> has also been working on a navigational tester in Kitplanes for the last
> few months.

[Rich S.]

"RST Engineering" > wrote in message
...
>
> Rich, there ought to be a little tweaky either on the rear of the OBS case
> or by removing a knob and finding a hollow shaft for a long, tiny
> screwdriver. Find your appropriate ground checkpoint using (as the fellow
> suggested) the AFM and tweak it in. Save yourself a few tenths of an AMU.
> However, you are merely adjusting, not CALIBRATING, which requires a
> certificated repair station.

Aha! Yoost like de compass, you betcha. . .

I don't suppose there's anything one can do as easily for the bearing
displayed on the digital thingy.

Thanks, Jim

Rich S.

[RST Engineering]

Dunno. THere was on the one I built, but it was an internal adjustment.

Jim


"Rich S." > wrote in message
...
> "RST Engineering" > wrote in message
> ...
>>
>> Rich, there ought to be a little tweaky either on the rear of the OBS
>> case or by removing a knob and finding a hollow shaft for a long, tiny
>> screwdriver. Find your appropriate ground checkpoint using (as the
>> fellow suggested) the AFM and tweak it in. Save yourself a few tenths of
>> an AMU. However, you are merely adjusting, not CALIBRATING, which
>> requires a certificated repair station.
>
> Aha! Yoost like de compass, you betcha. . .
>
> I don't suppose there's anything one can do as easily for the bearing
> displayed on the digital thingy.
>
> Thanks, Jim
>
> Rich S.
>

[Dan, U.S. Air Force, retired]

RST Engineering wrote:
> Dunno. THere was on the one I built, but it was an internal adjustment.
>
> Jim
>
>
> "Rich S." > wrote in message
> ...
>
>>"RST Engineering" > wrote in message
...
>>
>>>Rich, there ought to be a little tweaky either on the rear of the OBS
>>>case or by removing a knob and finding a hollow shaft for a long, tiny
>>>screwdriver. Find your appropriate ground checkpoint using (as the
>>>fellow suggested) the AFM and tweak it in. Save yourself a few tenths of
>>>an AMU. However, you are merely adjusting, not CALIBRATING, which
>>>requires a certificated repair station.
>>
>>Aha! Yoost like de compass, you betcha. . .
>>
>>I don't suppose there's anything one can do as easily for the bearing
>>displayed on the digital thingy.
>>
>>Thanks, Jim
>>
>>Rich S.
>>
>
>
>
"little tweaky?" "digital thingy?" Come on guys, lay off the technical
jargon and use plain English.

Dan, U.S. Air Force, retired