TACAN

Bob Moore wrote:

"M. J. Powell" wrote

Except ICs instead of valves?

It wasn't the size of the electronics, but rather the
large antenna array required of the VOR system. A VOR
antenna must be permanently aligned to the earth,
something not possible with such a large array onboard
a ship. The TACAN system operating on a different
principle than VOR solved the size and alignment problems.

The writeup at
http://www.radarpages.co.uk/mob/nava...can/tacan1.htm
has already been mentioned.

Aside from size and earth orientation, TACAN has two advantages
over VOR for shipboard use.

1. TACAN uses a bearing reference direction of due east. For a
shipboard installation, that means a properly corrected compass
reference and a means of correcting the antenna orientation.

2. TACAN incorporates a ranging transponder (DME) in the
transmitter site. The aircraft interrogates the system, and the
site's transponder responds after a fixed 50 microsecond delay.
The site's azimuth and range are typically displayed on a
combined bearing/distance/heading indicator. The combination of
bearing and range display clears up any of the to/from confusion
possible with VOR sites.

| George Ruch
| "Is there life in Clovis after Clovis Man?"

Bob Moore wrote:
A VOR
antenna must be permanently aligned to the earth,

Why? Why not have a heading indicator (or DG) to drive the 'angles' (i.e.
phase) it sends out?

Hilton

Hilton wrote:
Bob Moore wrote:
A VOR

antenna must be permanently aligned to the earth,


Why? Why not have a heading indicator (or DG) to drive the 'angles' (i.e.
phase) it sends out?


An advantage of VORs over TACANs is the VOR antenna does not physically
more, whereas it does in a TACAN. Electronic "rotation" of the antenna
intuitively makes shipboard use easier, but I might not understand ships
enough!

Stubby wrote:

Hilton wrote:
Bob Moore wrote:
A VOR

antenna must be permanently aligned to the earth,

Why? Why not have a heading indicator (or DG) to drive the 'angles' (i.e.
phase) it sends out?

An advantage of VORs over TACANs is the VOR antenna does not physically
more, whereas it does in a TACAN. Electronic "rotation" of the antenna
intuitively makes shipboard use easier, but I might not understand ships
enough!

Operating frequencies dictate the size of the antenna array.
Compare this picture of a TACAN site at
http://en.wikipedia.org/wiki/TACAN with this one of a VOR site at
http://en.wikipedia.org/wiki/VOR.

Other advantages:
Range: TACAN DME has a maximum range of 300 NM miles. VOR
reception range is limited to 25 - 130 NM, depending on the
site's transmitter power.

Bearing accuracy: TACAN can provide bearing resolution of +- 1
degree. Typical VOR bearing accuracy is +- 2 degrees.

A bearing error of 1 degree at 100 miles isn't likely to be
critical on land, but that same error at sea can mean the
difference between finding your carrier and a very long swim
home.

| George Ruch
| "Is there life in Clovis after Clovis Man?"

George Ruch wrote

Operating frequencies dictate the size of the antenna array.
Compare this picture of a TACAN site at
http://en.wikipedia.org/wiki/TACAN with this one of a VOR site
at http://en.wikipedia.org/wiki/VOR.

Actually George, the first picture is a VORTAC, a TACAN and VOR
installation. The TACAN is just the round cylinder part and that
is what makes it so easy to mount onboard a ship.

Bob Moore

George Ruch wrote:


Other advantages:
Range: TACAN DME has a maximum range of 300 NM miles. VOR
reception range is limited to 25 - 130 NM, depending on the
site's transmitter power.

But, civil aircraft use the TACAN's DME, so they should see the same
range for DME, shouldn't they

Bearing accuracy: TACAN can provide bearing resolution of +- 1
degree. Typical VOR bearing accuracy is +- 2 degrees.

A bearing error of 1 degree at 100 miles isn't likely to be
critical on land, but that same error at sea can mean the
difference between finding your carrier and a very long swim
home.

Help me with that one. The TACAN ground station is on the ship, right?

If so, angular errors diminish as you approach the station and you
should end up at the ship, whether you started at 150 miles out with a 1
or 2 degree error.

I wonder if the TACAN has to move physically. That may be an old
design. Looking at the portable tacan posted later in the threads, it
doesn't look very mechanical.


Stubby wrote:
Hilton wrote:
Bob Moore wrote:
A VOR

antenna must be permanently aligned to the earth,


Why? Why not have a heading indicator (or DG) to drive the 'angles' (i.e.
phase) it sends out?


An advantage of VORs over TACANs is the VOR antenna does not physically
more, whereas it does in a TACAN. Electronic "rotation" of the antenna
intuitively makes shipboard use easier, but I might not understand ships
enough!