Charlie Springer wrote:
On Thu, 2 Jun 2005 22:39:21 -0700, Eunometic wrote
(in article . com):

I'm not sure I understand what you mean. There were 'rossete scans'
that ended up in latter versions of sidewinder thse use a sort of
rotating and oscialting mirror. These also ended up in early German
infrared seekers intended for terminal homing on the Wasserfall missile
but actually derived from infrared imaging systems such as "Spanner".

There is a tracker form with a reticule that is half transparent and half
opaque and spun by a synchronous motor, so there is a reference for the
position of the reticle over time. The amount of time and the angle over
which the target is obscured generates the error signal. When perfectly
centered the signal is constant (half is always blocked).

If I could center it well enough, I could half mask the secondary of a
Cassigrain and spin it. I just find the analog solution more satisfying than
a digital image tracker.


I think I know how to do it.

You need to understand "phase sensitive demodulators". There are like
rectifiers whose polarity of rectification is dependent on a reference
phase. In their most basic form they consist of vibrating relays,
biased diodes or amplifier valves or transisters whose
gates/grids/bases are switched by a phase reference such that the
signals polarity is demodulated according to its phase.

So, consider, as the disk rotates you want to resolve into rectangular
x-y co-ordinates to opperate your star tracking device or missile fins.

To generate the x co-ordinate for instance you have a square wave
reference of period equal to the rotation of the disk and in phase with
it (generated by a light source and photocell on the priphery for
example or a commutating switch, or your stepper reference etc). This
is the reference phase for the demodulator. The demodulator could be
as simple as a fast relay or it could be electronic. The demodulator
will generate negative or postive value depending on whether the
'target' is in the positive (right) or negative (left).

For the y (vertical axis) co-ordinate you need to have a second square
wave 90 degree delayed created by a second light/photocell or some such
internal reference.

It's crude as you only get +/-x and +/-y signals. You don't really
need a square wave, sinusoid is uselff. Sin-Cos potentiometers also
resolve polar to rectangular co-ordinates.




I thought the turbine wheels in the fins of the Sidewinder were stabilizers
and generators, so it didn't need any batteries. I may be thinking of
something else.

I'm pretty sure they acted as gyros mechanically on the fins to roll
stablise it.



-- Charlie Springer