[Milsurplus] Navigation System

[J. Forster]

Unserviceable but Repairable wrote:

> You kindly sent me an excerp of the BC-431 manual & it shows that
> the BC-433/SCR-269 is same with 2050 thyratron loop/servo-drivers added to
> make it an adf... rather than a manual 'unilateral' (one null) df like the
> bc-431 or navy DZ  (neat - ed)

The 2050s were also used in the MN-31 Loop Controller, a box added to the MN-26
to make it into the MN-31 ADF.

> What confounds me is that if the one-null manual '431 & automatic '433
> were built by Bendix per legend, why'd the MN-26 manual two-null df
> soldier-on thru the war.  And go on 'til the manual one-null MN-31
> happened later.

The MN-26 is not really two nulls, if you look at the meter properly. If the
station is on one null of the loop, the meter pointer follows the loop direction
as you turn the crank. If it's on the other null, the meter pointer goes in the
opposite direction to the crank...  that's how you know where the station is. To
do this, you need both the loop and the sense antennas.

The MN-31 automated the process. One null (the wrong one) was unstable and the
servo loop would drive the antenna around to the correct one. Think of a peak
and valley...  the peak is unstable and the valley is stable.

BTW, there is a write-up of the ADF by the Bendix folks  here:
http://wireless-set-no19.trackpads.net/compases.htm

-John

> [snip]
> If it was some jurrasic two-null thing a "turn & watch null precession"
> would have eliminated ambiguity.  Lady B discoverers sed navigator's desk
> covered w. comics perhaps indicative that flight-deck didn't confide in
> navigator.  Have never seen that theorized.

See above. You either have to turn the plane or the loop to ID whether you are
on the true or false null with the MN-26.  BTW, if the sense antenna were lost,
it'd be hard to figure out which null was the correct one on either the manual
or ADF.

-John

> signed
>
>    the mf question man