Our new FDVI Mark 4 Systems are now in full- quadrature, push pull.

This improvement over our previous Mark III Systems provides two additional signals which are negative polarity versions of the normal "sin" and "cos" signals. This is the so-called "push-pull" implementation. It was originally discovered by Will Hemsing and has been the standard for years in "conventional" VISARs, those implemented with free-space beams and all the lenses, mirrors and other complex optics these old technologies require.

We are pleased to announce that the advantages of the "push-pull" configuration are now available in our all-fiber FDVI's as well.

The benefits of the "push-pull" configuration are:

1. Signal strength is doubled

2. Random noise is reduced by a factor of 1.414

3. Background (non-random) signal is virtually eliminated.

The principal benefit is that the two complementary signals can be subtracted from one another, either in the software or electronically by a differential scope input. As a result the signal level is doubled and any background is eliminated.

For example:

y = ("sin" + b.g.) - ("-sin" + b.g.) = 2 sin

x = ("cos" + b.g.) - ("-cos" + b.g.) = 2 cos

and the velocity is derived from arctan (y.x) as before.

In an experiment where backgrounds may be high and signal levels varying, this "push-pull" methodology is very desirable as the uncertainties in the analysis is much reduced.

The only difference in operation is that the new push-pull FDVI system has four output channels and four Series "G" photodetector modules, rather than the three of the standard system.