Thank you Mike and Mark for your replies.
I wasn't  to far off the mark in guessing it preceeded the ZB. Wishing you both a Merry Christmas.
Paul
N6FEG 

On Sun, Dec 24, 2023, 2:32 PM MARK DORNEY <mkdorney@aol.com> wrote:
The ZA radio system was an instrument landing system used by the USN and USMC during WW2.

 Mark D.
WW2RDO

“In matters of style, float with the current. In matters of Principle, stand like a rock. “.   -   Thomas Jefferson

Sent from my iPhone

> On Dec 24, 2023, at 1:57 PM, Paul Thekan <pfthekan@gmail.com> wrote:
>
> 
> Merry Christmas...
>
> I came across a Test Oscillator CDE-60050 for " ZA series equipt" Not sure if this preceeded the ZB radio...or this is something completely different.
>
> Tnx
> Paul
> N6FEG
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