[Boatanchors] CAA modulation indicator question...

[Gary Peterson]

I have an interesting piece of test equipment in a very nice, green, felt-lined, wood case.

The label on the hinged lid contains the following information:

MODULATION INDICATOR
made for
DEPARTMENT OF COMMERCE
CIVIL AERONAUTICS ADMINISTRATION
TYPE CA-1433  CONTRACT Cca-28705
SERIAL NO. 43
NATIONAL ELECTRONICS LABS., INC.
WASHINGTON 9, D.C.

The unit has a percent modulation meter with two ranges (35% & 100%) with switch for positive and negative peaks.

There are tuning and sensitivity controls and a headphone jack.

There is a laminated schematic with operating instructions on the inside of the wood box’s lid.  There is no indication as the the frequency range covered by this unit. 

There is an attachable whip antenna with N male connector.

I have not been able to find any information regarding this unit on the Internet.

I am guessing that this was used to measure the modulation on transmitters on the aircraft band (108 to 137 MHz?).

I would appreciate hearing from anyone who has familiarity with this cool device.  Thanks in advance.

Gary, KØCX