ME-61/GRC
Meter, Field Strength

©Brooke Clarke, N6GCE, 2001 - 2023

Introduction and General Information

Equipment Description

The U.S. military has many Field Strength Meters.  These are used for a number of purposes, but the key one is to tune up radios after they are configured on a new frequency.  Ham radio operators use a VSWR meter, but that is not possible on many military radios since the antenna attaches directly to the radio, i.e. there is no place that in the antenna system that's 50 Ohms.

The "PHONES" jack can by used to hear an AM version of the signal being received by the ME-61.  This signal monitor function may be done at the transmitter location in cases where the transmit antenna is located some distance away to confirm that a signal is getting out.

The TM shows the GRC-9 being used to provide a test signal for the ME-61. But the AN/GRC-9 covers only 2 to 12.
The AN/GRC-19 (T-195 & R-392) convers 1.5 to 24 MHz matching the ME-61.

Photos

Photo with 18" sense antenna extended.
Label - made by Multronics, Rockville, MD

Controls, Indicators and Connectors

 

Label	Description	Function
Phones	1/4" mono earphone jack	monitor
(meter)	0 - 1 mA, 100 Ohm	display signal strength
ANT.	18" telescoping	pick up signal
Meter Sensitivity	pot in series with meter	allow signal variations to be seen
Band Switch	select inductor to ground & short the other inductors	frequency range select 1.5 - 4 4 - 10 10- 24 MHz
Tuning	variable capacitor	peak desired signal

Manuals

TM 11-6625-682-15 Operator's and maintenence manual with spare parts C1,C2   21 Dec. 66
TM 11-6625-682-24P Repair parts and special tools. 18 Sep. 78
TM 11-6625-682-15 plus C1. Supercedes TM 11-263 C3 - Available from Robert Downs -

Maintenance Instructions

Opening

Inside the lid is a soft rubber gasket that has been molded around the sheet metal of the box.  It tends to stick to the box, making opening the lid difficult.

This is an air tight seal and if the air temperature in the box is colder than when it was closed there will be a vacuum inside.  Best to open when it's hot and close when it's cold.

Some type of prying persuasion between the latch and lid on the side opposite to the hinge may be required.

Once you have the lid opened, a small amount of Radio Shack Lube Gel (patent 5,037,566) on the box and in the depresion of the gasket is a good idea.

Schematic

I hand drew the schematic many years ago.  Much later I got a manual and extracted the official schematic.

Modification to improve performance with Lofer beacons in the 160 - 190 kHz frequency range by Mitchel Lee.
ME61U.pdf - 211k file

K4CHE op amp modifications. 

2109189 Electrical testing and detecting apparatus, Bly Merwyn, 1938-02-11, - cited by 15 other patents, Vacuum tubes

Potomac Instruments

makes Field Intensity Meters for the AM radio and both VHF and UHF TV broadcast industry.

Model	Freq MHz	Manuals	Antenna
FIM-21	0.54 - 1.6	FIM-21 & FIM-41 Steam Powered Radio	Loop in cover
FIM-22	0.2 - 0.55	1973 catalog World Radio History
FIM-41	0.54 - 1.8 1.8 - 5.0		Loop in cover
PI-4100	0.52 - 5.1	Factory Brochure
FIM-71	45 - 225		Fold up Dipole
FIM-72	450 - 960

This is related to Measuring EMFs - but only useful near broadcast stations.

Surecom SS-11

Surecom makes a passive field strength meter (SS-10) and a version with an op amp between the diodes and meter (SS-11).  Both are specified to wrok 100 kHz to 3 GHz with an SMAf antenna input and telescoping antenna.

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page created 10 June 2001.