U. S. Navy LM Series Crystal Calibrated Frequency Indicating Equipment

Comparison Between Models of the LM Series

Revision 2, December 16, 1998

BY

Ken Corwin, KF6NUR

kenc2@pacbell.net

The LM-(*) Crystal Calibrated Frequency Indicating Equipment was designed to be a simple, accurate, and reliable instrument for adjusting radio transmitters and receivers to any desired frequency in the range from 125 (195 prior to LM-10) to 20,000 kc. The equipment provides accuracies of 0.02 percent in the 125 to 2,000 kc band, and 0.01 percent in the 2,000 to 20,000 kc band. These accuracies can be obtained under the most unfavorable combined influences due to 10 percent changes in filament and/or plate voltage, error in calibration, changing tubes, crystal grinding errors, and variations of ambient temperature in the range from minus 32 to plus 65 degrees Centigrade.

All models of LM Heterodyne Frequency Meters provide RF output modulated at approximately 500 cps if needed for receiver alignment. The audio output impedance of these meters is 600 ohms, which will match the HS-33 headset.

Several contractors manufactured these units in addition to Bendix Radio Div., Bendix Aviation Corp. (CRR) and Mission Bell Radio Mfg. Co., Inc. (CKB). Among them: Loral Electronics Corp. (CBLC), and Admiral Corp. (CQC). The LM-21 is Navy-modified from LM-15 or LM-18 equipment. The prefix NT means, simply, Navy Type.

The Rectifier Power Units were of two types: The original -20104, equipped with a volt meter on the front panel above the compensating switches; and the -20104A, equipped with a red pilot lamp where the volt meter had been.

Each LM-15 Crystal Calibrated Frequency Indicating Equipment consists of the following component units:

QTY

Component

lbs.

1

CKB-74028 Heterodyne Frequency Meter with one set of vacuum tubes (one each of Navy types -76, -77, and -6A7), two neon regulator tubes, and one Navy type CJL-40023B crystal. Dimensions: 8-1/2" x 8-1/8" x 8-7/16".

11.5

1

CKB-10121 Frequency Meter Mounting Base. Dimensions: 7" x 7-7/8" x 1-1/2".

0.5

1

CKB-20104 or -20104A Rectifier Power Unit, complete with one Navy type -84 vacuum tube. Dimensions: 8-3/16" x 8-15/16" x 8-3/16".

13.6

1

CKB-10120 Shockproof Mounting Base for Rectifier Unit. Dimensions: 7-7/8" x 8-7/16" x 11/16".

0.5

1

Shielded Power Cable, per Mission Bell Drawing 15-0A001-3, 4-conductor, 9-feet long, 5-contact shielded plug at each end.

1.9

1

AC input cable, per Mission Bell Drawing 15-0A002-3, 4-conductor, 10-feet long, shielded rubber covered plug on rectifier end.

1.9

1

Calibration Book (typed)

---

2

Instruction Books

---

1

Set of Operating Spare Parts for C.F.I. and Rectifier Power Unit.

29.0

Components of other units of LM-(*) equipments include:

Type -10086 Waterproof Carrying Case

Type -10111 Carrying Case with batteries

All units of the series are completely interchangeable, electrically and mechanically, with the exception of the Model LM and Model LM-1 equipments, which are not designed for operation with 260-275 volt plate supplies.

It is believed that all Heterodyne Frequency Meters use the tube types shown above for the CKB-74028 and, beginning with Model LM-2, two each of RCA 991 (now NE-48).

Model

Freq Meas Unit Type

Het Osc Freq Rnge --KCs

Operating Voltage 

Mechanical Design

Note

LM

None

195-400

2000-4000

12-14

200-260

 

 

LM-1

None

195-400

2000-4000

External battery supply

Same as LM

 

LM-2

None

195-400

2000-4000

12-14

200-260/260-475

Minor improvements throughout

1

LM-3

None

195-400

2000-4000

External battery supply

Same as LM-2

 

LM-4

None

195-400

2000-4000

12-14

200-260/260-475

Same as LM-2

2

LM-4A

None

195-400

2000-4000

24-28

200-260/260-475

Same as LM-4

 

LM-5

None

195-400

2000-4000

12-14

200-260/260-475

Same as LM-4

 

LM-6

CRR-74023

195-400

2000-4000

Rect Power Unit Type CRR-20104

Same as LM-4

 

LM-7

CRR-74024

195-400

2000-4000

12-14/24-28

200-260/260-475

Redesigned shockmount base and capacitor and drive assembly

 

LM-8

CRR-74024

195-400

2000-4000

Rect Power Unit Type CRR-20104

Same as LM-7

 

LM-9

CRR-74024

195-400

2000-4000

12-14/24-28

200-260/260-475

Same as LM-7

3

LM-10

CRR-74028

125-250

2000-4000

12-14/24-28

200-260/260-475

Minor mechanical revisions

3, 4

LM-11

CRR-74028

125-250

2000-4000

Rect Power Unit Type CRR-20104 or CRR-20104A

Same as LM-10

 

LM-12

CRR-74028

125-250

2000-4000

12-14/24-28

200-260/260-475

Same as LM-10

3

LM-13

CRR-74028

125-250

2000-4000

Self-contained batteries

Same as LM-10, less shock mount base

5

LM-14

CKB-74028

125-250

2000-4000

12-14/24-28

200-260/260-475

Same as LM-10

 

LM-15

CKB-74028

125-250

2000-4000

Rect Power Unit Type CRR-20104A

Same as LM-10

 

LM-16

CKB-74028

125-250

2000-4000

12-14/24-28

200-260/260-475

Same as LM-10

3

LM-17

CKB-74028

125-250

2000-4000

Self-contained batteries

Same as LM-10, less shock mount base

5

LM-18

CRR-74028

125-250

2000-4000

Rect Power Unit Type CRR-20104A

Same as LM-10

 

LM-19

-74028

125-250

2000-4000

12-14/24-28

200-260/260-475

Same as LM-10

 

LM-20

-74028

125-250

2000-4000

12-14/24-28

200-260/260-475

Same as LM-10

 

LM-21

 

125-250

2000-4000

Rect Power Unit Type -20104 or -20104A

Same as LM-10

6

Notes:

1. Voltage regulator circuit added.

2. Symbol designations reassigned.

3. Included in Type -10086 waterproof carrying case.

4. Low frequency oscillator fundamental frequency changed.

5. Mounted in Type -10111 carrying case with batteries.

6. Recalibrated and new calibration pages inserted in book where necessary. Aluminum cover and beaded metal chain added to Calibration Book. Spare crystal installed in Meter Case. Set screw in Corrector Knob E replaced with a threaded extension to facilitate calibration to the meter's crystal oscillator.

References:

1. Data through LM-17 extracted from NAVAER 08-5Q-48 "Handbook of Operating and Maintenance Instructions for Model LM-15 Crystal Calibrated Frequency Indicating Equipment," 1 November 1943.

2. Data for LM-18, LM-19, and LM-21 extracted from NAVSHIPS 91277 "Handbook of Operating and Maintenance Instructions for Model LM-18 Crystal Calibrated Frequency Indicating Equipment," 25 November 1949, including Change 1, 15 December 1950, with undated Errata Sheet 0280-059-8003, changing the designation of the Navy-modified LM-18 to LM-21. From Ray Mote, K5FKT.

3. Data for LM-20 from Robert Downs, WA5CAB

Contributors: Robert Downs, WA5CAB; Ray Mote, K5FKT

Ken Corwin, KF6NUR (kenc2@pacbell.net) Santa Clarita, CA