Section III. OPERATION - TM-11-5820-554-120092

TM 11-5820-554-12

13-6. Lowering Procedure

Lower the antenna as follows:

vertical structure. Making a small coil of the rope

a. Untie the ropes and lower the antenna to the

will facilitate throwing it over the vertical structure.

ground.

NOTE

b. Disconnect the coaxial cable from the antenna

The antenna reel housing may also be

housing.

secured to a single vertical support

e. Loosen the wire lock knobs and free the wires.

structure, and the elements tied off at

WARNING

ground level with the guy ropes (fig. 13-

Keep fingers clear of the wire as it is

2).

Under certain environmental

wound on to the reels.

conditions, such as high wind and/or heavy

d. Wind the wires onto the reels.

ice loading, this method is more desirable.

e. Coil and tie the ropes.

Section III. OPERATION

indicated by a dial that is calibrated in frequency.

Figure 13-3 shows frequency versus per side wire

13-7. General

length. The wires are secured at the desired length

The Collins 637T-2 consists of two reels of

with the wire lock knobs mounted in the housing.

phosphor-bronze wire stored in a cylindrical

The end of each wire is attached through a swivel to

housing. Prior to unreeling the wires, set both wire

a length of nylon rope. The antenna is then raised to

length indicator pointers to zero.

the desired height by passing each rope over a tree

limb, tower, or other vertical structure. Connection

13-8. Operating Frequency Selection

to the equipment is made with standard 50-ohm

For operation at a particular frequency, each wire is

coaxial cable (before raising).

pulled out of the housing to the correct length as

Section IV. OPERATING PRINCIPLES

balanced dipole circuit by a ferrite balun contained

in the antenna housing. Figure 13-4 shows the balun

13-9. General

and antenna connections.

The Collins 637T-2 operates as a conventional half-

wave dipole (fig. 13-4).

The radiation

13-11. Gain

characteristics of a dipole antenna are dependent on

The Collins 637T-2 provides good gain on path

its height above ground.

Figure 13-5 shows

lengths varying from 0 to approximately 1,000

calculated elevation plane patterns at an average

miles. Longer paths require multiple hops. Figure

height of 25 feet.

13-5 shows the field intensity radiation patterns to

be expected for the various frequencies.

The 50-ohm

13-10.

Impedance Matching

unbalanced transmission line is matched into the

Section V. MAINTENANCE

To disassemble the antenna, refer to the exploded

view in figure F O 2 and proceed as follows:

13-12. General

a. Remove the retaining ring (9) from the rod

The Collins 637T-2 requires a minimum of

assembly (12) at either end of the antenna.

maintenance. Periodically, the antenna should be

b. Remove the three flat washers (10).

disassembled, and all gears washed with soap and

c. Unscrew and remove the clamp indicator

water.

knob (11).

d. Remove the dial indicator assembly (13, 14).

13-13. Disassembly Procedure

e. Remove the dial assembly (21, 22).

(fig. FO-2

13-4