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Richard Lehr/Lehr
01/09/2012 08:20 PM


Radio parts of my Mutt


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Let us start with the antenna. The antenna on the rear right is not for the M151. Would like to sell it to somebody who owns a HMMWV (High Mobility Multipurpose Wheeled Vehicle).

Here comes the data of the HMMWV antenna:
- AS-3900A/VRC
- NSN 5985-01-308-8988
- Contract DAAB07-97-C-C257
- P/N 80063/A3017899-2

The antenna in front, mounted to the rear left corner is the longer and correct one AS-1729/VRC.

This is a VHF Low Band, 30 - 76 MHz Antenna composed of the following elements. AS-1720/VRC Lower 52" antenna element that is like a coax with inner and outer conductors and the AT-1095/VRC Upper 66" antenna element which is a single conductor with a MS-11x style thread. The overall length from the bottom of the mounting flange to the tip of the safety cap is 123 inches (3,1242 m).

The band switch can be controlled manually or by means of a 12 conductor cable.  There is a rotary solenoid that rotates the switch until it gets to the desired band position then stops.

Used with vehicle installations which have the radio sets AN/VRC-12 series, AN/VRC-53, AN/VRC-64, AN/GRC-125 or AN/GRC-160. The matching unit MX-6707/VRC tunes the antenna elements automatically or by manual selection via a selector knob on the base.
The MX-6707 base tuning unit uses capactance and inductance to match the antenna, not lossy resistance as is used on the newer matching bases that are now needed for frequency hopping radios like the SINCGARS.  So the AS-1729 is more efficient than the newer antennas.

From the MX-6707/VRC we need two cables, one is the antenna cable, directly connected to the radio.

The second cable goes from the AM-2060 audio amplifier/power supply to the antenna.

AM-2060() Audio Amplifier / Power Supply

The PRC-25 or PRC-77 radio sets can be used in either a man pack (GRC-125, GRC-160) or vehicle (VRC-53, VRC-64) configuration. When used in the vehicle configuration the Radio Set is installed into the AM-2060 Audio Amplifier/Power Supply.  TheAM-2060 Audio Amplifier/Power Supply is installed into the MT-1029 mount which provides the DC power input, interface to the VIC-1 /vehicle inter communications) system, or COMSEC equipment like the KY-57 or KY-38 by means of the J-3513 Junction Box.

The PRC-25 was replaced by the PRC-77 late in the Vietnam era.  The form, fit and function of the PRC-77 are backwards compatible with the PRC-25 and, except for the label the two radios are identical from an outside visual inspection. The method of selecting frequency uses two knobs, one for integer MHz and the other for the 50 kHz steps.

CX-4655 Cable

The cable connects between the AM-2060 and the Radio Set. It porvides power to the Radio Set and gets the line level audio from the radio to feed the audio amplifier and drive the speaker. The CX-4655 comes in either a 9" or 11" long version.  They both have U-316 connectors on each end since the Radio Set POWER connector is identical to the AM-2060() Radio Set connector.  The cable has all the pins wired 1:1.  Note when this cable is used the DC vehicle power is fed to the MT-1029, which feeds the AM-2060 Power Supply which in turn feeds the PRC-25 or PRC-77 radio, therefore the radios's internal battery is not being used.

Finally we have the support bracket on the fender to which the MT-1029 will be mounted.

Here we go ...

... with the handset H-250.

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