AS-1729/VRC Antenna
Military Antenna Conversion Article
Updated March 10, 2009
This is a VHF Low Band, 30 - 76 MHz Antenna composed of the following elements.
- MX-6707 WSC Base Matching Unit
- AS-1720/VRC Lower 52" Antenna Element that is like a coax with inner and outer conductors
- AT-1095/VRC Upper 66" Antenna Element is a single conductor with a MS-11x style thread
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.
The overall length from the bottom of the mounting flange to the tip of the safety cap is 123 inches.
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.
Bottom of MX-6707 - Showing:
- Clockwise only band switch 30-33, 42-47.5, 47.5-53, 37-42, 33-37, 53-56, 65-70.5, 70.5-76, 60-65, 56-60 Notice that the bands are not in order.
- 12-pin connector PCI U-291/U The radio connector would be the 12-socket version.
- BNC(f) connector with a protective tube around it.
- Drain Screw - put in a straw, coffee stirrer, or something to break the vacuum once every few months to get the water out!
AT-1095 Upper antenna element
CX4722A/VRC (20 Ft. 0 in)cable NSN 5995-00-985-8090 CAGE 55928 (3/93) has a 12-socket connector U-290/U0CS66 that mates with the MX-6707 and a right angle 12-pin connector that looks like the one on the base of the MX-6707.]
Looking into the plug the pins are:
B
A C
D E F H
J K L
M N
Pole Bracket for MX-6707, this bracket weighs just over 1 pound, it must be made of Al. The CX-4722 needs to be fed through the bottom of the bracket and mated to the MX-6707 before the MX-6707 is attached to the bracket. The MX-6707 can only be installed in 1 of the 4 possible positions so that the cable will be in the notch on the bracket.
SCD-189023 Scoop mounting base
SCD-446058 Corner bracket
Extender for SCD-446058
DC Resistance of Antenna
The DC resistance looking into the BNC connector is an open circuit for all bands except for the 70.5-76 MHz band where it is a short. This means that this antenna can not be used with a direct connection to a PRC-126, etc. radio that requires a DC path to ground in order to sense that a 50 Ohm antenna is connected.
It should work with a any of the radios in the PRC-68 family when my 68AA Antenna Adapter is used because the adapter supplies the DC return needed for the PRC-126 or PRC-128 (low band in this case).
It does work with the OF-185 in either the AMPL or BYPASS modes.
Mounting
For military vehicle mounting there are standard brackets that bolt on.
3.3 Remote Antenna Band Selection
Using a BA-2 or 22.5 Volts DC with negative connected to pin C (Red)
A= Black |
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Other Pins are:
Pin C is the negative ground pin
Pin A is bank select, set to +22.5 for 30 - 53 MHz, open for 53 - 76 MHz
D,E,F,H, & J are sub band selects
N is always +22.5 (or +25) when the MX-6707 is operational (note on some vehicle mounts this there is a jumper so that you don't drain the vehicle battery).
B, L, K, & M are not used
Manuals
TM 11-5985-262-24P ANTENNA, AS-1729/VRC NSN 5985-00-985-9024
restricted TM 11-5985-262-14 ANTENNA, AS-1729/VRC NSN 5985-00-985-9024 - has the schematic diagram and testing methods.
TM 11-5985-262-15 Maintenance
MX-6707 - Notice that the BNC coax center conductor goes to the center antenna terminal and also goes through a network that is switched and then to the outer sleeve of the antenna.
Web Links
Shakespear - 4242-MK2 broadband, center-fed, dipole antenna. The antenna base is physically identical to that of the MX-6707 with the exception that it utilizes broadband circuitry that requires neither mechanical nor electrical tuning. The frequency coverage is from 30 MHz to 88 MHz. The matching is accomplished with loss, but the performance is supposed to be the same as the As-1729.
