Military Antenna Conversion for CB & Marine
Updated July 29, 2012
This article shows you how to use the MX-6707 military antenna for a CB antenna. It makes use of the tuning coils that are built into the antenna. You will not need an external antenna tuner.
I offered $30.00 each for three AS-1729/VRC Full Kits plus freight off of ebay. They were shipped in two boxes one for the MX-6707/VRC base unit and one for the AS-1730/VRC and the AT-1095/VRC whip. Ask the seller to over pack the whips
Two A3046166 Antenna Mounting Brackets
Two 5935714B2 Red Reflectors
Now some notes for the MX-6707 base.
- DO NOT PAINT IT!
- Overtightening will crack the base. Use a torque wrench 100 in. lb
Now for the fun part:
- Take the bottom cover off the MX-6707 and look at the bottom of the unit with the coax cable/connector facing you.
- Find the 5th tuning capacitor (small screw driver adjustment) counting from the coax cable in a counter-clockwise direction. This capacitor C8 tunes the lowest band 30-33 MHz on the antenna and will allow you to match the antenna at 27MHz.
- Make up a coax feed cable from the CB to the 2 antennas. Bring a ground and a hot to each antenna. You might be able to find a coax 'T' fitting.
- You will need to have the whip attached and preferably mounted on the H1. (This is a little trickey but it can be done). If not mounted to the H1, tune the antenna on a wooden ladder, away from any large metal objects. (Like the H1)
- Now with an SWR meter attached test to see where you are. Using the C8 adjustment (when making adjustments to C8 only use a plastic screw driver) tune it in.
- Reassemble and retest
The tuning switch on the bottom of the MX-6707/VRC is set to 30-33 however you retune that selection to encompass 27 MHz.
Set up for an AS 1729 Antenna on Marine Bands
- Icom 2200H 2m VHF (shhh... dont tell anyone, but it's unlocked for extended Tx)
- MFJ 822 SWR Meter (cross needle - measures both radiated and reflected power; the needle cross point shows SWR)
- MX-6707 Tunable HF Antenna Base
- AS 1729 HF Antenna
- PL-259 to BNC(m) adapter (the mil antenna uses BNC; the radio uses PL259)
The advertised Tx power for the transceiver is 65W. The best actual Tx power I saw (using the SWR meter) was 60W with 10W reflected, SWR of somewhere between 2.1 and 3 (the meter isn't that precise; I'd guess 2.4 - 2.5?). The setting on the antenna base that achieved the best result was "60-65MHz"... which is weird, because I would have expected an even fraction of 157ish. I did a radio check with the local coast guard radio station (157.125MHz, ch 83a) , and they got me "loud and clear". picked up a few broadcasts on 156.800MHz ch 16.