WWW.QSL.NET/K4MBE/bikemobile.htm

My Amateur Radio 'Bike Mobile' setup that has been used successfully to provide communications support for the 1999 and 2000
Marine Corps Marathon
in the Washington D.C. area.

Bicycle type and 'normal' accessories:

       1976 (model year) Gitane 10 speed bicycle with standard "rams horn" handlebar..
        Foam handlebar covers.
        Rear view mirror on the end of the left handlebar.
        Battery powered (2 "C" cells) halogen headlight mounted at the center of the handlebar.
        Battery powered (2 "AAA" cells) blinking red LED tail light installed in the seat.
        Book rack above the rear wheel with a spring loaded holder and red reflector on the rear.
        Reflectors in the spokes of the front wheel (yellow) and rear wheel (red).
        Frame mounted tire pump (on the tube between the pedals and front fork mount).
        Water bottle mounted on the seat riser frame tube (between the pedals and seat).
        Under seat 'tool pouch' with small bike 'multi-tool' kit, spare tube, tube patch kit, spare batteries for lights
            (2 "C" and 2 "AA"), and spare bulb for the headlight.
        "Saddle bags" that straddle the rear book rack with 2 compartments on each side (one large and one small).
        Triangular 'Bike carrying case/pad' mounted between the upper horizontal frame member and the seat riser frame post.
              Note:   This case is intended for BMX or off-road bikes and has one zipper on the left side to gain access for small item storage
                            and a shoulder pad for carrying the bike over obstructions.
            Most importantly, a helmet for bike riders.

Radio(s):

        Any 2 meter portable (HT) radio with a BNC connector.  I use a Radio Shack HTX-202, a Motorola MT-2000
          with a SMA/BNC adapter, or a GE MPD modified to have a BNC (GE MPD BNC modification link).

Antenna:
    2 Meter J-Pole.  (Now - here's where I got creative!)

    I wanted an antenna which did not require a ground plane but have some 'gain'.   After considering some antennas made for fiberglass cars and boats I found that most were either too expensive for me or did not provide any 'gain' (or both!).  A common J-Pole seemed to have all the properties I was looking for except flexibility (resistance to breakage).  One day I was looking through my garage and debating whether to throw that 20 year old worn out 'bike safety flag' away when I realized the whip is fiberglass and RF neutral!  A quick check at Arcade Electronics for the appropriate color heat shrink tubing and the idea bloomed!  Heat shrink a J-Pole made out of 300 ohm twin lead to the whip.  The end result is an antenna with 'gain', requires no ground plane, is easily removable for storage, will take up to 50 (or more) watts, and will not easily break if I take a spill!  Want to make one?  See the materials list below.

            Materials list:
                MFJ "Roll up J-Pole" (or make your own)
                6 feet of 5/8 inch YELLOW heat shrink tubing (barely fits before applying heat).
                6 to 7 foot bike "Safety flag" with mounting bracket and fiberglass whip.
                Three 6 inch thin wire ties (weather and UV resistant)

    I had no success making my own J-Pole out of 300 ohm twin lead so I bought the two made by MFJ (one to use and one to carry as a spare).  Remove the 'flag' from the mast to keep the finished assembly from flexing from wind resistance in use.  Slightly flex the flags' mounting bracket so the mast slides out of it with some resistance.   Measure and cut the heat shrink to fit the entire length of the J-Pole  plus 2 inches.  Feed the J-Pole through the heat shrink tubing so there is one inch above and below the twin lead.  Feed the fiberglass whip through bottom of the the heat shrink while holding the J-Pole in place by the RG-58 so the top of the J-Pole is within 1 inch of the top of the whip.  Check forward and reflected power with a Watt meter or SWR meter.  You will probably need to trim the J-Pole some to bring the antenna back to resonance in the 2 meter range as the fiberglass and heatshrink has changed thte RF properties of the J-Pole.  Use a heat gun (LOW setting) or a hair dryer (HIGH setting) to shrink the tubing and secure the antenna to the mast.  Install a wire tie at the top and middle of the of the captured J-Pole.  Install the last wire tie just under the point where the RG-58 exits the heat shrink at the bottom as a strain relief to keep the heat shrink from tearing at the bottom from age and stress.  Use good electrical tape or a plastic cap to weather seal the top of the assembly so rain (YUCK, I hate to ride in the rain!) and other moisture does not get down inside and cause any corrosion.   Mount the flags' bracket on the rear hub of your bike and you are almost ready!  Make a final check of the forward and reflected power with a Watt meter or SWR meter to make sure every thing is working properly. 

Additional RF power:

    Any 2 Meter 20 to 50 watt 'brick amp' with a switchable receive pre-amp.   The J-Pole gives a theoretical 3dB gain so your ERP (Effective Radiated Power) will be 6 to 8 watts with the 'brick' off (3 to 4 watt HT) and 40-100 watts with the 'brick' on.  The receive pre-amp is useful for pulling in a marginal signal.  I use a Radio Shack 35 watt 'brick' (no real RX pre-amp) or a old Lunar Electronics 30 watt 'brick' with a 6 dB RX pre-amp).  The amp is  mounted over the saddle bag material on the rear "book rack" and under the spring loaded 'keeper' with the power switch facing forward where it is easily reached by the rider while underway. (Pictures to be uploaded in the future).

    For the Marine Corps Marathons, I have only occasionally used the 'brick' for its' receive pre-amp.  The additional transmit power was not necessary over the entire 26 mile course.  Without the receive pre-amp I could 'fully copy' signals that other Hams could not even hear with their HTs (even with a 1/2 wave telescoping antenna and squelch set fully open).

System/Radio power supply and other 'Saddle Bag' items:

    To feed the brick amp I use one 12 volt 7 Ah gell cell mounted in a plastic box placed inside the right 'saddle bag' (right side large compartment) with a backup 12 volt 7 Ah gell cell placed in the left 'saddle bag'.  The plastic boxes encapsulate the gell cells so I can pack spare HT batteries in the right bag along with the gell cell and a lunch in the left bag.  The 'spare' J-Pole and wire ties are stored in the left small compartment.  The HT antennas and a complete 70cm HT are stored in the right small compartment.

Radio mount and antenna connections:

    The radio is clipped to the triangular frame carrying case mounted between the upper horizontal frame member and the seat post riser using the belt clip secured by the side case zipper.  I use a speaker-microphone clipped to my shirt or jacket with the spring clip sideways or upside down.  The "sideways or upside down" clip position setup allows the rider to separate from the bike without dragging all the radio equipment (or the entire bike) with him/her in case of a spill or fall.

coaxbar.gif (1488 bytes)

Please send me mail telling me what you think about this setup, if you used this information to go 'bike mobile', or suggestions on how I can improve it.

coaxbar.gif (1488 bytes)

Go back to the main page.

Copyright 2003-2004, Sterrett Carter
This page was last modified  -  May 06, 2004