HF MOBILE ANTENNA  (HB9ABX)
Felix Meyer
update 27th May 2003 / details July 27, 04, ... , 13.9.06
Last update =  link added

    This is not the new HB9ABX HF antenna.
    This antenna here was developed about 15 years ago.
    The new antenna is found under "NEW HF ANTENNA from HB9ABX"

    This mobile antenna is designed for all HF bands  from 10 to 80 meters
    an proved to be very efficient in my travels in South America on
    15 and 20m for contacts to Europe and within South America.
    The antenna is my own development.
    Compared to commercial HAM Antennas the performance was
    always much better, due to the larger size and lower loss in coil.
   
Comparing with the Screwdriver type antennas always resulted in 2-4 S-points
       advantage in favor of this antenna!
    In field tests we compared 3 different mobile antennas, all at the same    
    location, at the same time, each one with 100 W power.

    The 3 antennas were:

    - HUSTLER mobile antenna   (10 - 80 m)
    - YAESU ATAS-100                 (10 - 40 m)
    - HB9ABX mobile antenna      (10 - 80 m)

    In all tests the signal of the home made antenna was the strongest!


    -  1 S points (up to 10 db) stronger than HUSTLER

    -  2 to 4 S points  stronger than ATAS-100/ATAS-120

    These results in the ground wave (5 to 10 km), as well as in
    the far field at 70 km to 1000 km distance.

    For 10, 15, and 20 m the antenna consists of a fixed lower part and an
    extensible whip (telescopic antenna of 15 to 80 cm length) on the top.
    For 20, 40 and 80m a second  segment  is added and at the top
    follows the whip.

    Both  parts are made of  fiberglass rod of 10 mm diameter and 175/165 cm
    length, on which a piece of enameld copper wire (CuL) of 1.5mm diameter
    is wound. Aluminium tubes are used to join the parts together.
    On both fiberglass rods equally spaced windings of emameld copper wire of
    1.5 mm dia are wound. The lower part holds 320 cm wire (79 turns) and
    the upper part holds 470 cm wire (120 turns).

    The loading coil is wound on a plastic tube of  7.5cm diameter
    and 17 cm length.
    The same type of wire (1.5 mm CuL) is used for the coil as for the antenna.
    The coil has 33 turns in total, coil length is 12 cm.
    Seen from the bottum of the coil, there are taps at 21, 27, and 33 turns,
    which are shorted according to the operating frequency.
 

   Settings of the antenna in operation:
   10m : Lower part + whip + tap 3 + bridge from tap 3 to the whip
   15m : Lower part + whip + tap 3
   20m : Lower part + whip + tap 2
   20m : Both parts  + whip + tap 3
   40m : Both parts  + whip + tap 1
   80m : Both parts  + whip + no tap (full coil)
   The WARC bands 30, 17, and 12 m can be operated by just adding
   coil taps without changing the coils.

    Feeding:

    The antenna is fed by 50 Ohm coax (Type RG 58)
    of about 2 m length.
    On the antenna side the center conductor of the coax is connected
    to the antenna wire and the coax braid is connected to the
    car chassis ground.

    The antenna system requires a good ground !
    I soldered a flexible wire at both sides inside the door frame
    leading to the coax braid.

    Don't forget to connect the two windings on the fiberglass rod
    together, either through the metal sleeve between the rods,
    or simply by a connector. The whip on the top is connected to
    the end of the wire below.

    The desired resonance frequency is adjusted by changing the
    length of the whip on top of the antenna. Extending the whip
    lowers the frequency.

    The antenna requires an antenna tuner for operation, as
    the  impedance differs from 50 Ohms on 40 and 80 m.
    With the aid of the tuner, the antenna is adjusted to SWR 1.0 on all bands.

    The MFJ-901B tuner is fine for this use. It has little weight and
    is very small (12.5 x 5 x 15 cm).
    (Before its use it's recommended to open it to check the adjustment of
     the variable capacitors. They are frequently bad centered, which produces
    easily shorts ...)
    If the transceiver and tuner are without SWR meter then a separate
    instrument is to be connected between TX and tuner. I am using a
    DAIWA CN410M which is a small cross needle instrument best suited
    for this use.

   Mounting of the antenna:

    I installed the antenna on top of the car on a roof carrier.
    Two aluminum angles, 30 cm length, 30mm thigh, were fixed
    with screws to the carrier and the rod below the coil fixed to the angles
    by means of two hose clamps.

    Instead of the Aluminium tubes copper tubes may be used, whatever
    is found to be better. The tubes are glued in 5 cm length over the
    fiberglass rod. At the end of the 7 cm open part of the tube, a 2 cm
    long slot is sawed and a  small clamp is used to hold the inserted antenna
    part .

    The antenna is directed backwards at an angle of abt. 70 degrees.
    In order to prevent swinging up, the antenna is fixed slightly down
    at the end with a nylon rope. Use 2 nylon ropes, to both sides to prevent
    swinging sidewise when driving. This is required when both antenna
    elements are installed.

    The top of the antenne nearly reaches 3.2 m height above ground when
    both elements are in use and fixed by a nylon.
 

   Adjustment hints:

    Initially, the antenne has te be tuned to resonance on each band
    without using the tuner.
    This adjustment is done by changing the coil tabs and then varying
    the spacing between turns.
    In operating mode, only the tab setting is changed, the whip length set,
    and tuned with the tuner.

    Before initial adjustment, both elements have to be checked: click here

    The initial adjustment is done by using an antenna analyzer (e.g.MFJ-259).
    Resonance is found by obtaining minimum SWR on the instrument.

    Procedure of initial adjustment : (this is done without tuner)

    Lower part + whip (10 to 20 m)
    - Coil tap 3 ( = all turns closed)
      Adjust length of whip to obtain min. SWR at 21.2 MHz.
      Note length of whip. This is the 15 m setting.

     - Coil tap 2 (27 turns closed)
       Keep length of whip from previous setting.
       Adjust spacing of the upper 6 turns to obtain min. SWR at 14.2 MHz.
       Fix coil, this is the 20 m setting.

   - Coil tap 3
      Make a bridge using a flexible wire of 150 cm length with clips
      between tap 3 to whip connection (wound 2 - 3 times around rod).
      Adjust length of  whip to reach min. SWR at 28.4 MHz.
      Note length of whip. This is the 10 m setting.

  Both parts + whip (20 to 80 m)
  - Coil tap 3
    Adjust length of  whip to reach min. SWR at 14.2 MHz.
    Note length of whip. This is the 20 m setting.

  - Coil tap 1
    Measure SWR on 7.05 MHz and adjust spacing of coil between
    taps 1 and 2 to reach minimum SWR. Change length of whip only,
    if minimum SWR remains outside indicated frequency.
    Fix coil and note length of whip. This is the 40 m setting.

 - Coil without tap (33 turns active).
   Keep length of whip and measure  SWR on 3.7 MHz.
   Adjust spacing of coil of the first 21 windings to reach miminum SWR.
   Change length of whip only, if min. SWR remains outside 3.7 MHz.
   Fix coil and note length of whip. This is the 80 m setting.

    After terminating this adjustment the coil winding is fixed permanently.
    After this initial adjustment, the tuner is connected to mach the SWR
    exactly on operating frequency.

With my antenna the SWR without tuner on 10, 15, and 20 m
is better than 1.2 therefore tuning is only required for 40 m
and 80 m operation. This however depends from the actual
installation, especially from the ground connection.

See further details from the following drawings:
Drawing 1 (lower part)
Drawing 2 (upper part)

The photograph below shows the installed antenna in Chile as CE3CWF/mobile.
(The white antenna is a 2m antenna)

    Good luck in construction.

               For additional questions:    see  here

  my antenna as CE3CWF

Below the mobile antenna in Switzerland as HB9ABX:

And finally the mounting of the antenna on the roof of the car:


 

WARNING
Working with fiberglass rods produces dangerous dust, which easily produces allergies on the hands. Inhalation of the dust is extremly dangerous !
Already holding the raw bars with the hand can produce problems, therefore use protecting gloves
whenever working and handling raw fiberglass rods and observe appropriate care when sawing.
Wash well the hands with soap after the work !
After terminating the work paint the complete rods with a suitable lacquer to protect the surface.


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