The "BQH9-6C" Construction Notes
is assumed to be 2" diameter aluminum tubing, although slight
variations in diameter are not considered significant.You will need to
plot the element locations on paper versus the joints in the boom, to
make sure no elements end up on a transition joint.
It is normally a pretty easy thing to adjust the transition joint to
coincide with an element by either moving where the antenna starts on
boom or changing where the joint happens.
2) TRUSSING of
the boom at right angles to the elements can be done as required, with
turnbuckles and steel cable to keep boom sag minimal. Any lines
added to reduce side-to-side bending in the plane of the elements
should be done with non-conductive material such as Phyllistran, and
should be held out to the sides with non-conductive material such as
fiberglass tubing. Furthermore, any such lines should be
positioned so they do not bear down across the elements when encumbered
by ice or snow.
3) ELEMENT TO BOOM PLATESare made from 1/4" thick Lexan or HDPE insulated material. There is no boom correction for the type of insulated element mounting used here. That is, the boom correction is under a 1/64" and is beyond any reasonable cutting tolerances. This assumes that you are using small metal U bolts to fasten the elements to the lexan plates; alternatively, you could connect the elements to the plates with a pair of small diameter stainless steel screws and nylon locking nuts (such as 10-32) on each side of the centerline of the plate. In eithe case, this should introduce only a minimal disturbance (provided they are only as long as required to hold the materials together).
Each 1/4" thick lexan
(or HDPE) mounting plate is mounted to
the boom with a stainless steel "muffler" style clamp so the bottom of
is 5/8" above the boom. This dimension IS critical. If your
particular mounting U bolt has a saddle that introduces a different
spacing, use a thicker piece of insulated plate so that the elements
are still separated from the boom by 5/8".
4) DRIVEN ELEMENT is constructed using 1" diameter aluminum tubing, with some short sections of 7/8" diameter tubing sticking out on each end, to allow for some final VSWR adjustment. In addition, D1 may have to moved slightly to adjust VSWR. It is difficult to capture every capacitance in the program consequently the reason for some real world touch up.
For mechanical stability, it is suggested that a 7/8" diameter piece
of teflon be inserted in the ends of the two driven element
halves, to provide good alignment and rigidity where they are attached
to the mounting plate.
5) CONNECTION OF
to the split dipole must be kept as short as
possible. The inside ends of the split dipole should be no more than
1/2" apart to allow the coax connection to be kept short. VE7BQH
recommends you use crimp on spade lugs and also solder them with silver
bearing non lead solder (available in any large building supply
etc). If the antenna is going to be left installed for an
extended period of time, you can then seal all the connections with
non-taminating (non acetic acid curing) silicone.
6) FERRITE CORES with the proper mix, such as the 1/2" RFI CORE (available from THE RADIO WORKS at http://www.radioworks.com), are used to choke the RF currents in the outside of the coax. The number of ferrites you will need is dependent on the power you will use. 1 ferrite will handle up to 600 watts; 2 ferrites will handle 1200 watts, etc. The test is simple, the ferrite should only be warm to the touch under sustained power. The ferrites must be positioned as close to the feed point as possible. As the ferrites are snap on, they need to be well wrapped to ensure the two faces of the core are kept dry and firmly together. Large size shrink tubing works well for this.
7) PARASITIC ELEMENTS
are constructed using center sections of 5/8" diameter tubing, with the
outer portions of each element being 1/2" diameter tubing.
8) ELEMENT LENGTHS
shown in the table below are the HALF
Therefore, to obtain the overall lengths for the directors and
reflector, take the .625 length and the
.5" length, add them together and then multiply by TWO.
Example: Reflector = 12" +
46.4445" X 2 = 116.889". The
driven element is done the same way but uses the 1" and .875
diameters but will be kept in two halves.
There is no allowance shown for the extra material that will have to
be used when the smaller tubing is inserted into the larger
tubing. It is anticipated that each joint in the elements would
probably require several additional inches, and that the joints
would be secured with one or more short stainless steel screws with
nylon locking nuts.
Last updated May 22, 2010