Improving the 402BA by Jerry WN9JAT, WN9JAT@aol.com

I wish to thank all the great people who kindly offered the wealth
of experience and collected wisdom. Any mistakes are mine and mine alone.
Never forget the Sultans are COOL :-)

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The Hygain 402BA 2 element linear loaded 40 meter beam was never
a great design and its performance suffered, especially on the
lower cw portion of the band. Why this marginal perfomance out
of the box ?  The antenna was designed in the early 60's
without the benefit of the marvelous antenna design analysis
programs that we take for granted on our PC platforms. So
unless you had CPU time on a Mainframe, rf design was done
with first order approximations and a lot of cut and try.  
Short element antennas only made the task more difficult.

All that considered the 402 can be made to work and work 
quite well. First there is NO substitute for increasing
element lengths. In my case 9 inches on each 1/2 element
driven and reflector. The early instructions that came with
the antenna apparently gave dimensions for an ideal situation.
I.E. a minimum of a 1/2 wave above ground with no other
metal or antennas closer than a full 40m wavelength away.
Even then I suspect that the factory dimensions were very
"optimistic" for operation on the low end of the band.

Another critical factor in proper operation is the integrity
of the element to boom cycolac insulators on the driven
element. The antenna was designed when max power allowed
was 1000 watts DC input or about 600 watts delivered to the
antenna feedpoint. If you've loaded up with 1100 to 1500 watts
out, through away the old insulators. They either have pinhole
leakage or have an outright major rf burn thru. You should
certainly see the results with any SWR bridge and your
beautiful ceramic tubes will groan. New insulators can be
ordered from Hygain in Lincoln, Nebraska. The new insulators
will be just fine as long as you run 600 watts or less out. 

If you want to squeeze every last legal watt out of the amp
you will have to wrap the insulators with a high dielectric
withstand tape, such as Scotch 88 or similar. BUT be very very
carefull you will changing the series capacitance of the driven
element and therefore the electrical wavelength. What to do ? 
Make a single wrap and use the tried and true method of pointing
the antenna straight up about 4 ft. above the ground and check
the frequency of resonance. Adjust the element length as necessary.
Since the voltage developed at the feedpoint when loading to 1500
watts is approximately 6000 volts a single wrap will probably not be
sufficient for max power out, so make another wrap and test and
adjust again. If you have the resources and know something about
plastics and their electrical characteristics there maybe a better
material out there that will make this part a one step operation.

Because the 7/16" as well as the larger diameter tubing provided 
from the factory will probably not be long enough for low CW, I
used some old 7/16" X 68" tubing from a Hygain 153ba 15m antenna
which is 10" longer than what came with the antenna. It can be 
ordered from Hygain, part no. 174868. That coupled with an extra
inch from the 5/8" tubing gave me sufficient element length.
In the spirit of making do with want you have Charlie KD5PJ
used light duty aluminum angle stock 1/2" per side. They are 
available at most hardware stores. Use a stainless hose clamp
to attach. Ron WU4G used aluminum wire shaped as a long narrow
U. The shape with a heavy gauge wire will give you the approximate
proportions of the tubing not to mention you will avoid Corona
discharge off the ends. Electrons love sharp edges. There are
probably many materials just laying around your shack, garage or
other convenient places as long as you don't let your wife tidy
up these areas. "No honey thats not junk, it's Junque".

For the more ambitious adding a few feet to the boom length will
reduce that high feedpoint voltage to something less lethal to 
man and antenna. Note the the present day  shorty 40's use a 22
to 24 ft. boom length. The 402 boom is 16 ft. This will save a
lot of where and tear on the DE insulators. Just make sure you
have an accurate antenna analyzer and or grid dip meter etc.,
unless your a complete glutton for cut and try. Climb and groan.

Now on to the all to often overlooked obvious. Nothing beats a good
clean rf connection. Burnish the tubing at the ends where the 
connection will be made. A medium to fine grade emory cloth works
well. Apply a light coating of a good antioxident such as Penetrox
to the clean surface. This is sound advice for any antenna but
it is critical on a short element compromise design. Why am I
being so emphatic about this ? Yes I didn't follow my own advice.
Try humping a 80 pound antenna up and down the tower a few times.
Been there, Done that ? OK nuff said!

There is another method to achieve a low SWR without as much hardware
fuss. Jim K1ZX has succesfully used various lengths of 75 ohm coax
between the 50 ohm coax runs. Again a bit of cut and try but simpler.
My only mis-giving on this approach is that your using a form of
congugate matching which gives the rig a nominal impedance to load
into, but has no net effect on the antenna as an effective radiator.
This is how tuners work but some of the large magnitude current,
voltage products are not developed on that "flimsy inductor" or
close spaced variable capacitors. Coax is cheaper.

There maybe situations where you have to adjust the matching network
of the antenna, but make sure you have the necessary gear to make
accurate measurements or you could be in for a lot of frustating
cut and try. Fortunately I didn't have to and the factory tech
folks won't be much help on this antenna.


In summary:

1. lengthen the elements 5 or 10 inches depending on your
environment.

2.  Replace and tape the insulators on the driven element 
and adjust the element length for desired frequency.           

3. Be sure to clean and apply antioxide conductive paste
to all of the aluminum surfaces where rf connections will be made.

4. Ground test (see text) the antenna for low swr.
Remember 4ft above ground with the antenna vertical will give you
measurements that are within a few percent of the antenna's 70 plus
foot horizontal (installed) operation.

5. Work carefully with a plan. A plan on the ground is
worth two on the tower or something like that.

As I said at the start this antenna can be made to work quite well.
No you won't compete with the full size 40 meter beams but it beats
the heck out of a fixed dipole. A little F/B and a little forward
gain that you can rotate. It's either that or save the aluminum
for your next project or sell it.

73/Jerry/WN9JAT cu on 40