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 :-) ------------- 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