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Cobweb Antenna


· Add bands to a Hustler 5BTV (8BTV?)
· Simple Mods for your xBTV antenna
· 144MHz four-element arrow beam
· Simple 144MHz/440MHz groundplane

Additional Mods for the Hustler xBTV Series Vertical

WA4GWB provided us with details of his recent 4BTV modification. Although an SO-239 assembly is available commercially for this antenna, it costs about $25 (inc S/H) and provides no protection for the jack or connecting wires from weather. George's mod does provide excellent protection, and does it cheaper. Looks pretty slick too.

WA4GWB's Notes:

  • I added an SO-239 connector to a 4.3 x 4.3 x 2.3 plastic mounting box, which was drilled with holes to match the bottom of the 4-BTV antenna. I used spade bits to cut the holes, then used ss fender washers to reattach the box to the base of the antenna.
  • I use a short pigtail of RG-58 with wire terminals soldered to each end and the SO-239 center conductor. I added an additional ground jumper to all the screws to insure good continuity to the antenna base and later to ground radials.
  • I sealed the bottom of the box to the bottom of the antenna with a silicone adhesive. I will add an o-ring later on the upper side of the base of the antenna to prevent water from entering through the drain holes. I may add a small amount of silicone adhesive in these holes, however it is recommended to check silicone adhesive dielectric insulation properties prior to installation. While the entire box is not totally waterproof, it should keep 98% of the water out base of the antenna while providing a disconnect point for the coaxial cable. Also notice a small weep hole on the underside of the plastic box. This will help to reduce moisture that might enter the box.
  • The cost of this project was approximately $15.00

Close up of the completed box mounted on the antenna

Another view of the mounted junction box

View inside junction box showing the short pigtail of RG-58 with terminal lugs soldered to each end and the SO-239 center conductor. Notice the additional ground jumper connecting the coax braid and SO-239 shield to all the mounting screws

A view of the bottom of the box showing the small weep hole on the underside to allow for moisture draining. While the entire box is not totally waterproof, it should keep 98% of the water out base of the antenna while providing an easy disconnect point for the coaxial cable

View of the completed antenna, mounted on its base. A few radials have been added with more to come. Notice the common mode choke wound from the feed coax and mounted near the top of the base (see notes below).

Another view

From a distance

View of another junction box just before the feedline enters the house. Notice the second choke wound from the feedline.

ADDITIONAL NOTES: After installing the 4-BTV, I wound a coaxial isolator (feed line current choke) to decouple the transmission line to prevent it from becoming a radial. This was done with 10 turns over a 6" diameter form, then I repeated the choke just before the coax entered the shack. This will not impede the RF energy contained inside the coax, but it acts as a high impedance to the undesirable addition of currents on the outside of the braid of the coax. Some additional advantages of the current choke include:
  • Prevent unwanted RFI by eliminating feedline current and radiation
  • All power goes to the antenna, improving efficiency
  • Reduce noise or unwanted signals picked-up by the feedline
  • Overcome a less than optimal ground system
I tried to tune the 4-BTV without radials (not recommended), however my mounting pipe did not provide enough ground, so I added the radials. With dimensions given in the directions for a ground mount, the SWR was close, however, I will not re-tune the antenna until additional radials have been installed and buried. With my automatic antenna tuners, the SWR is currently less than 1.2:1. My first contact was with YU7ZEX.
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