Ed Fong DBJ-2 (Roll-Up J-Pole)
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| Frequency | 144-148 / 440-450 MHz (ham version; a 152-157 / 460-470 commercial version exists) |
| TX power | 50 W (50 W maximum on both bands (designer's own spec; the portable DBJ-2 rates lower than the 75 W mast-mount DBJ-1)) |
| Modes | FM, SSB, CW, digital |
| Connector | BNC on the attached feedline; SMA-F and SMA-M adapters included |
| feedpoint | integrated feedline w/ BNC + included SMA adapters |
Estimated (unverified): gain (half-wave J-pole class; no maker figure published)
The best performance-per-gram purchase in VHF/UHF: a true half-wave on both bands that weighs nothing, costs lunch money, rolls into a pocket, and - hung from a branch or curtain rod - outperforms every antenna that can ship attached to a radio. Designed by a university instructor, published openly in QST, and sold assembled for about the cost of the parts.
Twin-lead construction sets the limits: handheld power levels only, wind turns it into a streamer, and it wants vertical hanging clearance to work as designed. It is a deployable, not an installation - sun and weather will eventually eat the ribbon if you leave it out.
The go-bag standard. Every HT owner should have one coiled somewhere, because ten feet of height and a real half-wave beat anything screwed onto the radio - and at this price the only mistake is not owning it.
The DBJ-2 answers a question every handheld owner eventually asks (why can I hear the repeater but not reach it?) with seven dollars of TV twin-lead and some careful engineering. Ed Fong - BSEE/MSEE from Berkeley, PhD from the University of San Francisco, and a University of California instructor in RF and antenna design (Berkeley then, Santa Cruz's Silicon Valley campus now) - published the design in QST in March 2007 as the roll-up successor to his mast-mounted DBJ-1 of February 2003. It is a dual-band J-pole in 300-ohm ribbon, 55 inches of radiator presenting a true half-wave on both bands; the quietly brilliant part is a quarter-wave shorted stub of RG-174 coax that decouples the lower section at UHF, so 70 cm gets its own independent half-wave rather than the pattern-shredding 3/2-wave a plain 2 m J-pole turns into at 440.
The construction is the charm. The whole antenna plus its 36-inch feedline section deploys to 91 inches, rolls into a coil the size of a drink coaster, and terminates in a BNC with SMA adapters in the bag for whatever handheld you own. Hung from a tree limb, a curtain rod, or a gutter (height being the actual product here), it gives an HT the effective reach that no aftermarket whip on the radio itself can approach, because the whip's problem was never gain, it was being attached to a radio at belt height.
Limits are built into the materials: handheld power only, a dislike of wind, and ribbon that sunlight will eventually age. This is a deployable for go-bags, hotel rooms, and field exercises, not a rooftop installation; that job belongs to the original DBJ-1, the same design sealed in PVC pipe for mast mounting. At about sixty dollars assembled (the 2007 article's twenty-dollar price has aged like everything else), in ham and commercial trims, it has become the default first antenna upgrade in emergency-communications kits everywhere, and the QST article remains free on the designer's site for anyone who would rather build than buy.