Ed Fong DBJ-2 (Roll-Up J-Pole)
$$···
| 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.