The Alternative Multi-band Solution

Granite State Antenna -- Northwood, NH -- 603-942-7753 -- k1jek@k1jek.com



Now in use by Army Special Forces in Iraq

Frequently Asked Questions

Where did the Cobra come from?
The original Cobra was a homebrew design introduced by Ray Cook, W4JOH, in 73 magazine. The Cobra name, unrelated to a well-known CB manufacturer, came from the S-shaped configuration of the antenna's unusual multi-wire element.


What's special about a Cobra?
On its primary and harmonic operating frequencies, this antenna works identically to a ladder-line fed doublet. The big difference is, the Cobra's unique close-spaced multi-wire element also introduces two added resonant responses below the antenna's fundamental operating frequency. These responses extend frequency coverage far beyond that of a conventional doublet or G5RV. For example, the 140-foot (80-meter) Cobra also resonates near 2.8 MHz and on 160 meters. Similarly, the 73-foot (40-meter) Cobra also covers 60 and 75 Meters. Increasingly, hams are replacing G5RVs and other multi-band dipoles in order to realize the Cobra's extended coverage and great performance.


How efficient is the Cobra?
On its primary and harmonic operating frequencies, tests show no discernable difference in signal strength between a Cobra and a regular full-sized doublet or dipole. On its sub-bands bands where the Cobra is physically "short", efficiency is somewhat lower than for a full-sized dipole.


What is an UltraLite Cobra?
The original homebrew Cobra used unwieldy Romex house wire for its element--making the antenna difficult to handle and prone to breakage. UltraLite Cobras are different because they are professionally designed and engineered to survive New England's harsh winter climate. Weighing only four pounds including the feedline, they install quickly and pull up higher with far less stress on tree branches and support lines. At the same time, UltraLites are built to last! The black marine-grade ABS insulators won't deteriorate in sun or fracture in cold. All hardware is stainless. All wire is uV stable and pull-tested for strength. UltraLites come pre-assembled and ready to install with 81-feet of rugged copper-weld ladder line attached (UltraLite Kid comes with 40ft of ladder line).


Do I Need a Tuner?
All Cobras require a tuner. In most installations, the auto-tuner built into your transceiver should provide sufficient tuning range. Because the Cobra presents a balanced load, we recommend installing a 4:1 current-style balun at the station end of the feedline (many external tuners provide a built-in balun).


Why Use a Cobra UltraLite at my QTH?
Most people install the Cobra because it does what no G5RV or multi-band doublet can do-add low-frequency coverage without taking up added space. Customers also report they can install the UltraLite higher using light-weight support line and expect it to "stay put".


How is a Cobra UltraLite Installed?
For best results, support with 1/8" (or 3/16") UV-rated cord. Loop cord through both end-block holes to reduce chafing. Install so center is 30' feet or more above ground--well clear of conductive roofing or house wiring. Avoid routing ladder line over metal surfaces, near parallel cables, or along the ground (if the feed must run parallel to a metallic support, twist it one rotation per foot to prevent proximity imbalance). For center support, install the included support tab on the center insulator using the existing feedline support screws. Simply remove the screws, position the tab on the insulator surface opposite the ladder line, and reinstall (see below):


Ladder-line feed may be trimmed, but using the full 81' length generally results in easier tuning on all bands. Excess feedline should be suspended in loose coils rather than wrapped tightly in a roll.


I have more questions, how can I contact you?
I am happy to answer your questions. See the Contact Info page for all my contact information.

 


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