Linear Systems Antennas (LSA) the first 3dbd...

Initial Design Philosophy of LSA The initial design philosophy of LSA is based on the Cushcraft A3. This beam has good cost performance ratio. When it is time to “upgrade” the Cushcraft A3 is done; however, once a full-size element, always a full-size element. Design question: Will two full-size elements compare to the entry-level performance of Cushcraft A3?

LSA Design Motto . Knowledge... is knowledge of differences. We know nothing.... except in contrast to something else! ...so, lets make some comparisons! \

Cushcraft A-3 Manufacturer's specifications (before EZNEC) Maximum Forward Gain: 8dbd Front to back: 25db I purchased A3 years ago because I had to start somewhere! I was not influenced by impossible but claimed specifications! 13 feet, 9 inch of boom 6 feet, 1 inch 7 feet 8 inches director driven reflector

LSA-2: An entry-level tribander with a future LSA-2, 12 feet of boom LSA-2: An entry-level tribander with a future

LSA-2 Specifications 20M 4.5dbd gain and 10db front to back

LSA-2 Specification 15M 4.0 dbd gain 11 db front to back

LSA-3 Specifications 10m 4 dbd gain 13.2 db front to back

Cushcraft A-3 and LSA-2 predicted* gain and front-to-back 10m Tribander Gain Front-to-back A3 Minimum, on 10 meters only 3.5 dbd 11 db LSA-2 4 dbd 13db A-3 Maximum, full size elements 4.5 dbd 18db *Values predicted by EZNEC are not the same thing as measured performance. However, as a reference, the predicted and measured values of my 5 el 10m yagi, 24 foot boom, is 7.5 dbd and 23 db front-to-back..

More numbers that make sense: C-3, LSA-2, and A-3 ANT G, 10m FB 10m G, 15M FB 15m G, 20m FB 20m Boom C-3 4.4dbd 18db 4.8dbd 17db 4.6dbd 15db 18 ft LSA-2 4.0dbd 13.2db 11.0db 4.5dbd 10.0db 12 ft A-3* N/A 14ft *Cushcraft A-3 is a good reference in that the overall numbers make sense by in a comparative model that provided believable numbers on 10m. It seems safe to assume that A-3 is providing anyone with about 4.0dbd on each band, traps included.

Boom-length and gain LSA-2 has a pair of full-size elements for 10m, 15m, and 10m, all on 12 feet of boom, giving about 4dbd of forward gain and 10 to 12 db of front-to-back ratio. The first 3db are by far the easiest! After that...? Given a tri-bander with full-size elements, it takes double the boom length of LSA-2 (to 24 feet) to acquire an additional 1 db of forward gain on 20 meters (5 to 5.5 dbd) with the addition of one director. Placing a third and full-size 20m director on 14 to 18 feet of boom gives less than ½ dbd of additional gain, but front to back ratio will increase (reference, EZNEC models) This observation is why trapped tri-banders in the 14 to 18 foot range were, and still are, a good compromise in overall performance.

Driven els Reflectors LSA-2+ director Unlike trapped designs, full-size elements can be collected and used on longer booms! Driven els Reflectors LSA-2+ director

Matching... Do you recall the old “fan-dipole?” It worked, and well before Eznec. Add reflectors and use aluminum tubing....LSA-2. 20m 15m 10m Hairpin match 50 ohm coax

LSA-2 will match 50 ohm coax Eznec models are required.... 20m 15m 10m 50 ohm coax Hairpin match

How exactly to match LSA-2 to 50 ohms Feeding all driven elements together lowers the radiation resistance on 20 meters and raises radiation resistane on 15m and 10m Use Eznec to obtain approximately the same amount of capacitive reactance on all three frequencies. Use a hairpin match to tune out the capacitive reactance on the band with the lowest radiation resistance (typcially 15m) and adjust the element tips of the other bands to realize near 50 ohm impedance on all three bands.

SWR, 20m

Basic construction details (A) The boom and all elements of LSA-2 are made from telescoping 6063-T832 tubing, .058 wall for elements and .120 for the boom (1.75 inch reinforced splice). 20m element, OD in inches: 1, 7/8 (reinforced), ¾, 5/8, ½ and 3/8 inch 15m elements, OD in inches: ¾, 5/8 (reinforced), ½, 3/8 10m elements OD in inches: ¾, 5/8 (reinforced), ½ inch (B) Aluminum plate and u-bolt/saddle, boom to element mounts, all elements insulated from the boom.

LSA-2 is upgradeable by adding 12 feet more of boom, a struct, and a set of tri-band directors. ` Directors

24 foot monobanders versus 24 foot full-size tri-banders, and a reference Ant G 10m FB 10m G 15m FB 15 G 20m FB 20m Tri-band 24 ft boom 5.5dbd 15db 5.3db 18db 5.5db LSA-2 12 ft boom 4.0dbd 4.2dbd 4.5dbd Mono 8.0dbd >20db 7.3dbd . 6dbd 5 el 20m Mono 45'boom 24db

Monobanders After many years of playing with tri-banders I didn't want to accept compromises anymore, if I could do better! Mono-banders are the only way to achieve maximum gain and FB on a given boom length. Regardless of your preference, each additional 1dbd is very expensive after the first 3db!

WJ9B 40m/10m Tower stacked mono-banders

..but the place to start is here, LSA-2 Available in July, 2014 Compare at $799.00

LSA The First 3db.... 73, Will, wj9b