Verovatno je veliki broj amatera koji imaju „višak“ starih, iz raznih razloga, odbačenih antena, koje leže u šupama ili magacinima. Sve te antene se vrlo lako mogu preraditi ili redizajnirati za svega nekoliko dana u nove, vrhunske antene uz zaista minimalne troškove.

Ova antena dizajnirana je za N4BAA koji je imao višak neupotrebljivih antena KLM204 i KLM154 pa je ceo projekat koncipiran tako da se u potpunosti upoterebe originalni KLM elementi kao i originalni KLM nosači elemenata. 

Elementi za 18MHz su urađeni od antene za 14MHz a elementi za 12MHz su urađeni korišćenjem elemenata antene za 21MHz. Praktično, sve što je trebalo uraditi je bilo da se koriguju dužine krajnih segmenata na nove dužine – svi ostali segmenti su i dalje ostali kao i na originalnim KLM antenama. 

Cilj je bio uraditi duo band antenu za gornje WARC bandove ali da se ona napaja samo sa jednim koaksijalnim kablom – tzv. »open sleeve feed«. Prakticno, napaja se samo zračeći element za 18MHz dok se antena u radu na 24MHz napaja induktivnim kuplovanjem i nije električno povezana sa kablom kojim se antena napaja. 

Kao i kod ostalih antena koje sam dizajnirao, cilj je bio dobiti antenu sa što više pojačanja na raspoloživoj dužini nosača ali pre svega da SWR bude što manji i ravan peko celog opsega kako bi se izbegla potreba za korišćenjem Gamma Match, T-Match, Hairpin ili nekog drugog načina prilagodjenja i napajanja antene. To je značilo da impedansa mora biti 50 Oma sa što manjim reaktansama. Naravno da takva antena uvek ima i odličan stepen efikasnosti a reflektovana snaga je minimalna. 

Antena se napaja preko RFC (prigušnice) koja sprečava tok CMC struja kroz plašt koaksa, napravljene od 9 čvrsto namotanih zavojaka RG213 na PVC telu od 100mm, postavljenog što bliže samoj tački napajanja na zračećem elementu za 18MHz – kao što se može videti na slici. U svakom slučaju, bilo koji 1:1 strujni balun će uraditi isti posao ali je primenjeno rešenje naj jeftinije. 

OM Jose je antenu sagradio za nekoliko dana u decembru 2006 i podigao je radi merenja i testiranja na visinu od 35 ft (oko 10m) iznad zemlje. Ispostavilo se da je antena “iz prve” radila bas kako su to pokazali dijagrami i računice a SWR je čak bio bolji nego što NEC-2 simulacija pokazuje. 

Free Space pojačanje antene na 18MHz je 8.70dBi (6.55dBd) a na 24MHz je 8.84dBi (6.69dBd) 

Ova antena će biti u radnom položaju na 20m iznad zemlje pa su dijagrami zračenja urađeni za tu visinu.  

There is probably a very large number of amateurs who have an excess of old antennas, discarded for various reasons, which lie in sheds and storage rooms. All these antennas can easily be redone and redesigned in just a matter of days into new, high quality antennas with truly minimal costs.  

This antenna has been designed for N4BAA who had an excess of unusable antennas KLM204 and KLM154, so the whole project was designed to fully use the original KLM elements as well as the original KLM booms and element brackets. 

The elements for the 18Mhz were made from the 14MHz antenna, and the elements for the 12 MHz were made by using the antenna elements for 21MHz. Practically, everything that needed to be done was to correct the lengths of the end segments to new lengths — all other segments stayed the same as in the original KLM antennas.  

The aim was to make a duo band antenna for the upper WARC bands, but also that it is fed only with one coaxial cable — the so called »open sleeve feed«. Practically, only the driven element for 18 MHz is being fed, while the antenna is fed by inductive coupling when working on 24Mhz.  

As with other antennas which I have designed, the aim was to obtain an antenna with as much gain at the available length of the boom, but above all to make the SWR as small and flat as possible over the entire band in order to avoid the need for use of Gamma Match, T-Match, Hairpin or other ways of impedance transformation for the antenna feeding. That meant that the impedance had to be 50 Ohm with reactance as small as possible. Of course, such an antenna always has an excellent degree of efficiency and the reflected power and losses are minimal. 

Antenna is fed through an RFC that prevents CMC flow through the shield, made of 9 close wound turns of RG213 on a PVC form of 100mm, placed as close as possible to the very point of feeding on the driven element for 18MHz – as can be seen in the photo. Any 1:1 current balun will do well but solution used here is by far the cheapest solution. 

OM Jose built the antenna in a few days in December 2006 and raised it for measurements and testing to the height of 35 ft (around 10m) above the ground. It turned out that the antenna immediately worked as the diagrams and calculations had predicted, and SWR was even better than the NEC-2 simulation had shown. 

Free Space gain of the antenna on 18MHz is 8.70dBi (6.55dBd) and on 24MHz it is 8.84dBi (6.69dBd) 

This antenna will bi in its operating position on 20m above the ground, so the elevation radiation patterns were made for that height.