MORE ABOUT OBLONGS 5

My first models of oblong antennas with small element diameter had high gain, but this was a misleading impression. When I finally tried designs with diameter bigger than 5 mm, I was very surprised: larger diameter gave higher gain and, above all, spectacular figures for G/T ratio.

That was a good reason to revisit the oblong antenna designs for 432 MHz, and the results can be seen on my web site: http://www.qslnet.de/member/yu7xl/oblong_models_432.htm. Specially for Dubus readers, I want to give something extra, so here are three models of oblong, all designed for a boom length of 6,00 meters, which is suitable for home made construction because aluminum tubing is usually supplied in this length. I have added one more element to them, making this antenna very broadband, but giving excellent G/T ratio and gain. The element diameters are 6, 8 and 10 millimeters, respectively.

My goal was to achieve as good G/T ratio as possible. Therefore, the gain (and G/T also, derived from it) could be a bit higher, but a wide bandwidth is a good trade-off. Such an antenna should be `mild`, easy to construct, and well behaved when used under conditions of heavy rain or icing.

Of course,  aluminum tubes could be used instead of rods. Tubes make construction lighter, but request bending procedure that could be slightly more difficult then that for rods. Also, you must take into account that the total length of element must stay within the data given in tables (tube can change in length during bending) .

Again, I used a YU7EF yagi antenna of the same boom length, for comparison, just to emphasize the potential of Oblongs.

Finally, it is worth saying: it is a pity that NEC/EZNEC operate with round wires only. It is practically impossible to perform calculations with round or elliptically bent elements. If such options were possible, I would have tried G3JVL loop. I have made some provisional tests with doubled oblong elements in order to simulate strip instead of rod and found quite encouraging results. Furtherlmore, round or oval element cross section should give further improvement in loop antenna designs. Could someone try it?

OBLONG ANTENNA Q724D18XL

Performances: (no loss condition)

Dimensions:

Table 1: 24 element oblong Q724D18XL with 6 mm elements

Performance data, comparison with YU7EF Yagi and dimensions

See table 2 belov for version with 8 and 10 mm elements, respectively

Diagrams, loss included

Fig. 1: 24 ele oblong for 70 cm eith 6 mm elements –

Horizontal plane (left) and vertical plane (right)

(EZNEC simulation – losses included

Fig. 2: SWR sweep for the above 24 ele 70 cm oblong antenna (EZNEC simulation)

Fig. 3: Narrow SWR sweep for the above 24 ele 70 cm oblong antenna (EZNEC simulation)

OBLONG ANTENNA Q724D14XL

Performance data:

Diagrams, loss included

Fig. 4: 24 element oblong for 70 cm with 8 mm elements –

horizontal plane (left) and vertical plane (right)

(EZNEC simulation)

Fig. 5: SWR sweep for the above 24 ele 70 cm oblong antenna (EZNEC simulation)

Fig. 6: Narrow SWR sweep for the above 24 ele 70 cm oblong antenna (EZNEC simulation)

Dimensions:

OBLONG ANTENNA Q724D16XL

Performance data: (no loss condition)

Diagrams, loss included

Fig. 7:  24 element oblong for 70 cm with 10 mm elements –

horizontal plane (left) and vertical plane (right)

(EZNEC simulation – losses included)

Fig. 8: SWR sweep for the above 24 ele 70 cm oblong antenna (EZNEC simulation)

Fig. 9: Narrow DWR sweep for the above 24 ele 70 cm oblong antenna (EZNEC simulation)

Dimensions: