MORE ABOUT OBLONGS 2

by Slobodan Bukvic, YU7XL, yu7xl@nadlanu. com

In the last Dubus issue, I described a super oblong antenna for 1296 MHz. Now, I am going to describe two models of oblong for 432 MHz.

As I previously said, thinner element wire gives better antenna performance. I have found that by comparing different models I made. Higher gain, better side lobe suppression, and much wider range of frequency are always seen with thin elements, if the boom is long enough. This is, unfortunately, just in theoretical. In practice, the losses due to material resistance increases as element diameter gets smaller. Bellow a certain diameter, the losses become too high, and all benefits in theoretical performance are lost.

I have made a better design for 1296 MHz, than I previously described. The same number of elements, and approximately same boom length gives even 0,5 dB more gain and G/T. However, the losses are so high, that this antenna is worse in reality.

We could also talk about antenna temperature. Higher losses involve higher temperature, and the situation is quite comparable with dish antenna and its D/f ratio. Therefore, the higher gain antenna (with higher loss) could be better for transmitting purposes, but not for receive.

I do not intend to elaborate too much about this. My simple idea is: the better G/T ratio, the better antenna. That phylosophy has already been proven by YU7EF with hid yagi antenna. This means: low temperature and low losses, combined with bigger bandwidth and better G/T, though gain is sacrificed a little.

Let me mention the sky and earth temperatures are much lower on 432 compares to 144 MHz. Therefore, we adopt an average Tsky to be 15 Kelvin and Tearth 290 Kelvin. Derived from this, good antenna temperature is much more important on 432 MHz than it is on 144 MHz.

I have made nearly a hundred models of oblong for 432 MHz, trying to discover the best ratio between oblong element height and width, and found the best value of the element height h=0,05 to 0,1 wavelengths. I also discovered that the best oblongs can be achieved for the boomlength in the range of 10 to 20 wavelengths. In this area, the oblong is much better than the yagi! Here is the proof. The table shows performances of the original EF7032 yagi made by YU7EF versus my Q7032XL oblong. The oblong has got  a better G/T of nearly 1 dB! It is modelled on the basis of EF7032, though only the boomlengths are kept the same, in order to make comparison easier.

Note: YU7EF yagis are probably the best in the world at the moment.

For comparison, the results of the original YU7EF yagi versus my Q7032XL oblong are shown in table 1::

Remarks: Same segmentation density used. Same frequency: 432,200 MHz

Table 1: YU7EF yagi versus Q7032 oblong

Super oblong antenna for 432 MHz  - Q7034XL

Now, let us see the 34 element oblong antenna Q7034XL for 432 MHz. Later one more oblong antenna for 432 MHz (shorte, for moderate requeats) will be described. I made this model following the already shownm shorter model Q7032XL, Its elements are made of aluminium rods of 5 mm diameter. Some can decide that silver plated rods can be worth of effort, because the difference is approx 0,3 dB in G/T for silver. The total boom length is 9385 milimetres. The impedance value is exactly 50±j0 Ohms on the center frequency of 432,300 MHz, and the bandwidth for SWR=1,5 is 430,170 to 433,380 MHz. The other parameters are given in the following tables:

Performance Data: (No loss condition)

* ΔF given for SWR=1,5

Performances: (Losses included)

Dimensions:

Table 2: Simulated performance data and dimensions

Diagrams:

Fig 1 – SWR narrow (top) and wideband (bottom) sweep for the 34 ele 70 cm oblong antenna (4NEC2 simulation

Moderate Oblong Antena Q7023XL for 432 mhz

Now, here is an oblong antenna for “moderate” requests. Its boom is 5970 mm long, what is very suitable, because standard aluminum tubes for boom are supplied in 6 metres length. The system of 4 such antennas will provide around 25,0 dBi gain; more than enough for serious EME, and excellent for normal DX work. The central resonant frequency is 432,3 MHz, which will slightly slide down to 432,1 MHz when mounted in a system. The best stacking distance is 192 cm horizontally, and 189 cm vertically.

Performance Data: (no loss condition)

* ΔF given for SWR=1,5

Performance Data: (losses included)

Dimensions:

Table 3: Q7023XL oblong – Simulated performance data and dimensions

Diagrams:

Fig. 4: 23 element oblong for 70 cm –Horizontal plane (left) and vertical plane (right) (simulation)

Fig.3: SWR sweep for the 23 ele 70 cm oblong antenna

Read what Lionel, VE7BQH, writes about the 70cm Oblongs: „This is realy very impressive for several reasons. One, I have never seen a quad type antenna over about 4 elements ever even get close to a yagi. Two, it is the biggest single gain improvement I have seen in many, many years. A 4 bay on 70 cm would be a very reasonable standalone antenna. Please, pass along my „well done“ to YU7XL.

73, Lionel, VE7BQH