Owen (VK1OD) has pointed out something interesting to me about the recent 8el 439MHz beam I've built. Basically, it has a better gain with out the last 4 directors! After all my fiddling with the design, I basically made it less effective than a 4el beam – but slightly more than a 3el.
In light of Owen's email I've played with the model more to confirm, and then to see what can be done. The following was observed:
1. Owen is correct, if you chop D3, D4, D5 and D6 off one by one you will see the gain gradually increase;
2. You will however end up with a _bad_ SWR;
3. But if you then adjust the DE slightly you can get a great SWR – albeit now rather narrow band (but more than wide enough for FM use);
4. And if you increase the reflector you can get a modelled gain of 8.8dB+; and finally
5. The gain on my Diamond X-50N is said to be 7.2dB (430MHz)!!
So, the beam I've built has taught me a lot but is probably better left at home and I should just use the X-50N instead. It is better than my mobile whip (said to be 5.5dB @ 430MHz), but the X-50N is better again (assuming the gain on my built version is probably less due to the bracket etc).
None the less, I've included a remodelled 4el version here for your reference. And, I'm actually tempted to build it. I think it'd be a cute little beam and will allow me to try another method of socket mounting to the DE – with a short coax tail rather than the bracket (more on that latter (another suggestion courtesy of VK1OD).