Club House > Club Talk
Glider A & B Crets.
EI1638:
Don't think I've ever seen a Yagi fly well. They seem to have centre of gravity and control surface issues...
John: Best left for really strong wind conditions (force 10 and above)
Keith:
Moving slightly back towards the original topic I wonder whether the radiation pattern really is omni-directional.
I'm not arguing about the radiation pattern of the dipole, because there is nothing to argue about there.
When we're flying though we tend to be standing behind the tx, (I've only ever seen one pilot sit) so effectively there is a 'mirror' (in terms of RF energy - i.e. the human pilot - even if we're not great rf mirrors) on one side of the antenna, distorting the textbook donut shape of the field. I know I'm long since past being able to do the calculations on this - the exam was passed and promptly forgotten about - but does the pilot not distort (extend) the lobe and effectively add some gain in front of the pilot (and reduce the size of the pattern/donut/lobe behind the pilot)? i.e. better/more range (stronger signal at the model) if we always turn and face the model, assuming the antenna is vertical. Of course, standing on a slope will realign the radiation pattern too as the ground is no longer horizontal...
I'd better shut up before anyone starts to think I know anything about this stuff. It was a long time ago in a galaxy far far away.
I hope none of my old lecturers see this....
Happy Days:
Good heavens Chris, you're asking me detailed questions about stuff I did over 30 years ago! (oh god, I feel another white hair coming on :() The matter of exact rf energy field strengths, as you may know, is highly complex and was certainly never my strongest point.( In fact, I haven't got a "strongest point" in any topic! :'()
You imply that the pilot standing behind the radiating element could be acting as a reflector element.
Assuming he is wearing shoes that electrically insulate him from the ground I would have thought that as he is not a resonant wavelength of the radiated signal, nor probably at the correct distance 'behind' the radiating element, he would likely absorb as much rf as he reflected.
Certainly the pilot will distort the radiation pattern, though whether he would enhance any lobes I couldn't say.
Of course, we could always get a field strength meter and stroll about the slope doing tests Chris. (Providing everybody else stood still). However, while it can be interesting to ponder such matters, when I go to the slopes i prefer to fly and I'm sure you do too! :)
EI1638:
Lets leave it there. My antenna theory is very (very) rusty and was never used in anger (except during the relevant exam).
Still, the human body is not a great conductor and weirdly, neither is the ground (it helps that there's a lot of it though), so if the shoes were conductive(ish) there would be a kind of reflector behind the antenna.
Remember that some antennae are designed with a built in ground plane to shape/redirect the radiation pattern.
Having said all of that you're right though. When I'm flying I'm usually too busy trying to keep my airplanes out of the ground (and trees...) and away from everybody elses airplanes, not wondering about this stuff.
And besides, my models would probably be invisible long before I reached the extremes of the default theoretical radiation pattern anyway, never mind seeing if it was extended in any direction.
Looking back over this dicussion I'm reminded of a VHF radio operators course I did many years ago. One of the participants (not me) insisted on stating that at VHF signals would go 'over the horizon' Whilst in the extremes of Maxwells Equations he may have been technically correct, for all practical purposes they don't, which was all that was important to everybody else on the course.
I'll shut up now and let people get back to posting about A and B certs. 8)
Happy Days:
Er,..... I am a little confused Chris. (A state of mind that is quite common for an old git like me.)
On the 8th Feb you asked the question, Quote; "Keith, you mean like my satellite dish or the Yagi Uda we used to watch TV with?"
Now it becomes apparent that you not only have knowledge of, but indeed have passed an exam on, RF antennas. :o So by implication you must have known the answer to your own question. So why ask in the first place?
EI1638:
Keith,
You started the rot!
I asked a simple question about an acronym I'd not come across before and you introduced antennae with gain!
I thought you'd pick up me having named the yagi as for most people it's a TV aerial. Tongue firmly in cheek.
Not that any of it makes any difference when we're struggling with the sticks, or the pinkies are freezing off on the big L.
I still hate acronyms though
Chris
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