Tx Antenna mod
I was perusing online stores yesterday, when I found several flat panel 2.4ghz antennas in the 15 dollar price range. Coulld one of these be used on a Tx to extend range? I mean, they have the nice ones, with a very tight beam, but then Ii'd have to really get a good bead on the plane. Would one of these cheapies give me some gain by just facing the same direction as the plane? I figure i do that anyways.
Just a thought,
Tim
Replies to This Discussion
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Permalink Reply by Martin Seven on -
Of course it would, just make sure the impedances match (antenna's Ω and the TX's Ω should be the same). Also consider the possible issues with reliability - a narrower beam means it's easy to loose the link (and a plane). Always have a backup :)
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ModeratorPermalink Reply by Sgt Ric on -
I don't know about "cheapies", but patch antennas are a common mod to increase range.
I have added one to my Futaba TX and as usual have one for my 900mhz video RX.
That price is alot cheaper than most, so I wonder about quality and performance, but as we see alot these days, those are not always connected.
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Permalink Reply by Tim McMahan on -
I've never dealt much with 2.ghz systems besides my home phone, so please bear with any stupid questions. I am a HAM operator, so I have a basic understanding of radio waves. I was thinking something like this might be good....
http://www.dealextreme.com/details.dx/sku.30046
And something like this might be bad, in that I would have to be aimed dead-on...
http://www.dealextreme.com/details.dx/sku.29147
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Permalink Reply by Martin Seven on
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Expect a beam width of roughly 60° with the patch, and roughly 45° with the yagi. They're pretty much in the same ballpark as far as directionality goes.
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Permalink Reply by Morli on -
Tim,
The second antenna is not 2.4 Ghz!! So it is bad anyway i guess . I picked few of these yagi types recently , which were ex-telecom used . By rough measurement of driven element length found it to be 2.4 band :)).hope to test them some time this year ( in MMANA & field test)
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Permalink Reply by Lew Payne on -
As Martin Seven pointed out, all these antennas have a characteristic lobe pattern. That lobe is wide enough where "exact" aim is not necessary. I've noticed that many folks implement pan/tilt on their antenna tracking system, and I have yet to understand why they feel they need tilt control (moving the antenna vector up/down). An antenna that's pointing 15 to 20 degrees up from level ground is good enough, period... at the distances and wavelengths we're talking about here. Likewise, it's only necessary to pan (left to right) the antenna in the general direction of the craft. In addition, at close distances, the vertical lobe overlaps the horizontal so much that there's no need to turn the antenna when the craft is behind it and close by. The attenuation point behind the antenna is not very null, until you start moving away from it. From one amateur radio operator to another.
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Permalink Reply by Martin Seven on
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Some folks are using more directional antennas, I've seen things like 18 dBi patches with 15° beamwidths on trackers talking to UAVs and balloons, and I'm sure with these the null angles are much more dramatic.
Also, never forget about the coolness factor :)
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Permalink Reply by Lew Payne on
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Martin - A few questions; is the 15° lobe pattern both horizontal and vertical? Ground components tend to change that, and most people seem to ignore that fact. Antennas don't just "not radiate" outside their lobe... what happens is their gain drops off. Look at the 3dB point of a typical patch antenna, and a cross-section of the lobe from not only overhead, but the side, and you'll be surprised.
As to a 15° radiation pattern, do you realize how wide the visual diameter is 1300' (roughly a quarter mile) away? It's pretty darn wide... and the 3dB point is even wider. Panning the antenna will help, but unless you're going to soar to 30,000 feet directly overhead, tilting won't help at all.
One other thing, at low microwave frequencies, patch antennas made from PC board material tend to perform more poorly than free air ones. The dielectric on the PCB tends to detune them, and most designs don't compensate for that. Your typical clone antenna dimensions get selected by running them through the standard calculations, and cranking them out. Well designed antennas undergo some fine tuning during the design phase, utilizing a spectrum analyzer, sweep generator, and sensitive measurement equipment. I wouldn't trust the published lobe pattern of any "cheapo" PCB patch antenna, nor the cited gain. In reality, gain for these tends to be 3 dB less.
You're more likely to get stated (published) performance out of something like this grid parabolic antenna or this break-apart one than you are some "clone" PCB patch job.
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Permalink Reply by Martin Seven on
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That's true in most cases.
How about higher-altitude passes directly over the groundstation?
During a pass the aircraft antenna (dipole) would be pointing directly down at the GS, so I'd imagine you'd want maximum gain on the ground to ensure reliability. Plus high gain antennas tend to have significant zeros above them.
Take this rad pattern of a patch with a 3dB beamwidth of 10° (both H and E). Look at the H curve - notice the zero about 30° above the horizon? And the -28dB loss between 60 and 75? And so on. It spells "unreliable".
You're probably right that it doesn't make much sense for an american hobby plane to use tilt: you can nuke the antenna with 36 dBm output power and the plane would clear any zero before any drop would even be noticed.
But a VTOL in a country where the regs are a little more constrained (IIRC Japan allows no more than 10 dBm EIRP power) - i can see a -20 dB loss being a major issue resulting in the inability to bring your expensive bird down.
Consider the Condom Equivalency: it's better to have tilt and not need it, than to need it and not have it :-)
Oh and - the cool factor.
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Permalink Reply by Lew Payne on
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@Martin - Here in the USA, we are limited to a 400' AGL ceiling. Therefore, higher-altitude passes directly over the ground station aren't legal. In countries with a higher ceiling, or no ceiling at all, what you stated would make a difference.
With a 400' AGL restriction, an antenna of that type has plenty of signal leakage out the side lobes for an overhead flight. Antennas like these get their gain mostly by stealing from the back lobes. So, as long as the craft isn't flying behind the antenna (at a far distance), it's not going to matter.
For other countries... watch out!
As far as the "kewl" factor (got to know how to spell it... or you're not kewl), mount the antenna on a military surplus turret like this one, and you'll be the envy of your town! The nice part about it is that the choice of antenna becomes irrelevant - you'll be kewl no matter what you use!
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Permalink Reply by Morli on
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Now that is Kewl turret , but for those countries that don't have ceiling limits don't get these things in mil surplus either :))
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Permalink Reply by Martin Seven on
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Darn, that turret has um... kewl written all over it :-)
And yeah, I agree 100%. Most of my experience comes from hi-alt balloons and those tend to float a little bit higher, so that's where I got that pro-tilt bias.
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