bolar

My Feedback: (5)

I've been looking around at some of the new 2.4 radios. I've noticed some of their RX's have one antenna others two. From what I've been able to figure out, the RX's with two antennas are billed as "full range", and the RX's with one antenna, I guess, close range. The radios I'm looking at are 4 or 5 channel, I fly mostly glow/gas, no electric. The manufacture descriptions of radios with one antenna are vague on receiver range and function. Anyone flying anything other than electric with one antenna on 2.4?

Most of my radios are Futaba Conquests and 4 channel Tower transmitters. I'm looking to cross over to the Airtronics SD-5G.

JIMF14D

The number of antennas is not a firm indicator of RX range. Hitec has new 2.4 receivers, Aurora 9, that are full range with one antenna. Spectrum Rx can have two antennas but be "park flyer " ranges. All of the new Hitec 2.4 Rxs are full range. I have flown the 6 and 7 channel to limit of my eyes with smaller 30oz. size electric models and .40+ glow models. For the Spectrum Rx, you have to check over the specs carefully and they tell you full or park flyer range. Ihave no experience with the Futaba stuff.

Jim D.

JoeAirPort

My Feedback: (41)

There's some good info out there on the Dual antenna topic. Basically each antenna makes a huge 3D mushroom sort of shape projecting out and along the direction of the antenna length. It's not exactly like a mushroom but close enough for our purpose of discussion. If there's two antennas at 90 degrees it gives you the most overlap of those two mushrooms, or largest 3D space that the receiver can pick up a signal. That way you get a stronger signal in the space you fly in. The tx also sends out a mushroom like shape of siganls. The larger the space that all those mushrooms overlap, the bigger the space you can fly in. I'd post the link if I had it. It was very cool. I may have not explained it to the T but the concept was very much as I explained it. That's why you see park flyers with only one little wire coming out of them on some 2.4G receivers. Thy only are good for 300-500 feet (park flyers).

PS: I just realized that I had a sausage mushroom pizza for supper a few minutes ago. That explains all the talk about mushrooms.

pilotpete2

You have very good taste in food Joe.
Sausage and Mushrooms, that's classic Pizza
Pete, who hasn't had a real New Jersey Pizza for too many years[&o]

JoeAirPort

My Feedback: (41)

Thanks Pete. It wasn't the Jersey pizza you're talking about but it was good.

JPMacG

My Feedback: (2)

There is a nice discussion of pattern and polarization diversity here: http://en.wikipedia.org/wiki/Antenna_diversity

Two or even better, three antennas are definitely better than just one, all other things being equal.

JoeAirPort

My Feedback: (41)

Good stuff. I wish I could find that multimedia presentation I saw a year ago or so. I tried to Google it but couldn't locate it. Anybody know what I'm talking about? It was like a video or a link with graphics in it that showed it in 3D. It was a really good presentation (I need pictures myself).

Zor

Hello bolar,

The following written for fellows not well acquainted with this subject.

The range of a communication link depends mainly on ___
_ __The stregth of the radiated signal from the transmitter,
___The absorbed energy in he receiving antenna. This is maximum when the receivng antenna is resonant.
___The sensitivity of the receiver. Its ability to amplify weak signals.

All above can be accomplished with a single antenna.

The main purpose of two or more antennas is for diversity reception.

At 2.4 gigahertz the wavelength is quite short in the order of 2.475 inches

Any conductor having a dimension of 2.5 (2 1/2 the dot is hard to see) inches will not only resonate but will reradiate (will radiate back) some of the energy absorbed.

Such conductors closeto the antenna may, by their back radiation (reradiaton) affect the field strength at the receiver antenna. If the back radiaton was equal in strength and if the distance of the reradiating conductor was such that the reradiated wave was out of phase with the primary field then there would be no field strength at the receiver antenna. Make sure you understand this paragraph. Read it again if needed.

So a second antenna at such a distance from the first one that they cannot both be out of signal at the same location and orientation of the model aircraft is a safeguard against loosing a weak signal. A safeguard is not always guarantee but does work in the large majority of the model aircraft orientations.

On a small case (box) of tiny receivers there is not much distance toseparate the antennas so manufaturer's engineering have provided for further away antennas and different antenna orientaton.

The radiated field from the transmitter has polarization meaning some orientation.
Having a second antenna (or more than one extra antenna) makes it capable of helping the energy absorption as the antennas take differnt orientation as we fly.

Most second receivng antennas feed into their own "satellite receivers". The main receiver has the ability to pick up the strongest signal at any one time.

If you have further questions we will try our best to answer or we will say "sorry we do not know".

Zor

DougV

Joe, you talking about this one? http://www.rcgroups.com/forums/showthread.php?t=1177977

Doug.

JoeAirPort

My Feedback: (41)

YES !!! Cool. Thanks. That's some interesting stuff. Much easier to understand with graphics.

Only I have to confess I didn't really answer the 1 antenna VS 2 antenna question but I think it has something to do with what he explains in the video. Just not a direct answer to that question. This stuff is very advanced topic. Not my expertise. []

bolar

My Feedback: (5)

Thanks, there is a lot of information to go through. It looks like two antennas are the way to go.

Texastbird

Hobby People has a killer price on their little 5 channel rig, if you are looking for an entry level type radio. I can personally vouch for the single antenna Hitec 2.4 receivers as being full range. My flying buddy (an older guy) let his plane get away from him awhile back and it was literally just a speck way out on the horizon but fortunately I was able to coax the little fellow back to where he could see it well enough to fly it. This was using a Futaba 9C with the Hitec module and 7 Channel receiver. So I think Hitec did their homework pretty well before coming out with their 2.4 equipment. No satellite receivers or anything like that needed.

Dave McDonald

My Feedback: (19)

Looks like you need to go back through that information again. Just because a receiver has two antennas does not necessarily mean that it is a better receiver than a single antenna receiver. There is a lot more involved with receiver technology than simply the number of antennas.

For example, one of JR's receivers uses 8 antennas. Futaba's equivalent receiver only has two antennas. And Hitec's equivalent receiver only uses one antenna.

Zor

If anyone reads post #8 there is a simple explanation without perhaps puzzling about the high level stuff in these links.

These links will not answer any questions you may have remaining.
Ask here.

Zor

onewasp

Polarization Diversity

Polarization diversity combines pairs of antennas with orthogonal polarizations (i.e. horizontal/vertical, ± slant 45°, Left-hand/Right-hand CP etc). Reflected signals can undergo polarization changes depending on the medium through which they are travelling. A polarisation difference of 90° will result in an attenuation factor of up to 34dB in signal strength. By pairing two complementary polarizations, this scheme can immunize a system from polarization mismatches that would otherwise cause signal fade. Additionally, such diversity has proven valuable at radio and mobile communication base stations since it is less susceptible to the near random orientations of transmitting antennas.

also:

Antenna Diversity

Antenna diversity, also known as space diversity, is any one of several wireless diversity schemes that use two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and indoor environments, there is no clear line-of-sight (LOS) between transmitter and receiver. Instead the signal is reflected along multiple paths before finally being received. Each of these bounces can introduce phase shifts, time delays, attenuations, and distortions that can destructively interfere with one another at the aperture of the receiving antenna. Antenna diversity is especially effective at mitigating these multipath situations. This is because multiple antennas offer a receiver several observations of the same signal. Each antenna will experience a different interference environment. Thus, if one antenna is experiencing a deep fade, it is likely that another has a sufficient signal. Collectively such a system can provide a robust link. While this is primarily seen in receiving systems (diversity reception), the analog has also proven valuable for transmitting systems (transmit diversity) as well.

Inherently an antenna diversity scheme requires additional hardware and integration versus a single antenna system but due to the commonality of the signal paths a fair amount of circuitry can be shared. Also with the multiple signals there is a greater processing demand placed on the receiver, which can lead to tighter design requirements. Typically, however, signal reliability is paramount and using multiple antennas is an effective way to decrease the number of drop-outs and lost connections.


Easy pictorial: http://vimeo.com/8826952

Zor

i went to the link in "onewasp' post.

For some reason unknown it took about one half hour to come in.
A few seconds coming in and long pauses.

I prefer get my knowledge from sources like the illustrated handbook.

Zor

JIMF14D

I have gone to that site twice now and it pops up in a second or two here and seems to work fine.

JoeAirPort

My Feedback: (41)

Same here. Works fine. Also there's a link to a thread that has it embedded (RCGroups). It's earlier in this thread. Great video.

onewasp

Zor,

As usual you miss the major point.
You seem to feel that you are THE source on all things RF.
Witness this quote from your post # 14:

"These links will not answer any questions you may have remaining.
Ask here.
Zor "

That statement seems to indicate that you are absolutely THE SOURCE.
I find that at least egotistical if not worse.

The purpose of the "Fast Pictorial" site was to turn the information printed above that caption into an easily
understood graphic format. Too bad it isn't working as it is/was excellent.

BTW
Post #6 contains the best simple answer to the OP's question
"JPMacG

.......... Two or even better, three antennas are definitely better than just one, all other things being equal. "


P.S. I was able to run the pictorial just now though loading is quite slow.
For some reason, I had better luck running it at full screen settings.
With some patience, it is still there.

Zor

JIMF 14D

Yes the link http://vimeo.com/8826952 pops up in a second and gives a button to click just below the airplane picture.

I clicked that button and it starts a video that last a long long time (about 1/2 hour) .

Zor

Zor

Hi JoeAirPort,

The video that lasts for abouot 1/2 hour was made with good imagination showing (illustrating) the field strength in different polarization and the different antennas,

It is no doub usefull for fellows unfamiliar with radio waves radiation and reception.

I wrote "if there.is any question remaining, ask here" only meanthat ANYONE will no doubt try to help.

Zor

Zor

onewasp,

You seem to have some resentment about me and I have no idea why.

In these forums we have to live with fellows that know very little and some that know enough to help.
Please just try to be fair in your judgments.

Zor