CGRetired

My Feedback: (1)

Note the zenith cone at the top (and at the bottom) of that torroid (doughnut shaped radiational pattern) where there is no RF. This is the tip of the antenna and is why you should point the antenna up with the sides of the antenna facing the receiver.

CGr

ArcticCatRider

My Feedback: (6)

CGRetired, if I am not mistaken, the antennas used in LORAN-C chains exhibited the same characteristics. Although they were way more powerful than our RC transmitters

opjose

The signal is weakest at the top of the toroid as in your picture...

Mosetpeople point the antenna up, but if you turn it sideways you effectively get two areas of weaker signal... versus the one.

scooterinvegas

My Feedback: (1)

Has anyone mentioned that the Tx antenna is linear polarized, and when you turn it sideways its now a horizontal polarized and not vertical?

opjose

That's an interesting point, but some of the write-ups I've read about dispersion patterns seem to indicate that this is not problematic with the dual receiver units, and one of the reasons the Spektrum/JR systems use multiple receivers ideally oriented at 90 degrees to one another.

There is a graphic from Spektrum that I saw, which talks about reflected interference signals too, that are minimized by the 90 degree configuration.

ArcticCatRider

My Feedback: (6)

The polarization cannot be a problem. Through out the course of a flight, the polarization of the Rx antenna will undergo an infinite amount of changes to the vertical, horizontal, and everywhere in between.

Not too mention that it's never been critical on how a transmitter is held, so long as the antenna on the UHF radios don't point straight at the aircraft

opjose

Actually the polarization of the antenna is constant and never variable.

The orientation of the plane or TX is what changes.

The radio waves retain a type of polarity associated with the transmitting antenna, that is why gain can be better in one orientation versus another, but with most RC equipment this is not a big problem.

What is a problem is illustrated in the following image...



Note that the TX position has the antennas pointing up in this example...

ArcticCatRider

My Feedback: (6)

If the antenna is part of the plane, and the attitude of the plane changes, the attitude of the antenna changes.

EDIT: Of course this is in reference to the Tx antenna. In short, it doesn't matter.

If the antenna on the illustrated recievers were at 90 degrees instead of 180, the "blind spot" actor wouldn't exist.

opjose

Correct... and the polarization of the antenna remains constant.

Polarization itself is unimportant for our purposes, but the orientation of the antenna ( which is what we were discussing ) does matter.

At the tip of the antenna is the point of weakest signal tranmission.



Not true... on most RX's the two small wires are part of one 1/4 wave, and orienting them at 90 degrees to each other makes matters worst, since you are reducing the total element effective length...

( Why this isn't an issue with Fractal Antenna designs is beyond me, maybe someone would care to explain? )

That's why the TX's are built with the small wires at 180 degrees ( with some exceptions such as some of the small AR's where each small wire is itself a separate 1/4 wave unit usually with it's own amp).

Instead a separate receiver is used with the higher end Spektrum/JR's as in the photo to eliminate the blind spot issue.... each circuit acting independantly from the other.

Charlie P.

My Futaba receivers have two wires coming out of the same face of the case.  The wires are arranged so that the last 2" of each wire is perpendicular to each other.  I use a fuselage side and the rear "cabin" bulkhead and silde them into permanent coffee-stirrer sheaths.

wallace.tharp

Dear Gofast53, there is somethng in the JR Ops. man. for my 9303 that says caution to not have your airplane in the back of a pickup or shop with lots of signal reflection properties when initialising the radio to the Rcvr. The idea is you want to prevents a signal bouncing situation. I have been flying R/c for 30+ years, & I LOVE 2.4 Wallace L Tharp USAF RCO

Fastsky

There has been another interesting day at our site!! Three pilots all on 2.4 flying at the same time had to suddenly land when a low black storm cloud came directly overhead! They all started having severe glitches and losing control of there planes. A 4th pilot flying at the time wqs on 72 mhz and had no issues. Does this mean that the 2.4s are for only for fair weather flying?

Drone Ace

Definitely Agree with Charlie P. If you have a basic understanding of what radio waves are, then you should agree, that 2.4 GHZ setups are fine. I'm not saying they are better than basic MHZ setups, but GHZ setups are far less likely to mix with tons of ambient radio waves that we have constantly buzzing our air space. However, as technology is constanly improving and becoming more integrated into many things we use, like a 2.4 GHZ cordless telephone for example, I think that GHZ setups will eventually be replaced by an even faster radio wave. Both setups are fine, but scientifically, a 2.4 TX is going to give faster and more precise RX response because the radiant waves are closer together of course.... HAPPY FLYING, AND STAY SAFE !!

willig10

I find it very funny that the argument still continues about 2.4 radios. It really does not matter how the theory of reflection and cone of frequency and whatever else comes up. Look guys let's be real. There were problems with AM there were problems with FM and there were problems with PCM and there will be problems with 2.4.

I have flown all types as stated above, I have flown different brands. I had my first "Problem" last weekend with the engine running the left aileron was glitching. Hey it was an easy fix. I had the aileron connections to close to the ignition box.

Things are gonna happen and I just can't help but laugh when something goes wrong the first thing alot of people do is start blaming the radio or the "manufacturer then comes the brand wars etc. etc. etc.

I don;t know about you all but my radio works just fine not only in glow but giant scale gas. Yes I watch the recall and notice list but I am of the mindset that if the receiver is installed correctly and the voltage is correct (2.4 receivers like power) You keep the batteries charged correctly and you monitor your voltage on both the receiver and transmitter during your flying day. The radios (does not matter what brand) Will work the majority of the time. Yes there will be those that a "hard" failure but those are to be expected of any radio.

Well off my soapbox. Flame away. I bet it wont be too long that this thread goes to brand war.

Glenn Williams

scooterinvegas

My Feedback: (1)

No brand war, just 72 VS 2.4 war. Which Im not a part of, since I fly nether.....

flycatch

My Feedback: (26)

You received "zero" rebuttal to your post. Wonder why, could it be some of these people experienced the same problem? I fly on 72mhz and believe it had its problems until they updated to PCM and dual conversion PCM receivers. Naturally it cost more for PCM then PPM and I do believe 2.4ghz will follow the same path. What you should fear is the possibility that the FCC will dissallow the use of 2.4ghz by the model industry. I don't have proof this will happen but you are sharing this frequency with other commercial users who have more clut than the model industry.

numb3rulz

Please do not take this article as the gospel of frequency transmission. The person who wrote this article doesn't quite grasp the how frequencies differ.
The largest misnomer is that 2.4 behaves like visible light. It's true 2.4GHz is 2400MHz but visible light is 400–790 THz or 400000MHz to 790000MHz. This is a huge difference compared the differences in frequency compared to 72MHZ and 2400 MHz. All frequencies scatter reflect like light. It's true the higher the frequency the higher the loss. But that is also why your antenna does'nt have to be so long. An antenna can receive a larger portion of the a higher frequency more easily. That is why the 2.4 antennas can be so short. The conjecture that 2.4MHz can't be any faster and using the speed of light as the evidence is just asinine. It's not the speed of the frequency but the speed of the modulator and the modulation used. Simply put all consumer electronics are made from readily manufactured electronic parts. Very few are still manufacturing the chip sets still used in the 72MHz gear. However many manufacturers are creating faster and faster chipsets for the 2.4MHz electronics. The biggest changes are modulation schemes.
I've seen far more problems with the 72 gear than the 2.4. Nothing is bullet proof and no one should believe it is. I would not be flying my models in a heavily congested urban setting whether it was 2.4 72 or 27. With that said, I do not think 100 transmitters should be allowed to be turned on at any event.

If you do not believe in 2.4 than you do not have to use it. And if you don't think it's safe I can find far more things to be afraid of. Everyone needs to remember why we do this hobby. It's fun. Lets try to keep it this way and go easy on the drama.

ArcticCatRider

My Feedback: (6)

News to me. I guess Futaba has got it all wrong then, and my Rx isn't subject to the laws of physics.

The antennas are longer than 1/4 wave to begin with. At 2,400 Mhz, wavelength is 125 millimeters.

scooterinvegas

My Feedback: (1)

Who are you talking to? Me? What post are you talking about?

2walla

My Feedback: (10)

When harbor freight started selling 29.95 planes on 72mhz I was done with 72mhz.. You are nuts to fly in it in any sort of congested area.. Too high a probability of somebody turning on and shooting you down...

Dave

We have to look at the electromagnetic wave spectrum where the 72MHz band is in the broadcasting region and the 2.4GHz band is in the microwave region. Therefore, the 2.4GHz wavelength is shorter and closer to visible light on the electromagnetic wave spectrum. Since visible light is also an electromagnetic wave, 2.4GHz wavelength behaves more like visiblelight.

Since we can not focus a high gain directional parabolic dish antenna between our constantly moving model airplane and our transmitter, we have to use an omnidirectional vertical antenna system which has much lower signal intensity. Furthermore, our signal is scattered, reflected, deflected, diffracted or absorbed. Reflection and diffraction will create INTERFERENCE!

opjose

Re: Futaba

Their higher end RX's have more than one element, they leave positioning up to the end user, that's their design choice.

See: [link=http://martybugs.net/wireless/rubberducky.cgi]2.4gHz antenna info.[/link]

"Each half of the dipole is a 1/4 wavelength, with the length corrected based on the velocity of the coax being used. Assuming a centre frequency for 802.11b of 2.441GHz, a 1/4 wavelength in free space is 30.7mm. "

JohnB96041

Have read all the posts here and only have one comment. This is a bunch of gunk! 2.4 radio manufacturers are better than what is described here. I have been flying 2.4 Spektrum (DX7 and DX8) for a long time now and have NEVER experienced what is described in this thread. When any radio is set up properly and configured to do what you want with the manufacturers equipment you can trust the 2.4 system to work great. My DX8 now has the Telemetry module added with rec battery monitor, engine head temp, air speed, and altitude and all works flawlessly. Take a break and go fly after you have set your system up. Oh, I also use 2, 2200 mah, 4.8 volt NiMh batteries with the battery switcher, and a seperate battery for ignition. This setup is in a Funtana 125 with the SAP 180hp, 30cc gas engine. I love my setup and would highly recommend it to anyone from the small highwing trainer to the 100cc giant.

CGRetired

My Feedback: (1)

This is quickly becoming, as someone put it, a "brand war" between radio systems. Enough has been said by both sides of this argument and as it seems to be headed now, I’m shutting it down.

There is a radio forum that you can go to and continue this if you wish. The moderator there may be more tolerant than I am with regard to keeping things from getting any more heated than they appear to be getting, but I doubt it.

CGRetired
Moderator.