ClarkFlyer

I recently lost a plane due to my NOT raising my antenna.......sigh......thinking the Power Duck might be cheay insurance. Is there a downside and is there a preferred short antenna? I'm using the Futaba 6EXA radio system. Thanks in advance!!

wcmorrison

My Feedback: (2)

I think the pro's will tell you the long antenna is the best, you lose some performance with a short antenna (both in receiving and transmitting locations). Chalk up the loss to your experience and press on with what you have.

Cheers,

Chip

JohnBuckner

My Feedback: (1)

The down side is they all may not comply with FCC regulation in that is not equipment the Tx was oringinally certificated with.

The up side is they work and work well. What the poster mentioned above may well be true. However I beleve the practical range may even be better than a standard antenna and this is because of the way these types of antennas function. They have the strongest wave propagation directly in line with the axis of the antenna. A dipole is weakest on this axis (lull). Virtually all flyers will spent most of the time aiming the standard antennas null directly at the airplane Whereas with the wound antennas you spent the whole time pointing the strongest signal at the aircraft.

I have been using two of these antennas for several years now on four Tx's with the appropriate adapters and would honestly say I will never be without agine. Originally I started to use one in 428 pylon racing as on occassion the teams sometimes tend to drift together as you rotate around and end up playing dueling antennas, This is not fun while flying a 160 odd mph airplane in traffic.

I have noticed less problems with the occassional glitch using this antenna than stock and no perceptible differance on ground checks. I now use them on every thing without fail.

http://smileyantenna.com/


John

tande

My Feedback: (48)

Yes, Yes!

JPMacG

My Feedback: (2)

I have to speak up on this one. Short antennas do not radiate in the direction of their axis. This is a myth. I know that one of the manufacturers has it on their web site. They are incorrect.

I agree that these antennas are effective, and many modelers use them with good success.

JohnBuckner

My Feedback: (1)

I am not an expert in RF wave propagation or anything related so am not aware of any myth but there have been many, articals going back even years in the general RC press including model aviation about this all have described this effect. So I cannot disagree only to express my own success and obvious performance improvement with these antennas and will never use the conventional type agine.


John

JPMacG

My Feedback: (2)

John,

Yes, the axial radiation thing has been around for some time. I think it originated with an anecdotal observation by one of the ducky manufacturers, and then was parroted in the various RC publications.

I can't expect you or anyone to believe me over what they have seen in print many times, but please at least keep in the back of your mind that some of us disagree.

Best regards,
Jon

laryboy

My Feedback: (2)

pull out the regular antenna. place your fingers around it . your fingers are showing you how the electro magnetic wave is propagating.like ripples in a pond. go to the rubber duck. grasp it as if you can grasp a wire that is wrapped around it.see how the wave is propagated ?addition and cancellation shape the signal into a beam.

JPMacG

My Feedback: (2)

Sorry, but no, that is not ture.

There are two modes of radiation in a helical antennas in general. Small helical antennas radiate in the "normal mode", which means perpendicular to the axis of the helix, as if the helix were a dipole. Large helical antennas radiate in the 'axial mode', which means in the direction of the helix axis. To operate in the axial mode a helix needs to be about two-thirds of a wavelength in diameter. This would be a diameter of about 9 feet at 72 MHz! Smaller diameters radiate in the normal mode.

John Kraus is the inventor and first to describe this antenna. He has a famous textbook titled simply 'Antennas', published by McGraw Hill in the 1950s. You can usually find the first edition on eBay for a reasonable price. I can suggest many other textbooks that discuss helical antennas if you are interested.

callen

Go to this web site and it will answer all your questions on a rubber ducky..http://www.bergent.net/

Dizzy Pilots

They say the rubber duck has 4 to 6 DB loss, thats a Lot to lose.
Thats like saying up to 75% of the power transmitted is lost.

The rubber duck radiates at a higher angle of 60° as compared to the full size antenna that has an angle of radiation of 25°.

Their testing looks accurate but can be misleading if not understood.

Our radios only transmit at most 3/4 of a watt and I would want to use 100% of it.

laryboy

My Feedback: (2)

you cant "use " all of it. attenuation in the air uses up most of it. typical receiver sensitivity would be in the range 0f 90-100 dbm. assigning 6db to antenna loss is just one of many losses and is insignificant

modeltronics

My Feedback: (27)

Any antenna made shorter will not work as well as a full length antenna....this is fact.

If a shorter antennas worked as well as full length antennas NBC, ABC, CBS, FOX..... could replace those large towers with rubber duckies for the TV transmitions.

Pete

Dizzy Pilots

From http://www.bergent.net/
"RANGE:
We found a 4~6 dB difference in received signal strength between the factory-standard whip and the ducky. This was (to be) expected, and the amount of margin built into today's receivers tolerates that, as long as we remember that we are eating up safety margin."

I never said the full size antenna is 100% efficient. That is the reference that the duck is measured against.

laryboy

My Feedback: (2)

well you certainly didnt say the antenna was 100% efficient, because you have no idea what its efficiency is. to pete.......if longer antennas were so much better then they would'nt have to build such high towers...................................if we apply the 6dbloss as a 75% loss then the antenna is radiating about .5 watts. the receiver only needs a few microwatts.

Dizzy Pilots

How did you end up with .5 watts when you started out with .75 max and lost over 75% of that?
The signal at the receiver is in microvolts.

Bottom line is that the signal from the factory antenna is 4 times stronger then from the rubber duck. That is what their test showed.

The rubber ducky has a higher angle of radiation, but over all weaker signal.

The only place I would use a rubber duck is on a handheld two-way radio.

People do use rubber ducks to fly with and they don't have any problems that I know of.

6 DB is too much to give up. I wouldn't do it.

JPMacG

My Feedback: (2)

Electrically short antennas are less efficient (more power dissipated, less radiated). This is a well known fact.

However, modelers do use duckies with success and this is because our transmitter-to-receiver links are so robust that we can tolerate some additional loss.

The conclusions regarding directivity in Ap Note 01 are, in my opinion, nonsense. The authors are well intentioned, but appear to be quite clueless with regard to antenna measurements. Again, only my opinion.

laryboy

My Feedback: (2)

75% of .75 watts equals .56 watts. the energy that reaches the receiver is measured in watts i.e power. it causes current to flow in the receiver antenna. when that current flows in the input resistance of the receiver (usually 50 ohms ) it developes voltage. if you start out talking about power out of a transmitter it is easier to continue talking in units of power at the receiver. you may also use microvolts or micro amps if you want. all 3 are perfectly fine for discussing input sensitivity. the bottom line is that 6db is not significant . it like when bill gates goes to buy a new car and just before purchase he is told that he just lost 6db of his fortune, so what.

Dizzy Pilots

If you start out with .75 watts and have a 6 DB loss you would only have .1875 watts ERP.

Futaba says shorter antennas, "rubber ducky" antennas are not legal to use in North America on Futaba equipment.

http://www.rcuniverse.com/forum/fb.asp?m=2175686

Another concern would be developing a bad habit of not having to pull up the antenna.

Rodney

Lazy boy, a 6 db loss is a loss of 75% of your power. Each 3db loses you 1/2 your power.

laryboy

My Feedback: (2)

dizzy ....oops. i calculated (using your numbers ) amount lost, not amount left. 6db loss is insignificant compared to other loss.

JohnBuckner

My Feedback: (1)

[quote]ORIGINAL: Dizzy Pilots
Another concern would be developing a bad habit of not having to pull up the antenna.
[/quote



To the contrary this is indeed a safety advantage and was the whole point of the orignal thread starters question. It certainly is no concern to me as I will never use a conventional agine.

As I said in the original post the reason I tried them was for the obvious safety advantage while engaged in 428 pylon racing were four teams of pilot/callers haver to rotate a full 360 degrees about every 7 seconds. These teams can an do tend to drift together sometimes resulting in unintentional antenna swordfights. Another is pilots will sometimes tend to drag the antenna tip in the dirt as they rotate, this is not healthy to the RF link.

Another hugh safety advantage is handeling the airplane while holding the Tx. Say when you are going to sit the airplane down on the ground in position. I,ve no idea what you'll have seen but I.ve seen antenna/propellor strikes occur hundreds of times in this situation, Ain't going to happen with a duck.


Dizzy I agree with what you posted about the question of legality and Futaba's liability disclaimer. This neccessarily may not apply to all manufacturers. As I said in my first post Its likely this is because these antenna's are not the type the Tx was originally certificated with. JR has in the past possibly still does sell this type antenna for their equipment and this may not apply there.

Now to the bottom line for me. Agine no RF expert here for what ever reason 'propagation' or whichever argument you choose beleve over the last two years of very active almost daily flying of all sort of airplanes up to 165 mph racers, using these types of antennas I have realized a real life improvement in RF performance. Unscientific, You betcha but this represents real world safety for me not only on the RF level but also in the very obvious procedural safety factors. I doubt if anyone here has ever actually tried one for a real world trial.

I will never be without this type antenna Agine.

John

Dizzy Pilots

This is the way I always do it.

1 - Transmitter antenna up
2 - Transmitter on
3 - airplane receiver on

after I land

4 - airplane receiver off
5 - Transmitter off
6 - Transmitter antenna down

If I change the way I do this, I would slip up someday.

The only time I ever have my transmitter on with the antenna down is when I'm doing a range test.

I agree that a lot of people use them with no problem, myself I like the full size antenna.

RCAddiction

My Feedback: (87)

Theory is nice, and often it is directly applicable.

REALITY
I actually did ground tests with both an ACE rubber ducky on my Hitec Flash 5X and also the Smiley rubber ducky on my Futaba 9C some time ago. I did the Hitec when I lived in Cincinnati, and the Futaba a couple of years ago, since I've moved to the suburbs of Chicago.

In both cases, I set up a Kadet Trainer on my driveway, on top of my car, with the receiver on. My daughter was outside with the telephone, watching the control surfaces for me. I got in my car with the transmitter and drove away, down the street, while on my cellphone, staying in contact. I would periodically get out of the car, check whether there was still reception or not with the fully extended antenna, or the rubber ducky.

Results, in both cases, I drove approx 0.8 miles from my house through a flat suburban area, past houses, trees, and telephone lines, etc, until reception became a problem, and the surfaces started to glitch. In both cases, the rubber ducky was worse. However, the difference, at 0.8 miles was around 10 feet for one radio, and about 20 feet for the other. 20 feet difference at 4000 or so feet is not worth me being concerned about. I did notice a difference in that, at the fringe of reception, the telescoping antenna seemed best when aimed sideways, relative to my house, and the rubber ducky seemed a bit better when the tip was pointed toward my house. But the orientation only seemed to matter right at the edge of reception for me, like the last 50 feet or so as I vaguely recall, and it was not as pronounced as I expected it to be. Enough for me not to worry a whole bunch about it.

This was also worst case, since it was on the ground, through a neighborhood. The range surely would have been further had the radio and plane been line-of-sight to each other, with the plane several hundred feet up in the air.

I'm an engineer (with a P.E. license and everything!) and I like to pontificate as much as the next guy, but sometimes empirical testing is the best way to verify things. Our radios don't control our planes inside a test lab, (or in the street in my neighborhood for that matter), but I'm guessing that my neighborhood is a better approximation of the interference and other environmental factors we see when flying, than the test lab.

DISCLAIMER
My results are mine, and not yours. This was on my radio and my neighborhood. If you are concerned about it, get your own rubber ducky antenna (they are less than $30) and try the same experiment yourself. If you don't like the results, don't use the rubber ducky. I'm guessing that your results won't be enormously different than mine.

ClarkFlyer

Seems like I started a pretty good firestorm. Like many things in our addiction, there are many opinions about this subject. I think overall that the best thing for me to do is create a checklist and just insure that the antenna goes up.

I think my problem was this: For my first flight of the day, I always use my feet to hold the plane and then run up the throttle and check the control surfaces...like many of you do. This is when I ALWAYS raise the antenna. The day I forgot to, it was on my 2nd flight and I just started the engine, set the plane down, and hit the throttle. I think I'll vow to do the whole check routine prior to ANY takeoff. I thank you all so much for your responses.