JasonD

I just purchased a Rubber Duck for use on my Electric Helicopter a Corona. While I like it a lot I don't think it has quite the punch as the regular telescoping antena.

If I fly my helicopter down the flight line away from me in front and four or five guys I notice I can get a glitch on my helicopter. If I fly it away from them and closer to me the mighty duck does just fine.

I didn't experience this phenomina with my telscoping antena. That being said I still love the Duck and hate dealing with the telesope antenna.

Jason

thomasb

The RF beam spread from a loaded rubber ducky antenna is different than a whip. Unlike a traditional whip, the rubber duck's RF energy is directed TOWARDS the antenna tip.

If you are using a loaded R/C antenna, best performace occurs with the antenna pointed at the model. Do not do this with a standard whip or range will be reduced.

JasonD

Thanks Thomas for the info. I had just assumed that both antenna's behaved the same. That is you did not point the
Rubber Duck at the aircraft you held it parallel.

Next weekend I'll point at the model and see if I get any 'swamping' glitches from other pilots.


Jason

JPMacG

My Feedback: (2)

Thomas,

Unless there is some point that I am missing (ground reflection?), the radiation pattern maximum of a loaded antenna is the same as a "full length" antenna - perpendicular to the rod. There is a pattern null (minimum) in the direction of the tip.

Can you tell me where you heard that the maximum is in the direction of the tip? I would like to track down the source and verify or discredit the idea. This could be important for safety and I think that RCers need to have correct information.

Thanks.

Jon

thomasb

The reason that these loaded R/C antennas have good range is because they have a more directed beam pattern, which provides substantial RF gain. Without this trickery, the rather short rubber ducky antennas would have terrible performance.

On a typical Rubber Duck, Much of the RF is directed towards the tip of the antenna in a pattern that looks like an ice cream cone (tip of cone pointed towards Tx). It is possible to configure it with more radial beam spread, but then gain is affected.

I looked through my ham radio books looking for a beam plot of a loaded whip but I could not find one. But a web search quickly found this blurb at the New Creation R/C's site on its catalog page describing the ACE R/C rubber duck:

The RubberDucky Antenna is unique in that the radiation pattern is totally different than the conventional telescoping antenna. While the telescoping antenna radiates the least amount of power out the end of the antenna and the most power is radiated out the side of the antenna, the Rubber Ducky is the exact opposite. It radiates the most power out the end of the antenna. Since most people tend to point the transmitter antenna at the model, with the Rubber Ducky Antenna your receiver is usually receiving the strongest possible signal from the transmitter. The full text is at http://newcreations-rc.com/radios/ducky_antenna.htm

JPMacG

My Feedback: (2)

Thanks for the link Thomas. I have emailed Kirk Masey at NewCreations-RC and I'll try to get to the bottom of this.

As a professional engineer with 20 years of experience designing and testing antennas I have a hard time believing that the rubber duckie produces a directional pattern off the end. I'm not condemning the use of rubber duckies by RCers, but I do think it is important that we have correct information.

Best regards,
Jon

JPMacG

My Feedback: (2)

By the way, there is lots of information available on rubber duckies on the internet. Search for "normal mode helix antenna".

TomM

There is some mis-information here.
Radiation patterns are similar. They do not radiate out the end.
My antenna books are at work- I will scan some charts tomorrow.
In the mean time- here are some links.

http://www.qsl.net/kc4jgc/ht.htm

http://www.scc-ares-races.org/emerge...ons_and_ht.htm

http://www.qsl.net/ccares/aresdec01.pdf

http://www.races.org/docs/msg008.htm

http://home1.gte.net/rhashiro/am-rad...cles/tools.htm

Antenna Patterns:

http://www.cebik.com/p.html

http://www.rfcafe.com/references/ele...a_patterns.htm

Tom
Microwave Eng.
Ham- N3UJM

TomM

There is a Helical Cone antenna that is directional depending on coil spacing. Quite different windings and shape then a Helical Wound antenna (rubber duck)

http://www.nasatech.com/Briefs/May01/MSC22334.html

http://www.sekitech.co.jp/product/defense/ara_3/pdf/crs

thomasb

The provided rubber ducky links mention that gain is about -5dB when compared to a traditional mobile whip. That is consistent with what I have understood. I did not see any relevant beam plots though.

As a curious sort, I just took my RF wattmeter and built a simple probe for it using few loops of mag wire. Using my JR equipped Smiley rubber duck, I found that the relative RF power above the tip was stronger than anywhere else along the length of the aerial. This was a crude test and I could have been fooled, but the results were repeatable. Would someone else please try this out to see if they can confirm the behavior?

It would be nice if one of you antenna engineers would haul your R/C ducky to the fancy RF cage and make some measurements. I would sure love to see some good data for the various aftermarket R/C antennas. None of the mfg's have anything on their web sites. Dang.

If someone has some archived beam plots for a rubber ducky then I would love to see them. Since duckies come in different constructional forms, please try to dig up the details to the one used in the plots.

For sure, I would like to know if I am giving wrong advice! I am very open minded.

fiery

My Feedback: (2)

I while back I posted on this thread that I had ordered a " rubber duck" (who thought up that name?) antenna from Smiley.

Well, I did, But I had to cancel my order. I discovered Smiley's antenna's were apparently "not suitable" for 35/36 Mhz use They are only stated as being suitable for 72/75 Mhz or 50/53 Mhz use. Where I live, 36Mhz is the primary legal refequency for R/C flying.

Why is this? Why would 36 Mhz cause a problem with the antenna as opposed to 72 Mhz?

The telescoping antenna's supplied as original equipment with your favourite "Brand TX " Tx seem to me to be the same part in that same TX all over the world, as far as I can tell, no matter what the frequency.

As the experts will gather, I know nothing about RF patterns and loads. So please be a little patient and don't flame me (despite my user name!)

Assuming what I have been told is true, does anyone know where I can get a "rubber duck" antenna for my airtronics radio suitable for 35/36 Mhz use?

Here's hoping someone can help

thomasb

When an antenna is made shorter than normal, its capacitance goes up. This unwanted side affect compounds the aerial's efficiency issues since now you have to deal with a bad impedance match (causes RF loss due to standing waves). That, added to the poor resonance of the reduced element (an unrelated side effect of the shorter length), and you end up with a nasty antenna.

So, the trick is to add inductance to help cancel the effects of the higher capacitance. This is done by wrapping fine wire (the inductor) around the rubber duck's body. The amount of wraps depends on the operating frequency. Your 35/36Mhz Tx is not going to work well with a 72Mhz loaded antenna.

BTW, your 35/36Mhz Tx is internally "base loaded" to account for its stock antenna since it is shorter than a quarterwave. However, the inductive load in your Tx is not expected to ensure a good match to a 72Mhz rubber ducky.

Given the popularity of rubber ducks on R/C Tx's, I would expect that they should be available in Europe. Have you looked at the Graupner catalogs?

fiery

My Feedback: (2)

Thanks Thomas. I think I understand now. I will keep looking in the local R/C mags for this type of item.

One query - if you bought, say, a Futaba 9C Tx from tower, normally sold with a 72 Mhz module, and took it to Australia or New Zealand, where 35/36 Mhz is the legal R/C frequency, and put a suitable (ie 36 Mhz) module in it, it would seem this may not result in satisfactory operation due to there being no internal "base loading" in the Tx (designed for 72 Mhz use) for the standard antenna. Am I understanding this correctly?

thomasb

It may seem that way, but there is more to the RF amp module than meets the eye. All of the RF circuitry is in the removable module. When you swap it, the antenna matching components go along with the module and do not stay behind with the Tx.

salmon

My Feedback: (114)

Got to have one , I have a ? or two before I order one,
some guys are saying that the strongest signal comes out from the tip of the antenna, so I have to be facing the the plane all the time? how much signal I'll loose if I'm not facing it, most of the times I'm facing the front of the field I don't want make a hole. ( another one ) on the run way.
thanks
Edwin.

Forgues Research

My Feedback: (7)

Not scientific, but when I tested my Smiley Rubber Ducker, I didn't pay attention to the orientation, and I flew the airplane ( with a single conversion receiver) as high as I could see the dot, and no where at any time did I feel I was loosing any thing.
Hope this helps.

JPMacG

My Feedback: (2)

Guys,

I received a very responsive email back from NewCreations-RC. They are not sure where the statement on their web site saying the ACE ducky radiates off the end came from. They are no longer carrying the ACE ducky and now carry a line of Duckys made by Smiley. They will shortly be posting a new website that is "correct and up to date". I assume this means they will be dropping the statement about the radiation pattern. I checked the Smiley web site (www.htantennas.com/rcduck) and there is no mention of radiation pattern characteristics.

There are helical antennas that do radiate with a maximum along the axis of the helix and perhaps this is where the confusion arose. However, the diameter of such a helix has to be several tenths of a wavelength to radiate in this "axial mode". Several tenths of a wavelength is about 3 feet at 72 MHz. There are many other antenna types that produce directional patterns - conical spirals, dielectric rods, horns, yagis, log periodics, phased arrays, etc. They all are large and have to be to achieve this directivity. The Duckys we use for RC are electrically tiny (very much smaller than a wavelength). Electrically tiny antennas cannot have directive patterns - to do so would be a violation of basic concepts of physics, such as power conservation.

Antenna measurement is a whole art in itself and I would not try to draw too many conclusions from tests that we perform ourselves. When we hold a transmitter our body makes up part of the antenna and the antenna pattern will vary depending upon how we hold the transmitter. The antenna also interacts with the ground and whatever other objects happen to be nearby. The ground can have a large affect, producing many peaks and nulls in the radiation pattern (the antenna system including the ground is large). Also, don't forget that antennas are polarized.

The bottom line is that our RC radio links are so robust that they work regardless of all these variables and compromises. We don't need to worry about the details.

All this is, of course, just my opinion.

thomasb

I emailed Smiley antenna and they commented that the highest radiation appeared to be from the tip. They did not have beam plots to share. I also wrote to Peter Berg. He has designed R/C gear for over three decades and was one of the talented folks at Kraft R/C. He now owns his own R/C firm (www.bergent.net).

Here is his response:
We designed the first 'rubber duck' transmitter antenna when I still worked at kraft systems. They are typically not base loaded, but constant loaded at the bottom, then top loaded.

We did a lot of measurements at that time and we found that the strongest radiation is off of the tip, so pointing the antenna at the aircraft works well, which also killed the design for use with car racing, for which we originally started that design.

There probably are some side lobes as well, but we never did a complete measurement of those so I don't know. There is a loss of measured received signal strength at the receiver end with these things, but modern radios have so much margin in range that nobody notices.

So, this info seems to indicate that the rubber duck's beam spread will depend on how it was designed, per our previous comments in this thread. This is consistent with what EVERYONE is saying. For sure, a handy talkie (ie, ham radio) would be lousy if it were constructed to radiate from the tip since range would be limited when it was hanging on the users belt. I suspect that they are all continuous loaded duckies.

In the case of R/C rubber duckies, the RF beam spread is an unknown, since none of the after market antenna makers seem to have published any data. My Smiley appears to be constructed in a way that it supports Mr. Berg's findings (max power at tip), but that was determined by a very crude test.

However, it is best to position the antenna so that signal strength is maxmized (this will help reduce the occurance of glitches). What YOUR R/C rubber duck does is up to what YOU discover. Ground range tests should help determine the "hot" spots in your antenna's position.

Regardless of the antenna used, you seldom need to worry about the EXACT antenna position. In most cases, there is sufficient signal radiated in nearly all directions to freely fly around.

For example, have you ever cared how your factory supplied whip is aimed? It has the least amount of power at the tip, yet your model is usually in full control when you aim it at the model (a bad habit to get into, by the way). However, if there are situations where your model gets twitchy in flight, it is best to know how to hold the transmitter to regain control of your model.

I totally agree. It only matters when it matters.

JPMacG

My Feedback: (2)

LOL..... OK Thomas. I give up.

AJMoritz

Does anyone know if a Smiley rubber duck or other will fit a Multiplex Cockpit Tx? And would there be any diffrence between 72 & 75 mhz applications?

Thanks,
AJ

gavoss

My Feedback: (16)

Bill at Smiley Antenna explained to me that all transmitters used in the US will require the same length antenna. He explained something about a certain type of loading for 50-53mhz, and 72-75mhz.

For the Cockpit, you'll need the adapter type. I have them for $28 shipped. gv

[email protected]

Ladyflyer

My Feedback: (2)

Thank you JPMacG , YOU got it right. It is so very hard though to argue with third hand "facts" LOL
Of course believing ANYONE who tells you an antenna a fraction of a wave length long can just get screwed onto your transmitter and without tuning will work at least as well as the factory antenna ???? Oh well LOL does sum it up

jimcork1

My Feedback: (4)

I have only been using the r/d antenna for 10 years on all my tx's. They just work,, I do range check with the factory tele. antenna as per instructions.

I do approve me of using the r/d. But then I did buy my tx. and r/d from the mfg at the time of purchase.. It would seem the mfg would not sell something they didn't know would work.

I have checked mine on the freq meter we borrowed from AMA and all was right on the button for specs.,, but then who am I to know. Ya'll have a nice day.. Jim

aerowoof

Know this is an old thread but have a question anout rubber ducky antennas,are the same antenna used for both 72 mhz and 53 mhz or are they different ? have a Microstar 2000 single stick tx with a broken antenna mount and want to be sure I get the correct replacement.