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RX antenna mod..

Old 09-26-2005, 01:33 AM
  #1  
Positive Charge
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Default RX antenna mod..

I have a park fly jet that has a 24in carbon spar. Can I shorten the Rx antenna wire by 24in and mechanically fix the shortened wire to the carbon rod. Would it matter if the spar was solid or tubular? Should I still keep taking the tablets?

Thanks
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Old 09-26-2005, 04:11 AM
  #2  
timocharis
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Don't shorten the wire, wrap it in loops. The problem is, I don't know if you can get away with looping it around a carbon spar.

The antenna wire has to be a multiple of a specific length (I forget what), but I don't think it's 24 inches...

Dave
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Old 09-26-2005, 04:20 AM
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watt_the?!
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ahhh, this is an area that i wish i wasnt so familiar with.

ever since trying a base loaded antenna that didnt work ive been doing the internet hokie about some definitive answer on this phenom.

some things ive found and tested are:

1 unless you are already working on a non loaded (i.e. pre choked) antenna, multiples dont work.

in other words, 72mhz works fine for multiples, 36, 40, 35 etc not so good.

the caveat is that if you can do the math, you can actually use another choke for these frequencies, but do so with caution.

2. a choke can be emulated simply by coiling up the wire..afaik it is the same principle.

3. do not cross the coiling of the wires, or go back on itself. i.e. coil it along a plastic tube, not around a bobbin.

4. leave as much lenth as you can to the end of the antenna..this apparently has something to do with the fact that RC antennas are end loaded.

5. go for as long as you can within the airframe.

6. keep away from carbon and metal at all times.

7. expect a reduction in range.

8. range test over and over again.

9. range test.

10. range test.

......

hope this helps.
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Old 09-26-2005, 01:55 PM
  #4  
Positive Charge
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Thanks for the replies.
What I was intending to ask was, can I use the carbon spar as part of my Rx antenna by shortening it by the same length
as the carbon spar and joining the two to give me back the original length
so as not leave any wire hanging to catch in the prop..

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Old 09-26-2005, 06:12 PM
  #5  
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+:

I've heard one person say they did that effectively. Nobody else seems to believe it, and I haven't tried it.

Your call!


Dave North
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Old 09-27-2005, 02:35 AM
  #6  
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try it, then do several full range tests...

id like to mention at this point that in no way am i liable for advice given.

:p

tim.
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Old 09-28-2005, 02:45 AM
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Slightly over a week ago, I saw a thread on another site where someone with the training, experience, and equipment ran some tests. His basic finding seemed to be that anything you do to reduce the actual physical length of the antenna reduced the sensitivity of the antenna, and therefore also reduced the range. Also, many people have reported problems if the antenna got too close to metal or carbon fiber push rods, so wrapping the antenna around a CF tube probably isn't a good idea.
My only experience with shortening an antenna was with an Astro 020 powered RAM airboat. With the antenna coming up straight through a Deans antenna tube, I had control across the entire pond, almost 200 feet. When I wrapped the reciever antenna around a cardboard form provided by the radio mfg, I lost control of the AB about 20 feet from the far shore. Since I fly all types of planes, and may switch recievers among them or various reasons, I think I'll keep the antenna lengths as originally put on by the mfg.
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Old 10-18-2005, 03:11 PM
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http://www.uoguelph.ca/~antoon/gadgets/flywire.htm I have about six of these on different rcvrs. with no problems whatsoever. Some on alky burners.:p
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Old 10-18-2005, 09:40 PM
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Forget the speculation - this guy did some field testing of different antennas -

http://www.rc-cam.com/ant_exp.htm
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Old 10-18-2005, 10:21 PM
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very interesting....

so how come places like MAP can sell antennas that are basically wrapped around a straw and claim minimal loss in range?

Also, the testing didnt look at the base loaded antenna with a different (piano wire) material added to it.

this annoys me actually. What i am also concerned about is that these tests apply only to a 72mhz frequency.

The US uses this, sure, but the ROW use 35,36,40 etc.

The ROW use the same antenna length of 40", so must have internal choking.

The result of the internal choking is reduced range. however, choking an already choked antenna via base loaded apps doesnt seem to work too well.

Since the ROW effectively START at less than half the range of the US, any further works would seem risky.

the reason why we start there is that we are working at 1/2 wavelength, not a full lambda. On top of that we are choked.

So it might be ok for a US flyer to cut his antenna in half, but the effect will be different to other frequencies.

one of the other things in the document which wasnt evident, was if the tester had actually ''crossed'' the wound antenna.

and so on and so forth.

tim.
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Old 10-18-2005, 11:14 PM
  #11  
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FWIW, my micro antennae are available for all frequencies world wide. In Australia the 36mhz antennae are available from

http://www.modelflight.com.au/

To address the original question, the pylon guys use a piece of music wire or guitar string ("G") I believe and let it trail out the rear giving little drag. Carbon is conductive; however a lot of what is sold as "carbon tubing" is nothing more than a fiberglass matrix of some sort with or without some degree of carbon. My initial reaction would be "No", but there's no reason not to try it and range check, range check, range check.


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Old 10-18-2005, 11:20 PM
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Sounds like it would be interesting if some people from other countries would duplicate the testing, since 35 and 40 MHz equipment isn't easily obtained here. And if it were, it would be illegal to operate it, anyway.
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Old 10-18-2005, 11:46 PM
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Originally Posted by Azarr View Post

To address the original question, the pylon guys use a piece of music wire or guitar string ("G") I believe and let it trail out the rear giving little drag. Carbon is conductive; however a lot of what is sold as "carbon tubing" is nothing more than a fiberglass matrix of some sort with or without some degree of carbon. My initial reaction would be "No", but there's no reason not to try it and range check, range check, range check.
roger on the range check....do you have any comment on the use of piano wire on your antennas Azarr?

As opposed to the published tests where the guy used just regular old Rx wire?

(not asking for any secrets here).

Tim
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Old 10-19-2005, 01:38 PM
  #14  
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Hi Tim,

I feel we've used the optimal wire length for our product. As you know, our micro antenna line is designed for small parkflyer/indoor planes. changing it's length would not be a good idea.

Don't worry about secrets, I no longer will talk about the construction of my products, I learned my lesson on another group when I released our first wound type antenna and poor copies immediately appeared.

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Old 10-19-2005, 01:50 PM
  #15  
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ntohing spoils a scale plane like a piece of cables hanging out the back of it.

Tim
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Old 10-19-2005, 03:39 PM
  #16  
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How about if the trimming of the antenna reduces the range to a critical distance, and you exceed that distance.
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Old 10-20-2005, 07:31 PM
  #17  
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Nothing to do with the original question, but here's the answer to using a short receiver antenna.

http://www.horizonhobby.com/Shop/ByC...ProdID=SPM2460

I've got one on order, we'll see how the performance is although, for the life of me, I can't understand why they left DR and Expo off the rudder, just about every 3D parkflyer would want both.

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Old 10-20-2005, 09:45 PM
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Also they don't say what kind of range it gets. We'll let you be the ' Let Mikey Do It ' candidate Azarr
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Old 10-21-2005, 06:16 PM
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30 paces, or 90' with an output power reduction by pushing the binding switch doesn't sound too bad as far as ground range goes, but their warning that this radio is for park flyers only, and that other types of planes may exceed the available range, kind of triggers the "Warning, warning, Will Robinson" syndrome in my head.
Possibly, since it will be commercially available in maybe another month or so, I presume it meets all FCC requirements enabling it to be used in this country, but how does it fit into the AMA picture? Will the AMA honor the use of this system under their insurance program(or rather, will the insurance carrier honor the use of this frequency range until the AMA gets to include the band into the contract)?
When the system starts being produced with adequate range for all MA, then it will be a great thing for the sport.
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Old 01-23-2006, 08:49 AM
  #20  
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i use an antenna bobbin on my Hitec 555 in my SmoothE ( Antenna Bobbin: coil the wire around a plastic tube without overlapping the wires and make sure its no less then 3 inches and no more than 4 inches from the RX ) i only coil enough wire on the bobbin to make it so the antenna wire only "just" reaches the tail of the plane. ive range tested and I never could get far enough to actually cause it to drop reception. i still had full control with no glitching at 3/8th's of a mile (3/8 mile = 1980 feet) and since the SmoothE only has a 40 inch wing span its pretty much just a dot at 2000 feet. so im not too worried about any range reduction with the bobbin
i also run a bobbin on a Hitec feather RX with no ill effects. i never fly that plane more than 600 feet from me because beyond that i loose Orientation since its a rather small plane and im getting old and blind
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Old 01-23-2006, 10:07 PM
  #21  
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MtF: I've used that approach on one plane, with similar success. No problems at all. But it never flew much more than 200 feet away from me either. So it's not exactly conclusive.

Otherwise I've just been using these little antennas from some dink company called Azarr, which work very well for me. Well, one of them got sorta yanked apart in a completely spectacular Full Augur, but a little solder and it was back in action.


Dave
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Old 01-23-2006, 10:16 PM
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i havent had any luck at all with base loaded antennas...we are on 36mhz with a 39inch aerial, so i think that has something to do with it.

wrapping the entire thing around a drinking straw or similar has seemed to work somewhat.

Tim.
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Old 03-21-2006, 06:06 AM
  #23  
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Originally Posted by MountainFlyer View Post
i use an antenna bobbin on my Hitec 555 in my SmoothE ( Antenna Bobbin: coil the wire around a plastic tube without overlapping the wires and make sure its no less then 3 inches and no more than 4 inches from the RX ) i only coil enough wire on the bobbin to make it so the antenna wire only "just" reaches the tail of the plane. ive range tested and I never could get far enough to actually cause it to drop reception. i still had full control with no glitching at 3/8th's of a mile (3/8 mile = 1980 feet) and since the SmoothE only has a 40 inch wing span its pretty much just a dot at 2000 feet. so im not too worried about any range reduction with the bobbin
i also run a bobbin on a Hitec feather RX with no ill effects. i never fly that plane more than 600 feet from me because beyond that i loose Orientation since its a rather small plane and im getting old and blind
MF,
I've had almost identical experiences with my planes! I coil all my antennas on a flat piece of balsa, held in place with Goop and not crossed, with from 2 to 4" hanging from the tail. I have about 8 or 9 different RTX's I use this way. I only ever used a fully extended antenna with the first RC I had. I have only once lost contact with a plane and seldom think about it. I've also, very often, exceeded the range recommended with the RTX's, with no loss of contact. Like you, I have trouble seeing, even a plane of 54" span, at 3/8 of a mile.
I did lose an RC plane once because it got too far out to see. I got it back seven months later and consequently flew it to destruction! This was my first RC and it was 27 mhz; all others have been 72 mhz.
I live in the country and always fly alone. That might make a big difference. Most of my RC planes are in the 30" to 54" wingspan range. I have the old problem, too, although I can still see pretty well at a distance. Try it, it will work!
Dick

Last edited by Reddog; 03-21-2006 at 04:31 PM.
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Old 03-21-2006, 08:05 AM
  #24  
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I have since tested my "straw" antenna (JR reciever) to something on the order of about 1000 feet with no trouble at all. I'm feeling fairly secure with this setup.


Dave
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Old 06-17-2006, 08:11 PM
  #25  
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Default If you haven't seen this, it's worth the gander...

http://www.rc-cam.com/ant_exp.htm

The folks at the RC-Cam site did a very thorough follow through on the results of using non-standard antenna applications or using standard antennas in a non-standard manner... Well worth the look if you have not had the chance to see it.

Most of us have been aeromodeling for quite a span and I'd be willing to say that all have our little "tricks" to get things to operate within our comfort zone... there isn't any problems with this at all, but I do want to send a word of caution when dealing with "wive's tales" (ok...ok... for the ladies "husband's tales"... this is an equal opportunity thread )
pertaining to antennas.

Wrapping or using a base loaded unit may prove to be effective in the application we are using, but there is going to be a dB loss in all occasions... it's managing this loss that is important. The whole juggling appearance and signal strength required for our personal application is the game we as aeromodelers will constantly be playing.

Anyway, check the site.... it is very informational.
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