Antenna question
 

I've seen conflicting answers of this topic so that's why I'm asking the question.

My question is a simple one: my antenna on my PTS P-51 exits out the bottom of the fuse, and has a knot tied in it and hangs loose after the knot, but apparently is prone to getting eaten by the tailwheel. So I need to deal with it.

Some guys advocate "doubling back" the antenna along the bottom of fuselage and attaching it with a rubber band near the main wing. My question is not how to attach it, I've researched threads on that. My question is: does doubling back the antenna lesson the receivers range ? I've seen conflicting answers. Does the antenna (ideally) need to be stretched out as straight as possible for maximum range or if it's doubled back on itself is that ok ?

Thanks.

Joe

RE: Antennae question
 

Don't double back. Think of the outstretched antenna like the antenna on your transmitter. Would you fly with half of it bent down?

I use a T-Pin, and a small piece of fuel tubing. Slide the antenna through the tubing then pin it to the fuselage back near the tail wheel mount so it hangs down behind the wheel/ground contact point if possible. Don't push the pin through the antenna though.

RE: Antennae question
 

Joe,

Your planes RX has an antenna. Insects have antennae. Well, that is unless you have two receivers or an injured insect......ANYWAY. Doubling the antenna back on itself is just like cutting ti off wherever you make the 180* turn. You are better off bringing it down to the fuse and forward, or along the fuse, up the tail and then forward, or through the bottom of the fuse, forward and back through the top of the fuse and then back to the tail.....you could do it however you want. Just don't cut the wire or double it back on itself.

The likelihood of you flying far enough away to be out of range in either situation is pretty low, but better safe than um...hiking.

Later

RE: Antennae question
 

Never double back the antenna. How I attach mine is to get a servo arm that has three holes in it (cut it from the rest of the servo arm). Get a Tpin and place it where you want but be sure the antenna can reach it. There should be a gap between the Tpin and the end of the antenna of about an inch or two.

Now take the antenna and run it through one of the outer holes in the servo arm leaving about 2 or 3 inches extra length, take a rubber band, fold it in half over onto itself so if your thumb is in the middle of the rubber band you have a loop on each side, lay it across the servo arm between the hole you ran the antenna through and the second hole. Now while holding the antenna and rubber band, run the antenna through the second hole until it holds the rubber band tightly then run the antenna through the third hole and pull it snug. Now take the 2 loops of the rubber band and hook them to the Tpin. You may have to play around with how much antenna you have running through the holes until you get it to where the antenna is nicely stretched out and the rubber band is also a little streched. Any extra antenna just let it hang in the breeze

It sounds harder that it really is and you now have an antenna that will give a little bit if needed without breaking and will remain tight. I have been doing this for a while. The only time I have ever had to fix this is when glow fuel finally eats the rubber band away because I forgot to clean it when cleaning the plane.

If anyone wishes I can take pics later this evening

RE: Antennae question
 

Pics would be good [8D].

RE: Antennae question
 

I have a very sophisticated method that I crafted over many seconds of thought. I tape the antenna above the wheel so it doesn't roll over it. :D
The tape's actually lasted about 30 flights, but the methods the other guys are mentioning are a little more permanent.

RE: Antenna question
 

how about route the wire out the top of the fuse behind the canopy and attach it to the tail using a servo arm piece and rubber band to a pin method like bubba mentioned then any extra is hanging above the ground and your problem solved where you exit the fuse use fuel tubing to protect the wire from chafing on the fuse another way of dealing with your antenna

RE: Antenna question
 

Sorry for hijacking but..
Is there any problem with running the antenna inside the fuse, surley it wont affect the range too much will it?

Thanks

RE: Antenna question
 

Keep the wire away from metal pushrods and don't run inside carbon fiber tubes.

If you happen to have a carbon fiber fuselage, this would be bad. Fiberglass is OK.

RE: Antenna question
 

Respectfully, these are all pretty good answers.

However, doubling back the receiver antenna is not as bad as indicated as long as it doesnt cross back and forth over itself. I know because I (we) do it all the time.

On our foamies, we make a flat spool and carefully roll the antenna up around the spool so that the wire never overlaps itself but continually wraps from the front of the spool to the back. Then we leave a tail off the end of the spool that is just enough antenna to extend to the back of the airplane. It works perfectly over and over again. And I can range check and fly a foamy almost out of sight this way, just as far as with a fully extended antenna. This is not opinion,,, its fact. My little spool is a flat piece of depron about 2" long. Again, this is a very careful and definite wrap. You do not overlap the wire, you just wrap it around the spool carefully without an overlap in the wire. If you overlap the wire you are headed for a crashWe also double the antenna back on a heli. There is usually a plastic tube that is about 12" long that mounts through a couple of premade holes in the landing gear on 1 side of the heli. You simply run the antenna through the tube from back to front and then run it back along the outside of the tube from front to back and then secure it with a piece of shrink wrap tubing or a little o ring. Again, this is a tried and proven technique. Given the choice I would always run my antenna full length, but Im stating experience based fact when I tell you that the antenna can be not only doubled back, it can be wrapped around and around.

RE: Antenna question
 

From the Futaba FAQ site:

I am building a small model. Should I leave the antenna hanging out the back of the plane or wrap/fold/cut it?
Never shorten your antenna by cutting down its physical length or by folding it back upon itself. Always allow the antenna to extend its full length, even if it means having a 'tail' hanging out the back of your model. You might also consider running it out the wingtip rather than down the fuselage.

No matter what ANYONE tells you, if you double back, fold or curl your antenna you are detuning it and decreasing your effective range. You may still have ENOUGH range to operate your model or you may not, it's your plane. This is also a fact.
I base my information upon my Electrical Engineering degree, 30 years experience in full scale aircraft avionics and 25 years r/c flying. Take your choice. :) It may work and it may not, let us know.

RE: Antenna question
 

Nice response bruce! :D

A little off topic, but a guy just lost his trainer at my field Saturday because he cut the antenna & then twisted it back together. It actually range checked OK, but as soon as it was a few hundred feet away in the air it started glitching real bad & the instructor couldn't save it. (the instructor wasn't aware of the splice until after the fact)

RE: Antenna question
 

I digress, when "years of experience" by rule somehow supercede imperical data based on hundreds of thousands of successful flights... Its not even a rational discussion anymore. All I can say is go to a heli fest with helis from micros to 60 sized helis or a electric 3D foamy competition and look around at their antenna configurations. If the dozens and dozens of successful flights dont conclusively show that the antenna can be sucessfully doubled without any problems I will eat my hat...

I will add this caviot. If you are going to do it it has to be done correctly.. If you do it incorrectly you will crash so if you arent 100% sure of how to wrap or double the antenna correctly,,, DONT DO IT.

RE: Antenna question
 

have doubled back the extra 5" of my antenna using a servo arm piece to attach arubber band to then another at the end of the antenna to prevent it from touching it works fine as long as you dont twist the extra it will work fine. if your worried about it then take up the extra slack and hide it in the fuse. personally I would rather the extra be out side of the fuse.

RE: Antenna question
 

Just because one gets by by folding back or other wise changing the antenna does not change the fact that they now have less range. All valid scientific tests show that performance is degraded when the antenna is shortened. That doesn't mean that you can't successfully fly with the degraded equipment, it just means that ,in that case at least, maximum performance was not required. If range is a problem or you need maximum range, then, DO NOT fold back or shorten the antenna by any means. If you want to take the time to investigate this a little more thouroghly, check out RCCAM's site. He has the equipment and the knowledge to perform valid tests and has published some of them.

RE: Antenna question
 

Take this with a grain of salt, your mileage may vary, but I was trained as a sonar/radio technician in the military.

*looks at his iCOM portable VHF Radio..... hmmmmm

The antenna is a "rubber-ducky" type antenna. Inside underneath the roubber coating, is a very long insulated wire (sound familiar?) that is coiled around a central whip. It's range, however, is slightly less than when I use an external metal whip antenna. Why? While you are not changing the electrical length of the antenna when you coil it, you are altering its exposure to the RF. For best range the antenna should be full length in order that the full wavelength of a radio wave is expose "seen" by the antenna. A coiled antenna doesn't "see" as much of the radio signal so its range will be slightly less. My 4watt vhf radion can pull a repeater tower up from 50 miles away, so I do mean slightly.

When you cut an antenna you alter its electrical length, this "detunes" the antenna and causes the antenna to have a different natural frequency than the radio signals it receives which causes it to reflect the signal. It has a lot to do with impedence matching and such.

So.... cutting an antenna = "very bad!!" while coiling an antenna may reduce the range a bit, but I don't think it would change it to the point where you could still see the model at the time the change became noticeable.

That being said, I wouldn't coil the antenna unless I absolutely had to to prevent it from being caught in propellors or rotors.

Cheers,

RE: Antenna question
 

Now, you clever experts, here is a tough one: I've got a live steam, all metal locomotive for the garden (G-gauge, 45mm between the rails) and it is controlled by a transmitter for aeroplane models: I've got a Skysport 6a FM FP-T6VA (Serial No 50307398, 40MHz) and matching
receiver. Here is my question:

When my engine is under steam, the three servos work perfectly. As soon as the engine starts moving, there are places on the track circuit where the servos tend to get very "nervous" indeed and this makes the locomotive run forward/reverse, fast/slow or merely lets it do some sputtering that causes the safety valve to go off. A derailed train is often the result also.

The problem must be the antenna. Is there any way to increase the quality of the received signal or to enhance the receivers ability to give a more stable current to the servos? The problem is obvious: A locomotive of a train doesn't really have an antenna and the engine was delivered with a four inch long "spade" sticking out of the "coal" in the tender. Is there any way to connect a short (2 inch, or so) antenna to the system, an antenna that can be concealed easily, for instance under the heap of coal?


Thanks!

Getgoing

RE: Antenna question
 

More likely you are have a metal-to-metal interference causing rf noise generation that is upsetting your receiver. Metal wheels on metal tracks. Metal arms turning the wheels (pistons). And probably many more points. Some of these points can be fixed with proper bonding but many can't.

RE: Antenna question
 

Wow, now tht's a new one to me! Never ever thought of it. I'll really have a good look at that! Thanks for the tip!

RE: Antenna question
 

Look at the video in this review:

http://www.rcuniverse.com/magazine/a...article_id=706

Now I don't suggest trying this at home kids, but after this flight, I realized that I never put the antenna in the tube. It was just laying around the radio compartment like a big rat's nest.

Did I lose any range? Probably, but although most of the time the camera is zoomed in, you can get an idea of how high and far the plane got without any glitches.

There are however, some people who fly so high and far that you can hardly see the plane. To those people I say, "Fly the plane and stop letting the plane fly YOU!" - now, if you're one of those people, be concerned about every inch of reception.

RE: Antenna question
 

You might try using a double conversion receiver from Futaba. With all of that metal for the signal to bounce off of, your problem may be echos, espically if the problem always occurs in particuliar spots along the track. I don't know if Futaba makes a 40Mhz version of the Double conversion receiver but it's worth a try.
I know it's unsitely but try the receiver antenna fully extended and sticking straight up first. If the problem goes away, then it is an antenna length problem and spooling it may help. If not, it's echos and you need a better receiver.

RE: Antenna question
 

Nice thing about a train is that it won't come spinning down out of the sun and crash. :D

RE: Antenna question
 

That's true, but they don't do loops very well. And rolls... forget-about-it!!

RE: Antenna question
 

A couple of other things you can try:

1)Check the wire from the antenna to the receiver, if its unshielded, maybe slide it into a carbon fibre pushrod case, this may give you a bit of RFI shielding, perhaps wrapping it in foil may also help, if you don't have a pushrod, or its awkward.

2)Experiment with the antenna grounding. If the antenna is connected to the locomotive with a metal to metal contact, try running with the two insulated so that the mount isn't in electrical contact with the locomotive, or visa versa if they are already insulated.

3) If all else fails, why not solder a proper length antenna back onto the receiver, and do what Mike East mentioned, coil if carefully around a non-conductive core, and just leave the end out, perhaps running it under the locomotive inside of a pushrod guide?

On a side note, using aircraft frequencies for a ground based model is not kosher with the FCC is it? Shouldn't your radio be using terrain frequencies (75 MHz)? Excuse me if 40 MHz is okay for ground, it just popped into my head.

RE: Antenna question
 

First, he is in Switzerland so let's leave the freq band issue to him as we have no idea what their rules are.

Second - NO-No on the antenna inside the carbon tube. It will shield the signal from the antenna and reduce the amount of received signal. I'd rather see him get more signal. I believe carbon fiber is one of the problems some of the jet guys run into. No foil either.

Third - don't ground any part of the antenna

Fourth - While I'm not a big fan of wrapping up antennas like Mike suggested, I have no problem with that on ground vehicles at known short ranges