Antenna Length Question

[Willber-Force]

I am currently constructing a WingDing. The plans say to run the antenna along the main spar and back along the TE.

Here is the Problem, I would like to remove my radio equipment without tearing out my antenna from inside the wing. So I have decided to use my own wire as an antenna and cut off the original. I will use a simple connector to connect the new antenna to the receiver. I consider myself an obsessive compulsive symmetrist. So naturally, my antenna not being equal on both sides caused a problem to me... so I made it longer so it would be even. :) Would this pose a problem with range?

I know that antenna lengths are selected based on the wavelength of the signal it is receiving but I don't know the effect of lengthening the antenna.

[All__talk]

hi Willber-Force

I know how you feel about the summitry (I'm the same way), but leave it the stock length, any change in length longer of shorter will reduce range. Read my post in this thread for more detail on why.

http://www.rcgroups.com/forums/showthread.php?s=&threadid=75468

Gary

[Mr.RC-CAM]

I know that antenna lengths are selected based on the wavelength of the signal it is receiving but I don't know the effect of lengthening the antenna.R/C Rx antenna lengths are not chosen on the basis of the signal's wavelength. They are based on convenience. About forty inches is the norm for all R/C freqs (27Mhz thru 75Mhz). This is easy to mount on most sport models.

The front end of the Rx is designed to deal with impedance issues and the Rx's have enough reserve in their gain budget to accommodate lower antenna efficiencies. They are "tuned" to operate fine with the stock antenna and aerial length changes will impact this.

Changing the length, longer or shorter, is not in your best interest for optimum range. Going shorter has its place on tiny models, even with the resulting range reduction. Going longer does not mean it will be better (the range may be reduced).

RC-CAM

[Sabrejock]

I use a lot of "Dean's" antennae in my smaller planes. Using them entails cutting your Rx ant to about 6" and plugging in the Dean's. Well, I sometimes switch the Rx package around to a plane that I want to fly. I had done just that, then decided that I would fly my Mustang that day and did so. I noticed a bit of jumping in the far-out turns and attributed it to some unknown phenomenon. After landing I discovered that there was no antenna in the plane.

I bring this up to illustrate the fact that our modern radios have such performance that talking about antenna length as though it was a serious point of discussion is really a non-starter. Certainly, a few inches here or there won't matter given the distances at which we fly our models vis-a-vis the range of the Tx capability.

When the experts talk about a "something" percentage of range reduction, think about it. A 50% reduction in range is farther than most of us could see and control our models anyway.

Just my thoughts, Tex.

[Mr.RC-CAM]

Yes, there is often sufficient overhead in the Rx's RF gain budget to allow us to thoroughly dork the antenna with impunity. Despite that, it makes no sense to go out of your way to do so. ;)

RC-CAM

[KillerWatt]

hi Wilber F.... as long as you use some reasonable length of antenna wire & fly within good eye visibility distance, i don't think you will get out of control range.....but Why Not stick to the standard factory 40 inch wire length ??? ...... you can extend the wire just far enough toward the wing tip and then back toward the cabin with the long straights evenly split up, if you're that concerned about symmetry, but i wouldn't worry about the little stuff that much (it's electrical performance probably works best with the longest, undisturbed straights & cares none of the looks).............BTW, however you route the antenna, you might as well do it to the lightest wing half (there's always a heavy half) to latteraly equalize the craft in addition to the normal CG point attention and always use gold connectors & stranded wire............ kw

[vintage1]

I am thoroughly of the opion that 'exact' length is an urban myth.

As someone else pointed out, all receivers come with about a meter of antenna, on 27m, 35, 40 and 72Mhz bands...

There is no doubt that the front ends are tuned a bit, but not critically.

What I have usually done is to use the full antenna length buried somewhere out of sight, and loosely bundle the rest into whatever space I have.

On some models I have cut the aerail short with certainly still adequate range. On theres it goes wall over the houyses.

There is soething to be said for having teh antenna go up alng and sideways a bit, so it always has a bit edge on to the transmitter.

I suspect that any loss of range due to shortening the antenna is far more due to reduced entanna 'swept area' than loss of tuning. However whne you get very short a tuned antenna like teh Azar, apperntly works well, and if set up correctly, should give decent range on quite a short length.

[Foxy]

So is each reciever peaked, or matched to its antenna before it leaves the factory?

Adam

[Jim Finn]

It is so easy to make a six inch inductor loaded antenna for about 35 cents and 10 min work. No effect on range. I just lay the antenna inside the fusalage aft of the trailing edge. Works for lots of guys.

[vintage1]

Originally posted by Foxy
So is each reciever peaked, or matched to its antenna before it leaves the factory?

Adam

I dunno. Each receiver will be peaked for the band its used for for sure. But not for teh antenna is my guess.

But the aerial isn't *normally* coupled so tightly to the front end, that cutting it about a bit will make a huge difference. That's my *opinion*, but others strongly disagree.

Unlike the TX aerial, which is very critically coupled for best power output and low out of band emissions. Where everyone agrees :)

SOME Rx's may well be done differently tho, so always range check before and after messing with the antenna.

A short aerial with proper inductive loading looks almost the same as a longer one - e.g. the Azarr, or the various 'add a 1.2uH choke yourself' flavours ...excpet sometimes allegedly on some recievers they don't.

If your range suffers drastically, you have a problem, if it doesn't, then the combo is 'soft' enough to fly without any retuning.

Two things can go wrong with messing with the antenna...

(i) Overall sensitivity drops, so range is less, but proportionately so does interference picvked up via the antenna, so you shouldn't suffer any worse from other models flying around you. In fact if there are problems with front end overload (such as you might get with cheapo parkfly rx's) it may actually make things better.

(ii) There is an outside chance that you may push the front end tuning off slightly, making it slightly more susceptible to nearby channels. This might make you slightly more susceptible to e.g. getting shot down if you are flying far away, but near someone elses TX on another channel.

But my educated guess - which will no doubt be contradicted y others - is that all you get with most recievers if you shorten or lengthen the antenna a bit, is slightly less range.

If you go for bottom loaded antennas like teh Azarr, then they also should work, but again the range may be a tad less. Nothing however, beats a throughly good range check. I was really worried about my latest model with a Jeti REX4 in it and only about 20" of aerial supplied. Its built into the wing of the model its going into now, and I range cheked it with a buddy out to 300m - which is as far as that plane will ever fly under MY control, and it was rock solid. Phew. In the air thats gotta be at least 500m of rock solid, and thats the limit on that model anyway for visibility.

Interestingly with the antenna down it was twitcing like crazy at only 30m or so - I normally expect to get 50-60m on normal RX's before teh servos get St Vitus' dance...so that pretty much relates to the normal quoted range of a mile or so (1500meters) for normal sets, and about 750m for this one.

And, curiously, the antenna length is almost exactly half the normal length on a 'normal' rx...well I would think thst is coincidence.

Some people have reported increased range on parklfly recievers using longer antennas tho.

Well thats about the sum total of my knowledge and suppositions there.

The bottom line is try it, but TEST it before you fly, if possible at the place you fly with the other guys you fly with flying around. Its always best to get problems on the ground, where you can retrieve the model and sort them out :)

And a retracted TX antenna is a good way to make *relative* comparisons betywen setups. But never rely on it for a real assessment of full range. Walk the walk, with a buddy.

[Foxy]

Why I asked that is that I bought a secondhand R700 reciever that had recently been serviced/checked, and the coil closest to the antenna had been adjusted, its wax had been removed. Its antenna wire had been replaced also. So im guessing it had been retuned.

Adam