Hi all,

First off, I am brand new to this hobby and am LOVING IT! I bought the Hangar 9 P-51 PTS RTF kit. Have had a couple minor repairs I needed to do but she still looks good and flies great. I have been doing this for about 3 weeks now.

Anyway, my receiver antenna wire got wrapped around my tail wheel and eventually took off the housing around the wire and frayed the ends of the wire badly. I cut off about 2 inches of the frayed wire. A friend told me that the receivers are tuned specifically for the length of antenna wire that they come with and that cutting off the wire was probably not such a good idea. I have flown it several times since trimming it and haven't noticed any problems but I do keep it in at a comfortably close range. Should I be looking to replace the wire or is it ok the way it is? Will I lose any range due to trimming it? If so, how much?

Thanks for your help!
Dave

Dave,
Yes, the length of the antenna wire is important. If you cut off 2 inches of the antenna it could possibly affect the performance of the radio. It's possible for it to still work with the wire removed, but it could have bad effects that aren't immediately apparent. It would be best to get the antenna wire back to it's original length. You can simply solder on 2 inches of wire of the same gauge as you cut off. If you're not comfortable soldering ask some of the members of your club and see if you can find somebody that will do it for you.

Hope this helps

Ken

What you have done by shortening your wire is decrease the overall range of your RX as well as decreased the amplitude (signal level) that is getting fed to your RX at shorter ranges. You may verywell not have shortened it enough to notice during your subsequent flights, but do as ken suggests & put the length back on.

Trust me, It's not a good feeling to watch your plane fly away from you ignoring all inputs from your sticks. [&o]

Thanks guys for the info.

I called my local hobby shop and talked to a very knowledgeable rep there. He echoed your replies and said that I needed a 1 meter piece of wire for the antenna. He said that the guage was not as important as the length. I think I will go to the hardware store and see if I can get a similar guage wire and just solder me on a whole new 1 meter piece to the RX.

Everytime something goes wrong with my plane I learn something new. Man, I'm gonna be smart when it's all said and done!

Actually replacing the whole length would mean soldering and the accompanying heat, much closer to the heat sensitive portions of the RX.

This is how Futaba sells theirs.
http://www2.towerhobbies.com/cgi-bin...&I=LXH355&P=ML
I realize you probably have JR but they probably have a similar pkg available. If you are not a GOOD solderer then get someone who is and has a small iron to do the work for you. Inside the RX is NOT the place to be practicing.

Found the JR wire for you
http://www.horizonhobby.com/Products...ProdID=JRPA170

OK...so I bought some 18 guage wire...I realize that it is a little bigger than the original wire on the JR RX. If I were just going to replace a portion of the wire so I don't have to get inside the RX is the 18 guage wire ok? I only need to replace about 2 inches or so of wire but I thought it might be better to cut the wire back inside the plane and add on enough new wire to make a total of 1 meter (1000mm). Would this method be better? That way I don't have the splice outside the plane. I suppose after soldering the 2 parts together I should wrap the splice in electrical tape. I have soldered on circuit boards several times in the past but this looks like it might be a small area to work in. I don't want to ruin the RX for the sake of the wire so I thought this might be a safer route. Excuse my ignorance on this subject but I don't want to do anything that will further jeopardize the integrity of the RX signal. If I crash my plane I would like to at least have control of it right up till it hits the dirt!

Thanks!
DaveCFI

I'm not sure about the wire guage differences, but I would think soldering on the extra 2 inches would be the much more conservative route and that's what I would do.

Personally, I'd do a range check first and foremost. If the plane checks out with proper range with the engine off and the engine running, then I'd not bother with it at all.

Yes, in theory, the antenna is tuned.

But in the real world, the tuning is only approximate. If you buy 2 RX's one on channel 12 and another on 59, they will have the same antenna length. Yet in theory they should have slightly different lengths.

If you're on a low channel, losing that 2" might actually increase your range (ok, that's a joke, I didn't do the calculation to see how many inches channel 12 vs channel 59 would actually have, probably less than 2" though)

Not only that, but most of us don't have the antenna coming out of the RX in a nice straight line either. Usually it comes out and makes a curve or two exiting the fuse and so on.

That said, if you want to fix it, I suggest you just solder on the 2" at the tip for the reasons the guys gave above. I've done antenna replacements on RX board several times, and it's a pain. I usually just solder them together where they broke (or were cut).

Also, make sure that whatever wire you use as a replacement is stranded, and has as many strands as possible. Stiff wire will fatige under engine vibration and might break. Getting high quality wire with as many strands as possible is a good idea. Fwiw, Radio Shack doesn't seem to sell anything anywhere near flexable enough, at least not around here.

18 AWg wire is bigger than you need and MIGHT cause the end to whip around in the wind a tad more but not significantly. Make a good solder connection and then put a short (I said SHORT) piece of heat shrink tubing over the splice. A Monokote heat gun should have enough heat to shrink the tubing, if not then carefully use a match. Be careful not to damage the wiring insulation. The more individual strands a wire has (for a given gage and assuming the same metalurgy) the more flexable it will be. You do not want stiff wire or a stiff splice as this will cause a fatigue stress failure point. This is why most recommend total replacement when you can. The original wire is probably around 22 AWG and maybe 24 AWG.

NEVER use single-stranded (solid) conductor wire where vibrations occur unless it is well supported and clamped in place.

BTW - The difference in optimum antenna lengths from one end of the 72MHz band we use to the other end of the band is probably in the order of a few milli-meters.

I never know how to respond to questions like this.
Basically I agree with what Montague posted.
Range check it, fly the plane.
There is a lot of myth accepted as fact in regards to the electronics we use.
I will quote from a previous post ...... "I called my local hobby shop and talked to a very knowledgeable rep there. He echoed your replies and said that I needed a 1 meter piece of wire for the antenna." ..........
I think a 1 meter piece of wire is a fine antenna but according to the math it is to short by up to 2 inches on channel 11 and for channel 60 it is short by 1.4 inches.
Here is a link to a calculator that is easy to use and understand.
Antenna length in inches is usyally equal to 1/4 wavelength.
http://www.csgnetwork.com/freqwavelengthcalc.html

The actual quarter wavelength for channel 11 (72.01 MHz) is approximately 40.91431746 inches, and for channel 60 (72.99 MHz) 40.3649815 inches (very approximately!)

So the very approximate difference in antenna length for a quarter wave one is (very approximately) 0.549335952 inches.

(approximately)

Incidentally, that calculation can easily be done by taking the speed of light (and radio waves ) at 186,000 miles per second, expressing it in inches per second (times 63360) and dividing it by the frequency to get the wavelength of approx 163 inches, then dividing by 4 to get a quarter wave length.

(approximately)

[sm=bananahead.gif]

-David C.

Hey David...

Can you be a bit more precise? I want to get this right.

You forgot to then convert the 0.549335952 inches to 13.953133 mm. To me, that is just a few MM. The difference between the calculated 1/4 wavelength and the 1 meter wire is consumed by circuitry paths and tuning of the RX. The major point here is that the RX is designed and tuned to operate at optimum with a 1 meter antenna wire. The Futaba Hi/lo's are broken down even futher into 2 groupings. While a HI band Futaba would function with a LO band crystal it would be further from optimum than Futaba wishes to operate and range would suffer.

hehe, you guys crack me up.

[sm=punching.gif]

LOL yeah its pretty funny stuff especially considering the matching network in the RX can be engineered to make any specified length of wire work just fine

LOL.... I can't resist stirring the pot some more....

The 'optimum' length for a quarter-wave antenna is actually about 6 percent shorter than a true quarter wave. This shortened length compensates for fringing fields at the end of the antenna and produces the desired resonant condition.

If I take the average frequency of the RC channels of about 72.5 MHz this gives a length of 38.3 inches. That would be the ball park number to shoot for when replacing your antenna.

But really, it is not all that terribly critical. You will probably be just fine with a 2-inch shorter antenna. Just do a thorough inspection and range check. If your antenna wire was stressed there may be hidden breaks elsewhere within the plastic insulation, or the connection at the receiver circuit board may have been damaged. If in doubt it is always best to have the wire replaced.

By the way, the length of the antenna is not the whole story. The length and dress of the other wiring within the airplane has an effect similar to the length of the antenna. This wiring actually provides the 'other side' of the antenna - there is no such thing as a one-sided antenna. Since the receiver manufacturer has no idea what you will put in your airplane in the way of servos, extension, switch harnesses, etc, his impedance matching at the receiver is just a guess. The effect of lengthing or shortening your antenna by a few inches is probably smaller than the variations in wiring from plane to plane.

For those keeping score, 38.3 inches is 0.97282 meters.

And for those who have forgotten since high school 1 meter = 39.370079 inches

or (and this will be really helpful someday) 1 parsec = 30856776000000000 meters = 19173511691720.35 statute miles

Cool thread... Plenty of useful detail but put in simple terms. [8D]

Sorry. No.

I've run out of fingers.

-David C.

while on the topic of recievers is it ok to paint the reciever wire?

Depends upon the type of paint. Nothing with any metals in it. Most latexes would be OK. Problem is that with the flexing it will not last long anyway. You would be better off looking for wire with the correct color of insulation and replace your antenna.

JPMacG just about said it all. He is very correct. Remember, the antenna wire is only half the antenna circuit, the ground plane is the other half and, as JPMacG said, this can and does vary drastically with each plane. There is no good substitute for a good range check on each plane. And yes, most commercial receivers use a 1 meter length of wire for the antenna, regardless of frequency being used. Some park flyers are exceptions to this rule using much shorter antenna but they also have a greatly reduced useable range.