Broken Receiver Antenna Wire
 

I hope this is the right forum.
Well, the trees jumped up and caught my plane. When I was dragging it out of the tree's tangled clutches, the receiver antenna wire broke to about 8 inches length. I think the receiver is good except for the antenna. Is there any way to repair?
Thanks

RE: Broken Receiver Antenna Wire
 

Yes, it's an easy repair. You can solder the wire back together. The important thing to remember as your repair is to keep the antenna wire the same length as before it broke. After soldering it together put a little piece of shrink tubing over it to keep the solder joint clean.

Ken

RE: Broken Receiver Antenna Wire
 

Obviously you'll need to overlap the two wires to solder them, so keeping the exact same length will not be practical, but keep the overlap to a minimum - Like 1/8" - and you'll be fine

RE: Broken Receiver Antenna Wire
 

And don't forget a thorough range check when you finish!

RE: Broken Receiver Antenna Wire
 

Hey guys, thanks for the prompt response, however the other piece of the antenna wire got lost in the retrieval.
Is there any way to find out the correct total length from some other source?
Thanks

RE: Broken Receiver Antenna Wire
 

Go to Radio Shack, and look for 26 AWG Stranded wire. The more strands, the better. Better yet, go to Mouser.com and order three rolls(one each of black, red, and yellow. You can use it to make your own servo extensions. Get the 100 foot rolls and you'll have enough to last for a long time. The typical length of reciever wire is about 40 inches (1/4 wavelength at 72 mhz), but you should check with the manufacturers web-site for the specific length.

While you're at it, get one of the small "cold-heat" soldering tools (they seem to be everywhere these days). They work GREAT for soldering wires together. Keep it in the flight box for quick field repairs.

Brad

RE: Broken Receiver Antenna Wire
 

If you are going to use a solder connection for the antenna repair, get some small heat-shrink tubing and cover up the solder point. Shorting the antenna to something metal (landing gear for instance) can cause RF noise and can intefere with your received signal. Putting a length of heat shrink tubing over the repair will insure that the antenna is completely insulated.

This is just a short and simple precaution.

RE: Broken Receiver Antenna Wire
 

As long as the final length is 39 to 41 inches, you are good to go. That is the standard length on most receivers regarless of frequency (ignoring the new 2.4GHz units). Some park flyers have shorter antennas but usually much shorter range too.

RE: Broken Receiver Antenna Wire
 

Can't say enough about heat-shrink tubing...

It really makes for a professional looking solder joint. Years and years ago, before I knew about the stuff, I'd wrap a joint in electrical tape. The tape would get dirt and oil on it from my hands, and it wouldn't stick. In weeks, the tape would be unraveling. Just junky in my opinion...

Now with heat shrink tubing. No problems.

One trick I've come to practice... I use two pieces. The first piece is cut to the length of the joint itself. The second piece is much longer. Once I've soldered, I put the short piece on, essentially replacing the wire's original insulation. Then the longer piece seals it all together.

RE: Broken Receiver Antenna Wire
 

I never cease to be amazed at the wealth of knowlege in these forums and the willingness to share it.
Thanks guys

RE: Broken Receiver Antenna Wire
 

The manufacturer often publishes the length of their antennas.

If you need to get another piece of wire to splice on, the ideal fix is to replace the whole antenna rather than splicing in the middle.

If you're not really good at soldering in small places, the best option might be to send it to a repair center such as [link=http://radiosouthrc.com/]Radio South[/link] and have them do it. In addition to ensuring that the right wire is used and that the soldering is done right, they'll be able to do a quick tuning to make sure the receiver is operating at peak performance. The total cost of doing this will be relatively low and you'll have the peace of mind of knowing the right wire was used, that it was installed properly, and that the receiver is tuned to the new antenna length.

RE: Broken Receiver Antenna Wire
 

My local hobby shop stocks replacement Futaba receiver antenna wires for $1.49, part # FUTM1620.

RE: Broken Receiver Antenna Wire
 

Not so. The length is completely dependent on frequency. 1/4 wavelength for the 72 MHz band is about 39 inches. 1/4 wavelength for the 50 MHz band is longer, 59 inches, and is even longer for the CB bands, around 27 MHz, which is around 102 inches.

Now, antennas may be cut in shorter lengths, but they are in the wavelenth for the frequency involved but increments of 1/8 wavelength.

RE: Broken Receiver Antenna Wire
 

I don't see what difference it makes on a receiver. I can understand on the transmitter, but the receive circuit could care less about wavelength. I can attatch a pair of vice grips to a 200 ft. piece of RG 8, throw it over the roof of my house and recieve just fine on my heathkit (HAM radio). I'd have to use a matching unit to transmit though. I replaced the antenna on a Futaba receiver a while back. It's 64" long and has been working fine (I fly almost every day). I needed the extra length to route it through the fuse, back up behind the canopy and to the vert stabilizer (for scale appearance). According to your above statement, it shouldn't even work since it's neither 1/4 wave nor 1/2 wavelength @ 72 MHz.

RE: Broken Receiver Antenna Wire
 

The receiver still requires that the input circuitry be tuned to the right frequency. Part of that is the antenna. If the antenna is the wrong length, it will reject the fundamental frequency. Trust me. WIth a degree in electronics, I'm not blowing smoke. Yes, it makes a difference.

Disconnect the antenna on your car and see what happens to the received radio station. Shorten it by half and see if you get the same quality of signal. It will receive, but the level of signal, and the range (very important here... ) will be detremental to operation.

RE: Broken Receiver Antenna Wire
 

Yes, but a car antenna has 2 wires, a conductor and a shield / ground. It uses the resistance of the coax to know how long the antenna is. Replace the 75 ohm coax on your car antenna with some RG 6 (52 ohm) . You will have to add more antenna to get the same reception or resistance. I also have a B.S. in Electronics, a B.S. in Computer science, an A.A.S in applied Science and an A.A.S in Industrial Technologies. I wasn't saying you were blowing smoke ... I just don't see where the receiver gets any resistance to know how long the antenna is. I suppose it could be like a profibus, but with no termination on the end, it would still be an open circuit with no resistance. All an IC corcuit can do is guess and assume, and there's no logic circuit. I'm not in any way trying to start an arguement ... I'm just trying to understand how this thing works. I've been building and operating radios in the amateur bands since I was 14. All the antennas and receive circuitry I've dealt with relied on resistance.

RE: Broken Receiver Antenna Wire
 

go to your hobby shop they should have new ant wire and replace broken ant wire you will be better off

RE: Broken Receiver Antenna Wire
 

I believe the correct term is "Impedance", not resistance.

The "resistance" of a piece of coaxial cable that is about 10 feet long should be under one ohm.

The characteristic "Impedance" of the coax, derived from inductance and capacitance values, would be 50 ohms, 72 ohms, or whatever it was designed to be.

The one meter long wire on our R/C receivers acts as a "longwire" antenna, and is impedance matched to the RF amplifier in the receiver.

So, to answer the first guy's question, keep the antenna the same length as the original. Find someone else with the same receiver and measure his.

Or, get with the manufacturer and have a new antenna installed.

Radio South can do the very same thing quickly and easily. Google them for address and web site


WA2ROC (licensed continuously since 1959)

RE: Broken Receiver Antenna Wire
 

You're correct Dick, it is impedance. And when "Broke" said "All an IC corcuit can do is guess and assume" my guess is that he meant to say an LC circuit which would be tuned to maximize for the RX frequency and to compensate for antenna error. This is "one" of the reasons we send our RX's in for tuning/testing.

http://en.wikipedia.org/wiki/Coaxial_Cable

RE: Broken Receiver Antenna Wire
 

Yep, me too! It's inexpensive insurance.

Thanks.

RE: Broken Receiver Antenna Wire
 

64" antenna!! a crash waiting to happen

RE: Broken Receiver Antenna Wire
 

Do you really want to risk your plane for something as cheap as a piece of wire. Shorter wire will translate into shorter reception range. Yes it might work up close but when it get farther away you may have problems

RE: Broken Receiver Antenna Wire
 

You WILL have a problem. And, it ain't worth comparing shingles over. A receive antenna that has been shortened by some action is not optimum for that receiver. Period. The shield is part of the ground system and, like it or not, it is part of the antenna system also.. even on cars. And, it is impedance which could be referred to as 'AC resistance' for simplicithy. Ideally, the receive antenna would be 'cut' for the proper frequency, but that's not practical because many RX's are sold without crystals. So, they are more broadband than transmitters are, thus the reason for sending a transmitter back to a radio specialist (Radio South, Airtronics, Futaba, and so on) for re-tuning.