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cutting antenna wire - 6/25/2008 11:43:26 PM   
F-18


 

Posts: 56
Joined: 1/18/2006
From: East Kootnay, BC, CANADA
Status: offline 		When i totaled my alpha 60 i gutted all of the electronics so i could use them in another Alpha 60. When i was removing the receiver i noticed that the antenna was tied in a tight not at the end of the antenna tube. So i simply cut the not off to remove the antenna. Is this bad? I only cut maybe 2-3 inched off but i'm worried i might have killed it.
       Post #: 1

RE: cutting antenna wire - 6/25/2008 11:55:33 PM   
RCKen



Posts: 14747
Joined: 7/10/2002
From: Lawton, OK, USA
Status: online 		Yes, changing the length of an antenna is bad. They are set to a specific length (approximately 39" in order in order to function properly. When you cut off wire you risk radio failure and losing the plane. You should solder the wire that you cut back on to the remaining wire. If you can't resolder the wire that you cut off then you need to purchase new wire and solder it back on. If that's not possible then it should be sent in to a service center to have this done.

Considering that the receiver was in a crash it might be a good idea to send it in anyway to have the receiver checked to make sure that it wasn't damaged in the crash. Any receiver that I have involved with a crash goes in for service before it ever goes back into a plane. Trust me, it's cheap insurance against losing another plane. While the receiver is in they can fix the antenna wire.

Ken

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       Post #: 2

RE: cutting antenna wire - 6/26/2008 12:27:42 AM   
F-18


 

Posts: 56
Joined: 1/18/2006
From: East Kootnay, BC, CANADA
Status: offline 		well im going to calgary to buy a new plane and i could probably pick up some extra antenna wire. how difficult is it to replace?

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       Post #: 3

RE: cutting antenna wire - 6/26/2008 12:38:49 AM   
Campgems


 

Posts: 1928
Joined: 2/18/2006
From: Arroyo Grande, CA, USA
Status: offline 		It all depends on your experience soldering small components on PC boards and if you have a proper soldering iron for this job. Excesseve heat will start delamination the PC board and traces. To little heat and you end up with a cold solder joint and the leads to intermentent failures. There is a strain releif on the atenna wire where it enters the case and this will have to be properly reinstallled.

I've 40 years experience repairing electronics. I built my own radio system back in the lat 60's, Receiver, transmitter, and five servos. I soldered every component. Today, I would sent the radio in for repair and checkout as RC Ken said.

Don

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       Post #: 4

RE: cutting antenna wire - 6/26/2008 12:54:42 AM   
bruce88123


 

Posts: 10565
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From: Memphis, TN, USA
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quote:

ORIGINAL: Campgems

It all depends on your experience soldering small components on PC boards and if you have a proper soldering iron for this job. Excesseve heat will start delamination the PC board and traces. To little heat and you end up with a cold solder joint and the leads to intermentent failures. There is a strain releif on the atenna wire where it enters the case and this will have to be properly reinstallled.

I've 40 years experience repairing electronics. I built my own radio system back in the lat 60's, Receiver, transmitter, and five servos. I soldered every component. Today, I would sent the radio in for repair and checkout as RC Ken said.

Don

HeathKit?

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       Post #: 5

RE: cutting antenna wire - 6/26/2008 3:11:51 AM   
F-18


 

Posts: 56
Joined: 1/18/2006
From: East Kootnay, BC, CANADA
Status: offline 		well re-soldering the cut wire is kinda out since the wire that i cut off is probably still at my flying site and long gone. Do some hobby stores check receivers out or do you have to send them in to the company? also how bad will this impact the range if it was only about 2 inches?

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       Post #: 6

RE: cutting antenna wire - 6/26/2008 4:21:40 AM   
plugin



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From: Bogota, COLOMBIA
Status: offline 		It could have tremendous effects on reception. If I where you, I wouldn't even consider the idea of using that receiver at least until it gets a new antenna.

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RE: cutting antenna wire - 6/26/2008 5:32:27 AM   
F-18


 

Posts: 56
Joined: 1/18/2006
From: East Kootnay, BC, CANADA
Status: offline 		I'll go and buy a new antenna when im in calgary since im going to buy a new plane, but i was wondering if their is any way to check if my receiver was damaged in the crash at home. i heard a range check might work but...

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       Post #: 8

RE: cutting antenna wire - 6/26/2008 5:38:56 AM   
Campgems


 

Posts: 1928
Joined: 2/18/2006
From: Arroyo Grande, CA, USA
Status: offline
quote:

ORIGINAL: bruce88123


quote:

ORIGINAL: Campgems

It all depends on your experience soldering small components on PC boards and if you have a proper soldering iron for this job. Excesseve heat will start delamination the PC board and traces. To little heat and you end up with a cold solder joint and the leads to intermentent failures. There is a strain releif on the atenna wire where it enters the case and this will have to be properly reinstallled.

I've 40 years experience repairing electronics. I built my own radio system back in the lat 60's, Receiver, transmitter, and five servos. I soldered every component. Today, I would sent the radio in for repair and checkout as RC Ken said.

Don

HeathKit?


Nope, a Royal Clasic six channel with a Kraft three axis stick. I went the "cheap" route and bought the case, and PC boards instructions from Royal and gathered components where I could. Some from work and a lot more from Allide Radio (sp?)

I built my own Tx charger sans transformer, right into the Tx case. My son, now 43, remembers picking up the Tx while it was charging and getting his toes tingled on the basement floor. I never flew that radio. The plane I built for it was out of a magazine, but I made a fiberglass fuselage and foam wing. I had an old Fox .60 with two needle valves and I picked up a carb and cut the top off the intake stack and mounted the carb in it. I couldnt' get the engine running right, probably under 6000rpm looking back. No tach then. The plane weighed a ton. No field to fly from. The radio was a mess, servos chattering like crazy..

The plane ended in the trash. I think I gave my son the RC stuff after he left home. All and all a dismal experence. That was my last trip into RC until two and an half years back. What a change. I had close to $400 into the Royal in 1969 $$. All of it ending in a trash can. This was at a time when my house payment was $89.00, so it was a major ding to my budget at the time.

Don




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       Post #: 9

RE: cutting antenna wire - 6/26/2008 5:41:43 AM   
RCKen



Posts: 14747
Joined: 7/10/2002
From: Lawton, OK, USA
Status: online
quote:

ORIGINAL: F-18

I'll go and buy a new antenna when im in calgary since im going to buy a new plane, but i was wondering if their is any way to check if my receiver was damaged in the crash at home. i heard a range check might work but...


Not really. A damaged receiver can still pass a range check and then fail in flight. IMHO it's just not worth saving $15 to risk losing a plane. As I said earlier, I will not put a receiver that has been in a crash back in to any plane before it has been checked by a shop. I have had receiver that seemed to work fine come back from the shop with cracked crystals that could have failed in flight.

Ken

_____________________________

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RCU Community Moderator

(in reply to F-18)
       Post #: 10

RE: cutting antenna wire - 6/26/2008 6:02:10 AM   
Campgems


 

Posts: 1928
Joined: 2/18/2006
From: Arroyo Grande, CA, USA
Status: offline
quote:

ORIGINAL: F-18

I'll go and buy a new antenna when im in calgary since im going to buy a new plane, but i was wondering if their is any way to check if my receiver was damaged in the crash at home. i heard a range check might work but...


A range check might work. Might!. Might not. It will cost you about $30 including shipping to send the radio in for checkup and repair. Maybe a couple bucks more. You will be out of commision for a couple weeks. You can then fly with the confidance you have an undamaged receiver and do not have to worry about it failing in flight. OR, you can pick up a piece of wire, do a quick patch on the radio. buy a new plane and loose it all on the first flight because the receiver had a broken ceramic filter and just gave up.

I like to gamble, but only to the point it is entertainment. I don't go in and spend the rent payment thinking I'm going to hit it big. I set an amount that I'm willing to spend for entertainment for the night and that is what I gamble. If you are willing to gambel your new plane and equipement against the price of a proper checkup on your crashed receiver with a clipped antenna, be my guest. It is just like the casinos, the odds are against you.

Don

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       Post #: 11

RE: cutting antenna wire - 6/26/2008 11:49:09 AM   
doubledee


 

Posts: 558
Joined: 8/9/2003
From: Callahan, FL, USA
Status: offline 		Don't fool around trying to repair it yourself. Send it in and get it thoroughly checked out. You could have problems other than a shortened antenna. After all, it is a piece of electronic equipment and is relatively fragile. Impact with the ground could have cracked a circuit board, broken solder joints and a host of other things.
At the risk of repeating myself and others, send it in for check out and repair.
Regards,
doubledee

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       Post #: 12

RE: cutting antenna wire - 6/26/2008 11:51:02 AM   
CGRetired



Posts: 4225
Joined: 9/14/2004
From: Galloway, NJ, USA
Status: offline 		The antenna is cut to a specific length based on the operating frequency of the transmitter or receiver. In our case, this is approximately 72 MHz (more specific frequency is based on it's channel, channel 11, for instance, is 72.010 MHz and so on). The antennas are cut to a specific length because that length corresponds to the wavelength, or in this case, the quarter wavelength, of that frequency.

Antennas operate properly when they are cut to a specific length matching the wavelength. But, to cut an antenna to a full wavelength would not be practical. However, they also operate in increments of quarter length, and half length. (there are more multiples, but for our purposes, we can stick to 1/4 wavelength because that's where they are operating).

So, using a simplified formula (the real formula uses velocity of the wave in free space) use 300/Freq in MHz = wavelength. See the below drawing. The result is in Meters. Multiply by 39 then divide by 4 and you will get the approximate 1/4 wavelength in inches. Cut the antenna shorter and you now are not operating in the correct range.

Technically, and simplified, portions of the wave that do not meet the 1/4, 1/2, of full wave length begin to 'cancel' out making the antenna less efficient.

CGr

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< Message edited by CGRetired -- 6/26/2008 3:49:13 PM >

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RE: cutting antenna wire - 6/26/2008 2:25:36 PM   
bruce88123


 

Posts: 10565
Joined: 11/26/2004
From: Memphis, TN, USA
Status: offline
quote:

ORIGINAL: CGRetired

The antenna is cut to a specific length based on the operating frequency of the transmitter or receiver. In our case, this is approximately 72 MHz (more specific frequency is based on it's channel, channel 11, for instance, is 72.010 MHz and so on). The antennas are cut to a specific length because that length corresponds to the wavelength, or in this case, the quarter wavelength, of that frequency.

Antennas operate properly when they are cut to a specific length matching the wavelength. But, to cut an antenna to a full wavelength would not be practical. However, they also operate in increments of quarter length, and half length. (there are more multiples, but for our purposes, we can stick to 1/4 wavelength because that's where they are operating).

So, using a simplified formula (the real formula uses velocity of the wave in free space) use 300/Freq in MHz = wavelength. See the below drawing. The result is in Meters. Multiply by 39 then divide by 4 and you will get the approximate 1/4 wavelength in inches. Cut the antenna shorter and you now are not operating in the correct range.

Technically, and simplified, portions of the wave that do not meet the 1/4, 1/2, of full wave length begin to 'cancel' out making the antenna less efficient.

CGr

But this only works if there are NOT some "loading" characteristics built into the RX as well.

Just send it in. Cheap insurance.

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