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Question about Radio Interference

Old 06-23-2012, 04:50 AM
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gregoryshock
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Default Question about Radio Interference

I know Ihad written some about this before. But this seems a little different, so I thought it would ok to ask this type of question again. Only this time it's a little different.

I've always been in question about Radio Interference. Where Ifly almost nobody is around for miles. Isay almost because there could be people, but the nearest flying club is several miles away. Back when Iwas learning to fly, my trainer's manual that stated that one should turn on the receiver and watch and listen to the control surfaces. I Also had a guy tell me, this is a bad idea. Anyways I check for interference by turning on my receiver. This year, I took two planes out, and turn on the recievers. Both set quietly. However today, Idid the same thing with the third plane, and it jumped around a little bit and then got quiet. Itried this several times, and it behaved the same each time. When I turn on the Transmitter and then the receiver, everything is ok. Then when Ido a range check, everything works ok too. What really puzzle's me is, last year I was testing things out on the same plane. The reciever went bad, and Ihad to buy a new radio system for the plane. The year before the radio system went bad Iwas getting the same results every time Itested for interference. I'm trying to determine if there is something in the airplane causing this phenomenon. It's a 72 Mhz Radio System by Hitec. The old Radio System was also 72 Mhz system by Hitec. Both are the same frequency.

Old 06-23-2012, 06:13 AM
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LesUyeda
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Default RE: Question about Radio Interference

Radios will respond to any kind of "noise" in the spectrum, even though that noise may not cause you problems. As for miles, radios will transmitt a signal for a great many miles, and depending on the sensitivity of the reciever, and the terrain, the receiver may detect it. I am a radio amateur, and I once sat in my driveway in San Diego, and carried on a conversation with someone in Hawaii, on my mobile rig (low power), on 50 mHz. Propagation factors were just right.

Les
Old 06-23-2012, 06:56 AM
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JohnBuckner
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Default RE: Question about Radio Interference

ORIGINAL: gregoryshock

but the nearest flying club is several miles away.

Hi greg what Les explained is quite right and your equipment has demonstrated perfectly normal behavior and anytime only a receiver is on it will attempt to lock on to any stray RF out there commonly called noise.

One point that made me nervious though is your quoted comment and I gotta ask just how many miles is several?

You see anything less than three can indeed cause direct interferance. This indeed happened to our club several years ago when a few individuals decided to set up camp rather close and about a mile. They used mostly old swapmeet equipment and all attempts at diplomacy were shunned, Finally as the club president at the time I pushed for our club to abandon all but 2.4 and recommend only 2.4 just at our field. This as a protective measure for us and to prevent civil war.

There were a number of losses we experianced previously that we were able to confirm by scanner and visually with binoculars since they were active at the times.

John
Old 06-23-2012, 08:13 AM
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Default RE: Question about Radio Interference

Once we were outside a friends garage where he had his test stands set up. Someone came over with a engine problem so we took the plane to the test area and fired it up, the plane was going completely nuts with and without the radio on? Just for grins we went around the area looking and we found a couple of kids running there cars at a vacant lot using aircraft radios and gear.Things like John mentioned can happen a lot. We were getting hit at one field by a fellow with a park flyer flying in his own front yard. RF can happen and it is one of the reasons I like the 2.4 systems. I still have several planes left on 72 but I'm getting 2.4 RXs every chance I can for them.
Old 06-24-2012, 06:37 AM
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gregoryshock
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Default RE: Question about Radio Interference

Several Miles = 5 Miles away.
Old 06-24-2012, 06:42 AM
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Default RE: Question about Radio Interference

Cool and that works
Old 06-24-2012, 08:44 AM
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delman
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Default RE: Question about Radio Interference

At our club field, we had interference from construction cranes during the building of a large hotel 2-3 miles away except on sundays. Also read that some pipeline (gas/oil) valves are remotely controlled by radio signals.
Old 06-24-2012, 10:02 AM
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gregoryshock
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Default RE: Question about Radio Interference

I've been flying at my own field for 16 years, and never had any problems with interference.  The only plane in my fleet that has jumpy servos when just the receiver is on, is my U Can Do 3D.  My Zlin 526 is on the same frequency as my U Can Do 3D is.  The U Can Do 3D jumps around a little then stops.  The Zlin 526 sits quietly.  The old radio system I used in the U Can Do 3D also acted jumpy.  There may or may not be any connection between why the two radio systems (old and new) are Jumpy in the U Can Do 3D.  The main reason why I started this post is because old radio system I had in the U Can Do 3D went bad after 2 years of use.  Really when I'm checking for interference and the servos jump a little, doesn't bother me, unless 1 there is bad interference or 2 the receiver is going bad for some strange reason.

Additional Information (I write this because it's a little confusing):

The old radio system I used in the U Can Do 3D is the same frequency and make as the New Radio System in the U Can Do 3D.  The radio systems in both the Zlin 525 and the U Can Do 3D was always the same make and frequency.

My main Question

Why does the radio system in the U Can Do 3D jump around when the Transmitter is off, and the Radio System in the Zlin 526 does not?
Old 06-24-2012, 10:30 AM
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JohnBuckner
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Default RE: Question about Radio Interference

Its a fact of life that some brands as well as modulation types (FM, AM, PCM) may be more affected by stray noise when the tx is off. None the less that is not what you should be concerned with. What you do need to be concerned with is the way the system acts when the Tx is on and how it responds to range checks, that is an entirely different matter.


John
Old 06-24-2012, 12:04 PM
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Rodney
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Default RE: Question about Radio Interference

A lot of the better receivers (the super heterodyne) have a circuit in them that controls the gain depending on the strength of the input signal, this is the AGC circuit. Those that have a wide dynamic range (a usually desirable trait) will cause the servos to jump around a lot more with your transmitter off than when it is on as the AGC circuit is wide open. This is not a problem but instead a desirable thing.
Old 06-25-2012, 07:54 AM
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gregoryshock
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Default RE: Question about Radio Interference

I agree with everything that is being said.  And I'm very thankful to everyone that continues to answer my posts. However this still doesn't answer the question why two radio systems, made by the same company, and for the most part is identical, behave differently.  I'm going to follow John's advice, but I still tinker around, to see if something on the airplane is causing this behavior.

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