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Midair interference hits

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Old 08-26-2003, 02:00 AM
  #1  
Elric
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Default Midair interference hits

I have a Hanger 9 Sportcap (.40 size. I say .60 though. )
I have recieved 3 short, rather severe hits while flying in my last two flights. I was able to recover and they only lasted a split second where I had no control. In other words, I didn`t do what IT did. I have a tower hobbies standard reciever and a combination of Futaba 3004 and Tower standard TS-53 servos. It did take a crash in another plane due to dumbthumb, but that was 20 flights ago. What could I do to start eleminating possibilities. The RX battery is two years old. It was fully charged on both flights. What is the most common cause of this? It may be that I am getting channel interference, but I would like to know what the main mechanical causes would be. Any help would be appreciated. I have another plane on this channel, so I`m going to see if I get any hits on it too. Any ideas guys?
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Old 08-26-2003, 11:17 AM
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vinnie
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Default Midair interference hits

I would suggest trying a new crystal. It might have cracked when it crashed.
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Old 08-27-2003, 12:21 AM
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Default Midair interference hits

If the crystal cracked you couldn't even take off. Crystals won't oscillate at the proper frequency at ALL if they're broken. Go over all of your wiring just to double check it, check any bearings make sure they're nice and free. Check your TX as well. Also check out the immediate area of the place you had the incident and see if it may have been something nearby that caused it. Were other people flying? (Someone accidentally turn their xmitter on realize it and turn it right back off?) Things like that. Good luck though you may never find the cause, unless it happens again and plants your plane Then you're almost assured of finding out what it was =>
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Old 08-27-2003, 01:25 AM
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Crash_N_Burn
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Default Midair interference hits

Lynx is correct. If a crystal breaks it no longer works. But if it partially fractures it will become intermittent. This happens more often than you would think. I've had two (2) new crystals do this in the last two years.

Check and clean all your receiver plug-in connections. Check and clean your switch with contact cleaner. Load-test your battery.

...But don't write-off your crystal as being good. A swap would be prudent at the very least.
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Old 08-27-2003, 02:36 AM
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Elric
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Default Midair interference hits

I did have a slightly bare wire showing on my switch wire. The one going to (you guessed it) , my reciever. I swapped out the switch and I`m going to try it tomorrow, weather permitting. If that doesn`t do it, I will swap out the reciever. I have a Futaba with the same crystal channel. When the hits happened, there were two different groups of people present at the field , and nobody in the club runs my channel.

A strange thing that a few of us experience on different channels is a slight and unrelated hit at the same part of the one end of our field. What could cause this? Buried gas line? Telephone cable?

Hope I don`t crash. I like this plane.
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Old 08-27-2003, 06:00 PM
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Default Midair interference hits

Originally posted by Elric


A strange thing that a few of us experience on different channels is a slight and unrelated hit at the same part of the one end of our field. What could cause this? Buried gas line? Telephone cable?

Hope I don`t crash. I like this plane. [/B]
Hi Eric,

Could be a microwave link in the area and you are flying into the beam.

Just a thought

Jerry
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Old 08-27-2003, 08:54 PM
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Elric
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A microwave link? This sounds dangerous! Is the government involved? Can you explain this? I`m not familiar.

Thanks,

Elric
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Old 08-27-2003, 09:32 PM
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Crash_N_Burn
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Default Midair interference hits

What transmission_dr was referring to were point-to-point sources of communications used by many government and private entities.

They are in the 2-30gHZ range and are linked together by microwave dishes. Their signal is very narrow, maybe 1/2 of a degree (maybe 1-2 feet in the middle of the path which is usually mountaintop to mountaintop but the problem is the apparent power.

They usually transmit at 1-10 watts, not much more than our R/C transmitters, but they have a tremendous antenna gain. So, the power in that narrow path may be in the kilowatt range and would certainly swamp any of our receivers briefly.

The paths are usually high, but if the main station is near your field it would have a low angle attack and may cross overhead at a low elevation.

Some of the installations have so much radiated power that one can throw flash bulbs into the path and they fire. It'll cook a hot dog, too.
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Old 08-28-2003, 01:45 AM
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That doesn't make any sense at all Crash, A 10 watt transmission through an antenna regardless of how high the gain on it is will still only transmit 10 watts of power, you can't get power gain. Effective signal gain maybe but not power. And you'd need a lot more than 10 watts to cook a hot dog. It takes my microwave a minute to cook a hot dog and that's 1000 watts. =) Still if you through through one it'd be bad, it can generate high voltages although not very high current. High voltage can be enough to fry cmos chips.
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Old 08-28-2003, 01:45 AM
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Elric
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Default Midair interference hits

Never knew that. Very interesting. Thank you.

-Elric
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Old 08-28-2003, 02:00 AM
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Maxime
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Default Midair interference hits

Also check if nothing is loose on your plane...


My 46FX doesn't like to have a muffler attached to it, and it has a tendency to get rid of it in flight.


When I get some interference hits, I usually check the muffler and sure enough the bolts are loose.


Could be anything loose... a bad clevise, something touching your antenna, etc....
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Old 08-28-2003, 08:11 PM
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Default Midair interference hits

Originally posted by Crash_N_Burn
Lynx is correct. If a crystal breaks it no longer works. But if it partially fractures it will become intermittent.
I'll echo what Crash said - I've seen it many times when computers still relied on crystals to set the CPU clock.
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Old 08-28-2003, 10:24 PM
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Default Midair interference hits

"That doesn't make any sense at all Crash, A 10 watt transmission through an antenna regardless of how high the gain on it is will still only transmit 10 watts of power, you can't get power gain. Effective signal gain maybe but not power. And you'd need a lot more than 10 watts to cook a hot dog. It takes my microwave a minute to cook a hot dog and that's 1000 watts. =) Still if you through through one it'd be bad, it can generate high voltages although not very high current. High voltage can be enough to fry cmos chips."

Sounds impossible, doesn't it Lynx?

But It's not. I's called effective radiated power and it's a product of final output power x antenna gain.

Let's say a transmitter puts out 10 watts and the antenna has a power gain of 100, the signal that leaves the antenna will be just the same as if the antenna had unity (1:1) gain and the transmitter was putting out 1,000 watts. A gain of 100 in a dish (parabolic) antenna is not uncommon. Also what happens when a television broadcast station doubles the size of their antenna system? Coverage increase, yes? But the price they may have paid is a narrower signal as all that energy is now concentrated in a smaller beam.

Oh, yes, it takes more power to cook hot dogs at a lower frequency than it does a higher one. Microwave systems (not your home one) operate in the Gigahertz range where the wave spacing is tiny offering more heating value to anything in it's path.

Sounds unreal I know, but it's just part of antenna theory and physics and those are laws.

Trust me on this one, Lynx, I'm an antenna engineer.
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Old 08-28-2003, 10:48 PM
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Default Midair interference hits

I understand what you're saying Crash, but a 10 watt beam signal might have a relative signal strength of a 1000 watt omni directional antenna because the beam is more concentrated. The only thing I'm making an issue of is that it's still just 10 watts. It's not 1000 watts, it's just equivalent to what 1000 watts would be at the same distance if it were omni directional. I know what you're saying is technically correct, but to the layman it misrepresents the actual amount of energy involved. By the way you note above something I was always curious about, what exactly is the relation of frequency to power? Do you know the equations for it offhand or have any links where I could find out?
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Old 08-28-2003, 11:14 PM
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"it's just equivalent to what 1000 watts would be at the same distance if it were omni directional"

Yes, you said the magic word! Equivalent!

Equivalent = Effective. Interchangeable words.

This is a hard concept, I agree. Yes, it was 10 watts when it left the transmitter, but after it left the antenna it was equivalent to 1,000 watts (as the beam was narrowed and the energy 'combined' and multiplied.

1,000 watts ERP (effective radiated power by pure DC) has the same heating value as 10 watts x 100 antenna gain.

When anyone has to fill out an FCC form for a station license (broadcast) the questions are: Final output power= // antenna gain=// effective radiated power= // Even though it started with 10 watts the antenna gain acts as an amplifier and creates an equivalent power and it is the same as real power.

I can't tell you how difficult this was for many to grasp in college, and I was one of them!

On the frequency vs. power question, that's a deep one. It depends of which facet of the game your referring to. One can't simply say when the frequency goes up 10% the power drops 1% as it's all related to efficiency and application. Each volume of the book applies differently.

Anyway, Lynx, I think your doing a great job and as long as you realize there is an effective power correlated with antenna gain, it doesn't matter if it's 10 watts of apples or 1000 watts of oranges, yes?

Best regards, my friend.
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Old 08-29-2003, 02:53 AM
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Well think of it this way then. Compare a 100 watt laser, to a 100 watt light bulb. They're equivilant right? =) It is however pretty difficult to light up a room with a laser like that (unless you were blowing something up) and it was hard to cut through .06 inch thick steel with a light bulb => Thats' what I'm getting at.

You're right though it is apples and oranges. Never mind my bickering =>
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Old 08-30-2003, 12:36 AM
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Default Midair interference hits

You guys are a riot!!! These theories are quite simply the same that I learned at 16 years old when in C.B. Radio.
I'm not bright enough to know all of the complex ratios, however, our power output was always figured in a ratio of wattage output x antenna gain, which let you know if you could step on the idiot next door before he stepped on you.

Glad those days are gone!!!!!

Ken
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