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Transmitter radiation pattern

Old 03-11-2003, 04:59 PM
  #1  
hamaos
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Default Transmitter radiation pattern

Need info about the TX-antenna radiation
pattern, specially for Hitec-TX's.
Any good proposals (good links).
OKH
Old 03-11-2003, 09:51 PM
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Whyes
 
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Default Transmitter radiation pattern

Sure . Just do a search in YaHoo on Antenna hand held radio or antenna radio control . Try different combinations .

The RC extension antennas that come with radios tend to have a sharp null off the end. The Rubber Ducky antennas don't seem as critical in this direction . The signal is pretty strong off the end of the antenna. You won't get the Glitch with a rubber duck in the same way as an extension antenna.

I don't know if the rubber duck will give as great a range . Better coverage close in does not always mean better range.
That is what radiation patterns are all about . Good luck in your search.
Old 03-11-2003, 10:12 PM
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JPMacG
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Default Transmitter radiation pattern

Too many variables...

Height of transmitter above ground
Angle of antenna relative to ground
Conductivity and dielectric constant of the earth (varies a lot depending upon type of soil).
Coupling from the transmitter to the pilots hands (how transmitter is held, size of hands, dry or sweaty, etc).


Under controlled free-space environment with good counterpoise (solid metal pilot?), the 1/4 wave telescoping antenna radiation pattern is doughnut shaped with a null in the direction of the antenna axis. Rubber duckie is very similar but less efficient because of losses associated with low radiation resistance. Duckie also has null in direction of axis.
Old 03-11-2003, 10:30 PM
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hamaos
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Default Transmitter radiation pattern

Sorry, I forgot to mention that the transmitter
is supposed to be under controlled free-space environment
and so on as you said. So radiation pattern
is more or less theoretical.

But anyway why the manufacturers even lift
the antenna angle ( about 30 deg) so that
antenna surely points directly at the plane.
Are they really trying cause more crashes??

OKH
Old 03-12-2003, 02:29 AM
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JPMacG
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Default Transmitter radiation pattern

Good point. I gues the manufacturers go for simplicity and low cost. The antennas used for RC are certainly compromises, but the transmitter-receiver link is so robust that there is rarely a problem.

If the RC band were at a higher frequency (say 300 MHz or so) then much better antenna designs could be employed at both the transmitter and receiver. But again, the existing designs seem to be more than adequate in most cases.

Jon
Old 03-12-2003, 03:16 AM
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Ed
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Default Transmitter radiation pattern

Originally posted by hamaos

Are they really trying cause more crashes?? OKH
Hamaos: That would be a very poor way to prove the reliability of their product, and sell more radios.

I have seen people hold their transmitters below their hips, with the antenna almost touching the ground, and I have also seen it held up around the chest, with the antenna almost straight up. I think that the versatility of the long extendable antenna allows us to get away with this. My Tx sits in a wooden tray about waist high, antenna maybe 5 degrees above the horizon, and I never see any loss of contact. And yes, I have certainly been guilty of pointing the antenna straight at the aircraft.

> Jim
Old 03-12-2003, 09:25 AM
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4*60
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Default Transmitter radiation pattern

I thought the pattern was about 45 degrees (between the antenna and the transmitter. Holding the radio horizental, aimed at the trees at our field, would give me the strongest signal on the other side of the runway about 100 feet up. Right where I fly most of the time. Seems good to me. Angling the antenna would put the strong signal right above my head??
Old 03-12-2003, 03:36 PM
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Rich-RCU
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Default Transmitter radiation pattern

Originally posted by 4*60
I thought the pattern was about 45 degrees (between the antenna and the transmitter. Holding the radio horizental, aimed at the trees at our field, would give me the strongest signal on the other side of the runway about 100 feet up. Right where I fly most of the time. Seems good to me. Angling the antenna would put the strong signal right above my head??

The procedure commonly used in the 60's and 70's was to hold the transmitter directly overhead with the antenna pointing straight up yelling "I ain't got it". Running towards the plane is said to have helped.

Theoretically aiming the tip of the antenna towards the airplane would give the worst situation, weakest signal to the plane. But I wonder with the close range and possible radio wave reflections if it really makes any difference.

Rich
Old 03-12-2003, 05:30 PM
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adam_one
 
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Default Transmitter radiation pattern

But anyway why the manufacturers even lift the antenna angle ( about 30 deg) so that antenna surely points directly at the plane. Are they really trying cause more crashes??
Hamaos:
The reason to lift the antenna about 30 deg. is to keep it a bit away from the ground, thus improving its radiation.
It was not meant to encourage the pilot to point the antenna tip towards the model.

There's a null in the radiation at the tip of a straight vertical rod aerial.
This happens even with the receiver antenna, when its orientation is not optimal during the flight manoeuvres, when the projection of the receiver antenna is nearly down to a single point, the signal breaks down and the servos get false pulses.
However, these short glitches go unnoticed most of the time as they are smoothed out by the servo's response time and the model's inertia.
Nevertheless, the pilot should avoid pointing the antenna tip towards the model during long time, specially when the model is flying at a greater distance.

Cheers,
Old 03-12-2003, 05:48 PM
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JPMacG
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Default Transmitter radiation pattern

There's also the issue of polarization. The transmitter antenna, if held straight up, will be predominately vertically polarized. The receive antenna in level flight will be predominately horizontally polarized. Holding the transmitter at an angle avoids this problem.
Old 03-12-2003, 07:26 PM
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Whirley Bird
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Default Re: Transmitter radiation pattern

Originally posted by hamaos
Need info about the TX-antenna radiation
pattern, specially for Hitec-TX's.
Any good proposals (good links).
OKH
I just read all the feed back you received and it looks like everyone did their home work on antennas.
++++++++++++++++++++++++++++++++++++++++++++++++

This taken from JPmac,
Under controlled free-space environment with good counterpoise (solid metal pilot?), the 1/4 wave telescoping antenna radiation pattern is doughnut shaped with a null in the direction of the antenna axis


Unfortunately FCC does not allow us to use a counter poise wire.
I think what you want is a Smith chart and I tried for months to get one with no luck.
The best you can do is plot your own with a field strength meter
I thought it was against FCC regs to use a duck on the TX as they say we can't change anything on the TX?
Well from my testing I see that the TOA is high.
About 30* and thats OK since the plane is high and your not going to fly it out of site

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