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Antennas Spotted On Helicopters

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Ben Zonia
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Antennas Spotted On Helicopters

Post by Ben Zonia » Thu Jan 14, 2021 8:46 pm

https://www.ultralifecorporation.com/EC ... om-antenna

Looks like a simple loop turnstile to me. Nothing fancy. Look at the frequency range and reach your own conclusions.


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Turkeytop
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Re: Antennas Spotted On Helicopters

Post by Turkeytop » Thu Jan 14, 2021 9:24 pm

Looks like it's made out of cardboard.


I started out with nothing and I still have most of it.

km1125
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Re: Antennas Spotted On Helicopters

Post by km1125 » Thu Jan 14, 2021 10:20 pm

Where was the helicopter and what was it doing?



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Re: Antennas Spotted On Helicopters

Post by Deleted User 14896 » Fri Jan 15, 2021 10:40 pm

It appears to me to be an antenna that is polarized in all directions.



jimh
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Re: Antennas Spotted On Helicopters

Post by jimh » Mon Jan 18, 2021 12:51 pm

Read the data sheet. The antenna under discussion is an aircraft antenna for 243 to 318-MHz. It has right-hand circular polarization and a gain of 6 dBiC (decibels referenced to a circularly polarized, theoretical isotropic radiator).

The antenna is designated as a SATCOM antenna, which I presume means military satellite communication.



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Turkeytop
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Re: Antennas Spotted On Helicopters

Post by Turkeytop » Mon Jan 18, 2021 1:16 pm

Of what material is it constructed?


I started out with nothing and I still have most of it.

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SolarMax
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Re: Antennas Spotted On Helicopters

Post by SolarMax » Mon Jan 18, 2021 1:58 pm

Turkeytop wrote:
Mon Jan 18, 2021 1:16 pm
Of what material is it constructed?
Unobtainium, perhaps. :)



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Ben Zonia
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Re: Antennas Spotted On Helicopters

Post by Ben Zonia » Mon Jan 18, 2021 2:10 pm

So where does the gain come from? You can't call it passive antenna gain if its amplified. Is each blade some kind of multi turn inductor loop? If so, maybe a good plan for a gain radio receiving antenna.


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SolarMax
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Re: Antennas Spotted On Helicopters

Post by SolarMax » Mon Jan 18, 2021 2:19 pm

I came across a link to this item about curious helicopter flights over Los Angeles, most likely military, possibly conducting training exercises.
There is frequent mention and photo highlights of the "egg-beater" or "O Wing" type UHF satellite communications (SATCOM) antenna on the tail booms of these Bell 407 helicopters, as well as some identification of the many other antennas deployed about the aircraft.

Posted as on-topic for technical interest. Please, no conspiracy theory followups, at least on this forum! :twisted:



km1125
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Re: Antennas Spotted On Helicopters

Post by km1125 » Mon Jan 18, 2021 2:25 pm

Was the antenna on the top or bottom of the helicopter?

EDIT: (after I read the link Solarmax posted)

Is this the same antenna the OP observed?
Image

I worked on a project a while ago where we instrumented a small aircraft (Cessna 210) and flew over areas to detect RF signals. We had two GPS antennas on the top to give us good positioning info, and some antennas on the bottom and back of the aircraft to sense the frequencies we were looking for. None of our antennas had an appearance of the one in the photo above but I could see an antenna like that used for either GPS, satcomms or satdata to keep them connected while they are on their mission - whatever that might be.



jimh
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Re: Antennas Spotted On Helicopters

Post by jimh » Mon Jan 25, 2021 9:05 pm

Ben Zonia wrote:
Mon Jan 18, 2021 2:10 pm
So where does the gain come from?
All antenna gain referenced to an isotopic radiator occurs by concentration of radiation in a main lobe and reduction of radiation in another direction.



k8jd
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Re: Antennas Spotted On Helicopters

Post by k8jd » Wed Jan 27, 2021 7:46 pm

Ben Zonia wrote:
Mon Jan 18, 2021 2:10 pm
So where does the gain come from? You can't call it passive antenna gain if its amplified. Is each blade some kind of multi turn inductor loop? If so, maybe a good plan for a gain radio receiving antenna.
It's easy to illustrate with a vertical antenna. The goal of gain , here, is to increase signals toward the horizon where receivers are listening,
A quarter wave has a wide launch angle of signal density from nearly straight up, to down to the horizon. Consider it 0 dB or no gain as a reference.
A halfwave has a narrower launch window with less upward and more power radiated toward the horizon, consider this as 3 dB gain.
A 5/8 wave antena has the maximum power radiated toward the horizon, and less at higher angles, of any continuous vertical radiator and is considered to be 6 dB gain over the reference QW vertical.



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