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====== Antennas for receiving signals reflected from meteors ======

===== Plastic 1/4 lambda GroundPlane =====

It represents the basic antenna, currently used on most of our stations. It has an advantage of having small size and it is thus not difficult to install it on balcony, terrace, etc. Equally important is its relatively primitive designs which allows for easy construction suitable for beginners.
 
Disadvantage, on the other hand, is that the radiation pattern drops sharply to zero at zenith, making it very difficult to detect meteors flying directly over the head (compared to visual observation). 

[[http://www.ccars.org/projects/2mgp/tech_2mgp.htm|GP antenna]] is composed of two main emitter parts (vertical part), radial (horizontal part) and coaxial connector (mainly creating mechanical support).

Antenna socket connector is [[http://rasel.cz/www/obrazky/velke/209-210.jpg|panel mount UHF connector]] and 
antenna plug is [[http://rasel.cz/www/obrazky/velke/209-002_001.jpg|UHF coaxial connector]]. 

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The total length of 143MHz active element is 499mm and the length of short circuited stub from RG213 is 346mm.

==== Antenna location ====


Active element should be placed far enough (at least 2 lambda) from any large or conductive objects such as walls of buildings, wires, railing etc. 

The most suitable direction of antenna radial is to the west towards the GRAVES radar where we expect the best reflections from meteor trails.

===== Other types of antennas =====

An interesting antenna design, that should solve the drawbacks of GP antennas is so-called [[http://on6wg.pagesperso-orange.fr/Doc/Antenne%20Eggbeater-Engl-Part1-Full.pdf|eggbeater]] or an antenna of [[http://en.wikipedia.org/wiki/Turnstile_antenna|Turn style]] type.

A pair of crossed dipoles above a conducting plane could also result in interesting experimental solutions as it would be probably possible to integrate the amplifier directly into the antenna. The resulting active antenna would have better noise parameters and reliability compared to design with separated GP antenna and LNA.

[[http://en.wikipedia.org/wiki/Discone_antenna|Discone antena]] has also be tested for receiving the reflected signal. Although it works, it has an disadvantage of high bandwidth, that causes a penetrations of undesirable signals.


===== Installation of antenna's preamplifier  =====

==== Preamplifier LNA01A ====

Good quality preamplifier is essential due to antenna's low gain and low intensities of reflected signal.

[[http://www.mlab.cz/Modules/CommRF/LNA01A/LNA01A_Bottom_Small.JPG|LNA01A]] represents a preamplifier designed for meteor detection in 2m band. It amplifies the signal from antenna and thus decrease the effect of receiver's own noise. It further reduces complications connected with signal transmission via coaxial cable (it compensates for the cable attenuation and so it is possible to use cheaper coaxial cable of RG58 type).

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==== Further improvements ====

Antenna should fulfil these requirements.

  * It should have larger gain than currently used Ground Plane.
  * Radiation pattern should not reach zero at zenith.
  * It should have hemispheric radiation pattern.
  * It should be possible to integrate it with an amplifier.
  * Radiation pattern and directionality should be made adjustable via phasing of more antennas.