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====== Antennas for Bolidozor network ======

Antenna is the first signal input to a [[en:rmds|radio detection sattion]]. It is therefore necessary not to neglect its choice as a signal that is not received cannot be processed. A typical radio antenna receives not only meteor reflections, but also other radio signals - thus, the location of antenna is of high importance and should be chosen carefully. Suitable antenna characteristics can make the choice of location easier and can improve the overall antenna gain. Advantageous are following parameters: 

  * Sensitivity in the upper hemisphere with respect to observation site. 
  * High efficiency.
  * Insensitivity to signal linear polarisation angle.
  * Suppression of unwanted signals reception from vely low elevations (usually ground noise).


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

{{:cs:antennas:bolidozor_gp_antenna.jpg?600| GP anténa pro síť Bolidozor}}

{{:cs:antennas:bolidozor_gp_antenna_mount.jpg?600|}}

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 design which allows for an easy construction suitable for beginners.

A disadvantage is a low gain and a a radiation characteristic that has a sharp zero in zenith (meaning a very bad detection of meteors flying over the observation site, causing, subjectively, a big difference compared to visual observation). 

[[en:gpant|A more detailed description]].


===== Helixes - QHA =====

SC-QHA Helix is a type of circularly polarised antenna whose parameters can be almost homogenous 	over the whole hemisphere. The antenna is tuned mainly by a proper phasing of its four powering points. 

{{:cs:antennas:qha:bolidozor_sc-qha_antenna_prototype.jpg?600|}}

Bolidozor network would make use of a Helix design with a square ground area measuring 2x2m. Such constructions has an advantage compared to a standard self-phase QHA antenna in that it has a narrower receiver bandwidth and greater total efficiency. 

[[en:qha|A more detailed description]].
 
===== 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).

{{cs:antennas:gp_plast16.jpg?direct&300 | }}
{{cs:antennas:gp_plast17.jpg?direct&300 | }}



==== 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.