Antenna grounding..?

[Coto]

Can anyone explain what antenna grounding is and if it's necessary in radio astronomy? I've heard about it being used in transmitting antennas but I'm not really sure if is used in receiving/radio astronomy antennas. Will I need to have wires or conductive metals going from my dish into the earth or something?

[BiggarDigger]

For almost all purposes in radio astronomy, no you don't need to worry about antenna grounding for performance.  Any benefits with respect to the antenna efficiency will be negligible: the frequencies are so high that the length of any ground plane is very small and the superstructure of the antenna mount will more than compensate for the lack or formal ground plane.  Ground planes and antenna earthing is more often used at frequencies below 30MHz where unbalanced wire antennas can be used above a conducting plane.

For most radio astronomy, waveguides or long yagis are used in a balanced mode and there should be no common mode currents to speak of.

Here's a quick article that covers the basics if anyone is interested. 

https://www.electronics-notes.com/articles/antennas-propagation/grounding-earthing/how-to-ground-earth-antenna-aerial.php

Towards the bottom of page 2 it is recommended to employ a 3λ/2 ground plane for wire antennas.  In the KU band that equates to around 45mm ground plane and the dish is several metres wide.  Even for Hydrogen Line, the recommended ground plane for an unbalanced feed is 330mm and your yagi or dish is still much bigger, even if it operates unbalanced.

Note however, that in some phased array systems the antenna can be fixed and ground mounted.  A metallic ground plane forms an integral part of the antenna, but these tend to be wide area, low frequency antennas covering several hundreds of square metres.  I think the pictures I've seen of the receiving antennas at the 143MHz GRAVES radar site look like such an array.  From Wikipedia: https://en.wikipedia.org/wiki/Graves_(system)#/media/File:Silo_du_plateau_d'Albion.JPG, but it's difficult to be sure what is presented in the picture.

 

Be aware however that for any radio astronomy antenna you will have a large metallic object pointing at the sky and you will need to take basic lightning precautions. 

[RT65CB-SWL]

Hi @Coto and welcome to SGL. 

One of my other hobbies is shortwave radio listening. Antenna grounding is a must-have.

17 hours ago, BiggarDigger said:

Be aware however that for any radio astronomy antenna you will have a large metallic object pointing at the sky and you will need to take basic lightning precautions. 

Either the ground around you gets zapped ?... or your radio RX gets zapped. ?

I have a 'random' long-wire for an antenna in my attic/loft space and the earth/grounding wire is connected to and connected to the cold water supply pipe. Attach it as close to the supply as it enters your to your home. If the pipe is painted, scrape off some paint, then clamp the wire to the pipe. Better still... a one metre, (or longer), copper rod driven into the ground and the earth wire clamped to it.

[BiggarDigger]

Checking that the antenna is protected against lightning is essential.  Michael Faraday nearly paid the price for overlooking that step.

However pretty much any practical radio astronomy antenna should be grounded intrinsically.  For radio astronomy, either a set of long yagis or, much more likely, a dish will be used.  The antenna will be mounted on a substantial base, a post, mast or similar.  The mounting system itself forms the grounding section.  I guess an exception to that might be if a large dish antenna is mounted on a flat roof of a tall building.  Such an arrangement would need additional lightning precautions.

Lightning protection is a basic requirement of pointing anything metallic at the sky, but  it won't improve the performance of the system, as noted in my comments about groundplanes.

 

Richard