Types of Mount for dish anntena

[Steve714]

As a newcomer to radio astronomy, I am wondering about which type of mount to purchase. I notice that most people use AZ/EL mounts with their dishes as opposed to EQ mounts which are favoured in optical astronomy.  Is payload weight the reason for this? I note that AZ/EL mounts are more problematic for use when tracking because of field rotation and tracking motion. Are there methods for correcting for these?

[SteveBz]

How big is your dish?  My dish is 1.3m for satellites, not really big enough but still quite heavy.  It came with a consumer-style free-standing mount of the alt-az variety with one axis motorised, the other has to be manually adjusted with a spanner.  Like this:

Although the axis is motorised, it is not tracking, relying on the satellite being geostationary.  Therefore to track celestial objects, I needed to upgrade the mount.

I used my CG-5 GEM, which is still not really sturdy enough and relies on there being little or no wind.  I stuck a dovetail bar on the back and tracking worked "out of the box" so to speak.  Like this:

The issue is that a dish mounted like this will be at 90 degrees to an equivalent telescope, the scope in its home position pointing North parallel to the RA axis, whereas the dish is at right angles to the axis and points South.  Amazingly RA still works, but Dec just rotates it round the point it is looking at.  My Dec now has to consist of either extending one tripod leg, or alternatively using the latitude adjuster.  Neither is ideal.

Here is one where they seem to have resolved the issue and they've got what looks like an HEQ6 mount:

http://www.primalucelab.com/radioastronomy/blog/30-anni-radiotelescopio-di-medicina-radio-telescope-30th-anniversary

Really you'll need a customised mount, but I haven't yet procured or made one.

Good luck and post your results here!!!

Regards

Steve.

 

[Pippy]

On 08/10/2016 at 17:23, Steve714 said:

As a newcomer to radio astronomy, I am wondering about which type of mount to purchase. I notice that most people use AZ/EL mounts with their dishes as opposed to EQ mounts which are favoured in optical astronomy.  Is payload weight the reason for this? I note that AZ/EL mounts are more problematic for use when tracking because of field rotation and tracking motion. Are there methods for correcting for these?

Pointing accuracy with radio dishes is sooooo much more relaxed compared to the required optical pointing accuracy.

"Field rotation" only matters with dishes if you're using a linearly polarized antenna (dipole, quater wave etc) at the feed point. If your feed antenna is circularly polarized (left or right) then dish / feed rotation becomes meaningless.

 

[Steve714]

Thanks both. Very useful information.