A 4 GHz Observatory Under Construction
By Laurence Newell

Laurence Newell has sent in some photos and a description of his 4 GHz observatory. This under construction. We are looking forward to the first data!. Laurence is also working on a radio astronomy website. Click on the thumbnails below to view the full quality images.

This is the 3m dish as it once was, when mounted on the ground. Fully steerable azimuth/elevation mount. To be fitted with a 4GHz LNB (also shown), primarily for solar observations.

I had intended to add a Dicke switch for noise reduction. I have an Icom R8500 receiver (from eBay) as thebackend. The receiver will be driven directly by the Java software (also shown) to give logging, spectroscopy, etc. The whole assembly is being rebuilt on a trailer (also shown).

Lab and Telescope Trailer
The mounting assembly is on a 'sledge' which plugs into the trailer, so in principle it is possible to slide it off and use the trailer for other things. However, I think it would need a lot of manpower to plug it back in again, so I haven't ever removed it.

This shows the 3m pointing at the zenith, giving a clearer view of the mounting. The counterweights are made from British Gas pipe! The disk weighs about 40kg, and so needs a bit of help to keep it stable... The pipework is Aluminium scaffolding, from the local dump (I sandblasted it to make it look better). The pipes are held together with KeeKlamps, brand new, but from a scrapyard...

AzEl Assembly
This shows the parts of the azimuth/elevation drive assembly. Driven by two very high torque stepper motors (800 steps per turn) through a lot of timing belt gearing. Shaft encoders to give position. Disc brakes to lock the dish when parked. The bearings are from a combine harvester! Angular resolution is about 0.1 degree, I think, but backlash will make nonsense of that.

Dish mounting
This shows the dish cradle more clearly. I intended to add quite a bit of extra strength behind the dish in the form of struts connecting the dish to the counterweight arms, giving a triangular lattice.

This is my mobile lab, made from a box body (the back of a lorry). Fully insulated and serviced, a home from home - at my parents' place - I live in a second floor flat!

Instrumentation Rack
More for show than practical effect at the moment! The unit at the bottom is a rack PC, which has been round the world in one of the BT Global Challenge yachts. This will run the controller software...

Very prototype Java software, to drive one axis. The software framework has changed a lot as a result of my horse race results system development (!), but you get the idea. There's also a star map showing where the telescope is pointing, and clocks, and.... (not enough hours in the day)

The two high torque stepper motors are driven from 60V DC via load resistors to improve their response speed (L/R, larger R giving reduced time constant). The resistor array dissipates about 500W, I think (can't really remember). Would double as a toaster. The controller box is a simple TTL to FET driver, for each of the four phases. I need a PIC or similar controller to interface to the Java software.