My Shack Configuration - Spring 2002

Created 28 May 2002

Some big changes at the mast, and wow does it make a difference:

Homebrew dual-band 13 & 23cm dish, with the secret ingredient: three bags of rice

o    Put AC & a 13.8V 40A PSU up at the mast

o    I've put the 70cm & 23cm amplifiers at the mast rather than in the shack

o    Replace the helices for 23 & 13 cm with a dual band helix feed on a single homebrew 1.2m dish chicken wire dish

o    Implemented a new remote shack controller

o    Changed the 6/2/70 triband to a Comet UHV-6 with all bands 40m thru 70cm - and it tunes up 80m thru 70cm with the TS-2000 auto ATU.

o    The new box with the PSU and amplifiers in it has two large fans, weather protecting vents and fly screen.

o    The antennas can be viewed remotely in case of cable snagging.

How to build your own 1.2m stressed chicken wire dish (some notes I made)...

Why build your own? The prime advantages of a chicken wire dish are (a) low wind load and (b) lighter weight. Placing a solid TVRO dish off-center on your cross boom is a recipe for a busted rotator if you use the lighter duty models (eg, G-5400, 5500, 5600).

The dish is made out of eight 60cm long, 6mm diameter fiberglass struts sandwiched at the center with two 5" diameter octagonal pieces of PCB. The fiberglass struts are initially accurately laid out at equal angles and epoxied between the PCB hub. There is a 1/2" space left in the middle of the hub for a bolt to attach the feed boom. When the epoxy has set, the entire structure is strengthened with three M2.5 screws with nuts through each strut at the hub.

A mast clamp is also bolted to the central hub.

A neatly fitting nylon Rawlplug [dunno what you call 'em in the US, but they're used to hold screws into bricks] is epoxied to the exposed end of each strut. This allows a tensioning string to be threaded around the diameter of the dish.

Using the tensioning string, an initial tensioning test is performed in order to calculate the circumference for the desired illumination angle and f/D. Care is taken to check that the struts are fairly uniformly spaced during this measurement.

Once the circumference is measured, the tensioning string is removed and marked into eight equal lengths. The tensioning string is now re-threaded, tensioned and the struts accurately spaced using the marks.

The 1/2" chicken wire is cut into sections (see brollydish.htm on how to make the sections) and attached to the tensioned struts using a generous supply of cable ties. 3/8" or 1/4" is better at 13cm if you can get it. My local hardware store didn't.

The feed boom is a 53cm length of 10mmx10mm aluminum square section bolted to the central hub and supported by four equally spaced lengths of nylon string attached to the dish circumference.

Apart from the PCB and small screws used at the hub, the chicken wire, figerglass struts, epoxy, Rawlplugs etc was all purchased at the local hardware store.

Now for some more pics...

Remote Control unit

 

Dual band feed - don't do it this way. Offset the N sockets by 90 or 180 degrees from each other or you'll need to grind the panel mounts

 

Patented weatherproofing method. Seriously, there needs to be some care with this: snips in the corners allow the bag to breathe and drain without letting too much water in.

 

 

Mail Howard, G6LVB

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