Category Archives: 23cm

Dish Feedpoint Mounts

Tony G8DMU has a 2.4m mesh dish on his van. He uses a variety of feeds, and they are all different diameters. I made up a quick-detach support ring to fit an RF Hamdesign multi-band ring feed, but Tony’s 23cm feed is larger, so I made up some extension blocks and a set of cheeks and spiders to support the different feeds.

The original ring feed, with the adjustable ends on carbon fibre struts, QD sockets and attachment brackets

First step was to extend the ring to fit the large feed

Blocks inserted into the ring to increase the diameter and provide attachments for the spiders and cheeks

I made up a stainless steel internally threaded clamp nut to fit on a stainless threaded bar fixed into the block with Loctite, so I didn’t have to worry about threads in the aluminium getting damaged.

The big 23cm band feed in the clamp ring

Next step was to make support cheeks/crescents to hold the multiband ring feed

Adjustable crescent with a knurled brass head on a pointed stainless steel thread, with a brass insert to spread the force and prevent wear on the Delrin
Fixed crescent, milled from Delrin and threaded M5

The 3.4 GHz feed is the smallest, so I milled a support ring and fitted support rods with threaded ends to fix to the holes in the outer ring. The threads were M5 so they fitted easily through the M6 threaded hole in the clamping block.

Clamping ring and spider for the 3.4 GHz feedhorn
3.4 GHz horn fitted to the main ring.

The 13cm horn is a little larger, and had to be made in two pieces to fit over the backshort.

2.3 GHz feedhorn in the clamp

I milled the rings on my ancient Bridgeport mill using a shop-made fixture plate on a rotary table with a sacrificial plate made from acrylic sheet.

Finally, a photo from Tony of the big dish in use on his van at a portable contest site up in the hills

23cm Isolator enclosure

Nice simple machining job to enclose a 1.3GHz RFCI drop-in isolator (three-port circulator with a dummy load on the third port) and act as a heatspreader in case of a load fault. I had bought six RFSL2347s direct from RFCI, but only needed three. They can handle 200W CW, 1kW peak and 100W CW dissipation.

I sold two and this one was spare. I ran up a CAD design in Fusion360 to get the dimensions right, but then made it on my manual Bridgeport mill.

CAD drawing with transparent lid
Finished body with N sockets and isolator
With the lid, showing the 8-24 UNC hole for a feedthru capacitor from a diode to detect if there is any dissipation in the load from a mismatch on the output port
Underside of the body. 4.3mm clearance holes allow it to be bolted to a heatsink or chassis