I’m working on a simple, waterproof, reproducible design for a 10 GHz dish feed for folks who are taking part in the group buy project to build F6BVA 10 GHz to UHF transverters. This uses a probe launch into a round waveguide machined from solid aluminium. The lens is made from Rexolite 1422, which is a free-machining cross-linked polystyrene with well-defined relative permittivity and a loss tangent of about 0.0004. This one is designed for a rather flat offset dish I have with equivalent f/d about 0.75, but I will be doing some for more common offset dishes
DB0MU/b is a tremendous signal this evening in IO93NR on 10 GHz. Peaking 65 dB over noise in 12 Hz bins. 591 km/367 miles
And here is a spur from PI7ALK on 10368.0916 at the bottom of the band!
I’ve just completed a batch of 24 of these W2IMU feedhorns for the 122 GHz band. Thread as usual is M8 x 0.5 mm. Horn ID is 4.03 mm, 27.1 degree internal flare, 2.00 mm reamed waveguide core, rear duplexer cavity for VK3CV boards, four M2 threaded holes, 4.00 mm reamed barrel, 3.98 mm spigot on the waveguide. This is the version 2 with a flat step as the end stop. Rather than relying on the 7.5 mm tapping drill to make the bottom of the threaded section, I now machine that using a centre-cutting M7 end mill. Part number for this version is DBN-122-IMU-0.7-02 and price to bona-fide 122 GHz experimenters is £14
I needed a couple of transitions, so decided to try to make a very simple narrowband design, optimised for 10368 MHz with low loss and a good match over a few hundred MHz. I ran up a design with rounded corners to the cavity to make it simple to machine using an 8 mm slot drill. I chose aluminium for the body as it performs well, although without anodising, it is going to need protection from the elements. I used some good quality Radiall SMA four-hole flange-mount sockets.
Although this looks a simple part, the instructions I make for myself show the level of detail.
I’ll publish the measured performance soon. So far, I can get around -23dB across ±100MHz. Once optimised, I will have some of these for sale to bona-fide experimenters. Email email@example.com for details
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.
First step was to extend the ring to fit the large feed
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.
Next step was to make support cheeks/crescents to hold the multiband ring feed
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.
The 13cm horn is a little larger, and had to be made in two pieces to fit over the backshort.
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
The original flanged coupler has a solid core, so as it is adjusted, the flange rotates. This is fine if it is used with an axisymmetric flange-mounted horn or a dish or lens which can rotate relative to the transceiver board. Where an experimenter wishes to connect the flange to something which cannot rotate, or where adjustment of the polarisation is needed, a new approach is required.
I separated the flange and central waveguide from the threaded barrel, and reamed a hole through the barrel. That allowed the flange to float and rotate, but it needed a clamp. I decided that a split nut which would fit over a raised ring on the shaft might work OK.
More pics to follow…
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.