Category Archives: Uncategorized

Fusion360 stress simulation

I ran a quick test in Fusion360 to look at the stresses around holes in a 1 metre aluminium boom with a large hole in the top and a cross-hole, with one end of the boom fixed and 200N on the other end. Just testing the facility to see how it works.

Boom stress at 0-200N force. Red means bad times, likely to snap

Ideas for a 3.4 and 10GHz feedhorn

I’ve been trying out some ideas for a feedhorn that uses the dielectric-horn POTY approach with a 22mm circular guide for 10GHz suspended in the mouth of a 9cm horn. Quick video of the idea shows some issues, like it only works with the coax feed to the 10GHz horn when it is cross-polarized. Needs a lot more thought, but I needed to do this sketch to get it clear in my head. The outer tube is almost transparent in this rendering. It is 180mm long and 68mm OD. The open end of the 22mm tube will have an HB9PZK dielectric lens and the 68mm tube will have a thin dielectric plastic disk with a hole to support the 22mm tube. Hopeless like this though because of the cross-polarisation issue. More thought needed.

Lathe headstock spindle spider

I needed a spider to support long workpieces out of the back of the headstock spindle. I had a bit of EN8 round bar so I used that. Bored to 42mm to match the spindle ID, then counterbored to fit the spindle OD. I used a 1mm slitting saw to form a clamp and milled out pockets for a couple of M3 caphead bolts. Bored out a hole in the end of three M8 cap bolts and made brass inserts. Works a treat.

E-Field Active Antenna

This project is being implemented by the Goole Radio and Electronics Society. The antenna uses the modified PA0RDT Mini-Whip design. The PCB and component kit was put together as a kit by the late Dave Powis G4HUP and now sold by the UK Radio Astronomy Association. The kit only includes the electronics. I decided to make a proper enclosure, couplers and fittings to make a decent mechanical solution.

Standard post-mount base clamps and insulated offset mounts to fix to a shed or wooden post
The completed radome assembly mounted on a 32mm aluminium mast
Aluminium collar, PCB enclosure and radome mount
Radome cap with 22mm internal recess for the probe
Radome with cap
Probe support bush
PCB from UKRAA kit, assembled with a soldering iron and 0.3mm solder
PCB inside the collar. It will be potted to prevent moisture damage
Collar fitted to the mounting pole and radome. All sections will be filled with PU foam once tested
Brass end plug (tapped M4) soldered to the end of the 22mm copper tube
Base insulator and spacer with fixing screw – needs to be brass though!
Top cap fitted – I may need to shorten the probe, but best to start long
Exploded view of the larger probe. Standard probe is 100mm
Common mode choke enclosure
Adjustable mount in place (early version without the common mode choke)
Mounting plate, mast clamp and saddles
Mounting plate with angle adjuster
angle adjustment slot
Insulated gland at mast base for the coax connection to the screened, isolated common mode choke box

More 122GHz Chaparral® Style feedhorns

I made up another batch of my variant of the VK3CV model choked Chaparral®-style feedhorns. Chokes are 7mm diameter, bore is 2mm, Body is 30.75 x 15mm, with an adjustable 4mm diameter coupling cavity. These are made from brass.

Grooves are 0.5mm wide by 0.75mm deep, made with a toolpost spindle at 14,000 rpm using a two-flute carbide end mill in the lathe at 8rpm

First of the batch fresh from machining.
Batch of 122GHz Chaparral-style horns ready to ship
Locknuts
Microscope view of the 0.5mm grooves
Part-machined battels and coupler bodies
M8 x 0.5mm mandrel to machine locknuts to thickness
Spacer and part-machined locknut on the mandrel ready to machine to thickness
Toolpost spindle drive made to fit my Aloris-style toolpost. 600W, 48V variable speed motor

24GHz Round Flange Coupler

I was asked to make up some quick-detach coupling tubes to allow two 24GHz round flanges to be clamped together. I made a tube with a 22mm x 0.75mm thread outside and broached a keyway slot, then made a brass key to fit and fixed it with Loctite. So far I’ve only made up one of the clamp rings, I’m waiting for a real example to turn up so I can get the tolerances exactly right. All its fine so far though.

The coupling ring with key and one of the locking nuts
Pair of round flanges inside the coupling ring
Locking nut fitted to one side

HB9PZK POTY Lenses for 10GHz QO-100 downlink

Willi HB9PZK modelled a Rexolite lens for a “POTY” dual-band patch antenna to use on the 10GHz downlink from the QO-100 amateur satellite. https://rfantennas.wordpress.com/author/hb9pzk/

The design is a joy to make when compared with the dual-taper versions. I have some one-inch Rexolite 1422 round bar, so I’ve been making a few of these lenses to replace the lossy Nylon versions that some folks are using. Rexolite is a cross-linked polystyrene, which machines rather like plexiglas. It has a tan-delta around 0.0004 and almost zero water absorption.

Willi’s design has a stepped transition to the read. This latest batch is to fit UK 22mm plumbing pipe with a nominal wall thickness of 0.9mm and an inside bore of 20.2mm instead of the standard 20.0 bore.

Two Rexolite HB9PZK-designed lenses for 20.2mm ID waveguide
One of the lenses fitted to a POTY