Monthly Archives: March 2021

3cm, Antenna, Feed, Talks

10 GHz Dielectric lens Feedhorn

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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

Finished 10 GHz feedhorn with Radiall SMA connector

The body is turned and bored from a bit of aluminium round bar

The flat area is too large on this one, I’ll make it narrower on subsequent versions so I don’t have to shorten those M2.5 screws

Mount, UHF

432 MHz Moonbounce array elevation mechanism

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I’m working on an elevation pivot plate for a large 70cm moonbounce array for a friend. The design uses a 40 x 30cm plate with clamps and alignment blocks to carry GRP and aluminium tubes to support the array and LNA/phasing harness. This is the first stage, making the knuckle and pivot pin and bearing bushes/carriers. The bodies are aluminium, the shaft is 316 stainless steel and the bushes are phosphor bronze. It will have dust caps and grease nipples. The bushes are in two parts with a 1mm grease groove between them

So far, it is looking OK. More to follow.

One of the bearing bushes and mounting blocks being checked for fit

The original concept for the knuckle is here: http://www.g4dbn.uk/?p=1618 and this is the story so far of the machining,

The 100 x 100 x 150 mm aluminium block
Facing the block, bit of unnecessary slow-mo trickery
Shiny!
Nice rainbow caustic
First stage of turning
Forming the boss on the first side
Turning on a mandrel to form the second boss
Knuckle finished and bored to take the pivot shaft
Pivot shaft machined to size, with flats for the grub screws and locked in place
Machining and tapping the bearing carriers. M10 spiral flute tap clearing the chips very nicely
I made a mandrel with a threaded hole to turn the bearings from a piece of an ancient slab of bronze that I remember my dad using in the 1960s as a soft anvil
Block fitted to the mandrel ready for OD machining and facing
Initial facing done and OD completed
Removing the semi-finished bush from the mandrel
One half of the first bush pressed into one of the the bearing carriers
Boring the completed carrier and pair of bushes to fit the shaft with a 5 micrometre clearance
Test fit of the first bearing carrier