Part 2 of Machining almost RF-invisible** antenna mounting clamps from engineering plastic for a high-performance 432 MHz Yagi radio beam array. Lathe and milling machine action, custom collets, press-fitting threaded inserts. lots of Delrin ribbons and stainless steel chips.
**Before Proper Radio Engineers scold me for clickbaity terminological inexactitude, I do know "RF Invisible" isn't an official phrase, but these clamps must have no measurable impact on the antenna beam pattern, return loss or tuning, so "Invisible" in this instance is shorthand for "Having no effect on the radio frequency fields, performance and behaviour of the antenna system as a whole". That's 18 words and 106 characters, so I'm sticking with "Invisible". Fite me?
The radial distance from the antenna elements is at most 28 mm, but that's on the opposite face of the square boom, so in terms of a wavelength, the dielectric is immersed in the RF E-field of the horizontal elements by no more than 10 mm, which is 1/70th of a wavelength. Also, this is RU-vid, not a doctoral thesis or submission to a learned scientific journal.
AIMEE, my Artificially-Intelligent Machining and Engineering expert system offers "helpful" comments and snark as usual. She has dreams of being Quinn Dunki, but being a mere collection of JPEG bytes created by a Generative Adversarial Network at thispersondoesnotexist.com makes that a little unattainable.
Delrin is a compromise in this application. As Lauri Vuohensilta would say, it's pritty gooood mechanically, but doesn't behave as well in radio frequency electric fields as PTFE, UHMWPE, HDPE, Polystyrene and similar non-polar dielectric engineering plastics. It doesn't fall to bits in sunlight or soak up water and it's not soft and squishy. I tested a lump of it for ten minutes at 400 watts taped to the boom of a yagi beam antenna. Rather than getting hot and melting and bursting into flames, it actually COOLED DOWN, at least according to my FLIR infrared camera. That's probably because it's only a fraction of a wavelength across. The stainless fittings are small relative to the wavelength and are close to the boom and symmetrical so they don't seem to have any measurable impact either.
The antenna system belongs to a friend of mine in the Netherlands and he'll be using it in ham radio contests on the 70 cm (432 MHz) band, trying to reach extreme distances well over 1000 km via tropospheric ducting, troposcatter and other UHF radio phenomena.
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I'm a wee bit bored of Captain Obvious and Mr Actually and other mansplainy types informing me that I'd never be able to be a machinist/radio engineer/comedian/scientist. Well gosh-darn h*ck, my dreams are in tatters and my gratitude for your insights is bottomless. I am just a home-shop bodger, making stuff up as I go along.
I would starve in weeks if I had to earn my living doing any of those things. However, I'm having huge doses of this thing called "Fun", of which armchair warrior trolls may be unaware. They should try it sometime. Highly recommended.
In Real Life I spend my time fighting cybercriminals and fraudsters and designing secure information systems, which is a whole lot less interesting than I thought it would be when I chose that career path, but it pays the bills.
Disclaimer: Please bear in mind that I have literally no idea what I'm doing, so it's best not to follow my lead. I'm just as lost as you are. This is not an instructional video on "How YOU Should Make [thing]", it is an entertainment video about "How I Made [thing]".
Music clips are from the free library in Cyberlink PowerDirector or are licenced to RU-vid. Most of the sound effects were made by me using Audacity, or are in the public domain.
Chapters:
00:00 Pucks to Cuboids
03:25 Spigots and Saddles
10:01 Custom Collet
13:33 Screwdriver Slots
19:41 Holes and Counterbores
15 июн 2024
