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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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11th May 2022, 6:58 pm | #1 |
Hexode
Join Date: Apr 2021
Location: Crawley, West Sussex, UK.
Posts: 444
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Sub-100MHz attenuator - ground plane or not?
Am planning to make a small simple RF attenuator, which will be used sub-100MHz.
It's a 2,4,8,16dB Pi/T design which will be made with SMD components on a custom PCB, built into a die-cast Hammond box, BNC each end. Switches will be pin type, directly mounted to PCB. They will be slide switches - I seem to read as much pro as con so have concluded it won't be a needle mover on this design/frequency range. My question is: Should I used a double-sided PCB - with the reverse as a petty much complete ground plane? My intuition says this isn't necessary in a fully-shielded box at these frequencies. I could see it adding capacitance across the whole PCB... Similarly not sure I need to have e.g. copper sheet shields between sections? Appreciate any advice. |
11th May 2022, 8:57 pm | #2 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,005
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Re: Sub-100MHz attenuator - ground plane or not?
I wouldn't go full-on ground-plane in this instance; in times-past I built a similar sort-of thing from an old ARRL-handbook design, using Switchcraft dual-pole-changeover slide-switches whose cases were soldered to a 'box' made from soldered-together PCB offcuts, and using 2-watt wire-ended resistors; it worked just fine though my co-workers used to sneer at it.
It worked 'just fine' until I inadvertently transmitted 50 Watts into it... Search "A Step Attenuator You Can Build - ARRL" for the design [Sept 1982]
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I'm the Operator of my Pocket Calculator. -Kraftwerk. Last edited by G6Tanuki; 11th May 2022 at 9:15 pm. |
15th May 2022, 3:25 pm | #3 |
Hexode
Join Date: Apr 2021
Location: Crawley, West Sussex, UK.
Posts: 444
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Re: Sub-100MHz attenuator - ground plane or not?
Made it.
Seems to work OK. 0.6dB down at 100MHz, 1dB down at 200MHz. Will post in the 'successes' section! |