RF Power Supply for ICP Purposes

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
Erik smith
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Real name: Erik smith

Re: RF Power Supply for ICP Purposes

Post by Erik smith » Thu Dec 28, 2017 5:02 am

I have seen a lot of RF attenuators on ebay and Ali Express. My only concern is the very low VSWR (~1.2:1) rating for most of the 1dB attenuators widely availabel.

https://www.aliexpress.com/item/100W-N- ... 92558.html
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ian_krase
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Real name: Ian Krase

Re: RF Power Supply for ICP Purposes

Post by ian_krase » Thu Dec 28, 2017 7:21 am

Low VSWR is what you want, right?

Erik smith
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Re: RF Power Supply for ICP Purposes

Post by Erik smith » Thu Dec 28, 2017 5:47 pm

Ian,
Make a 1dB attenuator to put on the output - you lose 20% of your output at the gain of not blowing the devices
This immediately means the VSWR can not go over 8.7:1 with a dead short or open on the output (the two worst possible cases)
8.71:1 indicates the maximum VSWR the amplifier can see with a 1db attenuator on the output. Here is more info on it
(http://www.rfcafe.com/references/electr ... uction.htm). But you are right about the desired VSWR. For maximum power transfer, you want a VSWR of 1:1. However since ICP sources have been known to be very unstable. This means that the VSWR can change. Since the 1dB attenuators listed online can only withstand a maximum VSWR of ~1.2:1, I might need to build my own. There are many designs for RF attenuators however since 1dB reduction means a 20W power loss when the amplifier is at its maximum output (100W), I need to find high power carbon resistors (low reactance) which is no easy task. Does anyone know if it would be a good idea to still use the attenuator listed online?

John Futter
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Re: RF Power Supply for ICP Purposes

Post by John Futter » Thu Dec 28, 2017 6:35 pm

Erik
That VSWR figure is for the attenuator it is not its with stand rating
ie the attenuator matches nearly 50 ohms resistive
more here from my web site
http://www.iel-rf.com/AttenuatorsDescription.html

all you need is a 1dB 25 watt dissipation attenuator

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