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Attenuator for QRP-Labs VFO SigGen
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I am anxiously awaiting my VFO/SigGen kit from QRP-Labs International. I have ordered it as the 2.9 to 34 MHz default frequency span. The 10 mW output signal looks clean and stable across the band. However, 10 mW is huge for most of the work that I'll be doing. I have about 90 dB in fixed attenuators that i can put in-line BUT a variable attenuator would be nice.
Has anyone built a switched or variable attenuator on the order of 90 to 110 dB for use with this SigGen? Absolute accuracy is not crucial but something close to linearity in a variable adjustment would be nice. Perhaps this is a design QRP-Labs might want to take on in their spare time! Thoughts appreciated. Thanks! -- 73, Rick VE7TK Website: http://www.ve7tk.com |
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Curt wb8yyy
Rick
They are out there search web for qrp stepped attenuator. Now at 100 dB substantial shielding of generator and attenuator are in order, even your coax may not be that good. You can cascade the fixed attenuators with a smaller range stepped one. Possibly examples in a w7zoi book if you have one. Or look around web. It's all in the construction. Curt |
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David Fine
QEX had plans for a nice switched attenuators a couple of issues back. PCBs were available from the author of the article. Cascading two of them should get you more than 100db attenuation.
Sent from my iPhone. |
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They can be build quite easily, checkout PA1B's QRPp blog : https://pa1b-qrp.blogspot.com/p/power-attenuator-calculator.html
(my 20W version is overkill but you get the point). -- 73 Lex PH2LB |
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Many thanks for all the suggestions. I'm surprised at the variety out there. I see some research ahead of me!
Again, thanks to all for the suggestions. -- 73, Rick VE7TK Website: http://www.ve7tk.com |
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Jim Mcilroy
Hi
You can get a PCB from QRP-Guys and populate it yourself. It is a retired product. I built one and it is very useful. I guess you could modify it too. https://qrpguys.com/qrpguys-31-db-step-attenuator Jim G4EQX |
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UPDATE:
I have ordered the parts to build the attenuator published in the Sept/Oct 2021 QEX. This is a 0 to 60 dB switched attenuator with excellent specifications from 1 to 150 Mhz. and less than 10% degradation up to 440 MHz. I anticipate that the SMD attenuators (rated up to 100 mW into 50 ohm load), switches integrated into the PCB and shielded box, in combination with the QRP-Labs VFO/Sig Gen will be a great addition to the shack. Thanks again to all for the suggestions. -- 73, Rick VE7TK Website: http://www.ve7tk.com |
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I have a dozen or so SMA attenuators I bought for 6 to 10 dollars each on ebay. See image below:
They are rated to 6 GHz, and rated power is 2 watts. I haven't swept every one over the full 6 GHz range, but I have spot checked them up to 2.1 GHz, and they're fine. I will soon have the ability to test them to 6 GHz and beyond with reasonable precision and will sweep them all at that time. I also have a few nearly identical looking SMA attenuators that are rated to 18 GHz. I'm thinking I paid maybe 15 or 18 dollars for those. I was thinking to myself the other day, as I shopped for yet another attenuator, what an irony that many search for ways to increase their power output, and I have all these devices to reduce power. I must have 30 or 40 attenuators of various types in my lab/shack. |
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