Best cheap microwave noise source (DC - ~2.4 GHz)? - Page 1
Forum section: electronics / rf-microwave

author: ksmoltz
author_rank: Newbie
timestamp: June 14, 2024, 07:00:48 am
content: Hi all,I would like to be able to perform noise figure measurements in the 70cm band and at around 2.4 GHz. I may want to expand the range of frequencies I can test at a later date.Surveying what's out there, I see a number of options available to me:Buy a new HP 346A/B/C. Not an option--outside of my price range (ideally no more than perhaps ~$250-500 USD max).Buy a used HP 346A/B/C. Still too expensive (~$1k or more)Buy a used NoiseCom NC346. Cheaper than the HP-branded units, but still ~$500-1000.Buy a used NoiseCom MC63170 or similar. Getting warmer... (~$400 or even less, depending on model)Buy a new RF-Gadgets.com XDM-1600. Cheaper (~$250-300), but with (questionable?) calibration and construction (crappy case, cheap PCB, cheap parts), and very limited B/W (1.6 GHz).Buy a G8FEK BBGen or XGen. Not currently available for purchase!Build my own noise source. (Uncalibrated!)I foundthis threadfrom 2018 ("Diode noise sources and Calibration Club") which was very helpful. In particular, it contained links to Franco Rota's two VHF Communications articles (the first fromJanuary of 2007, and the latter fromApril of 2018), the latter of which describes a build based around the NoiseCom NS-303 diode.There are a couple of hurdles to duplicating his build:Requires a custom-machined enclosure. This is not really a problem for me (I have access to a milling machine.)Franco suggests using a Rogers laminate like RO4003 or RO4350. PCBWay is too pricey ($200-300) but JLCPCB offers RO4350 for ~$100. Somehow JLCPCB has Teflon for even cheaper ($30!)Requires a NoiseCom NS-303 diode. No idea how expensive these are or what MOQ from NoiseCom is (yet).Another build by Jay_Diddy_B can be foundhere.I could make use of a 70cm noise source sooner than a 2.4 GHz source. Below 1 GHz I question if a fancy NoiseCom diode is needed. I founda photoof the inside of the XDM NSE15-1 (predecessor to the XDM-1600, I think) on the Internet Archive which seems to show just a cheap-o SOT-23 part.But, if I build something, it won't be calibrated, and I might spend about as much as if I just bought something used (& calibrated) in the $4-500 range.I have never attempted noise figure measurements before, so I don't really know what's necessary. I'd like to be able to measure noise figures as low as ~0.5 dB with gains perhaps in the 10-20dB range, maybe a little more. I am also uncertain if I want/need an amplified noise source. I have only an E7495A base station test set, but I do have access to (much) nicer SAs at my work.Am I wasting my time at the low end of the price spectrum? Should I just "bite the bullet" and buy the most expensive noise source I can (not) afford? If I built one, how could I calibrate it? (e.g., if I could compare it to a calibrated noise source...)It does seem as though a small (5-10 units) production run of DIY noise sources could be economical if other forum users were interested in buying, especially if NoiseCom has some greater-than-one MOQ.EDIT: I also foundthis article from QEX(that I have not yet finished reading) as well asthis additional DIY build.