DIY 1.8GHz spectrum analyzer - Page 1
Forum section: electronics / projects

author: erikka
author_rank: Regular Contributor
timestamp: June 04, 2019, 01:38:37 pm
content: Hi all,I want to share my latest project, a 1.8GHz spectrum analyzer.Technology (see first picture):Double/triple conversion with passive mixer modules from eBay and ADF4351/SI5351 modules from ebay as LO'sLog amp (from AD8307 data sheet) for DIY wide RBW and audio based FFT stitching for small RBWArduino zero for embedded control and everything else on PCSW also DIY based on .net so PC onlySpecs:DC (I tested down to 10 Hz) till 1.8GHzIIP3 +18dBm (see second picture)Spur free dynamic range (depending on RBW) at least 70dBRBW from 300kHz to 1Hz (See third picture) Dynamic range reduced (but still acceptable) at small RBW due to phase noise of ADF4351Phase noise acceptable (see fourth picture)And results of an actual measurement of harmonics of a signal generator as fifth picture (ignore the IIP3 text at top of display, forgot to switch of)All still without shielding so you may notice some spurs

author: Theboel
author_rank: Frequent Contributor
timestamp: June 04, 2019, 04:39:37 pm
content: Very interestingwith max2871 and etc chip get higher is that possible You made this an open project ?

author: ogden
author_rank: Super Contributor
timestamp: June 04, 2019, 05:43:45 pm
content: Wow. Fine job! Could you show some photo of instrument as well? What is RBW and what Resolution? In case RBW is Resolution Bandwidth, in one screen it is 30KHz while span is 20KHz. How's that?

author: erikka
author_rank: Regular Contributor
timestamp: June 04, 2019, 06:01:32 pm
content: The RBW is the selected hardware filter bandwidth at 2nd IF.The actual resolution is displayed at the bottomIt goes from 300kHz an 30kHz for the hardware filters and from 10kHz down to 1Hz in FFT modeSo in FFT mode with 20kHz span and 10k points you get 2Hz bins

author: erikka
author_rank: Regular Contributor
timestamp: June 04, 2019, 06:11:40 pm
content: Quote from: Theboel link=topic=191295.msg2462010#msg2462010I guess yes.QuoteThere are no pcb designs or detailed documentation. It is more inspiration . I am still learning

author: ogden
author_rank: Super Contributor
timestamp: June 04, 2019, 06:25:04 pm
content: Quote from: erikka on June 04, 2019, 06:01:32 pmYou can't call it RBW then. Resolution bandwidth most likely is what you call "Resolution". BTW you do not mention detector bandwidth (VBW).Some "SA fundamentals" books worth to check, maybe answer about common name for FFT "IF filter" width is there:http://literature.cdn.keysight.com/litweb/pdf/5952-0292.pdfhttps://download.tek.com/document/37W_17249_5_HR_Letter.pdfhttps://cdn.rohde-schwarz.com/pws/dl_downloads/dl_application/application_notes/1ef77/1EF77_3e_Real-time_Spectrum_Analysis.pdf

author: erikka
author_rank: Regular Contributor
timestamp: June 04, 2019, 06:35:55 pm
content: I ment RBW as displayed in the UIThanks for the document links.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 04, 2019, 06:54:43 pm
content: Wow, very impressive!Can you put some pics with the hardware, please?

author: schratterulrich
author_rank: Regular Contributor
timestamp: June 05, 2019, 06:19:21 am
content: Great work and very impressive results.I have a question:How do you attenuate the image freqency?You directly downconvert from 2.6 GHz to 10.7 Mhz. So if you use 2.6107 GHz at the ADE-25MH LO Port how to you attenuate the signal at 2.6214 GHz which will also convert to 10.7 MHz?

author: erikka
author_rank: Regular Contributor
timestamp: June 05, 2019, 07:11:46 am
content: Here is a picture, true Arduino prototype style. I annotated the major componentsThe image surpression works because the cavity filter has very steep edges so I put the first IF at the lower edge of the filter and the second LO below the first IF. Image surpression is not perfect so I added wobbling of the IF frequencies to enable image suppression in SWI'm still looking for a very narrow cavity filter to improve.

author: Theboel
author_rank: Frequent Contributor
timestamp: June 06, 2019, 10:19:37 am
content: It's getting better with "eBay ready" parts like that

author: bd139
author_rank: Super Contributor
timestamp: June 06, 2019, 10:22:05 am
content: Nice job! That's seriously impressive work!

author: erikka
author_rank: Regular Contributor
timestamp: June 06, 2019, 03:35:16 pm
content: Quote from: Theboel on June 06, 2019, 10:19:37 amWell... There are some parts you better not order from eBay. I did receive my share of counterfeits and bad parts. Even from known good suppliersExamples:ADE-11X being relabeled as ADE-25HMMixer module with -27dB conversion lossADL5801 module with bad performanceUltra low noise MICC, 10 pcs, all with twice the normal current so they will self destruct within days

author: notadave
author_rank: Contributor
timestamp: September 15, 2019, 01:51:36 pm
content: How did you know the ADE-11X could output much lower than 5MHz ? Looks like it is meant for IF of 30MHz.I would not even have had the idea that one could by stuff like that off eBay!Earlier this year I had the idea to make something similar, but for much lower frequency, with DVB-T ICs or an ADC (I did not have the idea to use a sound card thinking they were 44.1kSps and 16bit.) but a 24bit sound card is a great/better solution.I concluded that generating the two LO signals in fine steps and without jitter was too hard.

author: erikka
author_rank: Regular Contributor
timestamp: September 15, 2019, 01:59:09 pm
content: Many double balanced diode mixer has one port that can go to DC. The port directly connecting to the diodes. Some mixers have a balun between the port and the diodes, those won't work to DC