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

author: han
author_rank: Frequent Contributor
timestamp: April 18, 2014, 12:09:22 pm
content: Is this the right ingredients for making Spectrum Analyzer?1. One teaspon MCP 4922 12 Bit DAC for tuning the LO2. One gram of ltc 5507es6 100kHz-1GHz log detector for IF detector3. Two gram of H6327CT-ND MMIC RF amp for TG4. AD 7680 BRMZ 16 bit ADC for digitizing log detector output5. One ounce of TDQ-37-5V TV tunner module for replacing LO + Mixer + LNA6. One jar of sweat and tear'sAnything i miss? or this project is meant to fail before born?Anybody have try this before, suggestion, and critique is appreciatedand because it's EEVblog.... please be gentle..

author: tautech
author_rank: Super Contributor
timestamp: April 18, 2014, 12:13:25 pm
content: 6. You forgot the "blood" to go with the sweat & tears.

author: dannyf
author_rank: Super Contributor
timestamp: April 18, 2014, 12:27:02 pm
content: The simplist approach would be a sdr stick.if that doesn't cover your band, use a fixed frequency oscillator plus a mixer to up or down convert your band to the sdr stick range.

author: han
author_rank: Frequent Contributor
timestamp: April 18, 2014, 12:31:04 pm
content: Quote from: tautech on April 18, 2014, 12:13:25 pmblood is too far(i don't plant to suicide when i fail),sweat is when i soldering in my hot chamber without air con,and tear when i finish the project

author: han
author_rank: Frequent Contributor
timestamp: April 18, 2014, 12:32:24 pm
content: Quote from: dannyf on April 18, 2014, 12:27:02 pmwhat is sdr stick?is it like radio receiver with fft spectrum analyzer? a.k.a cheap VSA?

author: electronics man
author_rank: Frequent Contributor
timestamp: April 18, 2014, 12:41:32 pm
content: I am about to build one, I'm going to use a double mixer approach, mine is only a low frequency one though, I will use a vco with a 200-400Mhz range then down convert it with a mixer with a fixed oscillator of 200Mhz to give me a 0-200Mhz output that I will mix with the Rf, then I will pass the If through an If filter, envelope detector then log amp, but I may do the log amp in software if its possible.

author: dannyf
author_rank: Super Contributor
timestamp: April 18, 2014, 12:41:41 pm
content: Software defined radio. The cheap ones go for like ten usd.

author: dannyf
author_rank: Super Contributor
timestamp: April 18, 2014, 12:43:15 pm
content: Plus many free software. Like sdr#.

author: han
author_rank: Frequent Contributor
timestamp: April 18, 2014, 12:52:41 pm
content: Quote from: dannyf on April 18, 2014, 12:43:15 pmany suggestion on the cheap but good one SDR?

author: han
author_rank: Frequent Contributor
timestamp: April 18, 2014, 12:54:43 pm
content: Quote from: electronics man on April 18, 2014, 12:41:32 pmLog amp in the software means you will need high speed high resolution ADC?

author: G0HZU
author_rank: Super Contributor
timestamp: April 18, 2014, 02:21:44 pm
content: QuoteIt depends on what your true goal is here...If you want to learn about RF design and many of the associated pitfalls, then making a basic homebrew spectrum analyser is a fantastic way to learn about practical RF design across LF through to UHFThis is because there is a bit of everything in a spectrum analyser. There's receiver technology, swept LO technology, logamp/detector/RBW technology and user interface and display technology all in the same box. But most people who attempt this will end up with something that will have very limited and very vague performance compared to something manufactured 40 years ago that you can buy on ebay for a few hundred pounds. So if the goal is to have a low cost analyser then the best option is to buy something on ebay.So basically your project is typical of something a lot of hobbyists attempted to do in the 1980s when there was no realistic alternative because even a used analyser was very expensive back then. Many used a scope for the display section. These days you have loads more options and a netbook or PC would be used as the back end and display for the analyser.If you still want to go ahead with it then I'd advise you to try and design/understand as much of it as possible even if the anticipated performance is very basic. This is where the real rewards are

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 18, 2014, 02:32:13 pm
content: This is the little Software-Defined Radio (SDR) USB gadget I got.The software is a bit fiddly, but once everything is installed, it works great.Of course, your results depend on how good your antenna is.http://www.ebay.com/itm/Newsky-TV28T-v2-USB-DVB-T-RTL-SDR-Receiver-RTL2832U-R820T-Tuner-MCX-Input-/160896092118?pt=LH_DefaultDomain_0&hash=item25762787d6

author: Fraser
author_rank: Super Contributor
timestamp: April 18, 2014, 03:46:40 pm
content: The first true spectrum analyser that I built was a kit from Electronics Australia in 1991 (I still have it and it still work well).The spectrum analyser consisted of Wide-band TV tuner that covered VHF and UHF frequencies. This was tuned across an area of the band using a ramp signal on the VCO input pin. The output from the tuner was around 47MHz. This was fed to an IF stage that filtered it and fed a common Motorola MC series IF/Demodulatir IC. The swept VCO ramp voltage and detector output was fed to an osciloscope X and Y inputs after appropriate processing. The unit was great fun to build and worked very well indeed. It contains a discrete component RF front end, in the form of the tuner, and this could be changed to other tuner types with different capabilities. A common (at the time) Philips Cable TV tuner improved coverage with a range of 50MHz to almost 1Ghz. The 0 to 50 MHz range was covered using a small and simple upconverter that shifted 0-50 MHz up to an area of the bands covered by the TV tuner. Such upconverters are now common on e*ay for use with USB TV SDR receivers. An SHF down converter could be built using a common manually tuneable satellite tuner that provided coverage from 900MHz to over 2GHz. The Sat tuner IF just fed the TV tuner front end. Simple and effective.As has been stated, the simplest form of spectrum analyser available at low cost is the very common RTL based USB TV stick/dongle that can be set to output raw data for processing in an SDR program. It all depensds what you want. I like building and modifying hardware and you learn a lot by doing so. The analogue TV tuner in the Electronics Australia design ensured that the tricky RF stages were dealt with for the hobbysit, so no complex RF test kit was needed for the build.I owned a Thurlby Thandar (TTi) Spectrum Analyser adapter for oscilloscopes a while back. It sold for a very good price (for me) on e*ay and there was much interest in it. Inside the unit was quite a disappointment....it was less complex than my Electronics Australia kit ! A relatively simple VCO was swept with a ramp waveform, and its output fed to a simple mixer to create an I.F. The I.F was filtered and fed to a detector stage. The output of the ramp generator and detector then fed an oscilloscope X and Y inputs. Simple, a little deaf, but very useable.Since the mid 1990's I have used 'real' spectrum analysers from Advantest or R&S, and I have to admit, I have no need of simple spectrum analysers as a result. Once you have access to a quality spectrum analyser you realise how much you have been missing with home brew types. My latest aquisitions (Advantest R3132's) are a joy to use but I was lucky to buy them for only GBP600 and repaired the simple faults that returned them to full operation. If you need a spectrum analyser for anything but hobbuist work, I recommewnd that you consider something a little more sophisticated than a homebrew or TV dongle SDR based solution. Saying that, the TV dongles can be impressive as a mini SA for monitoring purposes. The Signal hound is another SDR that I have seen but not used. It does have a following on the Internet so can't be all bad.Aurora

author: FrankenPC
author_rank: Unknown
timestamp: April 18, 2014, 05:38:07 pm
content: FYI: I went with this design from Murray and Bruce Barlowe (not affiliated!):http://www.science-workshop.com/Bookpage.htmMain page with kits:http://www.science-workshop.com/It mixes the HF product down to audio levels for consumption by PC software. It's a great way to get started.

author: codeboy2k
author_rank: Super Contributor
timestamp: April 18, 2014, 10:56:40 pm
content: Quote from: Richard Crowley on April 18, 2014, 02:32:13 pmI always wanted to play around with an SDR, and this is really cheap ..Thanks for the pointer, I just bought one from that seller to have a hack at it.. It's a good price... even though the I/Q data is only 8bits, it's still good enough to play with.. I suspect at 8-bits you just lose some dynamic range and have a worse SNR, but with a good antenna and local signals you can do ok

author: miguelvp
author_rank: Super Contributor
timestamp: April 18, 2014, 11:42:54 pm
content: from another thread that I replied:QuoteMore expensive than the ebay one linked above, but the interesting thing is the $45 rf upconverterEdit: Plus the upconverter is open hardwarehttps://code.google.com/p/opendous/wiki/Upconverter

author: dannyf
author_rank: Super Contributor
timestamp: April 18, 2014, 11:50:07 pm
content: QuoteA converter is fairly easy to build: a diode ring mixer (from $1 to a few dollars), a band pass filter, and a crystal oscillator. The connectors are probably more expensive than the parts.

author: han
author_rank: Frequent Contributor
timestamp: April 19, 2014, 12:53:08 am
content: Is there a good thread in EEVBlog about this SDR things?I can't find the software for simple Spectrum Analyzer, many of the software is focusing on decoding/ IF analysis .I didn't plan to make for anything fancy, just for proof of concept..Since i have access to decent SPA in my daily work job, so this is for toy only..

author: mhzghz
author_rank: Contributor
timestamp: April 22, 2014, 05:58:37 am
content: Scotty Spectrum Analyzer, if you want something decent.Those dongle SDRs are mostly for "spectrum display" and won't have the features and range of a real piece of gear.http://scottyspectrumanalyzer.comhttp://www.qsl.net/n9zia/scottyhttp://home.kpn.nl/rw.engberts01/slimmsa.htm