Author Topic: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer  (Read 40904 times)

0 Members and 1 Guest are viewing this topic.

Offline SaabFAN

  • Frequent Contributor
  • **
  • Posts: 543
  • Country: de
DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« on: September 28, 2015, 03:10:15 AM »
Hello,
I have toyed with the idea of getting a spectrum analyzer for quite a long time now, but even the cheapest ones on ebay are way outside my budget: Even defective ones are seldom below 700€, working ones start at 1200€ and go up quite fast.
There are a few PCBs out of China inside my budget-range, but those normally start at 500Mhz and go up to 1.5Ghz or higher. Again nothing for me there.
So I decided to build one. If I don't mess up the final exam, I have 5 months of time ahead of me which I can dedicate to fiddling with electronics and this project should keep me occupied for most of that time. Plus it's probably a good learning exercise. And who knows: Maybe I can do math afterall? (The VCO seems to require quite a bit of calculation) :D

To add a little challenge, I have set the max. Budget (For stuff to buy in addition to what I already have) to 70€. This means that I will have to build most of the device with stuff from my father and grandfather.

The specs so far:
  • Frequency Range: Dual Ranges: Audio-Spectrum & 100khz up to 225Mhz
  • 2 Input-Modes: 50Ohms for full Frequency Range & High Impedance (Input connected directly to fast Input-Amp) for low Frequencies up to 15Mhz - Switchable with Reed-Relay
  • Stepped Attenuator in the Input-Stage (Explanation: I plan to measure DC/DC-Converter and 12V-Rails on a sailing boat with this device to make sure the MPPT and Battery-Chargers - Another, mostly finished project - dont interfere with the Echo-Sounder and other navigation-equipment)
  • 2 Stage Superhet-Receiver with Digitizer at the end
  • 8/16bit parallel ADC with 2x 2K x 8bit SRAM as sample-memory (I have a ADC0804LCN 8bit ADC in my partbox, so I will start with that one and later put a 16bit ADC in there)
  • Digitally controlled Sweep
  • Integrated Display (I bought a 3.5Inch Touchscreen last year, which has lost its purpose because the project I wanted to use it for will use a bigger screen) with GUI
  • ARM-CPU (Arduino Due)
  • Fits into Schroff 19'' 2 Height-Unit Case
  • 220V, 12V (Optional, if it doesn't eat too much power: Internal Battery - I have a few Lithium Accumulators available from my not so successful attempt to modify a MHS-5200A Signal Generator)
[li]*UPDATE* Tracking-Generator - Frequency: TBD
[/li][/list]

Theory of operation (Aquisition):
INPUT -> Input-Attenuator/Amplifier -> Mixer with PLL-Controlled VCO (SA612 or 615 if the 612 is too "weak" for a 500Mhz LO / The PLL is a Philips TSA5514) -> 250Mhz Bandpass -> Downconverting Mixer -> 10.7Mhz Crystal Filter -> Variable Gain Amplifier -> Detector/Rectifier -> ADC -> SRAM(AQ)
Theory of operation (Output):
SRAM(AQ) -> Arduino -> Display / Serial Datastream

The whole design will borrow heavily from "The Simple Man's Spectrum Analyzer" by Hans Summers http://www.hanssummers.com/spectrumanalyser.html, as well as s PC-Bus based Spectrum Analyzer from DKD Instruments described in a PDF I found online (Written by Dan Doberstein and John Cardone - Link: http://www.n5dux.com/ham/files/pdf/Spectrum%20Analyzer.pdf).

I hope this will be at least a nice exercise and interesting learning experience that results (Best case scenario) in a functioning Spectrum Analyzer for less than 150€.
I will post first schematics sometime next week and will release the Software here too, once I have written it.

Do you guys have any ideas, suggestions, etc.? I'm rather new anything above 20Mhz. I looked over a few service-manuals for Philips Signal Generators and read a few Application Notes regarding HF, but that's basically it.
The first challenge will probably be to build a VCO that is able to reach the 450Mhz required to upconvert the input-signal to the 250Mhz of the first IF.

Btw. T&M-Equipment available: Rigol DS1104Z, Philips PM3320 200Mhz DSO, Fluke 87, Cheap Ebay 2.4Ghz Frequency Counter, 12Mhz Arb-Waveform-Gen.
« Last Edit: September 29, 2015, 03:44:58 AM by SaabFAN »
 

Offline SundayProgrammer

  • Contributor
  • Posts: 33
  • Country: fi
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #1 on: September 28, 2015, 03:51:38 AM »
Interesting project. Looking forward to see progress...

Axel.
 

Offline T3sl4co1l

  • Super Contributor
  • ***
  • Posts: 9337
  • Country: us
  • Expert, Analog Electronics, PCB Layout, EMC
    • Seven Transistor Labs
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #2 on: September 28, 2015, 02:08:35 PM »
Although I have an HP8590A now, it's not suitable for narrow bandwidths; I think I may yet build one for lower frequencies, perhaps audio to 10s of MHz or 100MHz.  I don't have any direct advice just yet, but this sounds like a good project.  8)

Tim
Seven Transistor Labs, LLC
Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
 

Offline m98

  • Regular Contributor
  • *
  • Posts: 242
  • Country: de
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #3 on: September 28, 2015, 10:43:04 PM »
Btw, with the Rigol DS1104Z you already have a Spectrum Analyzer: http://rheslip.blogspot.ca/2015/09/software-spectrum-analyzer-for-rigol.html

Online tggzzz

  • Super Contributor
  • ***
  • Posts: 5941
  • Country: gb
    • Having fun doing more, with less
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #4 on: September 28, 2015, 11:12:04 PM »
Depending on what you are using it for, there might be much cheaper alternatives in the 25MHz-1.5GHz range.

See https://entertaininghacks.wordpress.com/category/frequency-domain-analysers/ for some preliminary results. I must get around to writing up later results and "publishing" the post-processing code.
There are lies, damned lies, statistics - and ADC/DAC specs.
Gliding aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline SaabFAN

  • Frequent Contributor
  • **
  • Posts: 543
  • Country: de
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #5 on: September 29, 2015, 03:36:18 AM »
@m98: That software looks interesting. I will certainly give it a try to see if I can use it to verify the operation of my device.
Unfortunately, this solution doesn't seem very mobile to me and I would like something that is independent from a PC.

@tggzzz: I have thought about SDR and also have checked out the about 100€ NWT4000 available on ebay. Unfortunately, those devices only start at several megaherts (138Mhz in the case of the NWT4000), which puts them outside the frequency range I want to measure.
The ranges I'm interested in start closely below 100khz and (at least for the moment) end at about 170Mhz. This covers marine navigation equipment and marine radio frequencies, which start at 415khz and go up to 162Mhz. With the analyzer I want to see if my Energy Harvester and Chargers create any kind of interference (The charger my father bought 6 years ago makes the digital Echo Sounder go crazy once it starts activating the dummy-load and not even a massive LC-Lowpass was able to stop that) in these bands or if external signal sources can get inside the system and make the Power Point Tracker do crazy stuff.
I also want to see if I can pull this off. So far I have always opted for the cheap "just buy it"-solution when I needed stuff (Multimeter, Signal-Gen, Digital Counter, Scope), now I want to build something myself :)

About the device itself: I don't know about it yet, but I think adding a tracking generator might be a good idea to check frequency response from Filters. I have 3 TSA5514 PLL Chips here, as well as several 4046 and one 74HCT297-"Digital PLL". The latter ones won't go beyond 20 or 30Mhz, since they are available, why not put them in there? :)
*Specs in first post updated*
« Last Edit: September 29, 2015, 03:43:14 AM by SaabFAN »
 

Offline edpalmer42

  • Super Contributor
  • ***
  • Posts: 1201
  • Country: ca
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #6 on: September 29, 2015, 03:40:59 AM »
Have you checked out Scotty's Spectrum Analyzer?

http://scottyspectrumanalyzer.com/

It's a modular DIY system that can be built without sophisticated test equipment.

Ed
 

Offline Stupid Beard

  • Regular Contributor
  • *
  • Posts: 221
  • Country: gb
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #7 on: September 29, 2015, 03:56:10 AM »
I have thought about SDR and also have checked out the about 100€ NWT4000 available on ebay. Unfortunately, those devices only start at several megaherts (138Mhz in the case of the NWT4000), which puts them outside the frequency range I want to measure.
The ranges I'm interested in start closely below 100khz and (at least for the moment) end at about 170Mhz.

You could use a mixer to upconvert the lower frequencies into something the SDR can handle. Alan W2AEW has a couple of videos on that, for e.g.:

Edit: Nice project though, will be interested to see how it pans out.
 

Offline sain

  • Newbie
  • Posts: 3
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #8 on: September 29, 2015, 11:13:28 AM »
It doesn't have the reach you want (70Mhz upper limit), but Farhan (VU2ESE)'s SPECAN project might be of interest:
http://hfsignals.blogspot.in/p/specan-reboot-of-w7zoi.html
 

Offline SaabFAN

  • Frequent Contributor
  • **
  • Posts: 543
  • Country: de
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #9 on: September 30, 2015, 06:55:53 AM »
It doesn't have the reach you want (70Mhz upper limit), but Farhan (VU2ESE)'s SPECAN project might be of interest:
http://hfsignals.blogspot.in/p/specan-reboot-of-w7zoi.html

That one is quite interesting indeed. I have just ordered the SI570 Oscillator (Found one on Ebay, Digikey didn't have one) and I'm now reading through the rest of it.
I didn't know about i2c programmable oscillators, so thx for pointing me to that source. I also just realized that with 15bit available in the TSA5514 I would have had quite big jumps in the frequency instead of a smooth sweep^^

Offline SaabFAN

  • Frequent Contributor
  • **
  • Posts: 543
  • Country: de
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #10 on: September 30, 2015, 12:02:24 PM »
The Specan is a really nice piece of equipment. I'm certainly going to use some parts of it. The switchable bandpass for example, or the 20Mhz crystal-based 100Mhz oscillator for the second IF. And the software, of course. With a little luck, I can expand it to my needs without breaking too much.
What I can't quite figure out at the moment: How important is the width of the first IF-Filter? Would 10Mhz (requires "exotic" capacitor-values in the area of 0.3pf, which may easily exceeded by parasitics) be enough or can it be wider?
My understanding of the matter at the moment is this: Medium (several Mhz) quality selection of the first IF, very high quality (down to 1khz) selection with crystals of the second IF. Correct?

Offline T3sl4co1l

  • Super Contributor
  • ***
  • Posts: 9337
  • Country: us
  • Expert, Analog Electronics, PCB Layout, EMC
    • Seven Transistor Labs
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #11 on: September 30, 2015, 01:51:25 PM »
You want the bandwidth narrow to begin with, or decreasing, along the IF strip.  That way, as the signal becomes stronger, out-of-band noise is rejected rather than amplified (potentially leading to clipping and mixing, giving large IMD).

Tim
Seven Transistor Labs, LLC
Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
 

Offline SaabFAN

  • Frequent Contributor
  • **
  • Posts: 543
  • Country: de
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #12 on: October 01, 2015, 10:44:10 AM »
Update:
It is not exactly "Junkbox", but I think this one is a much better 1st-Stage Bandpass-Filter than I can build: https://www.digikey.de/product-detail/de/B39311B3768Z810/495-2356-1-ND/821882
313,85Mhz Center Frequency and 100khz Bandwidth Bandpass-Filter. And it is tiny! Saves a lot of shielding - Which brings me to a question: If I use plastic poles (I have 5 drawers full of Lego) as stabilizing elements and Aluminium-Foil from the kitchen as the conductive shield, could that be a replacement for copper-plates?

The big problem with this component: It raises the maximum LO-Frequency to about 540Mhz, which is 40Mhz above the specified input-frequency of the SA602. Can anyone here measure how this out-of-spec frequency affects the output? I don't have the equipment for that (yet^^).
If this distorts the output, what could be done to correct that? I guess it would be possible to use a different Mixer, like the LT5560, which is only 2,75€ when ordered from Digikey (Carrying the advantage of raising the max. Frequency to about 400Mhz with a fitting Filter), or I try to build one myself. I have 4 DB27316 Ultrafast Schottky-Diodes (Datasheet: http://www.semicon.panasonic.co.jp/ds4/DB27316_E.pdf) with 0.8ns Reverse Recovery-Time, as well as a few toroids salvaged from old PC-Mainboards and WireWrap-Wire. I also have 10 BF998 MOSFETs in one of my Partboxes. 

For the second IF-Filter, I tested several ceramic filters and so far, a 8Mhz HC49-Filter yielded the best result (This website http://www.giangrandi.ch/electronics/crystalfilters/xtalladder.html calculates about 3khz for an 8pole-Filter with my not too accurate measurements) - The 10.7Mhz ceramics I bought on ebay for 3€ for 10 pieces yield only 200khz.
Knowing this, the second IF-Stage is slowly coming together. The first stage still has a few question marks hanging over it :)

Offline NiHaoMike

  • Super Contributor
  • ***
  • Posts: 3413
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #13 on: October 05, 2015, 05:41:57 AM »
Depending on what you are using it for, there might be much cheaper alternatives in the 25MHz-1.5GHz range.
RTLSDR can be used as a spectrum analyzer for that frequency range. The main disadvantage is that it's really slow if you want to look at a big chunk of bandwidth.
Cryptocurrency has taught me to love math and at the same time be baffled by it.
 

Offline SaabFAN

  • Frequent Contributor
  • **
  • Posts: 543
  • Country: de
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #14 on: October 09, 2015, 12:02:18 PM »
Okay, little Update here: I have begun to build the device.

First I'm going to make a Low Frequency Stage similar to the Specan, because I didn't get the LVDS-Version of the Si570 Oscillator (Programmable Oscillators seem to be a dying breed). Once that one, and the software, are running, I might try to build my own VCO with a large enough sweep-range to be tuned with one of the PLLs I have to add another stage that then can be used up to the original required 225Mhz.
This, unfortunately, also means that I have to build my own Bandpass with the parts I have here. I guess, the best I can manage here will be something around 2Mhz Bandwidth at 80Mhz IF.
This whole inductor-stuff is still completely new territory for me. Up to now, I almost exclusively used Ohms law to design my circuits :)

Pictures will follow over the weekend.
Btw. I managed to put the Oscillator on the component-side and solder the pads through the holes. Looks a lot cleaner than dead-bug-style and was a lot easier than anticipated.

Offline ale500

  • Frequent Contributor
  • **
  • Posts: 265
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #15 on: October 12, 2015, 12:28:23 AM »
You can make some boards, I mean with like Eagle or so, and send them to one of the chinese fabs. for like 10 € you can get 5x5 cm boards. Shipping to Germany seems to take like 2 1/2 weeks or so. You get 10 pieces for that price. There is a thread on mikrocontroller.net about them. I used Smart Prototyping a couple months ago.
 

Offline SaabFAN

  • Frequent Contributor
  • **
  • Posts: 543
  • Country: de
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #16 on: October 14, 2015, 08:27:21 AM »
It might just come to that. I didn't think it would be so difficult and fiddly to build a Bandpass-Filter with a center-frequency of 80Mhz.

At first I tried to align it without shielding and thought I had it more or less on 80Mhz. When I tested the whole thing, still without shielding to have easier access to the coils, the whole thing produced something that looked like the output of a Mixer and not the output of a Filter: 215Mhz Sine at the output of the Filter at an input-frequency around 75Mhz. And almost no chance to see the real peak.
After adding the shield, this situation improved quite a bit, but the center-frequency was at about 92,3Mhz (The 20€ Frequency-Counter from Ebay was REALLY useful there and also looks nice with its Vacuum-Flourescent Disyplay :) ). So I tried to pull the coils a bit and ripped one off the board, which resulted in another 10 minutes trying to reattach it with all the shielding already in place. And it still isn't fully aligned.
Another problem: Without the Scope-Probes attached to the i2c-Bus, I cannot program the oscillator. Seem like I need some ferrites to filter out RF-Nastyness from the i2c-lines (I have an old Pentium III-Mainboard, which will provide those).

Summary of the past few days: Power-Electronics is childs-play compared to RF-Stuff. There is just so much stuff you can get away in the sub 20Mhz-Range that makes an RF-Circuit do everything except what you want it to do^^

Offline fcb

  • Super Contributor
  • ***
  • Posts: 1199
  • Country: gb
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #17 on: October 15, 2015, 01:45:19 AM »
Many moons ago I bought a TTi TSA1000 speccy (they also did a TSA250, with... 250MHz range).

The bottom end is 400KHz, but I reckon you could tweak that down.

Very low cost design I recall.
 

Offline SaabFAN

  • Frequent Contributor
  • **
  • Posts: 543
  • Country: de
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #18 on: October 16, 2015, 12:02:37 PM »
After struggling with the Filter for several days now, I decided to redo it from scratch.
I also altered my scope a bit: As I couldn't use the PLLs to get me the required 434,42Mhz (Available Steps: 50khz or 62,5khz), I decided to use the TV-Tuner from an old TV-Card, which is now usesless because 1st There are no drivers anywhere available anymore and Analog TV has been shut down.

The Analyzer will now have 2 Input-Stages: LowBand (0.1khz to 50Mhz), HighBand (50Mhz to 869Mhz). It is basically the Spectrum Analyzer from DKD Instruments with a few modifications: It doesn't need a IBM PC and uses an Arduino instead, the PLLs are already integrated into the Tuner-Module, it contains a Tracking-Generator (I paid for the Si570, now I'm going to use it!^^), instead of an 8bit ADC, it uses a 10bit ADC with optional 12bit High-Resolution-Mode (use of Oversampling), LowBand and HighBand use a common input that is switched via Relays instead of having two dedicated inputs for each band.

Offline AF6LJ

  • Supporter
  • ****
  • Posts: 2577
  • Country: us
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #19 on: October 16, 2015, 12:08:39 PM »
That sounds good, there was a period back from the mod 80s to 2000 where everybody and their brother was building an SA with a TV tuner module as the heart of the unit.
For "Cheap" it is the way to go.
Sue AF6LJ
Test Equipment Addict, And Proud Of It.
 

Offline SaabFAN

  • Frequent Contributor
  • **
  • Posts: 543
  • Country: de
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #20 on: October 16, 2015, 12:26:12 PM »
On a more positive note, I tested aluminium-foil reinforced by Lego-bricks. It worked rather well. I don't have any data on how it compares with copper, but given the fact that I already have spent the Budget of 70€ (mostly for passives and the Si570), I'm going to use the Aluminium-Foil solution for now.

Btw: Is there a way to directly post a link here to a CircuitMaker-Project so you guys can tell me what I'm doing wrong, or is it better to just upload screenshots here?

Offline rjeberhardt

  • Regular Contributor
  • *
  • Posts: 62
  • Country: fr
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #21 on: October 17, 2015, 01:43:03 AM »
That sounds good, there was a period back from the mod 80s to 2000 where everybody and their brother was building an SA with a TV tuner module as the heart of the unit.
For "Cheap" it is the way to go.
We cobbled some of those up in the 1970s for production line test rigs  :)

Russell.
Retired Chartered Engineer
 

Offline SaabFAN

  • Frequent Contributor
  • **
  • Posts: 543
  • Country: de
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #22 on: October 17, 2015, 04:28:15 AM »
I hope, this is the link that allows you to view the project-files: http://workspace.circuitmaker.com/projects/114BDE35-CF9F-49AA-95D1-50AE3D481AC5

Offline SundayProgrammer

  • Contributor
  • Posts: 33
  • Country: fi
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #23 on: October 17, 2015, 06:30:16 AM »
I hope, this is the link that allows you to view the project-files: http://workspace.circuitmaker.com/projects/114BDE35-CF9F-49AA-95D1-50AE3D481AC5

Perhaps... if you have logon credentials...

Axel.
 

Offline SaabFAN

  • Frequent Contributor
  • **
  • Posts: 543
  • Country: de
Re: DIY "Junkbox-Style" 100khz - 225Mhz Spectrum Analyzer
« Reply #24 on: October 17, 2015, 06:40:52 AM »
I think, I ran into yet another problem: As you can see in the attached block-diagram, the FM1216 has no 45Mhz IF-Output and already demodulates the Video-Signal and the Sound.
Is it still possible to use this tuner? I'm not sure if I can just take the Video-Signal, convert it down to 10Mhz and then filter it with crystals and measure the RSSI-Output of the SA615.
« Last Edit: October 17, 2015, 06:56:21 AM by SaabFAN »
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf