TinySA

I have been waiting for a long time for a usable low-cost spectrum analyzer and it looks like that wait is over.

TinySA Spectrum Analyzer

I bought a TinySA spectrum analyzer for $55 from R&L Electronics (one of the official dealers). If you get one, try to use the official sites; there are lots of bad clones out there. The TinySA is, as the name implies, a tiny, battery-powered, touch-screen, 100kHz – 960MHz spectrum analyzer. I have been very pleasantly surprised by its performance.

It has its limitations, but it is the first usable low-cost SA I’ve found for looking at sub-GHz FM signals. There are plenty of low-cost toys out there (see my earlier post regarding the “Simple Spectrum Analyzer”) that claim to do spectrum analysis, but they have always had fatal flaws (inaccurate or horribly coarse resolution bandwidth). This one has quite good frequency and amplitude accuracy out of the box and a usable 3kHz RBW.

It has some limitations too (But for goodness sakes, we’re talking about a pocket-sized spectrum analyzer for $55!!!):

  • 960MHz max frequency
  • 3kHz resolution bandwidth (RBW)
  • Amplitude uncertainty seems to be around 2dB
  • Easily over-driven (claims +10dBm max input, but works much better below -10dBm)

Below are some pictures showing the SA in action, including both strengths and limitations.

For comparison, here is what the signal generator output looks like on a higher-end piece of test gear (Anritsu MS8609A):

TPI-1001-B RF Signal Generator/Analyzer

An RF signal generator is an important part of my wireless workbench. In the lab, I use high end gear made by HP, Marconi, or Anritsu, but these are big expensive pieces of equipment with loud fans so I don’t want them at my desk. Enter the TPI-1001B RF signal generator/analyzer from RF-Consultant. This is a USB-powered signal generator that generates clean RF CW signals from 35MHz to 4.4GHz at up to +10dBm…and does it accurately! It even has an accurate power detector that can be used in conjunction with the generator to sweep filters and such (more below).

The TPI-1001-B generator/analyzer costs a good deal more (~$350) than the cheap RF signal generators on eBay. I assume it is based on the same Analog Devices ADF4351 synthesizer, but the price difference is fully justified. The cheap synthesizers are not calibrated for amplitude and many don’t use a good enough time-base to be accurate for frequency either. A signal generator without accurate frequency and amplitude is a toy, this is a tool.

Note: they offer a less expensive (~$275) version (TPI-1002-A) that has the same signal generator but does not include the analyzer (which I thought it was worth the extra $75). I might buy one of these later for another workstation.

The good news is that both the generator and the analyzer work extremely well. The software is straight-forward and easy to use; I love the frequency presets. The device is compact, silent, and performs admirably. I’ll share some pics below of the CW output including sweeps of a few filters. As promised, it stayed well within 1dB of the configured output setting across a wide range of frequencies and the frequency accuracy was impressive as well (the measurements below are from a spectrum analyzer with a rubidium standard).

The main difference between the TPI and a lab-grade generator is that it lacks output filtering to suppress harmonics (you’ll see that in the pics too), but that’s expected.

As it is, it replaces the lab gear for most of my needs, but here’s my wish list for future versions:

  • A set of switchable ceramic or SAW filters would add little cost and make their calibration process more complex, but it would make the generator able to fully replace lab-grade gear in many applications. Johanson makes great low cost SMT ceramic filters.
  • An internal FM modulation generator.

Below are some tests I ran with the generator into an Anritsu MS8609A transmitter analyzer. I did not compensate for cable loss, but it was a short, high-quality (low loss) cable and the results speak for themselves.

Signal generator configured for 915MHz at 0dBm.
915MHz harmonics – fundamental is 0dBm, 3rd is -10.8dBc, 5th is -23.11dBc
433MHz is also perfect for frequency and amplitude
433MHz signal and harmonics
3GHz signal at +10dBm
2.4GHz signal at -20dBm and harmonic
sweeping a 60MHz low-pass filter (microcircuit SLP-70+)
Sweeping a 2.2GHz-6GHz bandpass filter (high-pass for these purposes since only sweeps to 4.4GHz)

Frequency Counters

Although less exotic than the SA and VNA tools I use during development, I find I make use of basic frequency counters pretty often (mainly to calibrate equipment).

A frequency counter does only one thing: measures the frequency of an RF signal.  What’s important for a good counter is frequency range, timebase accuracy, speed of measurement, and of course cost.  I try to only purchase counters with an OCXO frequency standard although a good TCXO is often sufficient.  An external reference input is very useful when you need very high precision so you can slave the counter to a higher accuracy lab frequency standard (OCXO, GPSDO, or Rubidium).

Having had quite a few counters, I’ve concluded that older HP/Agilent counters offer the best value, especially if you’re willing to spend $200-250 on eBay for one with their excellent OCXO timebase option (4).  If that price is too high, you can find lower priced counters, but I think it’s a mistake to buy one without at least a good TCXO and/or external reference input.

I have a couple of HP5385A counters that work to 1GHz; one has the TCXO timebase and is quite accurate; the other has the superior OCXO timebase.  I also have an HP 5386A with OCXO that is good to 3GHz.  For higher frequency measurements, I have an HP 5347A that integrates a power meter and frequency counter up to 20GHz, its maximum frequency resolution is 1Hz (plenty for higher frequency measurements); it only has a TCXO timebase so I almost always use it with an OCXO or rubidium lab standard; it is larger/heavier than the other counters, but it’s hard to get an affordable counter with that much bandwidth.

For counters that are no longer officially in calibration (per certificate), I use a Trimble Thunderbolt GPS-disciplined oscillator (GPSDO) to calibrate them annually.

RF Test Gear

Most of the RF work I do is in the 902-928MHz ISM band.  I have lots of RF test gear, but concluded that I really only need a few pieces and found that great bargains can be had by purchasing and re-purposing surplus cellular test equipment on eBay.  Some cellular gear includes general purpose RF test capability and this has allowed me to equip my lab at a tiny fraction of the cost of comparable new general purpose equipment:

  • Update Oct 2020: small gear that I can use at my desk often gets more use than fancy lab gear that takes up too much space.  I bought a TPI-1005 RF USB-powered signal generator/analyzer and love it.  What distinguishes this from the toy signal generators widely found from China is that it is calibrated and accurate.  What distinguishes it from lab gear is harmonic suppression (or lack thereof).  However, it is an incredibly handy tool, compact, and reasonably inexpensive.  You can generate signals on frequency with precise amplitude, measure signal strength, and sweep antennas and filters.
  • Update Apr 2018: Last year I added an IFR/Marconi AN1830 22GHz spectrum analyzer (late 1990s vintage) and 2.5GHz 2025 signal generator to the lab.  The signal generator has proven surprisingly useful and the main benefit of the SA over the Anritsu MS8609 is its tracking generator.  I’ve also added a separate page on the frequency counters I use.
  • Update Feb 2016: An Anritsu MT8222A now serves as my primary RF development tool (see datasheet).  It is another device meant for cellular base station service, but it includes an even richer set of features than my prior favorite E7495 (below).  Most importantly, the MT8222A includes VNA capability!  It also provides a spectrum analyzer that covers 100kHz through 7.1GHz with decent specs and provides a broad set of 1 and 2-port swept gain/loss analysis tools for cable and antenna analysis from 10MHz-4GHz.  It is significantly smaller and much lighter than the E7495A and the battery works!  At some point I need to try it with Anritsu Handheld Software Tools or Master Software Tools. I use it with an Anritsu PSN50 power sensor (50MHz-6GHz) for high accuracy (0.16dB) measurements (see datasheet).  Unfortunately it has no CW/AM/FM/FSK signal generation capability although obviously the hardware is capable.
  • Although I still like it and it probably is one of the best values in RF gear, an Agilent E7495B now serves as my backup development tool and has been largely supplanted by the MT8222A above.  It has a nice big color LCD display, pleasant user interface, and includes: a 2.7GHz spectrum analyzer, CW signal generator, 1-port and 2-port swept gain/loss analyzer, power meter, and cable tester; I ignore the rest of the cellular test functions.  It is modern, quiet, and takes up the same bench footprint as a modern scope.  The specs are not lab grade but they are good enough for most purposes.  See the datasheet.  How folks can sell
  • A lab-grade 10GHz spectrum analyzer is needed to measure harmonic compliance prior to FCC testing.  I use an Anritsu MS8609A (13+GHz) which is not quite as good as the best HP gear, but is fairly modern and more than good enough for my needs; it includes a bonus power meter.  Mine has a rubidium frequency standard too so I can slave my other gear when high frequency accuracy is needed.  See the datasheet.
  • A decent RF signal generator capable of FM modulation; I use a Marconi/Aeroflex/IFR 2025 which generates pretty clean signals to 2.5GHz with analog modulation.  Again, not HP quality, but still plenty good and more than meets my needs.  See the datasheet and  manual.

BG7TBL USB RF Signal Generator

Some time ago, I purchased a super-cheap RF signal generator on eBay from fly_xy.  It was the same as this item.  This is yet another version of the the popular BG7TBL signal generator and “simple spectrum analyzer”.   It cost $65 and covers 138MHz through 4.4G; for another $20, you can get one that goes down to 35MHz.  It’s certainly not lab gear, but for the price and size, it’s still decent; the main challenges are the software and the resolution bandwidth.

USB RF Signal Generator

Harmonics are not attenuated; with the generator configured to output a 915Mhz CW signal, the fundamental lands at 914.993Mhz @ -5dBm signal (7ppm error), pretty clean to -40 to -50dBm, acceptable to -70dBm.  However the harmonics are ugly: 3rd = -13dBm, 4th = -24dBm, 5th = -36dBm, 6th = -48dBm, etc.

Inside are:

  • AD8307 500MHz demodulating log amp
  • AD4350 RF synthesizer
  • IAM 81008 Mixer
  • ATMega processor
  • FTDI FT232RL USB to serial interface
  • AMS1117 super cheap LDO

A review (translated from Polish) that measures harmonics and frequency accuracy and such:  http://sztormik.com/Radio/Wpisy/2014/10/1_BG7TBL_measurements_files/bg7tbl_lo_meas.pdf

It would be *much* more useful with selectable RBW filters; as it is, I can’t resolve much detail finer than 200kHz, so an FM signal with 25kHz deviation will look the same as an FM signal with 100kHz deviation.  See the pictures below for some sweeps of the 2m band.  The NWT4000 or NWT4000-2 might be more capable (but they are sufficiently more expensive that it would be better to buy a real piece of lab gear like a used R&S CMU200 – even though it is admittedly much larger).

Sweep of 2m band

2m band

Close-up of signal in 2m band

The software it uses is open-source LinNWT / WinNWT which supports many similar devices.  The English language documentation is not great and because the native language is German, there’s not much English language support.  A German magazine article is here it looks like it would be very useful if translated into English.  The author (Andreas) is friendly and helpful and responds to email.

To run WinNWT in English on windows, use the command (in the Target field of the shortcut properties):

“C:\Program Files (x86)\AFU\WinNWT4\winnwt4.exe” app_en.qm

To build/run the software on linux:

  • Download latest .tgz source here
  • Install tools if needed: sudo apt-get install gcc qt4-qmake libqt4-dev
  • tar xzvf linnwt_X_Y_Z.tar.gz
  • cd linnwt_X_Y_Z
  • qmake-qt4
  • make
  • If you want to make it available system wide: sudo cp linnwt /usr/local/bin/linnwt
  • sudo linnwt app_en.qm

To use the software, I configure Settings->Options->StartFrequency=80000000, StopFrequency=100000000, DDS clock=400000000, Interface=/dev/ttyUSB0 on linux or COMx on windows, max.Sweep=200000000, frequency multiply=10.  Then in the Sweepmode tab, to monitor the ISM band, configure StartFreq 902000000, StopFreq=928000000, Samples=1000 and press Continuous to sweep continuously; press Stop to stop sweeping.  This results in 26kHz steps.

I also bought the BG7TBL “tracking” (i.e. broadband) noise source in the hope of being able to do some basic antenna return loss/swr measurements; it does generate broadband noise at around -40dBm, but so far I’ve had no luck using it with the “simple spectrum analyzer” and a return loss bridge to sweep an antenna.
noise_source

Links:
https://www.facebook.com/media/set/?set=oa.809669625718111&type=1
http://ea4eoz.blogspot.com/2014/07/modifying-bg7tbl-noise-source.html
http://ea4eoz.blogspot.com/2014/07/installing-bg7tbl-noise-source-as-poors.html
http://www.mikrocontroller.net/topic/336482 (English Translation)
http://cas.web.cern.ch/cas/Germany2009/Lectures/PDF-Web/Caspers.pdf
http://bg7tbl.taobao.com/  (English Translation)
https://vma-satellite.blogspot.com/2019/04/new-simple-spectrum-analyzer-device.html (newer D6 version)
https://www.rudiswiki.de/wiki9/SpectrumAnalyzer_LTDZ#Links (newer LTDZ version)
http://alloza.eu/david/WordPress3/?page_id=478 (SNASharp software)