I do a lot of work in the sub-GHz ISM band and there are a lot of antenna vendors whose quality varies broadly. Consider the case of two antennae: The first was purchased from AliExpress vendor CS Family. These were sold as 915MHz antennae with 3dBi gain (this).
It’s centered at 910MHz and its best-case SWR is 1.34:1. At the band edges, it offers 1.57:1 at 902MHz and 1.77:1 at 928MHz. This is acceptable; I consider anything better than 2:1 acceptable for a cheap antenna and this meets its spec across the band. The impedance is 75 -j47. It’s not pretty, but it will do the job.
However, compare it to one of my favorite compact antennae from TE/Linx: the ANT-916-CW-HWR-RPS (datasheet) claims 1.2dBi and better than 2:1 VSWR.
This antenna is nicely centered in the band and offers an amazing 1:08 SWR at 915MHz, 1.57:1 at 902MHz and 1.40:1 at 928MHz. Impedance is 46.59 +j0.70. Now that’s pretty!
In fairness, both antennae meet their spec (better than 2:1) and the AliExpress antenna cost only $2.16 whereas the Linx antenna cost $13.50…so I cut the AliExpress guys some slack 🙂
Measurements taken using a NanoVNA SAA-2N with VNA Qt software. I might break out a nicer VNA some time and repeat these tests, but for quick measurements, I’ve found the NanoVNA2 to be remarkably accurate; it’s insane what $110 can buy these days. Note: if you have a NanoVNA2 SAA-2N, the firmware, manual, schematic, and a version of VNA Qt that works with it can be found here. The 1.3.07 firmware (Aug 30, 2022) offers many important features and if you’re running older firmware, you probably want to update (instructions are in the manual). The only thing I couldn’t find a way to do using the LCD UI was port extension, but it’s easy with VNA Qt.
For decades, lab-grade test equipment came from either HP or Tektronix. There were other providers in niche areas (R&S, Anritsu, IFR, etc.), but nearly all lab-grade gear was too expensive for mere mortals. With few alternatives, hobbyists and small businesses scrounged eBay and corporate liquidations to find used gear from these manufacturers.
Times have changed and while those companies still make great test gear, the competition from China has steadily improved and in many (most?) cases, it makes more sense to buy new gear from a budget Chinese manufacturer than 20-40 year old big-name gear.
I’ve bought (and liked) products from Rigol and Owon, but my budget manufacturer of choice is, increasingly: Siglent. My recent purchases include:
SDG2042X – 40MHz Arbitrary Waveform Generator hacked to SDG2122X (120MHz)
SSA3021X+ – 2.1GHz spectrum analyzer hacked to SVA1032X (3.2GHz SA + VNA)
Siglent (like Rigol) sells gear that is easily hacked to add functionality including bumping a lower-end model up to a higher model in the same line. This is smart marketing: it lets them get higher prices from larger companies that won’t hack while still providing very attractive price points to hobby and small business users who couldn’t otherwise afford the higher models, but are willing to hack the lower models.
For the most part, I’m quite pleased. The Siglent gear always seems to meet or exceed its specifications and the specs are quite decent. There is a huge community supporting them in places like eevblog with in depth reviews of SDS1104X-E, step-by-step guides to hacking the SDS1104X-E as well as usage, repair, and enhancement tips.
I buy much of my new test gear from Saelig and TEquipment, both of which have provided excellent service and I recommend. If you’re thinking about buying new bench gear, you might give Siglent a look!
I have been waiting for a long time for a usable low-cost spectrum analyzer and it looks like that wait is over
Update Jan 2023: I sold the original TinySA and upgraded to a TinySA Ultra. It is more expensive (about $140), but much more capable. The Ultra provides an extended frequency range up to 6GHz (level-calibrated to 5.3GHz) and adds several nice features including a remarkably functional bonus signal generator (cw, am, fm) and a 4″ LCD screen (welcome eye-relief for folks with high-mileage). This is not a toy; it has its limitations, but the specs now make it quite usable (PN=-92dBc/Hz, 2dB absolute amplitude accuracy, 1ppm frequency standard, 200Hz min RBW). So you can observe signals with reasonable accuracy and good resolution.
As before, I bought from R&L Electronics (the authorized US outlet – be careful to avoid poor-performing clones). I’ll do some testing with it soon, but you can see a few quick tests below.
The front-end is better but still easily over-driven (and damaged above +10dBm) so I usually use it with a 20dB fixed attenuator in line. As an example of how it compares to higher-end gear, here’s a 915MHz signal FM modulated at 5kHz shown (frozen) on the TinySA Ultra and on a Siglent SVA1015X. Peak measurements are within 1.5dB and 100Hz. Not bad!
I was recently looking for RF interference in the WiFi band and ran the tinySA Ultra and a (much more expensive) Anritsu BTSMaster for a bit with both in max hold mode to get a feel for what was out there and I was pleased with the results.The pictures won’t match precisely due to the nature of sweep times and max hold, but the results were quite good and immediately showed the strong channel 1 signal with fairly good accuracy on both frequency and amplitude. I’m quite fond of this little SA.
There is also a TinySA app in development; it lets you connect to the TinySA from your Windows PC and capture traces; it’s a little rough at present and the sweep rate gets very slow when you are capturing to PC at low spans (in part because the default is 1k points), however it’s still nice to be able to capture traces directly. Here’s an example of a 433MHz signal FM modulated at 1.5kHz
OLDER VERSION (note: below is about the older TinySA, not the Ultra)
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):
I do a lot of work in the 902-928MHz ISM band which is often impacted by strong nearby cellular signals. I looked at the 50MHz span around 915MHz using both a TinySA and an Anritsu CellMaster. The TinySA did an outstanding job, showing the same results but with much greater dynamic range (the Anritsu is meant as a cell tower service tool and supports looking at much stronger signals). On both analyzers, you can see a strong LTE signal at 892.5MHz. Measurements were using a Linx sleeved dipole centered at 915MHz.
TinySA showing LTE signal at ~892MHzSame LTE signal on my Anritsu MT8212B
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 -23.11dBc433MHz is also perfect for frequency and amplitude433MHz signal and harmonics3GHz signal at +10dBm2.4GHz signal at -20dBm and harmonicsweeping 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)
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 if you need more than ~200MHz, the 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 you aren’t buying a counter with an OCXO, I would make sure to get one with an external 10MHz reference input so you can slave it to an external high-accuracy standard. If a counter isn’t accurate, what good is it?
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; both are excellent. 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.
Recently, many companies have started adding bonus frequency counter functionality to their arbitrary waveform generators; for example, my SDG2042X has a counter input that is good to 200MHz. The counter’s internal reference is better than 2ppm, but it supports an external 10MHz reference so I slave it to an external DOCXO standard for higher accuracy. It requires around -10dBm (200mV) at 200MHz, less at lower frequencies: -20dBm (63mV) works at 35MHz. Overall, it does quite well up to 200MHz and has some nice features lacking in older counters such as min/avg/max and sdev, duty cycle reporting, deviation from a reference in ppm, etc.
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:
Aug 2023 I bought a Siglent SSA3021X+: which is a modern, compact 2.1GHz spectrum analyzer+TG that is easily hacked to become an SVA1032X (the same hardware platform running different software). The hack expands the BW to 3.2GHz, adds VNA (S11, S21) capability, and enables all options. The SpecAn covers 9kHz to 3.2GHz, VNA=100kHz to 3.2GHz, 0.7dBm amplitude accuracy, 1ppm reference, -98dBc/Hz PN, -161dBm/Hz DANL, and generally decent specs with a modern user interface. Costs around $1650 from TEquipment (whom I highly recommend).
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. Oddly, the device comes with two (rarely used) push-buttons without caps. The caps can be ordered very inexpensively from Digikey, Mouser, etc.: Wurth 714651010100, 714656010100.
Feb 2016: An Anritsu MT8222A (see datasheet). Is meant for cellular base station service, but it includes an even richer set of features than my prior favorite cellular test tool, the Agilent E7495. Most importantly, the MT8222A includes VNA capability! It also provides a spectrum analyzer that covers 100kHz through 7.1GHz with decent specs (PN = -100dBc/Hz, 1.25dB amplitude accuracy without PSN50, 1ppm reference). It 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 HP/Agilent 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, but probably not in a leveled way.
Anritsu MS8609A – 13GHz RF Spectrum Analyzer 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.
Marconi/Aeroflex/IFR 2025 – 2.5GHz RF signal generator Generates pretty clean RF signals with analog modulation. Not HP quality, but still plenty good and more than meets my needs. It is a pleasure to use. See the datasheet and manual.
Hobby-grade RF Tools Hobby-grade RF tools have gotten a *LOT* better over the last 5 years. I had earlier versions of these and they were marginally useful…more toy than tool, but their quality has improved steadily and these RF essentials (SA, VNA) are now useful as tools and an amazing value for a little over $100 each; they make RF design much more accessible to hobbyists.
Tiny SA Ultra (100kHz – 5.3GHz) spectrum analyzer (V 0.4.5.1) Yep, a 5GHz spectrum analyzer with bonus signal generator for under $150. Crazy! Specs are getting decent too: PN is now -92dBc/Hz, 2dB amplitude accuracy, leveled signal generator provides CW, and also AM and FM modulation. See the wiki. Some important limitations: 200Hz min RBW, the SigGen cannot serve as a tracking generator for the SA. See links here. and the developer’s youtube videos here which include honest assessments of the limitations and how to work around them. This video describes the ultra and its limitations. It’s most useful when you limit the signal level into it using a fixed attenuator.
NanoVNA SAA-2N (V2_2) 50kHz-3GHz – surprisingly accurate; also almost out of the toy category. Due to its size and battery operation, it is often what I grab to do a quick sweep of an antenna. The manual, firmware, VNA Qt PC software, etc. are here. $110 for a VNA…
I’ve also added a separate page on the frequency counters I use, however I rarely use counters these days. Most of what I need to measure is under 100MHz and for convenience, I just use the counter built into the SDG2042X signal generator which is already on my desk; when slaved to an external 10MHz DOCXO standard, it is quite accurate.
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.
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.
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).
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):
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.
